What Determines Your Savings With Solar?

Annual solar energy production

Panel orientation (ideally South) and your geographical location influence energy production. However, number of panels is the most important factor. More panels = more energy.

Solar panel installers generally provide an estimate of solar energy production when they give you a quote. Alternatively, PVGIS lets you estimate energy production for yourself. Finally, if you just want some approximate numbers to work with, use:

  • 2,000 kWh for a small home system (approx 2.3 kW rated power)
  • 4,700 kWh for a medium home system (approx 5.4 kW rated power)
  • 7,500 kWh for a large home system (approx 8.7 kW rated power)
5 solar panels in a row on the roof of a brick house
A small rooftop solar panel system

Electricity unit price

You’ll find this on your electricity bill. Be careful though! Many electricity suppliers quote prices excluding VAT. So add on 13.5% VAT if necessary to get the real price you pay. If you have both day and night rates then look at the day rate. It’s typically ~ €0.40 in Ireland.

Solar Onsite-Consumption

How much of your solar energy will you use onsite in your home? With solar panels alone, onsite-consumption can be as low as 30%. A hot water power diverter should bring that up to ~ 50%. Add a battery on top for 70%+.

Onsite consumption will also vary depending on your electricity usage and the size of your solar panel system. With few panels (relative to your needs), your onsite-consumption will be higher. On the other hand, onsite-consumption will be low if you have a huge solar panel system but don’t use much electricity.

Being smart about your electricity usage can boost onsite-consumption. For example, running power-hungry appliances (like washing machines) in the middle of the day will boost onsite-consumption.

Washing machine control knobs
Running a wash in the middle of the day can maximize solar energy use

Export payments for surplus electricity

The amount you get paid for selling electricity to the grid depends on two things:

  • How much surplus electricity you have
  • The unit rate for surplus solar electricity

The first factor is determined by your electricity consumption and the production from your solar panels. The second factor depends on your electricity supplier. You can get a higher rate by shopping round, as shown below:

RankSupplierPayment (per kWh)Notes
1 (joint)Flogas€0.24Increase from €0.20 to €0.24 reported by RTÉ on 20220-09-23
1 (joint)SSE Airtricity€0.24“payable twice yearly”. Customers still waiting for first payment
3Pinergy€0.21Increase from €0.135 to €0.21 reported by the Irish Times on 2022-09-16
4Bord Gáis€0.185
5Energia€0.18
6Electric Ireland€0.14Based on emails sent to customers
EnergyD league table of solar feed in tariffs Ireland 2022
High carbon prices push up the cost of electricity

Putting it all together

Our calculator makes some assumptions to estimate your savings and export earnings.

  • Typical Irish electricity consumption of 4,200 kWh per year
  • €0.40 daytime electricity rate
  • €0.20 export payment
  • No batteries or power diverters

If you have below-average electricity consumption and a cheap deal on your electricity, then your savings are likely to be lower.

Your savings are likely to be higher if you pay more for electricity, have higher electricity consumption, or add a battery or power diverter. Using power-hungry appliances mainly during daylight hours can also help.