Sunday, 4 May 2014

Solar Panel Performance - two years on


It's that time again...  

As of this evening, we now have exactly two full years' worth of data from our experimental 540 Wp solar array.  So, here are the graphs of the same parameters as previously reported - clicking on them shows larger images, and they can be compared with last year's figures here :-









Total AC energy production this year was 243 kWhr, i.e. just 2 more than last year !  At least the numbers are consistent.


The graphs give a good indication of the light intensity levels at our location and hence, to a large extent, of the weather patterns.   For both years, May and July were the two sunniest months respectively, although June having only 30 days is a factor here too, of course.  This year's March was better than last year's, but then again April just gone was significantly poorer than in 2013 - despite the very late arrival of spring weather last year, at least the sun was shining....  and although the summer months were much better last year, September & October 2013 were obviously much more overcast than in 2012.

I had still been toying with installing a full-blown 4 kWp or so system in the same location, but based on an average annual production of 4,000 x 242 / 540, this would only produce 1,800 kWhr per year, or way less than half our total electrical energy consumption.  And given that the installation costs would be around £4.5 to £5k, the value of the energy produced (at 16p per kWhr and before any subsidised feed-in tariffs) would be only £288, so it's still a piss-poor economic proposition. 

The relatively low-level roof location remains a major problem for energy production in the winter months because of the high trees to the south.  Although I could install a new and larger system much higher up, i.e. on the main house roof instead of over the kitchen / garage, the available area is much smaller up there and so I doubt I could install more than 2.5 kWp of panels.

I haven't totally given up on adding additional PV panels though - at the right price, and on a DIY basis, there may be some merits in smaller and independent systems, perhaps on the greenhouse roof or the west-facing garage wall, to power greenhouse growlights and the garden water features we're wanting to install.... 


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