Saturday 21 April 2012

First two weeks of solar power

Wet solar panels are not the most
productive solar panels
I was going to write this after one week, but time kept passing. We've now had solar panels on our roof for 15 whole days.

April has been extremely variable so far. We've had very bright times and also heavy rain and hail. Temperatures in the morning have been low enough for there to be a fairly heavy frost on some days.

The peak recorded output of the system so far is 3994 W, and most days a figure very near this is reached at some point or another. However, output can dip as low as 100 W during an otherwise sunny afternoon if the weather turns bad. This has happened quite often, and these two weeks have been far from optimal for generating solar electricity.

Over the last 15 days, our system has generated a total of 178 kWh. Our consumption over this period days was just 139 kWh so we've contributed 39 kWh to the grid. However, last year we consumed a total of 4048 kWh. This works out as 11 kWh per day, or 166 kWh over an average 15 day period. When viewed against this average, our excess is far smaller.

A day later, production was at 191 kWh
The figures for last year's consumption were what we used as a target when deciding on the capacity of our system. We benefit from the retail price of electricity (in our case about 18 cents per kWh) for any amount that we generate up to our own usage but can expect a far lower benefit for each excess kWh that we generate.

Our expectation is that in the summer, with consistently better weather, we'll generate more, but in the winter with worse weather we'll generate considerably less.

It's too early yet to say how well the system will work through the entire year, but performance so far does seem to be roughly in line with expectations. If electricity prices do not vary and we generate exactly the same amount of electricity as we consume then the system will pay for itself in just over 11 years. Any increase in the price of electricity makes the payback period shorter, and as soon as the system has paid for itself we're effectively on free of charge electricity for as long as it lasts.

This is part of our pension, and in essence, we have used it to make a bet that energy prices will increase. I'm not normally a betting man, but I like the odds for this.

Read more about our system.

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