Solar Calculator
What could your roof save you?
Build an evidence-led first estimate using your actual electricity use, roof capacity and operating profile, not a generic bill-band guess. Covers commercial buildings and private homes.
Build your solar scenario
Four short steps. Your results update live on the right as you go.
What are we sizing solar for?
Choose the option that matches your property — the calculator, assumptions and results are tailored to each.
Find your property.
Search your postcode or, better, your full address — the more specific you are, the more accurately we can centre the map on the right building. We’ll try to sketch your roof outline automatically; check it and adjust if needed, or trace it yourself.
Outline your roof using the tools top-left of the map (you don’t need to trace every section, just the main usable area):
- If we’ve already sketched a shape below, check it against your actual roof first.
- Shape’s wrong? Drag the round dots on the shape itself until it matches your roof, then let go — the area below updates automatically, no extra button needed.
- Wrong place, or nothing drawn? Click the bin icon (Delete layers) to clear it, then draw your own with the square or polygon tool — it becomes draggable the moment you finish.
Is solar right for your building?
How generation profile and daytime demand line up across the sectors we work with most.
Commercial solar performs best when there is a solid, predictable daytime electrical load to absorb what the roof generates. Rather than sizing a system to the roof alone, the calculator above works out how much of your daytime electricity use a given system could realistically offset, then checks that against what the roof can physically support.
Hotels & guest houses
Daytime laundry, kitchen extraction and a constant guest-room HVAC baseline give hotels a strong, steady load that lines up well with solar generation, especially on larger flat or extension roofs.
Leisure centres & pools
Pool halls carry some of the highest, most continuous daytime electrical loads of any commercial building: pumps, dehumidification and plant run through the hours solar is generating, making self-consumption unusually strong.
Care homes
Heating, hot water and ventilation run around the clock, but daytime-specific load (kitchens, laundry, communal lighting) is typically flatter than a hotel’s. Battery storage often matters more here, to capture value outside daylight hours.
Commercial & office buildings
Office-hours demand tends to match generation well, but multi-tenant or leased roofs bring added complexity around ownership, metering and planning that should be worked through early.
Home solar performs best when there’s a decent daytime electrical load to soak up what the roof generates — otherwise you’re mostly exporting at a low rate rather than saving at your full import rate. Rather than sizing a system to the roof alone, the calculator above works out how much of your daytime electricity use a given system could realistically offset, then checks that against what the roof can physically support.
Working from home
Laptops, monitors and a home office running through the day give a steady daytime load that lines up well with solar generation, on top of whatever the rest of the household uses.
Retired or usually home
A household that’s around during the day — cooking, heating, appliances running — will typically self-consume a much larger share of what the roof generates than one that’s empty until evening.
Electric vehicle owners
Daytime EV charging is one of the best matches for solar generation there is — a smart charger that prioritises solar can shift a lot of self-consumption into the hours the panels are actually producing.
Out at work all day
If the house is empty on weekdays, most generation happens while nobody’s drawing power. This is where battery storage tends to matter most, capturing daytime solar to use once everyone’s home in the evening.
Voltage optimisation, explained
A simple electrical fix that pairs naturally with solar.
UK electricity networks are permitted to supply at up to 253V, but most commercial equipment (motors, compressors, lighting drivers, IT and HVAC controls) is designed to run efficiently at closer to 220V. Where incoming supply runs consistently high, equipment draws more power than it needs, runs hotter, and wears faster. A voltage optimisation unit steps the incoming supply down to what the building’s equipment actually needs, without any change to how that equipment performs.
On a site with reliably high supply voltage, this typically delivers savings commonly quoted in a 5–10% range. The actual figure depends on your incoming voltage, any efficiency measures already in place, and building size, which is also what drives equipment cost — so rather than fold an assumed saving into the solar numbers above, the calculator simply captures your interest. If you flag it, we size and cost voltage optimisation properly as part of the same desktop assessment.
Battery storage, explained
Capturing the solar you generate but don’t use straight away.
A battery stores surplus solar electricity generated during the day for use later, when the building still needs power but the sun isn’t providing it: early morning, evening, or a low-demand stretch in the middle of a sunny day. For commercial buildings this usually matters most in two situations: sites with a lower or less-predictable daytime load relative to their roof capacity (many care homes and out-of-hours retail fall into this bracket), and sites looking to reduce exposure to high-cost peak-rate electricity later in the day.
Sizing a battery properly means looking at your excess daytime solar generation, night-time demand, charge and discharge patterns, import/export tariffs and the proposed solar system size together — a fixed battery size applied generically can be misleading, especially for a commercial site. Rather than assume a size and cost here, the calculator captures your interest and we size it properly as part of the same desktop assessment.
Current UK legislation & incentives (2026)
What’s actually in force for commercial solar right now, in plain terms.
What’s actually in force for home solar right now, in plain terms.
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VAT
Commercial solar installations carry standard-rate VAT (20%), which VAT-registered businesses can normally reclaim through their VAT return. The 0% VAT relief available for residential and some charitable installations does not extend to commercial organisations.
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Capital allowances
Solar panels are treated as “special rate” plant and machinery, so they do not qualify for the 100% Full Expensing regime, which is reserved for main-rate assets. Most businesses instead use the Annual Investment Allowance, giving a 100% deduction on qualifying spend up to £1 million a year. Where that allowance has already been used elsewhere, a 50% special rate first-year allowance may still apply to solar as a special-rate asset, with the remaining balance added to the special rate pool and written down in later years. The reduced 40% first-year rate introduced from 1 January 2026 applies to main-rate assets only, not special-rate assets like solar panels. Always confirm current rates and eligibility with a qualified tax adviser.
Source: HMRC HS252 capital allowances helpsheet -
Permitted development
Most rooftop solar on commercial and industrial buildings in England can be installed under permitted development rights (Class J), without a full planning application. Since November 2023, the previous 1 megawatt generation cap for non-domestic rooftop systems was removed, so larger commercial arrays can often proceed this way, subject to conditions: panels must sit at least 1 metre back from the roof edge, must not project above the highest point of the roof, and may need prior approval from the local planning authority where they could cause glare to neighbours. Listed buildings and conservation areas carry additional restrictions.
Source: Planning Portal: non-domestic solar panels -
Business rates exemption
Onsite renewable generation and storage used to power your own building, including rooftop solar, is 100% exempt from business rates in England. This relief runs from 1 April 2022 to 31 March 2035.
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Selling surplus power
Electricity you generate but don’t use on site can usually be sold back to the grid under the Smart Export Guarantee (SEG), which replaced the earlier Feed-in Tariff. Commercial SEG rates have generally been running in the low-to-mid teens (pence per kWh) through 2026, and vary by supplier and contract length.
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Minimum energy efficiency standards
Government proposals under discussion would raise the minimum EPC rating to band B, from 2031, for privately rented non-domestic buildings over 1,000 m², where cost-effective. Smaller buildings would remain at the current EPC E minimum. Solar generation, alongside other efficiency measures, is one of the practical routes to a higher EPC rating, though this remains a proposal subject to secondary legislation rather than settled law at the time of writing.
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VAT
The installation of solar panels (and battery storage installed alongside them) at a private home currently qualifies for 0% VAT under the energy-saving materials relief — there’s no VAT to reclaim because none is charged in the first place, unlike the commercial route of paying VAT and reclaiming it.
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Permitted development
Most home rooftop solar in England can be installed under permitted development rights, without a full planning application, provided panels don’t project more than 200mm from the roof slope, aren’t higher than the highest part of the roof (excluding the chimney), and are set back from the eaves and verge. Listed buildings and conservation areas carry additional restrictions, and flats have different rules than houses.
Source: Planning Portal: domestic solar panels -
Selling surplus power
Electricity you generate but don’t use at home can usually be sold back to the grid under the Smart Export Guarantee (SEG), which replaced the earlier Feed-in Tariff. Eligibility normally requires an MCS-certified installation and installer; rates vary by supplier and contract, generally a few pence up to the low teens (pence per kWh).
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Capital allowances & business rates
These are business-tax concepts and don’t apply to a private residence — there’s no capital allowance to claim and no business rates exemption to consider on a home installation.
None of this is tax or legal advice. Rates, thresholds and eligibility change, and your specific position depends on your business structure, existing capital allowance use and the detail of the installation. Confirm the current position with a qualified tax or planning adviser before making a decision.
None of this is tax or legal advice. Rates, thresholds and eligibility change, and your specific position depends on your property, existing planning history and the detail of the installation. Confirm the current position with a qualified adviser before making a decision.
FROM ESTIMATE TO EVIDENCE
Get a site-specific feasibility view, not just an estimate.
This calculator gives you a starting point. A free Remote Energy Assessment looks at your actual bills, roof and electrical setup to show whether solar, battery storage or voltage optimisation is worth pursuing first.
This is a high-level estimate based on the main roof area and standard assumptions. Final system size, generation, installation cost and savings will depend on a detailed desktop assessment and site survey. It is not a quotation, structural survey, DNO offer, planning determination, or investment or tax recommendation. Actual performance depends on your building, electrical infrastructure, location and a proper site survey. Legislation and incentive figures are correct to the best of our knowledge at the time of writing and are not tax or legal advice; confirm your position with a qualified adviser.
Frequently Asked Questions
Is the solar calculator free to use?
Yes. It is free, requires no site visit, and does not commit you to anything. It gives an indicative range so you can decide whether to take the next step.
Who is this calculator for?
It is built for commercial buildings, including hotels, care homes, leisure centres and other business premises, and also covers private homes. It is aimed at buildings considering solar for the first time.
How accurate is the estimate?
It is an indicative estimate based on the details you enter, not a formal survey. Actual capacity, generation and cost depend on factors a desktop tool cannot fully capture, such as roof condition, shading and structural constraints, which is why we recommend a proper site assessment before committing to a project.
What happens after I use the calculator?
If the indicative numbers look worthwhile, the next step is a proper site assessment or a wider free energy review. There is no obligation to proceed.