Solar payback time justification

upnorth

upnorth

upnorth

Associate
Joined
28 Jul 2022
Posts
48
Location
Northumberland
Does anybody else really want solar but struggles with payback time? Our annual consumption is 3800 kw/h. So assume that solar can generate and I can use (by way of battery) two thirds of that - 2508 kw/h. On the Octopus Go tariff split 70/30 peak/off peak, 2508 kw/h would cost approximately £740 making payback time on a £10k system about 13 years. I know you have to be in it for the long haul and as prices go up the payback time will reduce but 13 years seems sooooooo far away!

And right now, as we’re still on the old Octopus Go rates that payback would actually be……33 years!
 
Yeah I that the lower the usage the longer the payback time. But we’re pretty much bang on the national average of 3940kw/h,
 
Given that the lifespan of the panels is 25 years, if you get payback in 13 years you're going to be quids in for 12 years. Do check how long the batteries last, though - Tesla's Powerwall is warranted for 10 years so may need replacing twice.
 
Quartz said:
Given that the lifespan of the panels is 25 years, if you get payback in 13 years you're going to be quids in for 12 years. Do check how long the batteries last, though - Tesla's Powerwall is warranted for 10 years so may need replacing twice.
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In some respects the battery is a key part of it for me otherwise most of our solar generation would go back to the grid. Both the systems I have a quote for have a 10 year warranty on the battery.
 
upnorth said:
In some respects the battery is a key part of it for me otherwise most of our solar generation would go back to the grid. Both the systems I have a quote for have a 10 year warranty on the battery.
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And how does replacing the battery affect payback time?
 
There are other components that compliment the solar setups. You could have a cheap rate outside the sunrise/set times, electric car package or the battery systems. Some of these components will fail or need maintenance.

With the price of electric tripling or quadrupling in such a short space of time it may well be a much shorter 'payback' period than it was a few years ago. It seems to also benefit households that consume energy in the daytime and the new working from home shift so it pays to dyor.
 
Quartz said:
And how does replacing the battery affect payback time?
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No idea - haven’t worked it out but I’d hope it doesn’t mean it’s going to fail at 10 years and 1 day. But similarly, the inverter warranty is only five years.
 
Yes, one of our inverters on the FIT system died after 9years 4 months, struggling to get replaced... be close to a grand to get it done.
It died in the heatwave, Plus I'm losing £100 a month FIT payment by not generating in the Summer!.
 
I am hoping to earn some decent money from agile export. Have effectively got a 35p cap on the unit price being imported for a year, which isn't bad considering the unit cost from October will probably be more. The export price should help bring down the payback term.
 
Troop said:
Yes, one of our inverters on the FIT system died after 9years 4 months, struggling to get replaced... be close to a grand to get it done.
It died in the heatwave, Plus I'm losing £100 a month FIT payment by not generating in the Summer!.
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Was that covered on warranty? I guess the main ones to go (and are expensive) are the invertor and battery. It's just the initial outlay.
 
Yes, over 9 years is OK, heat wave just finished it off, fitted on the gable wall in the loft, hate to think what the temp was up there at the time.
 
Troop said:
Yes, over 9 years is OK, heat wave just finished it off, fitted on the gable wall in the loft, hate to think what the temp was up there at the time.
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Is it worth installing an extractor fan above it for the hot weather?
 
upnorth said:
Does anybody else really want solar but struggles with payback time? Our annual consumption is 3800 kw/h. So assume that solar can generate and I can use (by way of battery) two thirds of that - 2508 kw/h. On the Octopus Go tariff split 70/30 peak/off peak, 2508 kw/h would cost approximately £740 making payback time on a £10k system about 13 years. I know you have to be in it for the long haul and as prices go up the payback time will reduce but 13 years seems sooooooo far away!

And right now, as we’re still on the old Octopus Go rates that payback would actually be……33 years!
Click to expand...
What system are you looking at for £10k?
Depending on that, where you are located and roof direction you could be generating much more than 2500 kWh per year.

I recently had an £11k system installed which generates about 550 kWh per month (excepted from April to September) without a perfect roof location (shading for most of the morning).
Also, if you have a hot water tank then you can divert solar to heat water through the immersion heater. Using no gas, we are saving about £30-40 a month from doing this [at April 2022 gas prices]
 
upnorth said:
Our annual consumption is 3800 kw/h. So assume that solar can generate and I can use (by way of battery) two thirds of that - 2508 kw/h.
Click to expand...

Are you assuming your electricity use will not go up at all in the next 10-20 years? No BEV/PHEV or no sort of electric heating or even water heating?

upnorth said:
Does anybody else really want solar but struggles with payback time?
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Don't only focus on payback time, maybe you should try and focus on looking at the cost of electricity units over the last 10-12 years, in 2010 the cost per kWh was 12.7p on average (per kWh) and in 2020 it was 19.6p (per kWh). That is 54% more per unit in those 10 years, and now the cost is nearly 250% higher.
 
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