I have a related question to this. Does setting up a pair of Outback
GVFXs with the balancing transformer and allowing one inverter to go to
sleep at lower AC output improve efficiency? It seems we would be
reducing electronic loads, but adding transformer losses. Any
comments? I have a recently commissioned double Outback system with 200
AH @48v battery bank. He's reporting efficiency at 77% DC in to AC
out. I'd love to improve that, as his aging array of Sharp modules
seems to be under performing as well, (4.08 KW STC rated, 3 Kw actual
out) I haven't gone back and done testing with my insolation meter, so
I'm not sure exactly what is happening, but his overall efficiency (STC
rated to AC out) is only 56% .
Ray
On 1/4/2012 7:55 PM, Maverick Brown [Maverick Solar] wrote:
Please use the 90% of the CEC or PTC rating of the PV module at most.
Among several systems that I monitor daily, I have an example 11.760kw
(STC) system that has a 500Ah battery bank and it peaks at 77-80% of
the STC rating each day.
Peak is defined as the top of the bell curve that forms from the
graphing watts output versus nameplate watts.
If I use the CEC rating (10.54kw), it peaks at 86-90% of the CEC
rating each day.
If I go to the CEC list and copy & paste into a spreadsheet and enter
the values for the STC versus PTC, I /might/ find I would loose 10%
(or more) in the PV rating.
http://www.gosolarcalifornia.org/equipment/pv_modules.php (go ahead,
find your modules and divide PTC by Nameplate).
I also have a grid-interactive system that has a very large battery
bank (2600Ah @ 48V, with 9kw STC Array) and it only has a peak
efficiency rating of 69% because of the load of the batteries. The
larger the battery bank, the happier customers are for outage
situations, but the larger the battery bank, the more current goes
into "Floating" the batteries during selling. For that system, I may
lower "Grid Support/SellRE" and use Auto EQ to keep the batteries fresh...
Anyway, keep in mind that you cannot simply assume:
12kw Array x 6 hours of sun = 72kwh of generation each day. The brand
of PV, the size of the battery bank and even the charge controller's
Absorb & Float settings can greatly reduce what the inverter thinks it
can sell. With multiple inverters and charge controllers it gets even
more complicated (worse).
Good luck,
Maverick
------------------------------------------------------------------------
*From:* re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of
*b...@midnitesolar.com
*Sent:* Wednesday, January 04, 2012 5:14 PM
*To:* RE-wrenches
*Subject:* Re: [RE-wrenches] DC to AC derate
On 1/4/2012 3:01 PM, All Solar, Inc. wrote:
Wrenches,
Once again I am trying to size a grid tie w/battery system and I
struggle a little with the efficiencies of them.
With PV Watts (v.1), is changing the DC to AC derate an accurate
method for getting the output?
Thanks in advance!
Jeremy
If you keep the batteries charged to a voltage just above their
resting voltage,
say, 52 volts for a 48V system, and the battery bank isn't too large,
(~225 A-hours,
maybe a bit more), about 90% PV to grid AC efficiency is in the ball
park.
That's what we figured in the early days of GFX inverters at OB.
That's giving
5% for the electronics and 5% for keeping up the batteries.
Different and/or more accurate information may have come along since
that time.
boB
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