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# solar quote question - estimated return on investment timescale.

Discuss solar quote question - estimated return on investment timescale. in the Solar PV Forum area at ElectriciansForums.net

#### jouleflow

##### Regular EF Member
My suspicious nose sniffs out somebody who wants to complain about miss selling....
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.

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?

#### suffolkspark

Electrician's Arms
Lol

Respected Member
I doubt there could be any formula for calculating potential usage, it's very occupant / lifestyle /property specific.
It could only be a wild guess based on information from the occupants.

#### Murdoch

Electrician's Arms
Good luck trying to get any compensation. ... there seem to be faults on both sides.

Your usage could vary, the sun may not shine ......

#### Edtwozeronine

##### Regular EF Member
Even paying back the cost of an install could take about 17 years if the cost was approx £10K like it was for us, the best thing about it is you can put your yearly FIT payment (£600-ish depending on weather) towards paying the bills.

It's hard to say if it's a real win overall as that £10K is gone forever and getting replacement parts hasn't even been factored into those costs for up-keep for the foreseeable future.

#### jouleflow

##### Regular EF Member
Perhaps I should consider reinstatement as an option to compensation. This would involve steel roof repair/replacement + removal of equipment + my money back. Would this be seen as reasonable restitution?

#### jouleflow

##### Regular EF Member
Good luck trying to get any compensation. ... there seem to be faults on both sides.

Your usage could vary, the sun may not shine ......
I'm not sure what faults I have contributed to apart from being a bit too trusting.

It's true that my usage may vary & the sunlight will too, but remember the percentage usage figure was guessed by my installer.

As I mentioned before this figure is by far the most influential when converting the diligently calculated output into monetary savings.

I understand that I may well use 100% of the generation for 2/3 rds of the year, as the generation is so low. During the brighter months I may only be using 20% but this is 20% of the vast majority of my annual generation. So the percentage usage is not a simple as it seems & with my system can be nowhere near 95%.

p.s. my feedback is limited to 4kWh so the 15kWh potential in the brighter months is severely reduced, thereby reducing the fit payments.

Respected Member
Who decided a 15kwh system was the best option, was it a case of fill the roof?
And why was it capped, did they try to get FIT on 15kw?

#### jouleflow

##### Regular EF Member
Who decided a 15kwh system was the best option, was it a case of fill the roof?
And why was it capped, did they try to get FIT on 15kw?
The installer suggested that with my high usage ( no gas ) I should go for the maximum amount that I could fit on the roof. This worked out at 15kWh & they contacted the dno who were happy with it providing that it was capped to 4kWh max feeding back. I have 3 ct clamps, one from each 5kW inverter connected to my incoming live.

I do get the FIT & have to send the meter reading in every quarter. This first year I received £692 on the 15kW install.

#### jouleflow

##### Regular EF Member
Good luck trying to get any compensation. ... there seem to be faults on both sides.

Your usage could vary, the sun may not shine ......
The installer had to recalculate the potential generation as directed by the Inspector. It was found that the calcs were around 26% out so a settlement fee was agreed. This amount now gives me a payback within 4 years as quoted originally.

Good result!

#### The Solar King

Electrician's Arms
You can work this out easily using a full discounted cashflow calculation. However I wouldn't bother. If you installed simply to make money, I can make the payback period and internal rate of return what ever you like by altering the inputs to the DCF.

Remember your panels have a 30 year plus life expectancy. If you assess over this period, your purchase is a no brainer. Leave it at that and enjoy what you have.

My customers motivations for installation have moved way beyond this narrow little calculation to take in much wider considerations. They are far more interested in value rather than cost. They take pleasure from their systems, are loving life and moving forward.

As Shirley Conran said: "Life is too short to stuff a mushroom."