Make the numbers work for your home
Compare the decision. Understand the assumptions.
An attractive unit rate or a short solar payback can hide a lot of assumptions. These tools make them visible. No sign-up, installer referrals or supplier ranking.
By Samuel Mario Pop Achim · Calculation methods updated 28 September 2026.
Solar payback calculator
Results update as you type.
Illustrative defaults, not current quotes or tariffs. Replace them with your own figures. All prices should include VAT where applicable. Your entries stay in this page and are not stored or sent to us.
Simple payback
11.0years
Net cost
€7,200.00
Annual benefit
€656.00
- Used at home 1,440 kWh
- Exported 2,160 kWh
What the solar result includes
Use the installer’s annual generation estimate for your roof, allowing for orientation and shading. Generation is not your household consumption. Self-use is the share of that generation used in your home as it is produced. This simplified tool models a system without a battery.
Annual benefit = generation × self-use share × import rate + generation × export share × export rate − maintenance. Rates are converted from cents to euro. Simple payback is the cost after grant divided by annual benefit.
In the example, 3,600 kWh of generation with 40% self-use means 1,440 kWh avoids imports and 2,160 kWh is exported. At 30c and 15c respectively, the benefit is €756 before a €100 maintenance allowance, or €656 after it. A €9,000 quote less a €1,800 grant gives €7,200 net cost and about 11 years of simple payback.
With 60% self-use instead, the annual benefit becomes €764 and payback about 9.4 years. This is a sensitivity example, not a promise that your household can reach that self-use level. Do not add the full generation value to export income: that counts the same electricity twice.
What this cannot tell you
The result excludes loan interest, panel degradation, inverter replacement, tax on export income and changing tariffs. A battery requires separate costing and allowance for losses and replacement. Electricity standing charges usually remain. If the annual benefit is zero or negative there is no positive simple payback.
Enter only a grant you expect to qualify for and confirm it before committing. See SEAI’s solar grant conditions and our solar quote checklist.
Flat vs day/night calculator
Results update as you type.
Illustrative defaults, not current quotes or tariffs. Replace them with your own figures. All prices should include VAT where applicable. Your entries stay in this page and are not stored or sent to us.
Flat is cheaper by
€10.10/year
You: 35% · shaded zone: day/night cheaper
Compare a whole year, not just the night rate
Gather twelve months of consumption, both plans’ VAT-inclusive unit rates and standing charges, and any recurring levies or charges. Use rates after the applicable discount. Read the actual cheap-window hours: your current night use may not fall within a different plan’s window.
Annual cost = day kWh × day rate + night kWh × night rate + annual standing charge + other annual charges. The flat plan applies one unit rate to all usage. This is a two-rate comparison; do not put a three-rate smart plan into it without separately accounting for peak consumption.
With the example inputs, the flat plan costs €1,560 and day/night costs €1,570.10. Even though the night rate is much lower, day/night is €10.10 dearer because of its day rate and standing charge. It needs about 36.4% of consumption in the cheap window to break even.
Check whether a discount lasts the full year, whether an exit fee applies, and what happens at renewal. Subtract an eligible once-off credit separately. A meter change or tariff activation can affect future options: confirm with your supplier before switching.
For actual available offers, use the CRU list of accredited comparison services. This calculator is independent and is not a CRU-accredited comparison service. Read our night-rate decision guide.
Spotted a calculation error? Send a correction with the inputs and result. Do not send your MPRN, account number or unredacted bill.