The graph below shows kWh on the vertical axis, days of the month on the horizontal axis for our 1.98kW (8 panel) HIT solar panel array on a south-facing roof with a pitch angle of approx 35-40°.
I've added a linear trendline to show the average. With the sun getting so low in the sky now, on the 30th Novermber, even at midday with a cloudless sky the array was only just topping 1kW of power.
At 8.30am this morning (2nd December 2013) the sky is very gloomy and overcast, and the inverter showed a 0W input from the panels.
Predicted vs Actual:
On installation, we received an SAP forecast for the year of 1645kWh. Dividing by monthly average sunlight, for December we should have achieved an average of 2.17kWh per day to keep on track to hit this total. The panels actually achieved a daily average for the month of 1.93kWh, slightly below target.
Total kWh forecast for November = 65.01kWh
Total kWh achieved for November = 57.9kWh
For the year so far, the panels have achieved 93.49% of their forecast amount. Not a bad prediction, but I'd hoped they would have outperformed the prediction. Here's hoping that the spring/summer months turn things round for the year!
I've also put together a graph showing how the average amount of kWh generated per hour has fallen from month to month as we approach winter solstice. December's value is only based on 1 day's measurement, so it is not accurate. Note the number of daylight hours is not measured from sun-up to sun-down, it is from met office stats for average hours of actual cloudless sunshine over previous years.
I've also had the first request for the Feed-In Tariff (FIT) meter read from npower - a total of 315.89kWh generated since installation. When you fill in the FIT application forms, npower give you the option of supplying meter reads online or by post. I opted for online. They ask for a quarterly read, and you have 25 days to file the reading, otherwise it rolls over to the next quarter.
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