Trace Sell back modes [RE-wrenches]

[Jeffrey Wolfe, Global Resources]

Travis:

According to the Trace Engineer I spoke to about a year ago (Dean?), a 350 
A-Hr 24V battery bank draws about 30 W, continuous, for float. I think this 
is the power to the battery, not the power to the charger. (In other words, 
inefficiency of the charger is not included in the 30W.) It stands to 
reason that doubling the size of the battery bank doubles the float power 
draw. This power is needed to float the batteries whether or not the sun is 
shining. 24 hours/day times  30W = 720W-Hrs. Since we get an average of 4 
hours per day of full sun in Vermont, (and a 1kW array only produces 
790W-hrs/full sun hour), we are using 25% of the power just to float the 
battery.

Double the size of the array as compared to the battery, and the 
inefficiency is cut in half. Double the battery as compared to the array, 
and the inefficiency doubles. I know this may not make sense to a lot of 
people, as it would seem that off-grid folks would be getting much less 
power than they seem to. But this problem does not affect off-grid systems. 
This inefficiency only occurs at full battery, since when we try to full 
the bucket overfill, the juice just runs over the edge. (And the battery 
guys tell us that if we do not keep on filling it to overflowing, we'll 
rust out the sides, so to speak.)

These numbers are all rough, but seem to make sense with what we are seeing 
around here.

Based on the above, I have taken a very strong inititative to try to keep 
on-grid people from buying a battery system. If they are living without 
backup power now, I try to keep it that way. If they need backup power, I 
look for options. (Computer UPS's are very cheap.) However, as we all know, 
battery backup is a big selling point. (Here we are in marketing again!) So 
we're spending time educating people. I've done the comparisons on cost. 
For a small system, you're looking at about a 30-40% material adder, plus 
more shipping and installation costs. (This is based upon using the new   
Trace SL line tie inverters, versus those FETful SW's).)

The only way you can touch a 15 year payback is with energy costs in the 
mid teens per kWh, interest rate at 0%,  a direct grid tie batteryless 
system, and a lot more sun than we get in Vermont. If you can make those 
numbers work, give me a peak at them!

Jeff

Jeffery D. Wolfe, P.E.
Global Resource Options, LLP
A Woman-Owned Vermont Limited Liability Partnership
4 Kibling Hill Road
P.O. Box 51
Strafford, VT 05072
802/765-4632
802/765-9983 (Fax)
global at sover.net
www.globalresourceoptions.com




Travis Creswell said:

I don't see how the size of the battery bank matters.  A battery less 
system
allows the array to run at max power voltage.  To me this means that you
actually 1000 watts out of your 1000 watt array.  For example 12 Astro 
Power
120's would be 1440 watts in a battery less systems while in a battery
system they would be more like 1130 watts (21.3 Amps x 53 volts) depending
on the battery voltage at the time.  I can see that the larger the battery
bank the more of a maintenance charge they would take but this could only 
be
minimal.


It would be great.  I can't believe it either. I am putting together a 
quote
right now for a business who just might accept a 10-15 year payback for a
system.  As you say I had better put at least 20% more solar on the battery
system to produce as much annual kwh and the battery system will cost a lot
more just for the back up feature.  I'll post the comparison when I get
finished.


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