I've had the inspector visit from Certsure. He did highlight that the quote was not to the recommended guidelines & has to be re-calculated. There are lots of known variables to be used in the generation yield calcs & all contribute to a reasonably accurate forecast.My suspicious nose sniffs out somebody who wants to complain about miss selling....
It was agreed that the biggest factor to influence the savings is the "percentage usage". Sadly the estimated usage figure that is used is entirely at the discretion of the installer. There doesn't seem to be any accurate charts or formula for this percentage figure despite its enormous affect on the annual savings & ultimately the payback period.
Following the first full years generation it is now clear that the year following the installation saved a total of £1774.26 that includes both the reduction in the bought electricity plus the fit payments. The quoted annual savings were £2947.29 in total & equate to the actual return being 60.2% of the quote.
My next dilemma is how to calculate the amount I will be short & base any compensation on the difference. My initial thoughts are to see how much I will lose over the lifetime of the system. The quote gave a 20 year saving of £138 850.93. Using this 20 yr figure & the actual percentage return of 60.2% of the quoted figure gives an actual 20 year return of £83 587.86. This is a 20 yr shortfall of £55 263.07. So if I get no compensation this is a true reflection of the loss based on the measured output. Does anyone have any experience of how to calculate the loss over the systems 20 yr lifetime?