Energy
Solar Savings Calculator
Solar economics come down to two numbers: how much generation offsets your bill, and how long that takes to repay the install. This calculator estimates both.
Calculator
The calculation runs in your browser.
What this calculator does
Estimates monthly and yearly bill savings from solar by capping the generation you can actually use at your consumption, then divides the system cost by yearly savings to give a payback period.
How to interpret the result
Payback is the break-even point, not profit: everything after it is the return. A payback under your expected ownership period is encouraging; one close to or beyond it means the assumptions need checking, especially generation and tariff.
Assumptions
- All generation up to your usage is consumed on site at the full retail price.
- Surplus generation is worth nothing, since export payments vary widely.
- Generation and usage stay flat across the year, which understates winter shortfalls.
Limitations
- Ignores panel degradation (roughly 0.5% output loss per year), which lengthens real payback.
- Does not model batteries, which raise self-consumption but add cost.
- Excludes maintenance, inverter replacement and incentive changes over the system life.
How it works
Savings are based on the generation you can actually use, so generation is capped at your consumption. That offset is multiplied by your price per kWh for monthly savings and by twelve for yearly savings. Payback divides the system cost by yearly savings.
Worked example
A household using 450 kWh a month at 0.28 per kWh with 380 kWh of generation saves about 106 a month, or 1,277 a year. A 9,500 system pays back in roughly 7.4 years on those assumptions.
How to use it
- Take monthly usage in kWh from a recent bill, ideally averaged across a year.
- Use the installer quote for both system cost and expected generation.
- Test a lower generation figure — winter output is far below the annual average.
- Check whether local incentives reduce the system cost before entering it.
Factors to consider
- Self-consumption matters: energy used while the sun shines is worth more than energy exported.
- Panels lose a small percentage of output each year, lengthening real payback slightly.
- Rising electricity prices shorten payback; falling prices extend it.
Useful for
- Getting a conservative first estimate before requesting installer quotes.
- Comparing two system sizes by running the calculator for each.
- Checking how sensitive payback is to the generation figure an installer quotes.
Frequently asked questions
Why is surplus generation excluded?
Export payments differ enormously between tariffs and regions, and some pay nothing. Excluding surplus keeps the estimate conservative.
Is payback the same as profit?
No. Payback is when savings equal the system cost. Everything after that point, minus maintenance, is the return.
Do batteries change the result?
Yes. They raise self-consumption but add cost, so include the battery price in system cost and raise the generation you can actually use.