Expected In House Usage of Solar PV Output

[John Carroll]

 

A few facts/observations first, I have a modest self installed flat(2) plate solar thermal array, and take the daily, Cork,  Roches Point irradiation numbers for the past 14 years, the yearly/period numbers change very little from year to year, for example, periods 1/1 to 17/7 for years 2022,2023,2024,2025, are 665,643,663,703 kWh/m2. I also notice, see "10 Panel Solar PV" below, that the panel efficiency appears to change very little between low and high solar Irradiation, the (10 Panel) attachment shows a 2.6kWp system with a area of 16.4m2, the modelled yearly output is 2.454 Kwh which equates to a efficiency of 14.96%, all the monthly efficiencies are pretty close to this, does this sound plausible? my solar thermal efficiencies certainly vary quite significantly, from say 10% to 28%.

The real reason I'm posting here is that a neighbour is thinking of installing a 4.0kWp system and possibly a 6.0kWp one if his south facing roof can accomodate it. His yearly demand is ~ 3500kwh, 9.6kWh/day, he has a 9kW electric shower only used for 15 minutes/day, plus, electric cooking, electric kettle and the usual other low power users. The spreadsheet is just my estimation of the output, the solar irradiation are my measured ones.

The FIT here is  ~ 18P/kWh

Would someone venture their openion(s) based on the above, as to what the per centage  of self usage might be, based on a 4.0kWp system and on the the 6.0kWp system, or on your own personal experiences. Thanks, John.

Solar Array Output Cork 2024 Rev0.xlsx 10 Panel Solar PV.pdf

Edited 18 hours ago by John Carroll

[JohnMo]

Make life simpler use the link to work it all out fir you.

 

Big array unless you get paid to export and or have a battery - lots of energy will go to waste.

 

https://pvgis.com/en

[Dillsue]

Will your neibours demand profile match the generation profile? Usually there's a big seasonal mismatch because you generate the most in the summer but use the most in winter. Total annual Generation can match total annual demand but because they peak at differing times they'll not balance out.

[ProDave]

As above. Don't over think it.  

 

A typical solar PV with a 3.68kW inverter you can self use almost all of it providing you have a diverter to send any excess to an immersion heater in your hot water tank.

 

You need prior permission from your DNO for anything larger and only consider larger if being paid for export or you have batteries.

[Dillsue]

How big an array you install is a personal thing dependant on lots of factors that vary in importance from person to person.

 

We installed an additional 8.5kw of panels a few years ago on top of the 4kw we already had. No battery for us and no export payments at the time. All self installed and kit bought at discount prices. Having plenty of "free" eleccy and happy for the neighbours to use our surplus is a good enough ROI for me. Octopus now buy our surplus so a big dollop of unplanned icing on that cake:)

[John Carroll]

9 hours ago, Dillsue said:

Will your neibours demand profile match the generation profile? Usually there's a big seasonal mismatch because you generate the most in the summer but use the most in winter. Total annual Generation can match total annual demand but because they peak at differing times they'll not balance out.

 

His usage is a very constant 3315 kWh pa, 9.08 kWh/day, and usage is all day time so all the big users are on, most only briefly,  when the Solar PV should be productive.

I have put a few numbers together which might reflect what kind of savings he migh hope to achieve, currency is in Euros.

Solar Array Output Cork 2024 Rev1.xlsx

[JohnMo]

5 minutes ago, John Carroll said:

have put a few numbers together which might reflect what kind of savings he migh hope to achieve, currency is in Euros

Do you get a feed in tariff (FIT) still. Or that the rate for export with an approved system?

 

So savings are one thing, cost to install another. What sort of cost would the install be? 

[Dillsue]

8 minutes ago, John Carroll said:

 

His usage is a very constant 3315 kWh pa, 9.08 kWh/day, and usage is all day time so all the big users are on, most only briefly,  when the Solar PV should be productive.

Are you sure he uses the same every day all year round? If that's the case then you already have the figures in your spread sheet.

 

If that's not the case and his usage varies then you'll likely export more in the summer and import more in the winter. Because of the difference in unit rates between import and export your figures won't be quite so rosey

[John Carroll]

Don't know much about it John but I believe providers here (the EU) must offer to buy any exported PV, but don't know if they are required to offer a minimum rate for it. I have seen quotes of ~ €10k to €14k for installation, depending on size and location.

[John Carroll]

7 minutes ago, Dillsue said:

Are you sure he uses the same every day all year round? If that's the case then you already have the figures in your spread sheet.

 

If that's not the case and his usage varies then you'll likely export more in the summer and import more in the winter. Because of the difference in unit rates between import and export your figures won't be quite so rosey

 

Usage varies between ~ 8.5 & 10.5 kWh/day based on his two monthly bills over the past year or so.

[JohnMo]

38 minutes ago, John Carroll said:

must offer to buy any exported PV,

If anything like the UK, an approved install and the price you quote would be approved. Export prices without a smart meter is circa 4p and with a smart meter tariff closer to 15p.

 

The reason many on here do DIY installation of PV is the cost difference. 10 to 14k to save 1k is 10 to 14 years payback.

 

Looking at your spreadsheet, it seems there are some errors

 

Have you made allowance for rainy and cloudy days?

Allowed for angle of the panel and sun? i.e. used the link I provide to give a more accurate reality.

 

In May you aren't going to get 29.7kWh every day, maybe not any day, no cloud, no shade, and a tracking system maybe, but a fix array very unlikely.