Re: [EVDL] Off-grid solar house and electric car charging

[Cor van de Water via EV]

The *mounting* of the panels is still not wireless...

Cor van de Water 
Chief Scientist 
Proxim Wireless 
  
office +1 408 383 7626Skype: cor_van_de_water 
XoIP   +31 87 784 1130private: cvandewater.info 

http://www.proxim.com

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-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Mr23 via EV
Sent: Friday, June 10, 2016 1:58 PM
To: ev@lists.evdl.org
Subject: Re: [EVDL] Off-grid solar house and electric car charging

3.3kW wireless charging pads exist now for electric vehicles.
Why not wireless through the roofing/deck ?

-Chris

On 6/8/2016 3:03 PM, Seth Rothenberg via EV wrote:
> It's funny to see this discussion about panels.
> I spent 2 hours on the roof yesterday watching
> the Solar installer find a roof leak under the
> junction box.   (Each person defines his own "fun" :-)
> (It took about 4 years to show up in a storm)
>
> (Apparently, they stopped the practice of gluing
> the junction box to the roof.   Hopefully they also
> stopped making extra holes :-)
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> Please discuss EV drag racing at NEDRA
(http://groups.yahoo.com/group/NEDRA)
>
>

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Re: [EVDL] Off-grid solar house and electric car charging

[Mr23 via EV]

3.3kW wireless charging pads exist now for electric vehicles.
Why not wireless through the roofing/deck ?

-Chris

On 6/8/2016 3:03 PM, Seth Rothenberg via EV wrote:

It's funny to see this discussion about panels.
I spent 2 hours on the roof yesterday watching
the Solar installer find a roof leak under the
junction box.   (Each person defines his own "fun" :-)
(It took about 4 years to show up in a storm)

(Apparently, they stopped the practice of gluing
the junction box to the roof.   Hopefully they also
stopped making extra holes :-)
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Re: [EVDL] Off-grid solar house and electric car charging

[Robert Bruninga via EV]

Ah, my bad.  I was transmorgafying the limitations of peak voltage which
can allow greater power delivery on DC lines than AC.  That is,  a 240 VAC
line has peak voltages of 330 volts.  As the voltage rating of the line
becomes an issue, then a DC line can operate at that higher voltage and
deliver 1.4 times more power than the AC system while keeping within the
maximum voltage spec.  (ignoreing transients of course)..

So you are right.  Argument does not apply here since most wiring is rated
at 600 volts well above the 240 VAC peaks.
Bob


-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Roger Stockton
via EV
Sent: Wednesday, June 08, 2016 3:21 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Off-grid solar house and electric car charging

Robert Bruninga wrote:

> Yes, as far as VOLTS and as AMPS as averages are concerned.  Such as
> average power.  A 1500W resistor will be 1500W whether on DC or RMS AC.
>
> But the power loss in wires feeding that resistor will have greater
> loss on AC because of two factors important in distribution systems:
>
> 1) SKIN EFFECT where the AC current is pushed to the outside of the
> wire so that not all the wire is carrying the same current.  Thus the
> wire is not as effective since not all of its copper is being used in
> an AC system

The skin depth in copper at 60Hz is 8.47mm; this means that until you are
using a conductor with a diameter greater than 2 x 8.47mm = 16.94mm (about
0.67"), the AC resistance is the same as the DC resistance.

<https://en.wikipedia.org/wiki/Skin_effect>

> 2) Peak power losses.  As you note, the RMS current  is the same, but
> the PEAK current is 1.4 times higher during the peak of the waveform
> and since that is where the most power is delivered that is also where
> the most loss occurs in the wire.  So the average power lost in the
> wire for AC is almost twice (1.4 squared) the loss in the same wire at
DC.
>
> Google it...

"For a cyclically alternating electric current, RMS is equal to the value
of the direct current that would produce the same power dissipation in a
resistive load."
 - <https://en.wikipedia.org/wiki/Root_mean_square>

Cheers,

Roger.

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Re: [EVDL] Off-grid solar house and electric car charging

[Cor van de Water via EV]

Paul,,
Isn't irrelevant (double negative) means
it is relevant?
Not sure that I get what you are saying in the next sentence,
that there are building codes that must be followed.
While standard practices are quite standard, such as wiring a bunch of outlets 
on a 15/20A circuit all in a string with wire that can withstand the heating of 
a 20A load in the specified environment, there is a lot of freedom to wire 
things differently. It is not done very often due to cost concerns, but nothing 
prohibits you from wiring with thicker wire or wiring a star instead of a 
string. It is just easier and cheaper the way it is usually done and it meets 
code - building is one of many trades where it often is a sports how to do the 
minimal for max effectiveness while still meeting code. 

Cor van de Water 
Chief Scientist 
Proxim Wireless 
  
office +1 408 383 7626Skype: cor_van_de_water 
XoIP   +31 87 784 1130private: cvandewater.info 

http://www.proxim.com

This email message (including any attachments) contains confidential and 
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-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of paul dove via EV
Sent: Wednesday, June 08, 2016 6:22 AM
To: Robert Bruninga; Electric Vehicle Discussion List; Electric Vehicle 
Discussion List
Subject: Re: [EVDL] Off-grid solar house and electric car charging

Isn't irrelevant in the USA. We have building codes that must be followed.


  From: Robert Bruninga via EV 
 To: Electric Vehicle Discussion List  
 Sent: Wednesday, June 8, 2016 7:47 AM
 Subject: Re: [EVDL] Off-grid solar house and electric car charging
   
> The only time high voltage helps is when you need to have long wire
runs...

The operative word  is "long"  And when you wire a house for every room
and for every appliance and for every outlet (whether used fully or not)
then every wire is "long".

The academic argument below is like saying there is nothing wrong with
falling out of an airplane.  Its only when you hit the ground that you
have a problem...

Bob
-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Lee Hart via EV
Sent: Tuesday, June 07, 2016 11:24 PM
To: Larry Gales; Electric Vehicle Discussion List
Subject: Re: [EVDL] Off-grid solar house and electric car charging

Larry Gales via EV wrote:
> Thanks, I was somewhat aware of the increased use of copper, but not
> to the extent that you specify, so it looks like AC is the way to go,
> even for off-grid solar.

Lower voltage means higher current and bigger wires; but it's not as bad
as you think.

First, consider a motor or transformer. You would think that winding it
for a lower voltage / higher current would require more copper... but it
doesn't. Motors and transformers are exactly the same size, have the same
efficiency, same power rating, and use the same amount of copper no matter
what voltage they are built for.

Here's why: If you halve the voltage, you double the current (to get the
same power). But half the voltage requires half the turns. So the wire is
twice as think, but half as long. The total amount of copper thus stays
the same. This only breaks down if the voltage is so low that you need
less than 1 turn, or if the voltage is so high that excessive amounts of
space are taken up by insulation instead of copper.

Now consider a pair of identical 12v batteries. You can wire them in
series (24v), or parallel (12v). For the same power, you'll have the same
current in each battery (since their voltages are all the same).
So, the same wire size to every battery. For the sake of argument, let's
assume you connect a 12" piece of wire to every battery post, and it has
1 milliohm of resistance.

If they're in series, you have a total of 4 feet of wire total, all in
series, and so 4 milliohms of resistance. if the load is 24v at 100 amps,
then this 4 milliohms is burning up I^2R = 100^2 x 0.004 = 40 watts as
heat.

If they're in parallel, the free ends of the + wires connect together, and
the free ends of the - wires connect together. Now you have two parallel
strings, each with 2 feet of wire in it; so each string has half the
resistance or 2 milliohms. But there are two of these strings in parallel,
so the total resistance is 1 milliohm. The same load power is 12v at 200a.
I^2R losses are 200^2 x 0.001 = 40 watts.

Exactly the same size and length of wire, and exactly the same losses!

The same thing happens with PV panels, power semiconductors, and just
about any power devices. Arranging them for low voltage/high current
results in the same losses as arranging them fro high voltage/low current.

The only time high voltage 

Re: [EVDL] Off-grid solar house and electric car charging

[Cor van de Water via EV]

Ah, my bad, you are correct - I got confused with power factor concerns
but indeed for pure sine AC the RMS will make AC power identical to DC
power in both load and wires. Thanks for clarifying and setting me
straight!

Cor van de Water 
Chief Scientist 
Proxim Wireless 
  
office +1 408 383 7626Skype: cor_van_de_water 
XoIP   +31 87 784 1130private: cvandewater.info 

http://www.proxim.com

This email message (including any attachments) contains confidential and
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this message in error, please delete it and notify the sender.  Any
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-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Roger Stockton
via EV
Sent: Wednesday, June 08, 2016 2:08 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Off-grid solar house and electric car charging

Cor van de Water wrote:

> Roger,
> You used the wrong definition. The Wikipedia quote is about the power
> delivered to the *load* but the discussion was about the power losses
in
> the *wire* feeding the load.

No; just as the power dissipated in a resistive load remains the same,
the power dissipated in the wire feeding the load remains the same.

To see that this must be true, consider the case of a source connected
to a non-zero load by wires with zero resistance: the dissipation in the
load is the same for 1A DC or 1Arms.

Now, consider a zero-ohm load connected to the source by wires with
non-zero resistance: the dissipation in the wires is the same for 1A DC
or 1Arms.

The principle of superposition allows us to see that this situation
holds for any combination of load and wire resistances: 1A DC and 1Arms
will dissipate the same energy in the wires to the load, and they also
dissipate the same energy in the load, though of course the amounts
dissipated in the wire or load depends upon their respective resistance.

> To use a simple and somewhat excessive example as illustration:
> Case A: DC power to an (arbitrary) load: 1 Amp continuous, 1 Ohm line
> resistance so 1 Volt drop, meaning 1V * 1A = 1Watt of loss in the
line.
> 
> Case B: power provided with 10% duty cycle so 10A during 10% of the
> period and 0 during 90% of the period. Average current still 1A and
same
> power delivered to the load as in case A.
> However, the line load is still 1 Ohm so the 10A current causes a 10V
> drop and thus 100 Watt power is lost in the line during the 10% that
the
> current is flowing, the average power loss in the line is therefor:
100W
> * 10% = 10W
> so the average power loss in the line is 10 times as high as in case A
> due to the peak current being 10 times as high, even though it is only
> flowing 1/10th of the time.

No.  You are confusing average with RMS; the two are not necessarily the
same.

The RMS value of your 10% duty 10A peak square wave is 3.16Arms, and
this will indeed have higher I2R loss than a 1A DC current.

For your 10A peak square wave to have an RMS value of 1A, it needs a
duty cycle of 1%:
 RMS = peak * sqrt(duty cycle); average = peak * duty cycle.

Cheers,

Roger.
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Re: [EVDL] Off-grid solar house and electric car charging

[Roger Stockton via EV]

Cor van de Water wrote:

> Roger,
> You used the wrong definition. The Wikipedia quote is about the power
> delivered to the *load* but the discussion was about the power losses in
> the *wire* feeding the load.

No; just as the power dissipated in a resistive load remains the same, the 
power dissipated in the wire feeding the load remains the same.

To see that this must be true, consider the case of a source connected to a 
non-zero load by wires with zero resistance: the dissipation in the load is the 
same for 1A DC or 1Arms.

Now, consider a zero-ohm load connected to the source by wires with non-zero 
resistance: the dissipation in the wires is the same for 1A DC or 1Arms.

The principle of superposition allows us to see that this situation holds for 
any combination of load and wire resistances: 1A DC and 1Arms will dissipate 
the same energy in the wires to the load, and they also dissipate the same 
energy in the load, though of course the amounts dissipated in the wire or load 
depends upon their respective resistance.

> To use a simple and somewhat excessive example as illustration:
> Case A: DC power to an (arbitrary) load: 1 Amp continuous, 1 Ohm line
> resistance so 1 Volt drop, meaning 1V * 1A = 1Watt of loss in the line.
> 
> Case B: power provided with 10% duty cycle so 10A during 10% of the
> period and 0 during 90% of the period. Average current still 1A and same
> power delivered to the load as in case A.
> However, the line load is still 1 Ohm so the 10A current causes a 10V
> drop and thus 100 Watt power is lost in the line during the 10% that the
> current is flowing, the average power loss in the line is therefor: 100W
> * 10% = 10W
> so the average power loss in the line is 10 times as high as in case A
> due to the peak current being 10 times as high, even though it is only
> flowing 1/10th of the time.

No.  You are confusing average with RMS; the two are not necessarily the same.

The RMS value of your 10% duty 10A peak square wave is 3.16Arms, and this will 
indeed have higher I2R loss than a 1A DC current.

For your 10A peak square wave to have an RMS value of 1A, it needs a duty cycle 
of 1%:
 RMS = peak * sqrt(duty cycle); average = peak * duty cycle.

Cheers,

Roger.
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Re: [EVDL] Off-grid solar house and electric car charging

[Lee Hart via EV]

Re RMS: This stuff is tricky. I don't blame folks for being confused.

If you're powering a resistive load, AC RMS and DC are identical. Line 
losses are the same. The resistance in the wire is no different than the 
resistance in the load. The losses and power dissipated in both of them 
are the same for DC as for RMS AC.


This is true as long as the current waveform is sinusoidal. Yes, the 
loss is doubled during the peaks; but it is zero during the 
zero-crossings. The losses averaged over a complete cycle are exactly 
the same as for the DC case. This is the whole point of using RMS values 
for AC.


Now, if you're powering some *bad* load with a high crest factor (like a 
non-PFC switching power supply), the current is *not* sinusoidal. It has 
a drastically higher peak, and then is zero for most of the rest of the 
cycle. In this case, the line losses are indeed higher.


As for skin effect, it is negligible at 60hz. It only matters if you are 
dealing with high frequencies, or huge non-stranded conductors.


--
"IC chip performance doubles every 18 months." -- Moore's law
"The speed of software halves every 18 months." -- Gates' law
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Off-grid solar house and electric car charging

[Cor van de Water via EV]

 copying of any part of
this message is prohibited.


-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Lee Hart via EV
Sent: Wednesday, June 08, 2016 11:03 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Off-grid solar house and electric car charging

Robert Bruninga via EV wrote:
> Still not true.  The output of microinverters is at 240 VAC  and the
average
> current in the wires will be double as the same number of panels at
480 VDC.

But each microinverter has its own wire. The total current may be twice 
as much in a 240v system as in a 480v system; but there are twice the 
number of wires, each half the size. You wind up back where you started.

> Further, AC peak currents are 1.4 times higher than DC so the peak
currents
> (where the losses are) are 2.8 times greater

No; AC voltages and currents are normally expressed in RMS 
(Root-Mean-Square). RMS voltages and currents have the *same* effective 
values, voltage drops, and losses as DC. 120vac and 120vdc are 
completely equivalent.

> The difference in buying #6 wire instead of #12 is only $180 versus
$30.  Or
> you can ignore the extra 10% or so losses and use #10 wire.  But over
the
> life of the system (20 years) the losses in your solar system can add
up to
> many thousands of dollars.

Sure; it's basically an economic decision. How much can you afford 
up-front, to reduce long-term losses? It's further complicated because 
when you eventually scrap the system, much of the cost of the copper is 
recoverable.

Note that this is the EV discussion list. Besides these tradeoffs, 
weight is also an issue. You may be ahead by deliberately undersizing 
the wire to save weight. The benefit from weight reduction can exceed 
the efficiency loss. Racers know this well!

> Maybe I am just being nitpicky, but my solar arrays are all over my
yard and
> house.  Some runs are over 300 feet!  (shortest is maybe 60').

Ah; no wonder you are so concerned with wire lengths. I definitely 
consider 60-300 feet *long* runs! The PV panels on my house are only 20'

from my circuit breaker panel.

-- 
"IC chip performance doubles every 18 months." -- Moore's law
"The speed of software halves every 18 months." -- Gates' law
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Off-grid solar house and electric car charging

[paul dove via EV]

Isn't irrelevant in the USA. We have building codes that must be followed.


  From: Robert Bruninga via EV 
 To: Electric Vehicle Discussion List  
 Sent: Wednesday, June 8, 2016 7:47 AM
 Subject: Re: [EVDL] Off-grid solar house and electric car charging
   
> The only time high voltage helps is when you need to have long wire
runs...

The operative word  is "long"  And when you wire a house for every room
and for every appliance and for every outlet (whether used fully or not)
then every wire is "long".

The academic argument below is like saying there is nothing wrong with
falling out of an airplane.  Its only when you hit the ground that you
have a problem...

Bob
-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Lee Hart via EV
Sent: Tuesday, June 07, 2016 11:24 PM
To: Larry Gales; Electric Vehicle Discussion List
Subject: Re: [EVDL] Off-grid solar house and electric car charging

Larry Gales via EV wrote:
> Thanks, I was somewhat aware of the increased use of copper, but not
> to the extent that you specify, so it looks like AC is the way to go,
> even for off-grid solar.

Lower voltage means higher current and bigger wires; but it's not as bad
as you think.

First, consider a motor or transformer. You would think that winding it
for a lower voltage / higher current would require more copper... but it
doesn't. Motors and transformers are exactly the same size, have the same
efficiency, same power rating, and use the same amount of copper no matter
what voltage they are built for.

Here's why: If you halve the voltage, you double the current (to get the
same power). But half the voltage requires half the turns. So the wire is
twice as think, but half as long. The total amount of copper thus stays
the same. This only breaks down if the voltage is so low that you need
less than 1 turn, or if the voltage is so high that excessive amounts of
space are taken up by insulation instead of copper.

Now consider a pair of identical 12v batteries. You can wire them in
series (24v), or parallel (12v). For the same power, you'll have the same
current in each battery (since their voltages are all the same).
So, the same wire size to every battery. For the sake of argument, let's
assume you connect a 12" piece of wire to every battery post, and it has
1 milliohm of resistance.

If they're in series, you have a total of 4 feet of wire total, all in
series, and so 4 milliohms of resistance. if the load is 24v at 100 amps,
then this 4 milliohms is burning up I^2R = 100^2 x 0.004 = 40 watts as
heat.

If they're in parallel, the free ends of the + wires connect together, and
the free ends of the - wires connect together. Now you have two parallel
strings, each with 2 feet of wire in it; so each string has half the
resistance or 2 milliohms. But there are two of these strings in parallel,
so the total resistance is 1 milliohm. The same load power is 12v at 200a.
I^2R losses are 200^2 x 0.001 = 40 watts.

Exactly the same size and length of wire, and exactly the same losses!

The same thing happens with PV panels, power semiconductors, and just
about any power devices. Arranging them for low voltage/high current
results in the same losses as arranging them fro high voltage/low current.

The only time high voltage helps is when you need to have long wire runs.
If your PV panels are far from your inverter, then high voltage for the
wires between them will the reduce the amount of copper needed and/or
lower your losses. However, if you're using small low-voltage individual
inverters mounted right on each panel to one big central inverter located
far away, then the small inverters can "win" and use less copper overall.

You have to carefully consider the specifics of the situation, and not
make snap judgements about low voltages being automatically worse.
--
"IC chip performance doubles every 18 months." -- Moore's law "The speed
of software halves every 18 months." -- Gates' law
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Off-grid solar house and electric car charging

[Seth Rothenberg via EV]

It's funny to see this discussion about panels.
I spent 2 hours on the roof yesterday watching
the Solar installer find a roof leak under the
junction box.   (Each person defines his own "fun" :-)
(It took about 4 years to show up in a storm)

(Apparently, they stopped the practice of gluing
the junction box to the roof.   Hopefully they also
stopped making extra holes :-)
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Re: [EVDL] Off-grid solar house and electric car charging

[Cor van de Water via EV]

I am aware of industry looking at High Voltage DC transmission lines in
two distinct areas: Underseas transportation to islands or between
continents
and for long distance coupling of distribution nets.

The reasons for DC are rather simple and that is that when the
transmission line length becomes relatively long in comparison to the
wavelength of the AC then it may start acting as antenna instead of
transmission line and if the capacitance becomes significant (which
cannot be avoided in underseas transport, in contrast to open lines in
the air) then the losses of an AC line become so large that it makes
sense to go through the hassle of converting the AC to DC, transport it
without the associated capacitance or radiating losses and then convert
back to AC.

Added benefit of DC and the separate conversions from/to AC is that you
don't care about synchronising the two grids that you connect, you
simply transport current through the DC line in either direction and the
two grids can be at different frequency, phase or voltage, it does not
matter.

Today east coast and west coast USA are unconnected, the plans to do so
are using DC lines for all the reasons mentioned before.

Obviously disconnecting a high voltage DC line is an issue, but so is a
high voltage AC line since it does not matter that the voltage and
current goes through zero - once a plasma path in air is created by the
initial arc, it will continue to conduct until the line is disconnected
successfully elsewhere, no matter if it is AC or DC.

Cor van de Water 
Chief Scientist 
Proxim Wireless 
  
office +1 408 383 7626Skype: cor_van_de_water 
XoIP   +31 87 784 1130private: cvandewater.info 

http://www.proxim.com

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-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Peri Hartman
via EV
Sent: Wednesday, June 08, 2016 12:07 PM
To: Robert Bruninga; Electric Vehicle Discussion List
Subject: Re: [EVDL] Off-grid solar house and electric car charging

Robert,

I'm not sure how much effect the Skin Effect has.

But for #2, peak power losses, you also need to consider that part of 
the wave form is *below* the average voltage, thus contributing 
significantly *less* resistance.  You can't just look at the resistance 
caused by the peak voltage.

Thirdly, you note that the industry is looking seriously at a DC-based 
grid.  Do you have any references that claim the reason behind this is 
because of line loss due to resistance?  Or is it for other reasons?  
Even it it is line loss - and this is where Skin Effect may play an 
important role - 1MV is way different than 220V.

Peri

-- Original Message --
From: "Robert Bruninga via EV" 
To: "Electric Vehicle Discussion List" 
Sent: 08-Jun-16 11:53:51 AM
Subject: Re: [EVDL] Off-grid solar house and electric car charging

>Im sorry again, but this is simply not true when expanded to WIRE LOSS.
>
>>  No; AC voltages and currents... (Root-Mean-Square).
>>  RMS voltages and currents have the *same* effective
>>  values, voltage drops, and losses as DC. 120vac and
>>  120vdc are completely equivalent.
>
>Yes, as far as VOLTS and as AMPS as averages are concerned.  Such as
>average power.  A 1500W resistor will be 1500W whether on DC or RMS AC.
>
>But the power loss in wires feeding that resistor will have greater 
>loss
>on AC because of two factors important in distribution systems:
>
>1) SKIN EFFECT where the AC current is pushed to the outside of the 
>wire
>so that not all the wire is carrying the same current.  Thus the wire 
>is
>not as effective since not all of its copper is being used in an AC 
>system
>
>2) Peak power losses.  As you note, the RMS current  is the same, but 
>the
>PEAK current is 1.4 times higher during the peak of the waveform and 
>since
>that is where the most power is delivered that is also where the most 
>loss
>occurs in the wire.  So the average power lost in the wire for AC is
>almost twice (1.4 squared) the loss in the same wire at DC.
>
>Google it...
>
>That is why the entire industry is looking at DC transmission lines now
>that we are finally getting to the point where the up and down 
>conversion
>is becomming cost competitive with transformers...
>
>Bob
>-Original Message-
>From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Lee Hart via 
>EV
>Sent: Wednesday, June 08, 2016 2:03 PM
>To: Electric Vehicle Discussion List
>Subject: Re: [EVDL] Off-grid solar house and electric car charging
>
>Rober

Re: [EVDL] Off-grid solar house and electric car charging

[Cor van de Water via EV]

Roger Stockton quoted:
"For a cyclically alternating electric current, RMS is equal to the
value of the direct current that would produce the same power
dissipation in a resistive load."
 - 

Roger,
You used the wrong definition. The Wikipedia quote is about the power
delivered to the *load* but the discussion was about the power losses in
the *wire* feeding the load.
The situation is the same problem as with (bad) Power Factor: even
though the average power delivered to the load with bad power factor is
the same, the short and high spikes of current will heat the wires more
than in the case of a good power factor, simply because the loss in the
wire goes with the current squared, so higher peaks (and equal *average*
current) still results in higher losses in the line due to the squaring
of the current peaks in the formula for the power loss.

To use a simple and somewhat excessive example as illustration:
Case A: DC power to an (arbitrary) load: 1 Amp continuous, 1 Ohm line
resistance so 1 Volt drop, meaning 1V * 1A = 1Watt of loss in the line.

Case B: power provided with 10% duty cycle so 10A during 10% of the
period and 0 during 90% of the period. Average current still 1A and same
power delivered to the load as in case A.
However, the line load is still 1 Ohm so the 10A current causes a 10V
drop and thus 100 Watt power is lost in the line during the 10% that the
current is flowing, the average power loss in the line is therefor: 100W
* 10% = 10W
so the average power loss in the line is 10 times as high as in case A
due to the peak current being 10 times as high, even though it is only
flowing 1/10th of the time.

(Note that in case B it is claimed that the same power is delivered to
the load, so this means that the extra power loss in the line must be
delivered by a higher power draw from the source, we are after all
dealing with physics here)

Regards,
Cor.
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Re: [EVDL] Off-grid solar house and electric car charging

[paul dove via EV]

Oh, if only Edison could hear. He may finally win.


  From: jerry freedomev via EV 
 To: Electric Vehicle Discussion List ; Electric Vehicle 
Discussion List  
 Sent: Wednesday, June 8, 2016 8:26 AM
 Subject: Re: [EVDL] Off-grid solar house and electric car charging
   

    Hi Robert and All,   You way overstate your case in 
several ways.  First one can just use the same RMS voltage DC as AC.  It's not 
like we EV people are not use to it especially, it's arcing problem are greatly 
exaggerated with good DC practice.   Next most things even on 
12vdc run on under 2 amps, most under .5amp.  My fan is just 1 amp, LED lights 
.5 amp, computer 2amp, phone 1 amp charging, fridge 5 amps when running.
   I cook with just 5-20 amps, e blanket 2 amps at 12vdc.  Other than 
kitchen, bath, other high power unit like an A/C that one can bunch together 
you really don't need more than present 120vac wire size. And even some home  
model switches work at 120vdc IIRC, SqD?. Or use a low cost 
inverter for these .   I use a 3k wt peak, 2kw cont $129 inverter runs my a/c 
window unit.  My recent disassembly of a Miata for my next EV 
suspension also gave me an a/c unit I can drive very efficiently with a  PM 
motor  from 24vdc could make my a/c only be   200wt at about 3500btu.   
   And many power supplies now work off 300vdc+ from rectified ac so 
running 350vdc could end up using less copper if you want to get picky. And 
homes run on used EV packs as pulled from wrecks..  A well 
designed home will have centralized power, utilities, kitchen, bath making big 
copper runs very short and the rest little different.  The other savings and 
reliability of battery  DC with modern DC power supplies  makes DC at least 
competitive if not better.    Kind of like EVs fighting the 
established ICE machine, DC does have a future as homes, building go to clean 
and battery power.    And EVs will change to be part of these 
systems, especially 200 mile EVs with their excess capacity with 20-50kwhr to 
play with and still have 100 mile range. Many homes, businesses will be powered 
by these charged by solar.  Jerry Dycus

      From: Robert Bruninga via EV 
 To: Electric Vehicle Discussion List  
 Sent: Wednesday, June 8, 2016 8:47 AM
 Subject: Re: [EVDL] Off-grid solar house and electric car charging
  
> The only time high voltage helps is when you need to have long wire
runs...

The operative word  is "long"  And when you wire a house for every room
and for every appliance and for every outlet (whether used fully or not)
then every wire is "long".

The academic argument below is like saying there is nothing wrong with
falling out of an airplane.  Its only when you hit the ground that you
have a problem...

Bob
-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Lee Hart via EV
Sent: Tuesday, June 07, 2016 11:24 PM
To: Larry Gales; Electric Vehicle Discussion List
Subject: Re: [EVDL] Off-grid solar house and electric car charging

Larry Gales via EV wrote:
> Thanks, I was somewhat aware of the increased use of copper, but not
> to the extent that you specify, so it looks like AC is the way to go,
> even for off-grid solar.

Lower voltage means higher current and bigger wires; but it's not as bad
as you think.

First, consider a motor or transformer. You would think that winding it
for a lower voltage / higher current would require more copper... but it
doesn't. Motors and transformers are exactly the same size, have the same
efficiency, same power rating, and use the same amount of copper no matter
what voltage they are built for.

Here's why: If you halve the voltage, you double the current (to get the
same power). But half the voltage requires half the turns. So the wire is
twice as think, but half as long. The total amount of copper thus stays
the same. This only breaks down if the voltage is so low that you need
less than 1 turn, or if the voltage is so high that excessive amounts of
space are taken up by insulation instead of copper.

Now consider a pair of identical 12v batteries. You can wire them in
series (24v), or parallel (12v). For the same power, you'll have the same
current in each battery (since their voltages are all the same).
So, the same wire size to every battery. For the sake of argument, let's
assume you connect a 12" piece of wire to every battery post, and it has
1 milliohm of resistance.

If they're in series, you have a total of 4 feet of wire total, all in
series, and so 4 milliohms of resistance. if the load is 24v at 100 amps,
then this 4 milliohms is burning up I^2R = 100^2 x 0.004 = 40 watts as
heat.

If they're in parallel, the free ends of the + wires connect together, and
the free ends of the -

Re: [EVDL] Off-grid solar house and electric car charging

[Roger Stockton via EV]

Robert Bruninga wrote:

> Yes, as far as VOLTS and as AMPS as averages are concerned.  Such as
> average power.  A 1500W resistor will be 1500W whether on DC or RMS AC.
> 
> But the power loss in wires feeding that resistor will have greater loss
> on AC because of two factors important in distribution systems:
> 
> 1) SKIN EFFECT where the AC current is pushed to the outside of the wire
> so that not all the wire is carrying the same current.  Thus the wire is
> not as effective since not all of its copper is being used in an AC system

The skin depth in copper at 60Hz is 8.47mm; this means that until you are using 
a conductor with a diameter greater than 2 x 8.47mm = 16.94mm (about 0.67"), 
the AC resistance is the same as the DC resistance.



> 2) Peak power losses.  As you note, the RMS current  is the same, but the
> PEAK current is 1.4 times higher during the peak of the waveform and since
> that is where the most power is delivered that is also where the most loss
> occurs in the wire.  So the average power lost in the wire for AC is
> almost twice (1.4 squared) the loss in the same wire at DC.
> 
> Google it...

"For a cyclically alternating electric current, RMS is equal to the value of 
the direct current that would produce the same power dissipation in a resistive 
load."
 - 

Cheers,

Roger.

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Re: [EVDL] Off-grid solar house and electric car charging

[Peri Hartman via EV]

Robert,

I'm not sure how much effect the Skin Effect has.

But for #2, peak power losses, you also need to consider that part of 
the wave form is *below* the average voltage, thus contributing 
significantly *less* resistance.  You can't just look at the resistance 
caused by the peak voltage.


Thirdly, you note that the industry is looking seriously at a DC-based 
grid.  Do you have any references that claim the reason behind this is 
because of line loss due to resistance?  Or is it for other reasons?  
Even it it is line loss - and this is where Skin Effect may play an 
important role - 1MV is way different than 220V.


Peri

-- Original Message --
From: "Robert Bruninga via EV" 
To: "Electric Vehicle Discussion List" 
Sent: 08-Jun-16 11:53:51 AM
Subject: Re: [EVDL] Off-grid solar house and electric car charging


Im sorry again, but this is simply not true when expanded to WIRE LOSS.


 No; AC voltages and currents... (Root-Mean-Square).
 RMS voltages and currents have the *same* effective
 values, voltage drops, and losses as DC. 120vac and
 120vdc are completely equivalent.


Yes, as far as VOLTS and as AMPS as averages are concerned.  Such as
average power.  A 1500W resistor will be 1500W whether on DC or RMS AC.

But the power loss in wires feeding that resistor will have greater 
loss

on AC because of two factors important in distribution systems:

1) SKIN EFFECT where the AC current is pushed to the outside of the 
wire
so that not all the wire is carrying the same current.  Thus the wire 
is
not as effective since not all of its copper is being used in an AC 
system


2) Peak power losses.  As you note, the RMS current  is the same, but 
the
PEAK current is 1.4 times higher during the peak of the waveform and 
since
that is where the most power is delivered that is also where the most 
loss

occurs in the wire.  So the average power lost in the wire for AC is
almost twice (1.4 squared) the loss in the same wire at DC.

Google it...

That is why the entire industry is looking at DC transmission lines now
that we are finally getting to the point where the up and down 
conversion

is becomming cost competitive with transformers...

Bob
-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Lee Hart via 
EV

Sent: Wednesday, June 08, 2016 2:03 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Off-grid solar house and electric car charging

Robert Bruninga via EV wrote:

 Still not true.  The output of microinverters is at 240 VAC  and the
 average current in the wires will be double as the same number of 
panels

at 480 VDC.

But each microinverter has its own wire. The total current may be twice 
as
much in a 240v system as in a 480v system; but there are twice the 
number

of wires, each half the size. You wind up back where you started.


 Further, AC peak currents are 1.4 times higher than DC so the peak
 currents (where the losses are) are 2.8 times greater


No; AC voltages and currents are normally expressed in RMS
(Root-Mean-Square). RMS voltages and currents have the *same* effective
values, voltage drops, and losses as DC. 120vac and 120vdc are 
completely

equivalent.


 The difference in buying #6 wire instead of #12 is only $180 versus
 $30.  Or you can ignore the extra 10% or so losses and use #10 wire.
 But over the life of the system (20 years) the losses in your solar
 system can add up to many thousands of dollars.


Sure; it's basically an economic decision. How much can you afford
up-front, to reduce long-term losses? It's further complicated because
when you eventually scrap the system, much of the cost of the copper is
recoverable.

Note that this is the EV discussion list. Besides these tradeoffs, 
weight
is also an issue. You may be ahead by deliberately undersizing the wire 
to
save weight. The benefit from weight reduction can exceed the 
efficiency

loss. Racers know this well!


 Maybe I am just being nitpicky, but my solar arrays are all over my
 yard and house.  Some runs are over 300 feet!  (shortest is maybe 
60').


Ah; no wonder you are so concerned with wire lengths. I definitely
consider 60-300 feet *long* runs! The PV panels on my house are only 
20'

from my circuit breaker panel.

--
"IC chip performance doubles every 18 months." -- Moore's law "The 
speed

of software halves every 18 months." -- Gates' law
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Off-grid solar house and electric car charging

[Robert Bruninga via EV]

Im sorry again, but this is simply not true when expanded to WIRE LOSS.

> No; AC voltages and currents... (Root-Mean-Square).
> RMS voltages and currents have the *same* effective
> values, voltage drops, and losses as DC. 120vac and
> 120vdc are completely equivalent.

Yes, as far as VOLTS and as AMPS as averages are concerned.  Such as
average power.  A 1500W resistor will be 1500W whether on DC or RMS AC.

But the power loss in wires feeding that resistor will have greater loss
on AC because of two factors important in distribution systems:

1) SKIN EFFECT where the AC current is pushed to the outside of the wire
so that not all the wire is carrying the same current.  Thus the wire is
not as effective since not all of its copper is being used in an AC system

2) Peak power losses.  As you note, the RMS current  is the same, but the
PEAK current is 1.4 times higher during the peak of the waveform and since
that is where the most power is delivered that is also where the most loss
occurs in the wire.  So the average power lost in the wire for AC is
almost twice (1.4 squared) the loss in the same wire at DC.

Google it...

That is why the entire industry is looking at DC transmission lines now
that we are finally getting to the point where the up and down conversion
is becomming cost competitive with transformers...

Bob
-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Lee Hart via EV
Sent: Wednesday, June 08, 2016 2:03 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Off-grid solar house and electric car charging

Robert Bruninga via EV wrote:
> Still not true.  The output of microinverters is at 240 VAC  and the
> average current in the wires will be double as the same number of panels
at 480 VDC.

But each microinverter has its own wire. The total current may be twice as
much in a 240v system as in a 480v system; but there are twice the number
of wires, each half the size. You wind up back where you started.

> Further, AC peak currents are 1.4 times higher than DC so the peak
> currents (where the losses are) are 2.8 times greater

No; AC voltages and currents are normally expressed in RMS
(Root-Mean-Square). RMS voltages and currents have the *same* effective
values, voltage drops, and losses as DC. 120vac and 120vdc are completely
equivalent.

> The difference in buying #6 wire instead of #12 is only $180 versus
> $30.  Or you can ignore the extra 10% or so losses and use #10 wire.
> But over the life of the system (20 years) the losses in your solar
> system can add up to many thousands of dollars.

Sure; it's basically an economic decision. How much can you afford
up-front, to reduce long-term losses? It's further complicated because
when you eventually scrap the system, much of the cost of the copper is
recoverable.

Note that this is the EV discussion list. Besides these tradeoffs, weight
is also an issue. You may be ahead by deliberately undersizing the wire to
save weight. The benefit from weight reduction can exceed the efficiency
loss. Racers know this well!

> Maybe I am just being nitpicky, but my solar arrays are all over my
> yard and house.  Some runs are over 300 feet!  (shortest is maybe 60').

Ah; no wonder you are so concerned with wire lengths. I definitely
consider 60-300 feet *long* runs! The PV panels on my house are only 20'
from my circuit breaker panel.

--
"IC chip performance doubles every 18 months." -- Moore's law "The speed
of software halves every 18 months." -- Gates' law
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Off-grid solar house and electric car charging

[Lee Hart via EV]

Robert Bruninga via EV wrote:

Still not true.  The output of microinverters is at 240 VAC  and the average
current in the wires will be double as the same number of panels at 480 VDC.


But each microinverter has its own wire. The total current may be twice 
as much in a 240v system as in a 480v system; but there are twice the 
number of wires, each half the size. You wind up back where you started.



Further, AC peak currents are 1.4 times higher than DC so the peak currents
(where the losses are) are 2.8 times greater


No; AC voltages and currents are normally expressed in RMS 
(Root-Mean-Square). RMS voltages and currents have the *same* effective 
values, voltage drops, and losses as DC. 120vac and 120vdc are 
completely equivalent.



The difference in buying #6 wire instead of #12 is only $180 versus $30.  Or
you can ignore the extra 10% or so losses and use #10 wire.  But over the
life of the system (20 years) the losses in your solar system can add up to
many thousands of dollars.


Sure; it's basically an economic decision. How much can you afford 
up-front, to reduce long-term losses? It's further complicated because 
when you eventually scrap the system, much of the cost of the copper is 
recoverable.


Note that this is the EV discussion list. Besides these tradeoffs, 
weight is also an issue. You may be ahead by deliberately undersizing 
the wire to save weight. The benefit from weight reduction can exceed 
the efficiency loss. Racers know this well!



Maybe I am just being nitpicky, but my solar arrays are all over my yard and
house.  Some runs are over 300 feet!  (shortest is maybe 60').


Ah; no wonder you are so concerned with wire lengths. I definitely 
consider 60-300 feet *long* runs! The PV panels on my house are only 20' 
from my circuit breaker panel.


--
"IC chip performance doubles every 18 months." -- Moore's law
"The speed of software halves every 18 months." -- Gates' law
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Off-grid solar house and electric car charging

[Lee Hart via EV]

Peri Hartman via EV wrote:

I think Lee was referring to how you wire the panels together, not the
house. You could wire your panels in parallel and, as long as your
inverter is near the panels, not incur any more line losses than a
series system.


Right! PV panels are physically large, even larger than batteries. Thus 
there is inevitably a fair amount of wire needed to connect them together.


We must simply try to locate the source and the load as close together 
as possible. That minimizes the *total* amount of wire (both length and 
cross-sectional area), and that will tend to optimize cost, performance, 
and efficiency. Often, the differences between series/parallel aren't as 
significant as you might think. They can be small enough that other 
factors matter more.


--
"IC chip performance doubles every 18 months." -- Moore's law
"The speed of software halves every 18 months." -- Gates' law
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Off-grid solar house and electric car charging

[Robert Bruninga via EV]

Just to clarify...

>The only time high voltage helps is when you need to have
> long wire runs [and long means over a few tens of feet]
>
> However, if you're using small low-voltage individual inverters
> mounted right on each panel to one big central inverter located
> far away, then the small inverters can "win" and use less copper
> overall.

Still not true.  The output of microinverters is at 240 VAC  and the average
current in the wires will be double as the same number of panels at 480 VDC.
Further, AC peak currents are 1.4 times higher than DC so the peak currents
(where the losses are) are 2.8 times greater, and since losses in the wire
are proportional to current squared, the losses in the same wire will be
almost 8 times as much.  Hence you always have the choise to either use much
bigger wire, or accept the greater losses at low voltages.

The difference in buying #6 wire instead of #12 is only $180 versus $30.  Or
you can ignore the extra 10% or so losses and use #10 wire.  But over the
life of the system (20 years) the losses in your solar system can add up to
many thousands of dollars.

Maybe I am just being nitpicky, but my solar arrays are all over my yard and
house.  Some runs are over 300 feet!  (shortest is maybe 60').

>You have to carefully consider the specifics of the situation, and not
>make snap judgements about low voltages being automatically worse.

True, just be informed and make your design based on it.Bob
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Re: [EVDL] Off-grid solar house and electric car charging

[Lee Hart via EV]

David Kerzel wrote:

In example 1 series you have 2 12 inch leads out of the pack.
In example 2 parallel you use all the leads to connect them together and the
12 inch leads out of the pack are missing,  They would add .001 ohm each if
the same size wire which is a second 40 watts.


View with a fixed-width font like Courier. Ignore the dots; they just 
trick Microsoft into not deleting all the extra spaces.


Example 1 (series), four 12" pieces of wire (the / and \):
+O . . . . . . O . . . . . . O-
. \ . . . . . / \ . . . . . /
. .+ battery - . + battery -

Example 2 (parallel), four 12" pieces of wire (/ and \):
. .+ battery -
. / . . . . . \
.O+ . . . . . -O
. \ . . . . . /
. .+ battery -

Identical wire sizes, wire lengths, and wire resistive losses, 
regardless of whether wired for low voltage or high voltage.


The purpose is not to show that one way or another is always "best". It 
ain't that easy! The point of these examples is that you have to THINK 
about how things are wired, and not just fall for conventional wisdom 
that is often inappropriate or even wrong.

--
"IC chip performance doubles every 18 months." -- Moore's law
"The speed of software halves every 18 months." -- Gates' law
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Off-grid solar house and electric car charging

[Lee Hart via EV]

Robert Bruninga via EV wrote:

The only time high voltage helps is when you need to have long wire

runs...

The operative word  is "long"  And when you wire a house for every room
and for every appliance and for every outlet (whether used fully or not)
then every wire is "long".


What is "long" to you may be "short" to others. Let's put numbers on it, 
Robert.


In my house, the longest run from circuit breaker panel to the farthest 
outlet is about 35 feet. Current wiring practices use #12 wire on a 15 
amp circuit. #12 has a resistance of 1.588 milliohms per foot. So this 
35-foot run has a total resistance of 70 feet x 0.001588ohm = 0.111 
ohms. Google tells me that #12-2 with ground is currently selling for 
about $0.28/foot; so 35 feet costs $10.


You're only allowed to load a 15 amp circuit to 12 amps continuously 
(1440 watts). So the worst-case voltage drop is 12a x 0.111ohm = 1.33v, 
and power loss is I^2R = 12^2 x 0.111 = 16 watts. 16w/1440w = 0.011 or 
just over 1% of your power is lost.


24vdc is a common PV panel voltage. Let's assume we simply distributed 
this power directly, through the same 35 feet of #12 wire. (It would be 
silly to do it this way, but just for the sake of argument...)


We have 24v/120v = 1/5th of the voltage, so we need 5 times the current 
to get the same power. The voltage drop will be 5 times more; 1.33v x 5 
= 6.65v. The current is 12 x 5 = 60 amps, and I^2R losses would 25 times 
more, so 16 x 25 = 400 watts. We'd be wasting about 25% of our power in 
wire losses. Besides, #12 wire would overheat and isn't safe at this 
current.


So realistically, we'd increase the wire size; probably to #6. We only 
need 2 wires (not 3) because you don't need a separate ground wire on 
24v systems. Google says #6-2 is $0.87/foot, so the 35-foot run is 
$30.52 ($20 more).


#6 resistance is 0.3951 milliohms/foot, so a 35-foot run is 70 feet x 
0.0003951ohm = 0.01383 ohms. The worst-case voltage drop is 60a x 
0.01383ohm = 0.829v, and power loss is I^2R = 60^2 x 0.01383 = 49.7 
watts. 49.7w/1440w = 0.0345 or about 3.5% of our power is lost.


Bottom line: The 24v approach works fine, but costs $20 more and is 2% 
less efficient. Whether you consider that a little or a lot is a matter 
of opinion.


And... this is the EV list; no one is going to have a 35-foot run in 
their car. And PV panels (or more likely batteries) are a distributed 
source, so you have many small individual wires to each of them anyway; 
not one big cable. Design the system around the situation you've got; 
not with rules of thumb that don't apply to the situation.

--
"IC chip performance doubles every 18 months." -- Moore's law
"The speed of software halves every 18 months." -- Gates' law
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Off-grid solar house and electric car charging

[Robert Bruninga via EV]

I thought the original question was about wiring an off grid house for low
voltage DC versus throughout and using all DC appliances and equipment
instead of 120/240 VAC like all other houses

-Original Message-
> I think Lee was referring to how you wire the panels together,
> not the house.  You could wire your panels in parallel and,
> as long as your inverter is near the panels, not incur any more line
> losses > than a series system.


Peri

-- Original Message --
From: "Robert Bruninga via EV" 
To: "Electric Vehicle Discussion List" 
Sent: 08-Jun-16 5:47:59 AM
Subject: Re: [EVDL] Off-grid solar house and electric car charging

>>  The only time high voltage helps is when you need to have long wire
>runs...
>
>The operative word  is "long"  And when you wire a house for every room
>and for every appliance and for every outlet (whether used fully or
>not)  then every wire is "long".
>
>The academic argument below is like saying there is nothing wrong with
>falling out of an airplane.  Its only when you hit the ground that you
>have a problem...
>
>Bob
>-Original Message-
>From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Lee Hart via
>Sent: Tuesday, June 07, 2016 11:24 PM
>To: Larry Gales; Electric Vehicle Discussion List
>Subject: Re: [EVDL] Off-grid solar house and electric car charging
>
>Larry Gales via EV wrote:
>>  Thanks, I was somewhat aware of the increased use of copper,
>> but not to the extent that you specify, so it looks like AC is the
>>  way to go,   even for off-grid solar.
>
>Lower voltage means higher current and bigger wires; but it's not as
>bad as you think.
>
>First, consider a motor or transformer. You would think that winding it
>for a lower voltage / higher current would require more copper... but
>it doesn't. Motors and transformers are exactly the same size, have the
>same efficiency, same power rating, and use the same amount of copper
>no matter what voltage they are built for.
>
>Here's why: If you halve the voltage, you double the current (to get
>the same power). But half the voltage requires half the turns. So the
>wire is twice as think, but half as long. The total amount of copper
>thus stays the same. This only breaks down if the voltage is so low
>that you need less than 1 turn, or if the voltage is so high that
>excessive amounts of space are taken up by insulation instead of
>copper.
>
>Now consider a pair of identical 12v batteries. You can wire them in
>series (24v), or parallel (12v). For the same power, you'll have the
>same current in each battery (since their voltages are all the same).
>So, the same wire size to every battery. For the sake of argument,
>let's assume you connect a 12" piece of wire to every battery post, and
>it has
>1 milliohm of resistance.
>
>If they're in series, you have a total of 4 feet of wire total, all in
>series, and so 4 milliohms of resistance. if the load is 24v at 100
>amps, then this 4 milliohms is burning up I^2R = 100^2 x 0.004 = 40
>watts as heat.
>
>If they're in parallel, the free ends of the + wires connect together,
>and the free ends of the - wires connect together. Now you have two
>parallel strings, each with 2 feet of wire in it; so each string has
>half the resistance or 2 milliohms. But there are two of these strings
>in parallel, so the total resistance is 1 milliohm. The same load power
>is 12v at 200a.
>I^2R losses are 200^2 x 0.001 = 40 watts.
>
>Exactly the same size and length of wire, and exactly the same losses!
>
>The same thing happens with PV panels, power semiconductors, and just
>about any power devices. Arranging them for low voltage/high current
>results in the same losses as arranging them fro high voltage/low
>current.
>
>The only time high voltage helps is when you need to have long wire
>runs.
>If your PV panels are far from your inverter, then high voltage for the
>wires between them will the reduce the amount of copper needed and/or
>lower your losses. However, if you're using small low-voltage
>individual inverters mounted right on each panel to one big central
>inverter located far away, then the small inverters can "win" and use
>less copper overall.
>
>You have to carefully consider the specifics of the situation, and not
>make snap judgements about low voltages being automatically worse.
>--
>"IC chip performance doubles every 18 months." -- Moore's law "The
>speed of software halves every 18 months." -- Gates' law
>--
>Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
>___
>UNSUBSCRIBE: http:

Re: [EVDL] Off-grid solar house and electric car charging

[Peri Hartman via EV]

I think Lee was referring to how you wire the panels together, not the 
house.  You could wire your panels in parallel and, as long as your 
inverter is near the panels, not incur any more line losses than a 
series system.


Peri

-- Original Message --
From: "Robert Bruninga via EV" 
To: "Electric Vehicle Discussion List" 
Sent: 08-Jun-16 5:47:59 AM
Subject: Re: [EVDL] Off-grid solar house and electric car charging


 The only time high voltage helps is when you need to have long wire

runs...

The operative word  is "long"  And when you wire a house for every room
and for every appliance and for every outlet (whether used fully or 
not)

then every wire is "long".

The academic argument below is like saying there is nothing wrong with
falling out of an airplane.  Its only when you hit the ground that you
have a problem...

Bob
-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Lee Hart via 
EV

Sent: Tuesday, June 07, 2016 11:24 PM
To: Larry Gales; Electric Vehicle Discussion List
Subject: Re: [EVDL] Off-grid solar house and electric car charging

Larry Gales via EV wrote:

 Thanks, I was somewhat aware of the increased use of copper, but not
 to the extent that you specify, so it looks like AC is the way to go,
 even for off-grid solar.


Lower voltage means higher current and bigger wires; but it's not as 
bad

as you think.

First, consider a motor or transformer. You would think that winding it
for a lower voltage / higher current would require more copper... but 
it
doesn't. Motors and transformers are exactly the same size, have the 
same
efficiency, same power rating, and use the same amount of copper no 
matter

what voltage they are built for.

Here's why: If you halve the voltage, you double the current (to get 
the
same power). But half the voltage requires half the turns. So the wire 
is

twice as think, but half as long. The total amount of copper thus stays
the same. This only breaks down if the voltage is so low that you need
less than 1 turn, or if the voltage is so high that excessive amounts 
of

space are taken up by insulation instead of copper.

Now consider a pair of identical 12v batteries. You can wire them in
series (24v), or parallel (12v). For the same power, you'll have the 
same

current in each battery (since their voltages are all the same).
So, the same wire size to every battery. For the sake of argument, 
let's
assume you connect a 12" piece of wire to every battery post, and it 
has

1 milliohm of resistance.

If they're in series, you have a total of 4 feet of wire total, all in
series, and so 4 milliohms of resistance. if the load is 24v at 100 
amps,

then this 4 milliohms is burning up I^2R = 100^2 x 0.004 = 40 watts as
heat.

If they're in parallel, the free ends of the + wires connect together, 
and
the free ends of the - wires connect together. Now you have two 
parallel

strings, each with 2 feet of wire in it; so each string has half the
resistance or 2 milliohms. But there are two of these strings in 
parallel,
so the total resistance is 1 milliohm. The same load power is 12v at 
200a.

I^2R losses are 200^2 x 0.001 = 40 watts.

Exactly the same size and length of wire, and exactly the same losses!

The same thing happens with PV panels, power semiconductors, and just
about any power devices. Arranging them for low voltage/high current
results in the same losses as arranging them fro high voltage/low 
current.


The only time high voltage helps is when you need to have long wire 
runs.

If your PV panels are far from your inverter, then high voltage for the
wires between them will the reduce the amount of copper needed and/or
lower your losses. However, if you're using small low-voltage 
individual
inverters mounted right on each panel to one big central inverter 
located
far away, then the small inverters can "win" and use less copper 
overall.


You have to carefully consider the specifics of the situation, and not
make snap judgements about low voltages being automatically worse.
--
"IC chip performance doubles every 18 months." -- Moore's law "The 
speed

of software halves every 18 months." -- Gates' law
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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(http://groups.yahoo.com/group/NEDRA)





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Re: [EVDL] Off-grid solar house and electric car charging

[jerry freedomev via EV]

    Hi Robert and All,   You way overstate your case in 
several ways.  First one can just use the same RMS voltage DC as AC.  It's not 
like we EV people are not use to it especially, it's arcing problem are greatly 
exaggerated with good DC practice.   Next most things even on 
12vdc run on under 2 amps, most under .5amp.  My fan is just 1 amp, LED lights 
.5 amp, computer 2amp, phone 1 amp charging, fridge 5 amps when running.
   I cook with just 5-20 amps, e blanket 2 amps at 12vdc.  Other than 
kitchen, bath, other high power unit like an A/C that one can bunch together 
you really don't need more than present 120vac wire size. And even some home  
model switches work at 120vdc IIRC, SqD?. Or use a low cost 
inverter for these .   I use a 3k wt peak, 2kw cont $129 inverter runs my a/c 
window unit.  My recent disassembly of a Miata for my next EV 
suspension also gave me an a/c unit I can drive very efficiently with a  PM 
motor  from 24vdc could make my a/c only be   200wt at about 3500btu.   
   And many power supplies now work off 300vdc+ from rectified ac so 
running 350vdc could end up using less copper if you want to get picky. And 
homes run on used EV packs as pulled from wrecks..  A well 
designed home will have centralized power, utilities, kitchen, bath making big 
copper runs very short and the rest little different.  The other savings and 
reliability of battery  DC with modern DC power supplies  makes DC at least 
competitive if not better.    Kind of like EVs fighting the 
established ICE machine, DC does have a future as homes, building go to clean 
and battery power.    And EVs will change to be part of these 
systems, especially 200 mile EVs with their excess capacity with 20-50kwhr to 
play with and still have 100 mile range. Many homes, businesses will be powered 
by these charged by solar.  Jerry Dycus

  From: Robert Bruninga via EV 
 To: Electric Vehicle Discussion List  
 Sent: Wednesday, June 8, 2016 8:47 AM
 Subject: Re: [EVDL] Off-grid solar house and electric car charging
   
> The only time high voltage helps is when you need to have long wire
runs...

The operative word  is "long"  And when you wire a house for every room
and for every appliance and for every outlet (whether used fully or not)
then every wire is "long".

The academic argument below is like saying there is nothing wrong with
falling out of an airplane.  Its only when you hit the ground that you
have a problem...

Bob
-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Lee Hart via EV
Sent: Tuesday, June 07, 2016 11:24 PM
To: Larry Gales; Electric Vehicle Discussion List
Subject: Re: [EVDL] Off-grid solar house and electric car charging

Larry Gales via EV wrote:
> Thanks, I was somewhat aware of the increased use of copper, but not
> to the extent that you specify, so it looks like AC is the way to go,
> even for off-grid solar.

Lower voltage means higher current and bigger wires; but it's not as bad
as you think.

First, consider a motor or transformer. You would think that winding it
for a lower voltage / higher current would require more copper... but it
doesn't. Motors and transformers are exactly the same size, have the same
efficiency, same power rating, and use the same amount of copper no matter
what voltage they are built for.

Here's why: If you halve the voltage, you double the current (to get the
same power). But half the voltage requires half the turns. So the wire is
twice as think, but half as long. The total amount of copper thus stays
the same. This only breaks down if the voltage is so low that you need
less than 1 turn, or if the voltage is so high that excessive amounts of
space are taken up by insulation instead of copper.

Now consider a pair of identical 12v batteries. You can wire them in
series (24v), or parallel (12v). For the same power, you'll have the same
current in each battery (since their voltages are all the same).
So, the same wire size to every battery. For the sake of argument, let's
assume you connect a 12" piece of wire to every battery post, and it has
1 milliohm of resistance.

If they're in series, you have a total of 4 feet of wire total, all in
series, and so 4 milliohms of resistance. if the load is 24v at 100 amps,
then this 4 milliohms is burning up I^2R = 100^2 x 0.004 = 40 watts as
heat.

If they're in parallel, the free ends of the + wires connect together, and
the free ends of the - wires connect together. Now you have two parallel
strings, each with 2 feet of wire in it; so each string has half the
resistance or 2 milliohms. But there are two of these strings in parallel,
so the total resistance is 1 milliohm. The same load power is 12v at 200a.
I

Re: [EVDL] Off-grid solar house and electric car charging

[David Kerzel via EV]

In example 1 series you have 2 12 inch leads out of the pack.
In example 2 parallel you use all the leads to connect them together and the
12 inch leads out of the pack are missing,  They would add .001 ohm each if
the same size wire which is a second 40 watts.
david

-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Lee Hart via EV
Sent: Tuesday, June 07, 2016 11:24 PM
To: Larry Gales; Electric Vehicle Discussion List
Subject: Re: [EVDL] Off-grid solar house and electric car charging

Larry Gales via EV wrote:
> Thanks, I was somewhat aware of the increased use of copper, but not 
> to the extent that you specify, so it looks like AC is the way to go, 
> even for off-grid solar.

Lower voltage means higher current and bigger wires; but it's not as bad as
you think.

First, consider a motor or transformer. You would think that winding it for
a lower voltage / higher current would require more copper... but it
doesn't. Motors and transformers are exactly the same size, have the same
efficiency, same power rating, and use the same amount of copper no matter
what voltage they are built for.

Here's why: If you halve the voltage, you double the current (to get the
same power). But half the voltage requires half the turns. So the wire is
twice as think, but half as long. The total amount of copper thus stays the
same. This only breaks down if the voltage is so low that you need less than
1 turn, or if the voltage is so high that excessive amounts of space are
taken up by insulation instead of copper.

Now consider a pair of identical 12v batteries. You can wire them in series
(24v), or parallel (12v). For the same power, you'll have the same current
in each battery (since their voltages are all the same). 
So, the same wire size to every battery. For the sake of argument, let's
assume you connect a 12" piece of wire to every battery post, and it has
1 milliohm of resistance.

If they're in series, you have a total of 4 feet of wire total, all in
series, and so 4 milliohms of resistance. if the load is 24v at 100 amps,
then this 4 milliohms is burning up I^2R = 100^2 x 0.004 = 40 watts as heat.

If they're in parallel, the free ends of the + wires connect together, and
the free ends of the - wires connect together. Now you have two parallel
strings, each with 2 feet of wire in it; so each string has half the
resistance or 2 milliohms. But there are two of these strings in parallel,
so the total resistance is 1 milliohm. The same load power is 12v at 200a.
I^2R losses are 200^2 x 0.001 = 40 watts.

Exactly the same size and length of wire, and exactly the same losses!

The same thing happens with PV panels, power semiconductors, and just about
any power devices. Arranging them for low voltage/high current results in
the same losses as arranging them fro high voltage/low current.

The only time high voltage helps is when you need to have long wire runs. If
your PV panels are far from your inverter, then high voltage for the wires
between them will the reduce the amount of copper needed and/or lower your
losses. However, if you're using small low-voltage individual inverters
mounted right on each panel to one big central inverter located far away,
then the small inverters can "win" and use less copper overall.

You have to carefully consider the specifics of the situation, and not make
snap judgements about low voltages being automatically worse.
--
"IC chip performance doubles every 18 months." -- Moore's law "The speed of
software halves every 18 months." -- Gates' law
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
___
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Re: [EVDL] Off-grid solar house and electric car charging

[Robert Bruninga via EV]

> The only time high voltage helps is when you need to have long wire
runs...

The operative word  is "long"  And when you wire a house for every room
and for every appliance and for every outlet (whether used fully or not)
then every wire is "long".

The academic argument below is like saying there is nothing wrong with
falling out of an airplane.  Its only when you hit the ground that you
have a problem...

Bob
-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Lee Hart via EV
Sent: Tuesday, June 07, 2016 11:24 PM
To: Larry Gales; Electric Vehicle Discussion List
Subject: Re: [EVDL] Off-grid solar house and electric car charging

Larry Gales via EV wrote:
> Thanks, I was somewhat aware of the increased use of copper, but not
> to the extent that you specify, so it looks like AC is the way to go,
> even for off-grid solar.

Lower voltage means higher current and bigger wires; but it's not as bad
as you think.

First, consider a motor or transformer. You would think that winding it
for a lower voltage / higher current would require more copper... but it
doesn't. Motors and transformers are exactly the same size, have the same
efficiency, same power rating, and use the same amount of copper no matter
what voltage they are built for.

Here's why: If you halve the voltage, you double the current (to get the
same power). But half the voltage requires half the turns. So the wire is
twice as think, but half as long. The total amount of copper thus stays
the same. This only breaks down if the voltage is so low that you need
less than 1 turn, or if the voltage is so high that excessive amounts of
space are taken up by insulation instead of copper.

Now consider a pair of identical 12v batteries. You can wire them in
series (24v), or parallel (12v). For the same power, you'll have the same
current in each battery (since their voltages are all the same).
So, the same wire size to every battery. For the sake of argument, let's
assume you connect a 12" piece of wire to every battery post, and it has
1 milliohm of resistance.

If they're in series, you have a total of 4 feet of wire total, all in
series, and so 4 milliohms of resistance. if the load is 24v at 100 amps,
then this 4 milliohms is burning up I^2R = 100^2 x 0.004 = 40 watts as
heat.

If they're in parallel, the free ends of the + wires connect together, and
the free ends of the - wires connect together. Now you have two parallel
strings, each with 2 feet of wire in it; so each string has half the
resistance or 2 milliohms. But there are two of these strings in parallel,
so the total resistance is 1 milliohm. The same load power is 12v at 200a.
I^2R losses are 200^2 x 0.001 = 40 watts.

Exactly the same size and length of wire, and exactly the same losses!

The same thing happens with PV panels, power semiconductors, and just
about any power devices. Arranging them for low voltage/high current
results in the same losses as arranging them fro high voltage/low current.

The only time high voltage helps is when you need to have long wire runs.
If your PV panels are far from your inverter, then high voltage for the
wires between them will the reduce the amount of copper needed and/or
lower your losses. However, if you're using small low-voltage individual
inverters mounted right on each panel to one big central inverter located
far away, then the small inverters can "win" and use less copper overall.

You have to carefully consider the specifics of the situation, and not
make snap judgements about low voltages being automatically worse.
--
"IC chip performance doubles every 18 months." -- Moore's law "The speed
of software halves every 18 months." -- Gates' law
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
___
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Re: [EVDL] Off-grid solar house and electric car charging

[Lee Hart via EV]

Larry Gales via EV wrote:

Thanks, I was somewhat aware of the increased use of copper, but not to the
extent that you specify, so it looks like AC is the way to go, even for
off-grid solar.


Lower voltage means higher current and bigger wires; but it's not as bad 
as you think.


First, consider a motor or transformer. You would think that winding it 
for a lower voltage / higher current would require more copper... but it 
doesn't. Motors and transformers are exactly the same size, have the 
same efficiency, same power rating, and use the same amount of copper no 
matter what voltage they are built for.


Here's why: If you halve the voltage, you double the current (to get the 
same power). But half the voltage requires half the turns. So the wire 
is twice as think, but half as long. The total amount of copper thus 
stays the same. This only breaks down if the voltage is so low that you 
need less than 1 turn, or if the voltage is so high that excessive 
amounts of space are taken up by insulation instead of copper.


Now consider a pair of identical 12v batteries. You can wire them in 
series (24v), or parallel (12v). For the same power, you'll have the 
same current in each battery (since their voltages are all the same). 
So, the same wire size to every battery. For the sake of argument, let's 
assume you connect a 12" piece of wire to every battery post, and it has 
1 milliohm of resistance.


If they're in series, you have a total of 4 feet of wire total, all in 
series, and so 4 milliohms of resistance. if the load is 24v at 100 
amps, then this 4 milliohms is burning up I^2R = 100^2 x 0.004 = 40 
watts as heat.


If they're in parallel, the free ends of the + wires connect together, 
and the free ends of the - wires connect together. Now you have two 
parallel strings, each with 2 feet of wire in it; so each string has 
half the resistance or 2 milliohms. But there are two of these strings 
in parallel, so the total resistance is 1 milliohm. The same load power 
is 12v at 200a. I^2R losses are 200^2 x 0.001 = 40 watts.


Exactly the same size and length of wire, and exactly the same losses!

The same thing happens with PV panels, power semiconductors, and just 
about any power devices. Arranging them for low voltage/high current 
results in the same losses as arranging them fro high voltage/low current.


The only time high voltage helps is when you need to have long wire 
runs. If your PV panels are far from your inverter, then high voltage 
for the wires between them will the reduce the amount of copper needed 
and/or lower your losses. However, if you're using small low-voltage 
individual inverters mounted right on each panel to one big central 
inverter located far away, then the small inverters can "win" and use 
less copper overall.


You have to carefully consider the specifics of the situation, and not 
make snap judgements about low voltages being automatically worse.

--
"IC chip performance doubles every 18 months." -- Moore's law
"The speed of software halves every 18 months." -- Gates' law
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Off-grid solar house and electric car charging

[Haudy Kazemi via EV]

I would agree. Lower priced mass produced commodity AC appliances and lower 
wiring/switch/outlet costs will make up for the inverter inefficiencies. Keep 
in mind the amount of useful energy that you need to get out of a system and 
then choose components that will get you there. Max technical efficiency (kWh 
usefully used vs kWh produced by array, or kWh produced/sq. m) is unlikely to 
match max economic efficiency ($/kWh), rather there will be a range of choices 
with tradeoffs, some large, some small. 

Even if you increase the size of your PV array by 10% to offset the 
inverter...you're only talking two extra 250 watt modules (500 W total) on 5 kW 
system. Parts cost can be under $1000 here ($2/watt). (You could also try 
increasing the array size to offset the losses from using a bit smaller DC 
wiring, if you really didn't want AC involved. There is going to be a financial 
sweet spot between various array sizes and the losses associated with a chosen 
wire size.)

Another consideration: future inspectors and owners will likely appreciate the 
use of standardized equipment and techniques.

The math may be a bit different if the electric loads are minimal (e.g. only 
efficient lights) and/or distances short (small cabin/trailer).


On June 7, 2016 11:10:49 AM CDT, Larry Gales via EV  wrote:
>Thanks, I was somewhat aware of the increased use of copper, but not to
>the
>extent that you specify, so it looks like AC is the way to go, even for
>off-grid solar.
>
>On Tue, Jun 7, 2016 at 9:06 AM, robert winfield via EV
>
>wrote:
>
>> my inverter (Omnion 2200) has 2 legs. +/- 186v DC (~370v) small
>wires.,
>> inverted to 110v AC about ~8 amps with a 20 amp circuit breaker (made
>back
>> around 1995 - 1997 or so)
>>
>>   From: Robert Bruninga via EV 
>>  To: Electric Vehicle Discussion List 
>>  Sent: Tuesday, June 7, 2016 10:39 AM
>>  Subject: Re: [EVDL] Off-grid solar house and electric car charging
>>
>> > If you build an off-grid solar house and use it for both your house
>> > and charging your electric car, are there any disadvantages for
>using
>> > DC current (household appliances can all be converted to DC) and
>> > avoiding AC since you are off the grid?  You avoid the cost,
>> > maintenance, and (slight) inefficiency of inverters, but are there
>> > significant disadvantages to this approach?
>>
>> A big question is what voltage.  Home solar typically uses high
>voltage
>> 300 to 600 VDC so that currents are less and smaller copper wire can
>be
>> used (think #12 standard wire).
>>
>> Remote, Off -grid DC systems typically operate no higher than 48
>volts.
>> Right there is a 10 to 1 drop in voltage so a 100 to 1 increase in
>cable
>> losses.  Now think big battery cables everywhere and a huge
>investment in
>> copper.
>>
>> Some people then drop to 12v to use many common 12 camping
>accessories to
>> live by.  That then further multiplies wire losses by another eight
>to one
>> factor, or almost 800 times more losses for the same wire.
>>
>> So In most cases, it is far, far easier to accept the 5% Inverter
>lossess
>> and keep your house at the 120 VAC standard so you can use all
>existing
>> home wiring techniques and all existing home appliances and all
>existing
>> electrical things in the home than to deal with ALL specialized much
>more
>> expensive DC appliances and HUGELY expensive specialized wiring.
>>
>> Bob
>> ___
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>> Read EVAngel's EV News at http://evdl.org/evln/
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>> http://groups.yahoo.com/group/NEDRA)
>>
>>
>>
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>> http://groups.yahoo.com/group/NEDRA)
>>
>>
>
>
>-- 
>Larry Gales
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Re: [EVDL] Off-grid solar house and electric car charging

[Larry Gales via EV]

Thanks, I was somewhat aware of the increased use of copper, but not to the
extent that you specify, so it looks like AC is the way to go, even for
off-grid solar.

On Tue, Jun 7, 2016 at 9:06 AM, robert winfield via EV 
wrote:

> my inverter (Omnion 2200) has 2 legs. +/- 186v DC (~370v) small wires.,
> inverted to 110v AC about ~8 amps with a 20 amp circuit breaker (made back
> around 1995 - 1997 or so)
>
>   From: Robert Bruninga via EV 
>  To: Electric Vehicle Discussion List 
>  Sent: Tuesday, June 7, 2016 10:39 AM
>  Subject: Re: [EVDL] Off-grid solar house and electric car charging
>
> > If you build an off-grid solar house and use it for both your house
> > and charging your electric car, are there any disadvantages for using
> > DC current (household appliances can all be converted to DC) and
> > avoiding AC since you are off the grid?  You avoid the cost,
> > maintenance, and (slight) inefficiency of inverters, but are there
> > significant disadvantages to this approach?
>
> A big question is what voltage.  Home solar typically uses high voltage
> 300 to 600 VDC so that currents are less and smaller copper wire can be
> used (think #12 standard wire).
>
> Remote, Off -grid DC systems typically operate no higher than 48 volts.
> Right there is a 10 to 1 drop in voltage so a 100 to 1 increase in cable
> losses.  Now think big battery cables everywhere and a huge investment in
> copper.
>
> Some people then drop to 12v to use many common 12 camping accessories to
> live by.  That then further multiplies wire losses by another eight to one
> factor, or almost 800 times more losses for the same wire.
>
> So In most cases, it is far, far easier to accept the 5% Inverter lossess
> and keep your house at the 120 VAC standard so you can use all existing
> home wiring techniques and all existing home appliances and all existing
> electrical things in the home than to deal with ALL specialized much more
> expensive DC appliances and HUGELY expensive specialized wiring.
>
> Bob
> ___
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>
>
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>
>


-- 
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Re: [EVDL] Off-grid solar house and electric car charging

[robert winfield via EV]

my inverter (Omnion 2200) has 2 legs. +/- 186v DC (~370v) small wires., 
inverted to 110v AC about ~8 amps with a 20 amp circuit breaker (made back 
around 1995 - 1997 or so)

  From: Robert Bruninga via EV 
 To: Electric Vehicle Discussion List  
 Sent: Tuesday, June 7, 2016 10:39 AM
 Subject: Re: [EVDL] Off-grid solar house and electric car charging
   
> If you build an off-grid solar house and use it for both your house
> and charging your electric car, are there any disadvantages for using
> DC current (household appliances can all be converted to DC) and
> avoiding AC since you are off the grid?  You avoid the cost,
> maintenance, and (slight) inefficiency of inverters, but are there
> significant disadvantages to this approach?

A big question is what voltage.  Home solar typically uses high voltage
300 to 600 VDC so that currents are less and smaller copper wire can be
used (think #12 standard wire).

Remote, Off -grid DC systems typically operate no higher than 48 volts.
Right there is a 10 to 1 drop in voltage so a 100 to 1 increase in cable
losses.  Now think big battery cables everywhere and a huge investment in
copper.

Some people then drop to 12v to use many common 12 camping accessories to
live by.  That then further multiplies wire losses by another eight to one
factor, or almost 800 times more losses for the same wire.

So In most cases, it is far, far easier to accept the 5% Inverter lossess
and keep your house at the 120 VAC standard so you can use all existing
home wiring techniques and all existing home appliances and all existing
electrical things in the home than to deal with ALL specialized much more
expensive DC appliances and HUGELY expensive specialized wiring.

Bob
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Re: [EVDL] Off-grid solar house and electric car charging

[Robert Bruninga via EV]

> If you build an off-grid solar house and use it for both your house
> and charging your electric car, are there any disadvantages for using
> DC current (household appliances can all be converted to DC) and
> avoiding AC since you are off the grid?  You avoid the cost,
> maintenance, and (slight) inefficiency of inverters, but are there
> significant disadvantages to this approach?

A big question is what voltage.  Home solar typically uses high voltage
300 to 600 VDC so that currents are less and smaller copper wire can be
used (think #12 standard wire).

Remote, Off -grid DC systems typically operate no higher than 48 volts.
Right there is a 10 to 1 drop in voltage so a 100 to 1 increase in cable
losses.  Now think big battery cables everywhere and a huge investment in
copper.

Some people then drop to 12v to use many common 12 camping accessories to
live by.  That then further multiplies wire losses by another eight to one
factor, or almost 800 times more losses for the same wire.

So In most cases, it is far, far easier to accept the 5% Inverter lossess
and keep your house at the 120 VAC standard so you can use all existing
home wiring techniques and all existing home appliances and all existing
electrical things in the home than to deal with ALL specialized much more
expensive DC appliances and HUGELY expensive specialized wiring.

Bob
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Re: [EVDL] Off-grid solar house and electric car charging

[Lee Hart via EV]

Michael Ross via EV wrote:

Mike is correct - a single old inefficient panel can draw a sustained arc
an inch or longer. Some decent sized farms have burned down because you
can't just turn off the sun. There are important safety concern to learn
about.


120v DC was used for power distribution in the early 1900's (the Edison 
system). It certainly worked! The light switches, fuses, etc. were all 
built to safely switch DC, despite the extra arcing. You can still find 
some of the old porcelain switches, fuses, and light sockets lurking 
around in Grandpa's garage, often still in service. A little digging 
into history should reveal the pluses and minuses of this approach.


But I think it makes more sense to aim a DC system for a lower voltage; 
say 24v to 48v DC. Arcing is a lot less of a problem, and lots of 
equipment is already designed to run on these voltage.


--
"IC chip performance doubles every 18 months." -- Moore's law
"The speed of software halves every 18 months." -- Gates' law
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Off-grid solar house and electric car charging

[Robert Bruninga via EV]

Sanity check:  The only reason to build off-grid is if the Power Company
wants more than $15,000 to run the lines to your house.  If you are near
the lines, and for some reason insist on not connecting, then you will be
wasting $2 of every $3 your solar investment on batteries and maintenance
for the rest of your life.  Don't even think about it.  In most states,
with net metering, the grid is your storage system.  And its FREE (well
mine is about $5 a month minimum).

See http://aprs.org/off-grid-NOT.html

Though some backwards states with fossil fueled politicians are holding
back their state's progress on solar.

Bob, WB4APR

-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Larry Gales via
EV
Sent: Sunday, June 05, 2016 10:29 PM
To: Electric Vehicle Discussion List; SEVA
Subject: [EVDL] Off-grid solar house and electric car charging

If you build an off-grid solar house and use it for both your house and
charging your electric car, are there any disadvantages for using DC
current (household appliances can all be converted to DC) and avoiding AC
since you are off the grid?  You avoid the cost, maintenance, and (slight)
inefficiency of inverters, but are there significant disadvantages to this
approach?

Thanks,

--
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Re: [EVDL] Off-grid solar house and electric car charging

[Michael Ross via EV]

Mike is correct - a single old inefficient panel can draw a sustained arc
an inch or longer. Some decent sized farms have burned down because you
can't just turn off the sun. There are important safety concern to learn
about.
On Jun 6, 2016 12:28 AM, "Mike Nickerson via EV"  wrote:

The main issue I can think of is the risk of someone unplugging something
drawing high current.  There could be a lot more flash and arc than people
would expect from AC.  Also, the conversion to DC would require new
switches that were DC rated on the appliances.

How would you put DC into the electric car?  I could see how a conversion
could be set up for DC, but it seems it would be difficult for a commercial
EV.  They have a way to take DC direct inputs, but only under certain
specifications.

Mike


On June 5, 2016 8:29:08 PM MDT, Larry Gales via EV 
wrote:
>If you build an off-grid solar house and use it for both your house and
>charging your electric car, are there any disadvantages for using DC
>current (household appliances can all be converted to DC) and avoiding
>AC
>since you are off the grid?  You avoid the cost, maintenance, and
>(slight)
>inefficiency of inverters, but are there significant disadvantages to
>this
>approach?
>
>Thanks,

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Re: [EVDL] Off-grid solar house and electric car charging

[Michael Ross via EV]

Inverters are really quite good and getting better. Micro inverters (one
per panel that output 240 VAC) Solve a lot of design problems and make it
easy to expand over time. But going off grid is very costly with many
tradeoffs. You have to really want it and educate yourself well.

If you are near North Carolina the Clean Energy Technology Center at NC
State regularly offers pertinent classes online and in classrooms. I
recently took two new ones on electrical storage for solar and operations
and maintenance of solar installation. There are scholarships is you are
underemployed. Other NABCEP classes are offered elsewhere.

Off grid is a long road and will be a significant life style change.
Attractive as it seems at first, I can't see it for myself so I am happy to
use the grid for now.  Things change and the utilities want customers. Who
knows how it will shake out. Take the money you save using the grid and
invest for when there is a clear advantage not just an emotional one. Maybe
you won't need to go so far with it.

If you are really remote the equation is different and the life style
change already cooked in.

Take some classes, there are so many choices how to do this and optimal
varies a lot.
On Jun 5, 2016 10:29 PM, "Larry Gales via EV"  wrote:

If you build an off-grid solar house and use it for both your house and
charging your electric car, are there any disadvantages for using DC
current (household appliances can all be converted to DC) and avoiding AC
since you are off the grid?  You avoid the cost, maintenance, and (slight)
inefficiency of inverters, but are there significant disadvantages to this
approach?

Thanks,

--
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Re: [EVDL] Off-grid solar house and electric car charging

[Jorg Brown via EV]

As I understand it, the DC output from solar panels is not at a fixed
voltage, so you end up having to convert one DC voltage to another in order
to power your house appliances.  This DC-to-DC conversion isn't necessarily
any more efficient than the DC-to-AC conversion that you would normally
have to do.  And the cost of buying new appliances than can deal with DC is
not small.

There are other better ways of avoiding inefficiency, I think.  One is that
many panels are set up in series, which means that if any one cell is
covered by shade, the output of the entire system is reduced. (Use a
different inverter technology, and set up your cells in parallel, to avoid
this)  Another is that high temperature reduces the efficiency of cells.
 (One way is to put the entire system on top of water, which will limit how
hot it gets)

On Sun, Jun 5, 2016 at 7:29 PM, Larry Gales via EV 
wrote:

> If you build an off-grid solar house and use it for both your house and
> charging your electric car, are there any disadvantages for using DC
> current (household appliances can all be converted to DC) and avoiding AC
> since you are off the grid?  You avoid the cost, maintenance, and (slight)
> inefficiency of inverters, but are there significant disadvantages to this
> approach?
>
> Thanks,
>
> --
> Larry Gales
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Re: [EVDL] Off-grid solar house and electric car charging

[Mike Nickerson via EV]

The main issue I can think of is the risk of someone unplugging something 
drawing high current.  There could be a lot more flash and arc than people 
would expect from AC.  Also, the conversion to DC would require new switches 
that were DC rated on the appliances.

How would you put DC into the electric car?  I could see how a conversion could 
be set up for DC, but it seems it would be difficult for a commercial EV.  They 
have a way to take DC direct inputs, but only under certain specifications.

Mike


On June 5, 2016 8:29:08 PM MDT, Larry Gales via EV  wrote:
>If you build an off-grid solar house and use it for both your house and
>charging your electric car, are there any disadvantages for using DC
>current (household appliances can all be converted to DC) and avoiding
>AC
>since you are off the grid?  You avoid the cost, maintenance, and
>(slight)
>inefficiency of inverters, but are there significant disadvantages to
>this
>approach?
>
>Thanks,

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[EVDL] Off-grid solar house and electric car charging

[Larry Gales via EV]

If you build an off-grid solar house and use it for both your house and
charging your electric car, are there any disadvantages for using DC
current (household appliances can all be converted to DC) and avoiding AC
since you are off the grid?  You avoid the cost, maintenance, and (slight)
inefficiency of inverters, but are there significant disadvantages to this
approach?

Thanks,

-- 
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