Interesting, but I'm not sure I completely follow.
Batteries, particularly Li ion, don't have linear voltage. They stay
pretty much near their nominal voltage until nearly discharged and vice
versa. I don't know the voltage curve for solar panels but I'll make an
assumption it is more or less linear with the amount of light. Given
that, doesn't that mean that the panels will charge the battery only
part of the time, when there is strong light ? Is that an adequate
percent of the time ? Also, you have to monitor by hand, right ? Once
the battery is up to max voltage, you need to disconnect or you will
destroy the cells.
Peri
------ Original Message ------
From: "Robert Bruninga via EV" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Cc: "Robert Bruninga" <[email protected]>
Sent: 02-Sep-19 7:20:27 AM
Subject: Re: [EVDL] V2G for my grid tied solar? (constant current
charging)
One final point about grid down charging (under a must have armagedon
scenario): (And only for those fully experienced in HVDC)
Remember that Solar panels are current limited power sources. This means
It will provide its rated current at ANY voltage from 0 (short circuit) up
to its nominal operating voltage.
This means I can just clip the 450 volts DC straight from any one of my 3
kW solar panel arrays and run it straight to a 12, 24, 48, or 72 volt
battery (or 240v prius) directly for a temoporary 7 to 9 amp charge. WHICH
ONE MUST MONITOR to know when to disconnect. AND one must have arc-flash
eye protection because you will draw a lightening bright arc flash when you
disconnect (and or while connecting if the connection is not made
cleanly). But you will get a 7 amp charge (in my case of older panels).
New 300W panels can give 9 amps.
(You MUST disconnect from your GT inverter of course,. You do not want any
capacitor holding the 450v or it is no longer a perfect current limited
source).
And with 6 such separate panel arrays, I can combine the currents at the
battery to give me up to 42 amps at 12, 24, 48, 72... (or 240) volts if
needed. But again MUST human monitor in real time. It is not easy to
throw together a charge regulating circuit to open a relay when the charge
is complete as agaiin, you must use very expensive HVDC contactors and or
snubbers. And by th time you do all that , you could have build a more
direct DC/DC converter.
So again, this is just an emergency data point. For example, while drawing
1 kW (80 amps) from my prius 12v battery to power the house, all I need at
240v DC is 4 amps from the solar array. And in my 14 year old Priuses I
know exactly where the HV battery posts are and can connect there and am
happy to take the risk. Not sure I wouild take the risk for the 350v
battry in the newer Volt (which could give me 2 kW from its DC/DC
converter)..
Anyway. just thought I would mention it. Oh, and the open circuit voltage
of the solar arrays on the brightest and coldest day can approach 600
volts, not the 450 nominal load point... But again, just short that 600
volts with an ampmeter and you will still see only the 7, 8 or 9 amp
current from your arry even at zero volts. Just protect your eyes from the
arc flash when you disconnect (oh, it will also vaporize pieces off your
clip leads too each time), and it can just melt the tip off the copper wire
to molten copper and catch fire to the insulation and anything else within
a few inches if you let the arc continue...)..
NOT SOMETHING TO PLAY AROUND WITH!
But you can charge any battery... ;-)
Bob
On Sun, Sep 1, 2019 at 2:17 PM Robert Bruninga <[email protected]> wrote:
Again, if you find a 72v UPS (6 12v batteries) then you can tap your
arrays in groups of three and use that to provide the current to the UPS to
dirive your car charger. Just 9 panels in 3 parallel strings of 90v will
give maybe 20 amps (or the minimum needed to charge L1) But 12 panels (or
about one string array) will give you plenty of current over more hours of
the day. That's why I like string inverters beccause I have access to all
the DC inputs and ground mount so I can get to them any time I want.
Bob
On Sun, Sep 1, 2019 at 1:20 PM Robert Bruninga <[email protected]> wrote:
You already have what you need for continuous operation at night in the 1
kW class (refrigerator, well pump and lights, etc)
See http://aprs.org/powerwheels.html
But it assumes you have the Sunny Boy GT inverter with "secure" power
when the grid goes down to charge your EV. $1500
Or if you are lucky to find a UPS of at least 1800W capacity to charge
the car, and then you can drive that from batteries that you charge from
voltage taps on y our DC array that match the input voltage of the UPS.
But ONLY if you seriouisly know what you are doing and do not overcharge
the intermediate battery., etc.
Bob
On Sun, Sep 1, 2019 at 12:28 PM Damon Henry via EV <[email protected]>
wrote:
I know there has been a lot of churn the last few years over Vehicle to
Grid technology. I'm not sure how many people really want the utilities to
take over their vehicle state of charge, so I'm not sure how viable the
whole concept is.
With my grid tied solar system my solar stops producing if the grid goes
down. One way to prevent this is to have a battery backup system in
place. That's usually an investment of at least several thousand dollars.
I have two factory OEM PHEVs sitting in my driveway with significant
battery packs. I also have a Juicebox 40 for charging which has some
charging intelligence already built into it for their Juicenet program, but
not really V2G. I feel like I am tantalizingly close to a great solution.
So here is the question that I have. How far am I from being able to
utilize my car batteries through the OEM port and an EVSE charger, to feed
an inverter and keep my house alive and my solar producing during a power
outage? Is this tech currently being developed, or is it still just a
dream that my come true some day?
BTW - I have lived in my house for 20+ years and rarely lose power, but
"being prepared" is always on my agenda. I suspect that if I really want a
solution within the next couple of years I will need to buy a separate
battery for my solar system, or a generator...
thanks
Damon
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