cost per kWh [RE-wrenches]

[Hugh Piggott]

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Thanks Eric for the nice simple approach.

>I think it makes more sense on a battery based system without MPPT to
>use peak sun hours and array mpp amps (Imp). Amps are pretty much
>proportional to sun light intensity and the modules are going to produce
>Imp or greater at battery charging voltage and elevated temperatures.
>For simplicity, I keep all my calculations on battery based systems in
>terms of amps and amp hours. Working in watts means using two different
>"typical" battery voltages -- one for charging and one for discharging
>-- which is necessarily vague.

Looking back at my previous reports, I see that I have used peak amps 
and then assumed a certain charging voltage.  That's because I was 
interested in the energy input to the battery. This approach gives a 
factor of  about 14/17.6=0.8 between rated output and useful output.

Now I have been pointed at Bill Brooks' pv installation guide 
http://www.solarexpert.com/grid-tie/CEC-PV-Guide-2001-09-04_500-01-020.pdf
and I find that he has many more factors based on manufacturing 
tolerance, temperature, dust, and wiring loss.  I hope I don't have 
to worry much about wiring loss, because the module is capable of 
much higher voltage than the battery is assumed to be at (without 
loss of current) so I hope I have already paid that particular toll. 
( I don't understand why people size for 3% wiring loss in battery 
charging systems.)  But the other loss factors make 0.95 x 0.89 x 
0.93 = 0.8

Multiply my 0.8 by Bill's o.8 and we have 0.64!  And that's before we 
even look at losses in the battery/inverter system, or at energy lost 
because it is rejected or dumped by the charge controller.

Does anyone have data to confirm this estimated factor?

This is all very interesting.  Thanks for the inputs :-)
-- 
Hugh

hugh at scoraigwind.co.uk
http://www.scoraigwind.co.uk/

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