Solar Panel Savings Calculator for Homeowners

Saving on energy bills is the goal of installing solar panels. But how much will you save?

  • Read for a detailed (but worthwhile!) overview
  • Or skip to the end for a handy calculator

What Determines Your Savings With Solar?

Annual solar energy production

More panels = more energy. Panel orientation (ideally South), location (also ideally South) and distance from the sea (ideally within 10 km) also play a role. Number of panels is the most important factor though.

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, there’s a formula at the bottom of this page: A special gift to the maths-lovers!

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. Also, if you have both day and night rates, then look at the day rate: This is the most relevant when it comes to solar. It’s typically ~ €0.22 in Ireland.

Solar Self-Consumption Percentage

This is the percentage of your generated solar energy that you make use of in your home. With solar panels alone, self-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%.

These figures will also vary depending on your annual electricity usage and the size of your solar panel system. With few panels (relative to your needs), your self-consumption is likely to be higher. On the other hand, your self-consumption is likely to be lower if you have a huge solar panel system but use relatively little electricity.

Being smart about your electricity usage can also help to increase self-consumption. For example, running power-hunger appliances (like washing machines and showers) in the middle of the day will boost self-consumption.

Payment per kWh of electricity exported to the grid

The Irish government is working on a scheme to pay homeowners for their surplus solar electricity. We don’t know all the details of the scheme yet. However, the idea is that payments will be based on the wholesale price of electricity. It’s also likely that you’ll be able to count those payments as credit against your electricity usage. So we’ll count them as savings here, even though they’re technically revenue.

At the time of writing (October 2021), wholesale electricity prices are high due to the European gas shortage (~€0.25 per kWh). Previously, €0.06 per kWh was more usual. However, with higher EU carbon prices, we might not see prices fall to those levels again. So €0.10 is my best medium-term estimate.

Putting it all together

Once you have the above info, use our calculator to get an estimate of your annual savings:

The EnergyD Solar Panel Savings Calculator

Solar Panels in Ireland

Read Are Solar Panels Worth it in Ireland next to keep growing your knowledge of solar energy.

[Appendix for maths lovers] Estimating solar energy production

The following formula gives a rule of thumb for solar panel energy production:

Kilowatts_of_solar_panels X Standardised_output X Optimality

Where:

  • Standardised output =
    • 850 for Northern third of Ireland
    • 900 for Middle third of Ireland (latitude-wise)
    • 950 for Southern third of Ireland
    • +50 if on East/South coast.
  • Optimality =
    • 100% for panels facing due South
    • 96% for panels facing Southeast of Southwest
    • 86% for panels facing East or West




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