William,<div>I must confess to being totally confused by your post.</div><div><br></div><div>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.</div>
<div><br></div><div>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.</div>
<div><br></div><div>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).</div><div><br></div><div>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.</div>
<div><br></div><div>As we are in the Caribbean, the insolation levels are pretty continuous, so it does make calculations easier.</div><div><br></div><div><br></div><div>Chris</div><div><br></div><div><br><br><div class="gmail_quote">
On Mon, Apr 16, 2012 at 1:50 AM, William Miller <span dir="ltr"><<a href="mailto:william@millersolar.com">william@millersolar.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Friends:<br>
<br>
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>
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>
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>
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>
Off-grid production will also be reduced is consumption is curtailed.<br>
<br>
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>
William Miller<br>
<br>
<br>
Miller Solar<br>
Voice :<a href="tel:805-438-5600" value="+18054385600" target="_blank">805-438-5600</a><br>
email: <a href="mailto:william@millersolar.com" target="_blank">william@millersolar.com</a><br>
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</blockquote></div><br><br clear="all"><div><br></div>-- <br>Chris Mason<div>President, Comet Systems Ltd</div><div><a href="mailto:masonc@cometsystems.co" target="_blank">masonc@cometsystems.co</a></div><div><a href="http://www.cometsystems.co" target="_blank">www.cometsystems.co</a></div>
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