cost per kWh [RE-wrenches]

[Hugh Piggott]

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Hi PV guys

I am more into wind and hydro.  But I am called upon to do PV, so I do.

I wonder if anyone can help me with solar pv kWh performance 
prediction?  I want to know about kWh into the battery from a pv 
array.

My approach has been to find the kWh/sqm/day (same as 'sun hours'?) 
and multiply by the array watts-peak.  But I feel uneasy with this. 
Of course you will not see that peak watts in a system unless it has 
MPPT.  And even MPPT is not perfect is it?

Would it be better to look at the output in amps and multiply by a 
typical system voltage and then multiply by sun hours?  I have used 
this approach too but it seems a bit vague.

Now we have discussion of module performance degradation over time...

I have been using the retscreen software and it is very good for 
predicting kWh/sqm/day for different azimuths and angles in different 
locations.  Then it has loads of other stuff, but it is not explicit, 
so I cannot tell what variables are controlling which other ones and 
how.  Without some sort of flow chart describing what it is doing 
with the numbers I cannot use the answers reliably.

What do you guys do and are there any databases of actual performance 
relative to 'sun hours' that I can use to calibrate my assumptions?

thanks
-- 
Hugh

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

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