Sizing my solar setup

[xcentric]

A common enough question. But with panels coming down in price, and the additional cost of putting a few more up when installers already on site being low, I want to get it right. Have already upped initial panel number and need to know where to stop!!

Per day:
House usage 29kWh (about 90th centile real usage) but quite consistent usage
Probable hot tub - 5 kWh
Probable ASHP - 12 kWh
Allowable grid export 7kW
Economy 7 aga (possible dump load) - 32kWh runs at cheap rate

Peak loads for house 4kW without hot tub or ashp.

We do not yet have hit tub or ashp but both likely in near future once solar done - consumption is estimate.

Battery will be 15.5kWh

Do people size for the sunny 5-6 months?

Assume aga runs on E7 from grid, and export is 0 - ie treat putting into both as a bonus - then need is 46kwh. Probably lower as well move washing/drying to when solar production highest etc.

40 420w panels 16.8kW (10 on garage, 30 on roof) gives 40kwh/day for about 7 months according to pvgis, 54-70 for peak 4-5months. Shropshire, uk, with Octopus.

Is this oversized? Undersized? About right? I can put a few more panels on the roof if needed, or fewer. Planning on paralleling 2 solis inverters either 5.5kw or 8 just need to check over panelling specs.

All input welcome.

Thanks!

 

[wpns]

But with panels coming down in price, and the additional cost of putting a few more up when installers already on site being low, I want to get it right.

I went way overboard by maxing out my panels. Our typical day was 60KWHR and I was suddenly making 120-150KWHR/day, which was way too much. Then we had visitors and cloudy days and ran the AC and ended up buying a few KWHR per day (more batteries would have helped some but probably not enough and very expensive). Sure am glad I don’t have to order more stuff, wait 3 months for delivery, deploy the install crew, and climb up on the roof (ever) again.

 

[kommando]

Depends upon how much sun you get.

I sized mine to cover 100% for 6 months of the year. In the UK during winter the location means you just have to grin and bear it or waste too much money oversizing the array. If you plan to be on grid then the DNO will need to pre approve any installation over 3.68kw of inverter.

7kw array, best day in June was 40kwh production, worst 5kwh. Need a lot of battery's to cope with that variation. I have 32kwh of batteries and had to go back on grid after 10 days off grid when that 5kwh day showed up.

 

[SeaGal]

House usage 29kWh (about 90th centile real usage) but quite consistent usage
Probable hot tub - 5 kWh
Probable ASHP - 12 kWh
Allowable grid export 7kW
Economy 7 aga (possible dump load) - 32kWh runs at cheap rate

That's a lot of load, even excluding your probables. We have 6.2kWp in sunny East Anglia (but in process of doubling that); best week production was 240kWh in June and worst week was 14.5kWh in December, with worst day just under 1kWh. At the latitude of the UK there is a huge variation between summer and Winter - currently self-sufficient for 6 months of the year (including immersion heater diversion), but we're only using 10-15kWh typical daily consumption.

Is this oversized? Undersized? About right?

I'd say about right for your 29kWh consumption for 5-6 months of the year, but you will need to top up occasionally in summer and for remaining 6 months of year. But adding extras like the ASHP you will be undersized.

Has anyone complained of having too many panels? They're so cheap right now, so incremental cost is small compared to savings.

Peak loads for house 4kW

I find that figure hard to believe if your daily consumption is 29kWh - having run a 3.6kW inverter for a year before getting a bigger one. A typical UK kettle is 3kW, oven 2 to 2.5kW, air-fryer or microwave about 1.5kW each, washing machine 2.5kW when heating. So, unless you never put the kettle on when the oven is on or the washing machine is on when you want to microwave and air-fry, then you will will exceed 4kW. Can be done, got the t-shirt, but it requires planning and an OCD approach to turning the oven off to make a cup of tea.

 

[Offgrid Jungle]

Agreed, the peak load is more like 18kw.

 

[SeaGal]

Agreed, the peak load is more like 18kw

With an ASHP maybe, from my experience, I'm thinking typical peak is more likely to be around 8kW - depends on so many factors though - do they have an induction hob or cook from gas, for example.

 

[kommando]

My battery inverter is two SI5048's with a max continuous output of 10kw and I have yet to see more than 7kw peak off grid but then we do stagger the starting times of the 2 washing machines and dishwasher when off grid. On grid it might accidentally go to 10kw if the heating cycles of all 3 machines are on simultaneously. No need for any AC here . But who would have their ASHP on in the 6 months of peak PV production when you only need hot water, which an immersion heater could provide. All down to local conditions.