Solar PV expected and actual generation

By John Swindells 16 Nov 2011 | Comment
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Will update this section as the numbers roll in. For now, to get started, here is a plot of two sets of expected Solar PV generation compared to actual input, over the period 9 Nov 2011-8 November 2012.

Notes: The graph displays daily expected or actual totals. PVGIS values are from an EU website which only predicts monthly totals (expected) for our location (our grid square to be accurate, I expect). Hence why the data are flat for each month rather than smoothed out.

Predicted line is a smoothed average of the PVGIS estimates plus 4 actual sets of daily numbers (extrapolated from weekly or monthly data, scaled to the same size (kWp) installation as ours) Actual numbers were from installations in Oxon, Gloucestershire, Newcastle, and Surrey. Most data from 2011, some from 2010 or 2007. I smoothed the graph lines by taking just the daily (average) values for 21st of each month and assuming a constant increment between those dates.

Actual line on the graph is our own data, and has also been smoothed. Instead of real kWh, the line folllows daily average for the week both sides of each date. I did this because I wanted a nicer looking line! And because I'm trying to come up with typical forecasts and outputs for any particular date, customised to our location. I will put the real numbers on this page in weekly listings below, once we get a few months worth of data.

A few unexpected findings:
I had thought that the PV panels would produce noticeable energy on cloudy days; but no! Not really; they want sun. Even weak winter sun.
As a result, you could in theory have high readings for December and low(ish) ones for June. Because the energy generated depends so much on cloud cover, not just day length.

Also, I believe that the panels are calibrated so as to make the most of sunshine year round, I suspect with the most efficient conversion of sunlight into electricity in about March/September. As a result, they may tend to under perform in intense summer sunshine, but this is a reasonable compromise so that they can still produce something in the other seasons.

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by phil on 15 November 2011
unfortunetly it tells you nothing.

do the same for the previous 12 months and it may provide the answers we are looking for.

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