How efficient is a capacitor in offsetting the power factor error? 99.9%...
±2%...?
Jim Duncan
-----Original Message-----
From: [email protected]
[mailto:[email protected]]on Behalf Of Exeltech
Sent: Sunday, January 09, 2011 9:03 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Xslent?
--- On Fri, 1/7/11, Peter Parrish <[email protected]>
wrote:
> What ever is done to reduce the reative power, it has to be done
> in real time (with a fraction of 0.016 seconds, the 60 Hz cycle).
> You can’t wait until later in the evening to solve a problem that
> is occuring during the day.
Peter is absolutely correct. Power factor correction MUST occur on a
half-cycle by half-cycle basis, and at the exact moment of power consumption by
the reactive load. Anything else won't be effective, and may in fact worsen
the power factor at a given point in the grid.
> Real time compensation can be often done with capacitors alone
> or in conjuction with some smart electronics. Remember that for
> short periods of time capacitors can store considerable amounts
> of energy and can smooth out these reactive currents.
Capacitors placed across a power line will store energy for exactly
one-half cycle. At that point, the polarity reverses, the capacitor is
discharged to to zero, then recharged to the opposite polarity. This process
repeats every cycle.
What DOES take place is a phase shift (displacement) in the current
flow relative to the voltage waveform. Power factor correction is done with
capacitor banks (we see them in substations and on power poles) to offset the
power factor of the grid itself, which by its design is inherently inductive
due to long runs of wire. Very large motors will have individual "tuning"
capacitors installed to offset inductive reactive current flow. These
capacitors are disconnected whenever the respective motor to which they're
connected is not in use. On occasion, excessive capacitance exists in a
circuit that must be offset by inductance, but this is rare.
Like Tom Cruise said in Top Gun .. "It's complicated."
Dan
--- On Fri, 1/7/11, Peter Parrish <[email protected]> wrote:
From: Peter Parrish <[email protected]>
Subject: Re: [RE-wrenches] Xslent?
To: "'RE-wrenches'" <[email protected]>
Date: Friday, January 7, 2011, 5:39 PM
I know only a little about Power Factor “charges”, but we can figure
out some other “engineering” issues.
Power Factor is a measure of the amount of reactive (out-of-phase)
power compared to real (in-phase) power. It is somewhat complicated but the PF
is unity for 100% in phase and 0 for 100% out-of-phase power.
The important thing to remember is that (while holding the real power
constant) for PFs less than unity there is in addition to the real power, and
“in-flow” of power and an “outflow” of power four times a cycle. One might say,
“Why do I care about reactive power? It flows in and out with no net
contribution over the long run!). True, but the in-flow and out-flow represents
higher currents on the lines and more losses. Or it means that there have to
be oversized service conductors to avoid the extra losses. Even if the losses
are avoided, the higher currents can trip overcurrent protection devices, and
of course the utility company needs to supply (and take back) the extra
currents in real time.
What ever is done to reduce the reative power, it has to be done in
real time (with a fraction of 0.016 seconds, the 60 Hz cycle). You can’t wait
until later in the evening to solve a problem that is occuring during the day.
Real time compensation can be often done with capacitors alone or in
conjuction with some smart electronics. Remember that for short periods of time
capacitors can store considerable amounts of energy and can smooth out these
reactive currents.
I can well imagine how an inverter can be designed to generate both
real and reactive power, and therfore an inverter can reduce the amount of
reactive power that needs to be supplied by the utility company – but not when
the sun isn’t shining. I suspect that these types of inverters will have
oversized output circuit wiring to handle the reactive currents without
adversely impacting their efficiency rating.
If I have time this weekend, I will take a look at Apparent’s website.
- Peter
Peter T. Parrish, Ph.D., President
California Solar Engineering, Inc.
820 Cynthia Ave. , Los Angeles , CA 90065
CA Lic. 854779, NABCEP Cert. 031806-26
[email protected]
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885
----------------------------------------------------------------------
From: [email protected]
[mailto:[email protected]] On Behalf Of Jamie Johnson
Sent: Friday, January 07, 2011 2:03 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Xslent?
It's an interesting product for a niche market if it actually works
as they say (Disclaimer:I am not claiming that it does), after speaking with an
individual who I believe is the VP of Production for Apparent (use to work for
EnPhase according to their website), he claims that the product is currently
installed at the Google campus on a solar canopy for some of their EV chargers
(can anyone verify this?)
They have several other beta installs as well, however the individual
I spoke to said they were only installing small systems at beta test sites
(where the Util co charges for VAR's using separate meters like for EV
charging) for now. No pricing has been set for the inverters, and they are not
available for sale to installers yet.
Apparently they claim the inverter can create/produce VAR's by taking
1 watt of power from the grid at night or from the solar output during the day
and turning it into approximately 9 VAR's to offset the customers charges for
VAR usage from the Grid. This is where the KVAh production on the graph before
sunrise and after sunset comes from.
I still would need to see a third party head to head comparison test
before I believed it. Again niche market inverter for when the utility co
charges for VAR's.
Jamie
-------- Original Message --------
Subject: Re: [RE-wrenches] Xslent?
From: August Goers <[email protected]>
Date: Fri, January 07, 2011 10:24 am
To: RE-wrenches <[email protected]>
Hi All -
Thanks for the helpful info! We did a little more research on our
end and
I guess Apparent is the new brand name for the Xslent product. What
baffles me is the chart where they show that they're producing power
before and after sunrise and sunset:
http://www.apparent.com/products/mgi.html
The system must include batteries? Someone on their marketing team
is
really going to town...
Best, August
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of jay
peltz
Sent: Thursday, January 06, 2011 4:43 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Xslent?
HI Peter,
I agree with you that for now on residential it makes no sense.
However for commercial that might have to pay extra for PF issues,
to have
the inverter adjust for this makes sense.
Its the reason they( inverter companies ) are doing it.
I"ve heard a better more complete reason of course from Bill
Brooks, who
maybe can chime in.
sorry got away from me,
jay
peltz power
On Jan 6, 2011, at 2:34 PM, Peter Parrish wrote:
> I can't understand how any inverter WOULDN'T deliver its power
with the
> voltage and current 100% IN PHASE.
>
> When the voltage and current are not 100% in-phase that represents
reactive
> power. Reactive power flows positive for a quarter of the AC
cycle, then
> negative for a quarter of a cycle, then positive and then
negative. The
net
> result over one AC cycle is ZERO power delivered to the load.
>
> So reactive power is worthless.
>
> Worse, it results in higher currents (and voltages) for the same
amount
of
> in-phase power, putting additional stress on circuits.
>
> - Peter
>
>
> Peter T. Parrish, Ph.D., President
> California Solar Engineering, Inc.
> 820 Cynthia Ave. , Los Angeles , CA 90065
> CA Lic. 854779, NABCEP Cert. 031806-26
> [email protected]
> Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885
>
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