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Big roof solar - sharing power...
Posted: Mon Jan 13, 2025 4:18 pm
by drjim
So I am the Chairman of a Scout group, and we have a hut with a southerly roof that can easily have 30-70 panels installed. I want to do it for several reasons, but primarily because the pitched part on the main building is a metal roof overlying the original felted one, and it gets absolutely boiling in the building in the summer. Shading will help. If I shade it with solar panels I can make electricity (which can of course run an air conditioner for free if so desired).
Budget is a consideration but with the level of DIY talent we have and our MCS qualified electrician I can do a city plumbing panels and inverter buy for around 3-4k, which is amazing! Obviously shopping around needs to happen, especially for the inverter; but that's a good start.
The problem is we don't really use much electricity in the daytime, most use is the electric heating in the winter evenings. We run 10 3kw radiant heaters to warm the place up in winter!
This is the building
https://maps.app.goo.gl/dSfrSj6NWVYewHfY7
And there's a big care home next to us.
I was thinking of suggesting we run a 3 phase cable to their plant room and just feed the power generated to them with a metered rate somewhere below their commercial tariff to make it worthwhile for them. Probably have a second inverter/array on one of the many bits of roof we have to feed the hut itself. Sadly the cost of batteries and the usage pattern makes storage a non starter.
I know some members have large arrays on commercial premises, but has anyone ever done a power sharing/selling arrangement like this? Alternatively I suppose we could just export on whatever tariff we can get but summer daytime isn't going to be the most profitable to export I guess. I also like the idea of keeping it local. It's also been suggested we set up some EV chargers in our parking bays, which would fit nicely with Solar.
Re: Big roof solar - sharing power...
Posted: Mon Jan 13, 2025 5:16 pm
by Saladin
The problem you will face is that the national grid is a state sanctioned monopoly with legal rights to enforce anti-competition measures. Hence it is illegal for end users to trade electricity with other parties on "their network" for financial gain.
You could look into battery solutions or barter.
Sorry* {not sorry*}. Closed shop. Move along now. Innovation and collaboration are ideologies we actively discourage. Use it, accept a lower than market price for it or lose it.
drjim wrote: ↑Mon Jan 13, 2025 4:18 pmhas anyone ever done a power sharing/selling arrangement like this?
I have/do. I build independant micro grids. I rather trade kWh than FIAT pretendy money.
Re: Big roof solar - sharing power...
Posted: Mon Jan 13, 2025 5:22 pm
by AGT
Do you have a 3 phase supply?
Re: Big roof solar - sharing power...
Posted: Mon Jan 13, 2025 5:22 pm
by Stinsy
drjim wrote: ↑Mon Jan 13, 2025 4:18 pm
So I am the Chairman of a Scout group, and we have a hut with a southerly roof that can easily have 30-70 panels installed. I want to do it for several reasons, but primarily because the pitched part on the main building is a metal roof overlying the original felted one, and it gets absolutely boiling in the building in the summer. Shading will help. If I shade it with solar panels I can make electricity (which can of course run an air conditioner for free if so desired).
Budget is a consideration but with the level of DIY talent we have and our MCS qualified electrician I can do a city plumbing panels and inverter buy for around 3-4k, which is amazing! Obviously shopping around needs to happen, especially for the inverter; but that's a good start.
The problem is we don't really use much electricity in the daytime, most use is the electric heating in the winter evenings. We run 10 3kw radiant heaters to warm the place up in winter!
This is the building
https://maps.app.goo.gl/dSfrSj6NWVYewHfY7
And there's a big care home next to us.
I was thinking of suggesting we run a 3 phase cable to their plant room and just feed the power generated to them with a metered rate somewhere below their commercial tariff to make it worthwhile for them. Probably have a second inverter/array on one of the many bits of roof we have to feed the hut itself. Sadly the cost of batteries and the usage pattern makes storage a non starter.
I know some members have large arrays on commercial premises, but has anyone ever done a power sharing/selling arrangement like this? Alternatively I suppose we could just export on whatever tariff we can get but summer daytime isn't going to be the most profitable to export I guess. I also like the idea of keeping it local. It's also been suggested we set up some EV chargers in our parking bays, which would fit nicely with Solar.
IMO you're better off selling the power to the grid at 15p/kWh.
I get that you want to maximise value. But selling the power to the care home could mean buying and digging a trench for a 50m 25mm² 4-core armoured cable. Then you've got all the billing to deal with.
I'd fill both the North and South roofs with panels.
I'm guessing you'd get 36x 400W panels on each roof.
Here are some rough costs:
- Panels £60 x 72 = £4000
- 15kW 3-phase inverters £1200 x 2 = 2400
- Mounting system, cabling, isolators, and other sundries = very hard to guess from afar but maybe £2500?
- TOTAL £8900
Return:
- South array 14,400kWh per year at 15p = £2160
- North array 7,200kWh per year at 15p/kWh = £1080
- TOTAL £3240pa
I hope you agree that is a very good return indeed!
Re: Big roof solar - sharing power...
Posted: Mon Jan 13, 2025 5:33 pm
by drjim
Yes we have 3 phase. Had a quote from a solar firm who wanted 50k to put 72 panels on, but it's a single story building, we have scaffold towers and many DIY capabilities plus our Scout leader has just retired from his job as a construction site manager and needs stuff to do.
I was thinking straightforward rails as sold by CPS and just screw then directly to the steel roof with a rubber washer. Probably just do the south facing initially, bank balance took a pasting when we rewired last year, but we are thus easily able to stick inverters etc in now.
I think we are with EON who will do 16p to sell back...
Re: Big roof solar - sharing power...
Posted: Mon Jan 13, 2025 5:39 pm
by AGT
I agree with Stinsy
Plenty bespoke brackets for metal roofing, try dragonsbreath
Get everything up and DIY as much as you can
Re: Big roof solar - sharing power...
Posted: Mon Jan 13, 2025 6:19 pm
by AE-NMidlands
I agree that private sales look horribly complicated (dual supply in their premises to start with) and the metering... But Dane Valley Hydro do sell all their output to the adjacent Siemens plant - it helps that the leading lights there are working or ex-Siemens engineers! You might ask them how it might work for you.
Also (to keep it relatively simple but to maxmise return) I would investigate batteries and sticking with an Octopus tariff... exporting 3.6kW per phase for 3 hours in the evening peak might well offset the cost of 35 or 40 kWh of batteries quite quickly.
The other thing is that Dane Valley Hydro and some other not-for-profits round here are acting as facilitators, managing the pv install and supplying it to the plot-holder. I don't think they have moved on to batteries yet, so for them it is only about daytime consumption! Shame.
A
Re: Big roof solar - sharing power...
Posted: Tue Jan 14, 2025 9:33 am
by dan_b
This probably doesn't answer your question, but Octopus has a "Solar Sharing" tariff where you effectively donate your excess solar generation to charity
https://octopus.energy/solar-sharing/
Could you find enough budget to install a DIY battery kit as well - some PylonTech stuff perhaps - that would at least allow the hut to use some of the solar for its evening activities?
Installing a public EV charge point could be a nice idea - you can get grants to subsidise public charge points and you could pop in a 7kW PodPoint or two - then set the tariff to be much lower during the day time to incentivise charging when the panels are generating?
Re: Big roof solar - sharing power...
Posted: Tue Jan 14, 2025 9:47 am
by robl
There's a petition to allow local selling of electricity here - it looks like exactly what would help!
I signed it.
https://powerforpeople.org.uk/the-local ... icity-bill
Re: Big roof solar - sharing power...
Posted: Tue Jan 14, 2025 10:26 am
by Ken
The whole solar thing is very cheap now. Even the biggest panels are well below £100 inc vat. You could easily do this as a DIY job for less than £10K.
My concern would be is the roof fit enough to take the weight of the panels and people working.
I am not fully sure why you want to fit PV, is it to warm the place in the evenings as you do not seem to have any real use for the electricity ?
The real solution is to replace the roof with steel insulated panels. I have a shed made from this and it is never really cold and if you fill it with scouts then might have to open the door but it will keep the heat out in summer. Also the insulated roof will not drip water in winter and maintain a much better atmosphere.
The whole thing can be paid for by fitting PV at the same time as the roof and exporting all the production. This will give you a negative leccy bill ie make money. If you fitted the max allowed without permission and possible expensive reinforcements. 16A/phase or 48A in total = 12kw
12 kw of panels could produce 12,000kwh/yr and at 15p export rate = £1800 /yr