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Chris:<br><br>
I would willingly clarify but I am confused about what you are confused
about. I think we are saying the same thing about off-grid
systems: If you don't consume power, battery voltage stays high and
charge controllers reduce energy harvest.<br><br>
William Miller<br><br>
<br><br>
At 06:57 AM 4/16/2012, you wrote:<br>
<blockquote type=cite class=cite cite>William,<br>
I must confess to being totally confused by your post.<br><br>
I am currently at my office writing to you using electricity from our
off-grid solar system. We only have the solar power, no grid
power.<br><br>
We get exactly as much power as I predicted we would, in fact a little
more. But, there is an intrinsic issue with off-grid systems that many
people miss. Unless you have a use for the power, it won't be
"harvested". If you allow the inverter to charge the batteries
from the grid, there will be nowhere for the PV power to go.<br><br>
To give you an example, our warehouse and office has 2,580 watts of PV on
a 60 amp charge controller and a 3.5KW outback inverter, with 250Ah of
VRLA batteries (4 x 12V).<br><br>
Each day, I read the amount of power the charge controller makes. It
averages about 12KWh, depending on how much we used that day and the
state of the batteries at the beginning of the day. We have found that
the loads did not adequately exploit the power product capabilities of
the system, so we moved our freezer from the house to the warehouse to
use up some more power.<br><br>
As we are in the Caribbean, the insolation levels are pretty continuous,
so it does make calculations easier.<br><br>
<br>
Chris<br><br>
<br><br>
On Mon, Apr 16, 2012 at 1:50 AM, William Miller
<<a href="mailto:william@millersolar.com">william@millersolar.com</a>>
wrote:<br>
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<dd>Friends:<br><br>
<dd>There has been recent discussion on this forum about PV production in
grid-tied with battery systems. I have been faced with this same
problem in a 3 XW system installed in 2009.<br><br>
<dd>The customer's power bill never went down. PV harvest was
abysmal. The system would create great short circuit current but
would not harvest into the batteries.<br><br>
<dd>It is starting to appear the XW firmware was at fault. The
inverters would charge the batteries too high so the charge controllers
would back off. Upgraded firmware seems to be helping, but the data
set is still limited.<br><br>
<dd>Remember this: just because a PV system can produce does not
mean it will. The charge controller knows only one thing:
battery voltage. If it is high, production is curtailed.<br><br>
<dd>Off-grid production will also be reduced is consumption is
curtailed.<br><br>
<dd>Charge controllers that can be set for grid-tied applications help,
but only if the inverter(s) do not keep the battery voltage too
high.<br><br>
<dd>William Miller<br>
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