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<DIV><FONT size=2 face=Arial>Hi Jesse,</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>If I read this correctly your customer is wanting
to go off-grid during peak hours. I recently went through this same thing with a
customer. I received feedback from an old SMA tech and some Wrenchers (thread
titled "Battery Back-up and Grid Tie"). Here's what I learned:</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>1. Inverters are more efficient at inverting than
charging, anywhere from 5-10%. Add to that about 10% transmission loss...you'll
always have significant energy losses associated with trying to put back that
power that you're drawing out during those peak hours. Energy loss = $$
loss.</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>2. Compare the utility peak kWh
cost against the cost of cycling the battery bank. Just for
an example, let's say for a 48V system you're using 150Ah 12V
Trojan AGMs $2000 for 8 batteries. If the specs say those batteries,
at 50% discharge, get 1000 cycles in their lifetime, that's $2.00 per
cycle. 300Ah X 48V X 50% = 7.2kWh. $2/7.2kWh = $0.28/kWh. Add to that 20%
round-trip efficiency losses, you're up to $0.33/kWh. What else
does daily, unnecessary cycling add: Extra maintenance? Shortened life so
probably should factor in some replacement cost?...</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>3. Murphy's law says that the power will go out at
the end of one of these non-essential discharge cycles. Then what?</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>Probably not worth it.</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV>Eric Stikes</DIV>
<DIV>SunHarvest</DIV>
<DIV>530-798-3738</DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: black"><B>From:</B>
<A title=dahlsolar@gmail.com href="mailto:dahlsolar@gmail.com">Jesse Dahl</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=RE-wrenches@lists.re-wrenches.org
href="mailto:RE-wrenches@lists.re-wrenches.org">RE-wrenches</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Monday, June 24, 2013 8:50 PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> [RE-wrenches] Battery bank
during peak times</DIV>
<DIV><BR></DIV>
<DIV dir=ltr>Hello,
<DIV><BR></DIV>
<DIV>I was contacted by a local co-op about installing a PV system at their
office. At first they wanted a straight grid-tied system, and after
they received the bid they changed their minds and now
want a battery based system price. What they want now is a system that will
allow them to draw the battery bank down starting at 5pm during
their peak demand time. Has anyone worked on or installed a system of this
type?</DIV>
<DIV><BR></DIV>
<DIV><BR></DIV>
<DIV>Thanks as always!</DIV>
<DIV><BR></DIV>
<DIV><BR></DIV>
<DIV>Jesse</DIV></DIV>
<P>
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