Commercial Solar Calculator
Calculate your commercial solar savings. Enter your electricity spend to see system size, costs, payback period, and 25-year returns. Free instant results.
Calculate your potential savings with commercial solar panels. Enter your electricity bill to see system recommendations, estimated costs, payback period, and 25-year ROI for your UK business.
Quick Answer
How do you calculate commercial solar savings and payback?
Take your annual electricity spend, divide by your day-rate per kWh to get usage, then size a system to cover 40–70% of daytime demand. A 100kWp system costs £75k–£105k and saves £18k–£30k per year at current commercial rates, giving a payback of 4–6 years (or 3.5–4.5 years after AIA tax relief). Multiply annual savings by 25 years, minus the system cost, for lifetime return.
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Your Estimated Results
System Size
kW
Panels Required
~
Roof Space Needed
~m²
Estimated Cost
£ - £
Financial Summary
Environmental Impact
tonnes
CO2 Offset Per Year
Trees Equivalent
Calculation Assumptions
UK average solar irradiation: 900 kWh/kWp/year
Panel efficiency: 500W per panel
Self-consumption varies by business type
Export rate: 5p/kWh (SEG estimate)
* These are estimates for illustration purposes. Actual results depend on site-specific factors. Request a detailed survey for accurate projections.
How the Commercial Solar Calculator Works
A commercial solar calculator turns three inputs — your annual electricity spend, your day-rate per kWh, and your usable roof area — into an estimated system size, cost, annual saving, and payback period. The logic is straightforward:
- Usage: annual spend ÷ day-rate per kWh = your annual kWh consumption. A business paying £50,000/year at 25p/kWh uses around 200,000 kWh.
- System size: a solar array is sized to cover 40–70% of daytime demand without over-exporting. In the UK, each 1kWp generates roughly 900 kWh/year, so a 150kWp system generates ~135,000 kWh.
- Self-consumption: the share of generation used on site (rather than exported). Higher self-consumption means higher savings — typically 60–80% for daytime-operating businesses, rising to 85–90% with battery storage.
- Saving: self-consumed kWh × your day-rate, plus exported kWh × the SEG export rate (8–20p/kWh).
What Payback Period Can You Expect?
Commercial solar payback in the UK typically runs 4–7 years, depending on system size, your electricity rate, and self-consumption. The Annual Investment Allowance shortens this materially — a £100,000 system returns £25,000 in first-year tax relief at the 25% corporation tax rate, cutting payback by 12–18 months. Worked examples:
| Annual Bill | Suggested System | Cost | Annual Saving | Payback (post-AIA) |
|---|---|---|---|---|
| £20,000 | 50kWp | £40k–£50k | £8k–£11k | 3.5–4.5 yrs |
| £50,000 | 150kWp | £120k–£150k | £24k–£32k | 3.5–4 yrs |
| £120,000 | 350kWp | £260k–£320k | £55k–£70k | 3.5–4.5 yrs |
For a full breakdown of the numbers see our commercial solar payback period guide and cost guide. The calculator gives a first-pass estimate; an installer's survey refines it with your real half-hourly meter data, roof orientation and shading.
Get Your Detailed Analysis
This calculator provides estimates. For accurate projections based on your specific site, request installer quotes and a detailed proposal — including site-specific irradiation analysis, roof structural assessment, precise financial modelling, financing comparison, and a grid-connection assessment.
Frequently Asked Questions
How accurate is a commercial solar savings calculator?
A calculator gives a solid first-pass estimate — typically within 10–15% of a full survey — when fed your real annual electricity spend and day-rate. It can't see site-specific factors like roof orientation, pitch, shading, or your exact daytime demand profile, which is why a free survey using your half-hourly meter data is the next step for a precise, bankable projection.
What information do I need to calculate commercial solar payback?
You need three things: your annual electricity spend (or kWh usage), your day-rate per kWh, and your usable roof area or a target system size. With those, the calculator estimates system size, installed cost, annual saving, and payback. Adding your daytime usage pattern and whether you want battery storage refines the self-consumption assumption.
How much can a business save with commercial solar?
A typical commercial solar system saves 40–70% of a daytime-operating business's electricity bill. A 100kWp system saves around £18,000–£30,000 per year at current commercial rates of 20–27p/kWh; a 250kWp system saves £45,000–£60,000. Over a 25-year system life, total savings commonly exceed five to ten times the installed cost.
Does the calculator include grants and tax relief?
Use the calculator for the gross saving and payback, then apply incentives separately: the Annual Investment Allowance returns 19–25% of the system cost via first-year tax relief, and the Smart Export Guarantee pays roughly 4–12p/kWh for exported electricity (Octopus's fixed outgoing rate has been 12p since 1 March 2026). These can cut the effective payback to 3–4 years.
Ready to Reduce Your Energy Costs?
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