Many people think instantly of solar power as something very unreliable because they are weather-dependent, particularly in the UK. For example, do you really want to be relying on that outdoor BBQ taking place without the possibility of going inside? With weather forecasts predicting two months' worth of rain over the next five days, the answer is probably a resounding no!
However, this is very much the nature of solar power – it always will be dependent on what nature throws at us. The weather, on average, is fairly constant and over long periods, the average is predictable. A study from CSIRO, 'Solar intermittency: Australia's clean energy challenge', is the first proper piece of research covering specifically the fluctuations to be expected in solar panel output depending on the weather.
Whilst they are based in the rather warm Australia, the conclusions can be applied elsewhere – Dr Platt, team leader of the CSIRO, says that whilst the problem isn't just confined to the arena of large-scale plants, but localised interruptions in output are already visible at the grid level depending on the weather. He continues to stress the importance of good weather forecasting in the long run, which can be combined with shorter run forecasts to ensure electricity outages are prevented as reliance upon this source increases in the future.
The conclusion overall is that sufficiently-accurate forecasting is possible for solar to be a viable power source – indeed, intermittency due to localised issues or just changes in power usage (cup of tea during the adverts, anyone?), are much more significant.
For home-owners in the UK, the government has provided an official calculation, known as a Standard Assessment Procedure (SAP), which takes into account weather patterns on average. This figure ought to be provided to you when you get a quote from any MCS-registered company, so that you know that the potential installer you've chosen isn't providing an artificially-high estimate of potential earnings to try and win your business, although it is important to remember that solar earnings will always, at least with the FIT system, be a good guess rather than 100% accurate. Anecdotally, solar panels tend to generate 25% to 30% more than this figure, but comparing the SAP figure between installers means you can at least pick between them and their different systems.