Solar maths not adding up

new_owner

Hello all, 

Just want to run this past you, as I am struggling justifying the cost vs gain on solar.

I already use batteries that are charged during Octopus Go Rates and last the whole day. My roof (East-West) is an odd shape and being a three story house means the scaffolding price is pushing up quotes.

so 9 x 415w panels is estimating an usable output of 2,220-2600 kWh - not great. but realistically I only see this saving me about £35-65 per month. 

I currently use around 1100kWh per month and I am wanting to get Air 2 Air system(s) to start looking to move away from gas. This will increase my electric consumption by around another 4-6000kWh per year at a guess.

Do I just except this house is just not going to give me any realistic return on solar?

Martyn1981

Hiya, how much is the price for the PV?

If you already have batts, cheap rate tariff, and are contemplating A2A, then all of these factors will increase the economic benefits of PV. But, it does depend on the cost of the install.

Also, when you say 2,200-2,600kWh 'useable' output, do you mean that you can use in total, or the annual total output of the PV will be just 2,200-2,600, as that sounds quite low for 3,735Wp, even on an E/W roof, do you have shading? For instance my partially shaded E/W system of 5.58kWp has an annual target of about 4,400kWh, so proportionately, yours would be around 2,950kWh .... if next door ..... obviously location will impact generation.

Have a play on PVGIS for a good guestimate.

new_owner

Hi Martyn1981,

The 2,220-2600 was the breakdown on one of the solar installers quotes. 

Year 1. Estimated Output = 2,640.22 kWh - Used on site = 2,217.78 kWh (I suspect I would use 100% on site personally)

I cross referenced this with https://re.jrc.ec.europa.eu/pvg_tools/en/ which gives

Yearly PV energy production [kWh]:

2768.02

The scaffold costs are adding 1.8k+ to the quotes I am getting (detached three story house) so the total quote is around the 8k mark.

I don't really have any shading - a TV arial would be the only thing. 


It seems to me to add more batteries and another inverter to increase my charge / discharge rate and cater the batteries for the A2A system would be a better use of money and remove gas from my property at this point.

ABrass

To pay back in 10 years you'd need to average around 32p return on each kWh.

With Octopus Go you are offsetting night time power, which you're buying at a lower rate.

No, PV doesn't make sense.

Martyn1981

Yeah, £8k's not cheap, but with high prices at the moment, and £1.8k* for scaffolding, I suppose it works out.

The tricky maths is how much will it save you in the longer term when leccy prices come back down. If you are happy with the battery solution, and it can meet your daily demand, then I suppose the PV gen is worth the equivalent of the night rate (x 2,700(ish)) per annum.

Given your leccy use circumstances, I'd say the idea of PV is perfect, but as you've found, it will depend on your circumstances, which aren't ideal.


*Not really funny, but that price made me laugh. My second install in 2012 (the WNW) was a real rush job, racing against a Gov deadline. So the installer who was from the Midlands asked me if I could organise the scaffolding. He gave me a budget of upto £500, and we'd split the saving on anything under £400. I found a small family firm from the S. Wales valleys, who did it for £180, hence my giggle. My times have changed, and scaffolding costs do go up when PV firms are busy.

new_owner

I suspect in the short term for electrify prices to go up but running the number they would have to go up quite some bit.

I was a little shocked at the scaffolding prices - but this is something I know nothing about. I am sure I can call around, but even if I got the price down to say £500 - the solar still comes in with a looong payback. Maybe the next house.

I think I will wait on the solar for the prices to come down and push ahead with A2A and extra batteries.

Good to know its not me not being able to add numbers.

Thank you all for your comments

arty688

My installers didn't use scaffolding, not sure I would install panels without it but they did

Pile_o_stone

To try and make the scaffolding costs a little more palatable, is there any other work you could get done on your roof while it's up there? Maybe a check on the condition of your roofing slates and remedial action before the solar is fitted. Checking the brickwork on your walls and redoing any loose pointing. Checking your guttering and maybe fitting gutter guards while you're up there. Fitting or relocating a satellite dish to a gable end or chimney pot as installers typically don't go above the roofline these days and the dishes really stand out when attached to the side of a house rather than out of sight on the roof (providing it doesn't add shade to your panels).

new_owner

Pile_o_stone said:

To try and make the scaffolding costs a little more palatable, is there any other work you could get done on your roof while it's up there? Maybe a check on the condition of your roofing slates and remedial action before the solar is fitted. Checking the brickwork on your walls and redoing any loose pointing. Checking your guttering and maybe fitting gutter guards while you're up there. Fitting or relocating a satellite dish to a gable end or chimney pot as installers typically don't go above the roofline these days and the dishes really stand out when attached to the side of a house rather than out of sight on the roof (providing it doesn't add shade to your panels).

Unfortunately not. The roof is in good condition and not that old. I don't watch TV (just Netflix, Apple TV+ etc)

I suspect I need to have a much bigger array to make the costs add up and unfortunately, my roof is just not suitable.

arty688

My solar cost around £8K for 20 panels spread over 6 roofs , struggled to get quotes as i was told the scaffold costs would be too highbut got there in the end. So I might be tempted if I was you to try and get a few more quotes maybe someone will do it without scaffoding?.

ABrass

A three story climb might be a bit too much for ladders.