PV system payback in less than 5 years?

So I have installed a GE PV system almost 2 years ago: Gen 3 HY5.0, 2x9.5 batteries, 10kw worth of panels plus the GE EV charger for aprox £20k.
Cosy 6 installed last month for £1.8k but it's too new to capture it's potential savings in my calculations.
Our household also has 2 EVs that cover quite a lot of miles every month - aprox 2200 miles

Most of the time on the Octopus IGO tariff but dabbled a bit with Flux last summer.

According to my spreadsheet, the £20k (or even £22k when including the heat pump) would be paid off in less than 5 years - this seems like an extremely short period of time. Do anyone else's calculations show such short amounts of time to recoup the investment?

dragos.balaban

Checkpoints

Did your pre change figures also include IGO, they should else your not doing true savings of hardware.

Also check you pre change control figures are based on best approach now if you didn't have hardware over just converting kWh to standard rate for current use - aka would you do more load shifting etc

If all fine then yeah probably right and well done 🙂

@DreadorUK thank you for your reply

Very good point, and no, they do not.

I've used the monthly Octopus tracker values to calculate "how much I should have paid"
But looking into your suggestion, and knowing I could not have shifted a lot of the load anyways, I think using IGO prices instead of the Tracker would have yielded even bigger savings aka quicker return of the investment time (IGO is 28p/7p and tracker is average 20p)

Another way of looking at this is a bit simpler than vast spreadsheets.

Situation before...
All house load at standard variable rates (£4 a day? =£1500)
Petrol costs for 2 cars. (£50 per full tank? x 120 tanks per year?=£6000)
Gas for HW/Heating (£1000?)
Total £8500

Situation after
Most house load on solar (£500?)
Most car load on 1/4th standard variable rate (7p) (£2000?)
Most heating load (with batteries) at 7p (£1000?)
Exporting excess (-£500?)
Total £3000
Net improvement £5500 per year. Payback on £22000 = 4 years

It is the high car use and a decent sized array that paying dividends.

What a great investment.

I'm looking at a 4year 9month payback.

5kW gen 3 Hybrid, 1 9.5 battery and 6kWp array. costing £9,440

Previous annual electricity bills have been £1,550-£1,600 when using the best tariffs we could.

We've just completed our first year on solar+battery, and are £390 in credit, a saving on previous years of £1,985.
I'm hoping to work the system harder this year and improve that.

Based on this, 4y9m

Yea its possible i have a 7kw system with battery, 8Kw Heat pump cost was around 14k and an etron
before i moved across i was paying 1.8k gas and Elec and around 1.5kdiesel

its only May and i am already £101 in credit with octopus using IOG.

Just to note i dont count the cost of the etron as i replace my car every 3/4 years so when i replaced i just got an electric which was around the same i would have spent on another diesel

My payback is currently 5 years, although the heat pump that I am having installed next week will push the overall payback period to around 7.5 years.

I calculate my payback based on what I would have consumed for the house and ASHP (no EV) on the standard variable tariff as that was what I was on with the ASHP before I got the GivEnergy inverter and batteries.

My solar and battery payback is around the 6 year mark.

The heat pump is harder to work out because of the solar battery install afterwards. But if I look at the saving from how much the electricity costs vs heating oil, and add on the RHI grant payments, it’s somewhere around 7 years.

The neighsayers have another way of looking at investments in PV.

Using my own example I am saving £1200 on a £14800 investment. That's a return of 8%. However the value of my capital is decreasing as it has a limited life.

8% on a 10 year investment is not brilliant but if you factor in the depreciation it might be more like 4% over 20 years which is quite poor.

My answer is it isn't just measured in financial returns.

And you can put the savings from the reduced electric bill into a savings account and earn money from it.

https://youtu.be/XSeiTkwfRTg?si=IIe68tLxdSK0-01O

Really should be adding "Net Present Value" calculation into the mix.

My decision for my 1st set of panels and inverter 2020 and more panels/inverter and battery we based on thumbnail maths and feelgood about doing something positive for the world. It still feels right to me

I wrote a piece on our PV + battery + heat pump install, which folks on here might find interesting, including an attempt to forecast the economics. With crystal ball firmly in place, we're looking at something like 9 years payback on all of that, but the HES loan/grant we received reels that in to less than 4 years.

https://www.linkedin.com/pulse/our-positive-heat-pump-solar-experience-jo-wilson-ceng-mimeche--mnfqe/

But as others have said, it's not just about the bills. It's also about the 75%+ drop in energy use.

Josephiah Very interesting and well written article, thanks for sharing it with us.

If I had the time to write it, my own story would be very similar. There are some bits I would do differently knowing what I know now, getting the heat pump to work efficiently took probably 2 winters before I trusted the 'low and slow' approach, but the benefit of the house being comfortably warm all the time can't be understated. Annual net import-export bill was zero last year (actually -£5) and overall very happy

SteveCook
Even though it costs me money, & the ROI may not be the greatest, I get a warm & fuzzy feeling knowing that I'm "sticking it" to the energy company fat cats by reducing my bills & their obscene profits. I'm not sure if I'm actually having any effect on energy company profits but it makes me feel better all the same. I'd love to get off of gas but until the powers that be make it easier to adopt alternatives I'll stick with my boiler & offset it's cost with solar export - long may that remain a thing!

Josephiah You're obviously on the A9/on the eastern side of the A9 then?*

If so your winter temperatures are going to be a fair bit below the west coast so well done with the heatpump figures.

*for those not from northern latitudes there is no mains gas on most the west coast of Scotland, east coast is nearly all mains gas.

Vestas Yeah, Inverness area - close enough in for mains gas, and not in a deep glen with -10 to -20°C winter lows!

Josephiah I'm from Lewis but had relatives who lived in Ballater. Pretty nippy there 🙂

It'd be interesting to see heatpump figures from the wind-blasted (but "warmer") west compared to other northern areas.

Vestas Heh, I remember doing a camp there in the middle of summer. Overnight frost in July, and they even shifted 'camp time' by an hour to make best use of the daytime...

Windy Miller
You're not comparing apples with apples here. The bulk of the savings come from the switch from petrol to EV.

rjp Yep. As I said

Windy Miller It is the high car use and a decent sized array that paying dividends.

Windy Miller I think you've missed my point: Your "before" maths is based on petrol vehicles. Just buying EV's (which isn't included in the £20k capital cost) reduces fuel costs from about 20p to 7p per mile on a standard tariff, (or down to 2p per mile on off-peak.)

Surely with an EV, the sensible option is to ignore batteries (apart from for home load), sell all your excess PV to the grid at _15p/kWH then charge your car battery overnight at 7p/kWH?

I believe we are on for about 4y9m payback on ours.
We heat/cook with gas and have diesel cars..

£9400 purchase costs (6kWp/9/5kWh battery and 5kW inverter.

Previous elec bill averages were £1,585 PA, now it's -£400, a saving of £1985 PA (-£575/£2160 if you exclude standing charge, or 4yr4m)

I believe we are on for about 4y9m payback on ours.
We heat/cook with gas and have diesel cars..

£9400 purchase costs (6kWp/9/5kWh battery and 5kW inverter.

Previous elec bill averages were £1,585 PA, now it's -£400, a saving of £1985 PA (-£575/£2160 if you exclude standing charge, or 4yr4m)

rjp The original poster describes their before and after situation. I assumed that before included petrol driven vehicles which is why the payback time is so short. If you don't include petrol driven vehicles in the before the costs of running EV's should be removed from the after as they are still a cost just a lot less (and not a saving). I believe it is the move from petrol to EV's with the high monthly usage that makes the payback 5 years. Only the original poster can say whether that is the case or not.

Of course you can be on Octopus Go without a solar array or house batteries. If you only ever charge at the 7p rate (£5 for a 200 mile charge) then you save immediately as the equivalent petrol rate for 200 miles might be £30. But then, as you say, you should include the capital expenditure on the EV's in the calculation.

Windy Miller surely only the depreciation or lease costs on the EVs?

Avenir Yes although it starts to get very complicated with what to include and what not to include. I run a hybrid and in my spreadsheets I count the cost of running the car as being the sum of depreciation, lost interest, petrol and service costs all of which might be different with an EV. My car is now 10 years old and costs me 37p per mile only 12p of which is petrol.

I think we're over-complicating what the OP asked which was Payback in less than 5 years? and my original reply was a scenario where I thought that it was possible. My PV/Battery payback is actually 12 years as I don't have an EV. I think having one helps considerably.