There have been recent reports of poor solar PV system performance from owners who are concerned about their productivity
A quick look on the Met Office website presents a probable cause; 2015 was a fairly dreary year.
Although it started off well, with the first four months of the year seeing good amounts of sunshine, things turned in May. Sunshine was slightly below normal in many areas and the UK received 95% of average sunshine hours.
June saw an improvement but sunshine amounts were unremarkable generally in July, with a UK total amounting to 96% of average.
August sunshine amounts were mostly below normal, especially in the south with only around 70% in some locations.
September looked up, apart from in parts of Yorkshire where sunshine totals were slightly below average, before another drop in October. Sunshine in England was 91% of average, and it was a rather cloudy month for many southern and eastern areas.
In November many parts of the south and west had less than 50% of the normal sunshine amount. With just 64% of average sunshine, it was the dullest November in the UK since records began in 1929.
Similarly, in December there were only 73% of average hours of bright sunshine and it was the dullest December since 1989, being particularly dull in the west and south.
So what started off as a fairly bright year, ended as one of the dullest in a long time.
Solar PV system performance predictions are based on MCS guidelines and while installers take great care in providing a reliable estimate, they cannot predict the weather.