I have just done my reckoning for the year and the solar panels after 9 years have paid back the cost of purchase. They cost £6000 and at the end of this year have paid back £6150.
Lots of caveats in here though. I figure that if the £6000 had earned 2% it would now be worth over £7000 but of course interest rates have been down and are now up again. I have not adjusted it annually.
I costed in the benefit due to reduced electricity/gas bills compared to the cost of these in 2014. Except for the last two years my bills have been £2-300 lower than 2014. Caveat: consumption may be different.
Caveat: the last two years the cost of electricity and gas has been much higher and therefore my costs have been greater than 2014, so I have not offset them in my calculations. It wouldn't have been easy as the rates have fluctuated in the last couple of years.
RECALCULATIONS December 2024:
Putting together the results of emails with a friend with solar panels.
When I got my solar panels fitted in December 2014, in order to calculate the breakeven point, I took the cost of elec/gas for the previous year [2013] and used that as a base point to calculate the savings. Of course this didn't include in the calculations the varying price/unit of these. What has happened over the last couple of years is that the cost of gas/elec over the year has been higher than the 2014 value so my calculations of savings are negative.
I have most of the bills over these years so I could recalculate everything if I had to. It's difficult I know because my consumption has varied over the years, and now that I have all new appliances in my kitchen and no more gas oven/hob, the usage is going to change.
At the moment my calculations for this year only include the FIT payments because a negative figure isn't relevant any more.
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Some parts of mine are more complicated as I did an annual calculation on the reduction in the bills, based on annual usage taken from bills, and also had an increment on the initial cost of 2% which would be the interest the money would have earned in the bank. In many cases the annual interest on the capital would have varied, but I didn't worry about that, and also the annual cost calculation is only an approximation as the rates would have changed mid-year. It could have become very complicated to try and get it totally accurate.
Good Energy handle my FIT payments, and I did query the fact that my calculation of FIT payment was different from what they gave me, but didn't get anywhere. I am still about a year from breakeven I think [Dec 2024].
see sheet 'totals' on attached link
https://docs.google.com/spreadsheets/d/1_KJGPu5fO4yIRw5Hr7BDt3Ia9UJRNkx0twsA16mEl_Q/edit?usp=sharing
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I have reworked it all using a different calculation, not based upon cost differences, but on usage.
Every year I compared the usage to the reference usage in 2013, before panels, and using the rate for a year, calculated the savings due to using less electricity. I created a new sheet[NEWTOTALS], and in column I for each year is the rate and then the calculation for that year. It's not entirely correct because for a couple of early years I couldn't find bill copies to get the rate, and also in each year the rate was usually renegotiated about June/July. I used the rate in September for the calculations. Interestingly the saving in the early years was less than with the previous method, and in later years was greater (esp. when values went negative!).
An added factor from 2020 on was that the rate did not include VAT and this was added later to the bill, so a multiplication factor of 1.05 is added.
This gives me a much closer to breakeven than the previous method of calculation.
Breakeven = 7314 (Interest on Purchase price) By the previous method of calculation= 6482,
The new Calculation has a saving so far of = £7174 to November 28 2024. This assuming a FIT payment the same as last year for the last quarter.
So it all depends on how you do it! And there is margin for error.
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