UK Solar FiT Calculator
Estimate generation, bill savings, export income, 25-year benefit, and payback time for a UK solar PV system.
Complete UK Solar FiT Calculator Guide for Homeowners and Landlords
If you searched for a UK solar FiT calculator, you are usually trying to answer one practical question: how much money can my solar PV system save or earn each year? The answer used to depend heavily on the Feed-in Tariff, often called FiT, but the policy landscape in Great Britain has changed. FiT closed to new applicants in 2019, and the replacement route for export payment is now the Smart Export Guarantee, known as SEG. A modern calculator therefore needs to estimate both on-site savings and export income under SEG style rates. It also needs to model assumptions like roof orientation, shading, self consumption, electricity prices, and panel degradation.
This page gives you a practical calculator and an expert-level guide so you can interpret the result properly. It is not just about chasing a single payback number. A credible estimate should show year one performance, expected cumulative benefit over 20 to 25 years, and a clear view of what drives upside or downside. If you are comparing installer quotes, this approach helps you avoid optimistic marketing projections and focus on assumptions that materially move financial outcomes.
FiT vs SEG: what changed and why your calculator inputs matter
The original UK Feed-in Tariff paid eligible small-scale generators for electricity generated and for deemed export, under fixed structures that changed over time. Today, new domestic solar systems generally rely on bill savings plus export payments from an SEG licensee. In plain terms, your return is now more sensitive to your own consumption profile and chosen export tariff. Households that run appliances during daylight or use a battery can often increase value from each kWh generated.
Key policy points homeowners should know
- New installations cannot join the historical FiT scheme, but legacy FiT participants can continue under their awarded terms.
- Most new systems monetize exports via SEG with licensed suppliers.
- Import electricity rate and export tariff can vary substantially by supplier and tariff structure.
- Performance assumptions such as roof direction and shading can shift annual generation by hundreds of kWh.
Official background can be reviewed at these sources: Ofgem SEG overview, UK Government SEG decision publication, and UK Government solar deployment statistics.
How to use a UK solar fit calculator correctly
A calculator is only as good as the assumptions you feed it. Start with your proposed system size in kWp, then check regional yield. Yield per kWp reflects local irradiation and climate. A 4 kWp system in one region may produce meaningfully less energy than the same size system in a sunnier part of the country. Next, add roof orientation and shading factors. South-facing unshaded roofs generally outperform east-west roofs, while tree or chimney shading can reduce output throughout the year.
After generation assumptions, set your economic assumptions. The most important are import price, export tariff, and self-consumption. Import price is what you avoid paying for units consumed instantly from your solar production. Export tariff is what you earn when surplus electricity goes to the grid. Self-consumption is the share you use at home instead of exporting. In many homes, self-consumption may sit around 30 to 50 percent without a battery and can increase with load shifting, smart controls, or storage.
- Enter realistic system size from installer design.
- Use local yield and adjust for orientation and shading.
- Set import and export rates from current tariff options.
- Choose self-consumption based on occupancy pattern and storage setup.
- Include panel degradation and expected electricity price growth.
- Review year one return and long-run cumulative return together.
A robust estimate should show that payback is not fixed forever. If import rates rise, avoided grid cost can improve solar economics. If export rates improve, exported units become more valuable. If your self-consumption is lower than expected, returns can soften unless you optimize usage.
Regional generation comparison in Great Britain
The table below gives practical planning ranges that are widely used in early-stage estimates. Exact performance depends on roof pitch, microclimate, and system design, but these ranges are useful for quote filtering.
| Region | Typical annual yield range (kWh per kWp) | 4 kWp annual generation estimate | Comment |
|---|---|---|---|
| Scotland | 850 to 950 | 3,400 to 3,800 kWh | Strong summer output, lower winter irradiation |
| North England | 900 to 1,000 | 3,600 to 4,000 kWh | Balanced output with weather-driven variability |
| Midlands and Wales | 950 to 1,050 | 3,800 to 4,200 kWh | Common baseline for national sales estimates |
| South England | 1,000 to 1,150 | 4,000 to 4,600 kWh | Often attractive for shorter payback scenarios |
| South West England | 1,050 to 1,200 | 4,200 to 4,800 kWh | Generally among the highest domestic outputs |
Ranges are indicative planning values. Site-specific modeling and installer design data should be used before final decisions.
Electricity and export pricing context for your forecast
Financial returns are very sensitive to your unit rates. The following comparison table provides broad context for typical retail import rates and representative SEG style export ranges in recent years. Real offers change over time and by supplier, so always validate against live tariffs before committing.
| Year | Typical domestic import unit rate (p per kWh) | Representative SEG export range (p per kWh) | Impact on solar economics |
|---|---|---|---|
| 2020 | 14 to 18 | 3 to 6 | Savings relied heavily on daytime self-use |
| 2022 | 28 to 35 | 5 to 15 | Higher import rates materially improved avoided-cost value |
| 2024 | 23 to 30 | 8 to 20 | Supplier choice became critical for export revenue |
| 2025 to 2026 planning | Use current local offer | Use current SEG contract | Regular tariff reviews can significantly improve outcomes |
When you compare installer proposals, run your calculator with at least three scenarios: conservative, base case, and optimistic. This gives a realistic confidence band instead of one fragile headline figure.
Worked examples: why two similar homes can get very different returns
Example A: 4 kWp, south facing roof, no battery
Suppose a Midlands property installs 4 kWp with an adjusted annual generation around 3,900 kWh. If self-consumption is 45 percent, around 1,755 kWh offsets import purchases and 2,145 kWh is exported. At 27.5p import and 15p export, year one value is roughly £482 in bill savings plus £322 export income, around £804 total. If system cost is £7,000, simple payback is roughly 8.7 years before modeling degradation and price growth.
Example B: same system, with battery and better load shifting
If that household raises self-consumption to 60 percent with storage and smart usage, import-offset units increase significantly. In the same pricing environment, year one value can rise even if annual generation stays similar. The added battery cost has to be included, but improved self-consumption can improve resilience and increase independence from future tariff volatility. The right decision depends on total package pricing, battery cycle life, and household demand profile.
These examples show why quote comparisons must be normalized. If one installer assumes unrealistically high self-consumption without explaining behavior change or storage, projected returns may be overstated.
Common mistakes when using a UK solar fit calculator
- Using national average generation without correcting for roof direction and shading.
- Assuming all generated electricity offsets expensive import units.
- Ignoring degradation in long-horizon financial projections.
- Forgetting maintenance or inverter replacement in lifecycle planning.
- Locking in a single export tariff assumption for decades.
- Comparing installer payback claims that use different tariff inputs.
A professional approach is to maintain a model that you can update annually with real production and tariff data. This turns a one-time purchase estimate into a living household energy strategy.
How to improve your return after installation
Operational strategies that usually help
- Shift flexible loads to solar hours, such as washing cycles and dishwashing.
- Use smart EV charging to prioritize midday solar where possible.
- Review SEG contracts periodically and compare available suppliers.
- Keep modules clean where local dust, pollen, or bird activity is significant.
- Track monthly production and investigate underperformance early.
Many households discover that behavior and tariff management can unlock as much value as hardware upgrades. Even a modest increase in self-consumption can materially improve annual savings because avoided import units are often worth more than exported units.
Final expert takeaway
A modern UK solar fit calculator should be interpreted as a decision tool, not a guarantee. The strongest calculations are transparent about policy context, site physics, and tariff assumptions. If you treat generation, self-consumption, and tariff rates as variables and test multiple scenarios, you can make a confident investment decision that remains sensible even when the market changes. Use the calculator above as your baseline, then calibrate with installer-specific design outputs, your household load pattern, and live tariff offers. That combination gives the clearest pathway to realistic payback and long-term energy cost control.