Commercial Solar Calculator
Costs, savings and payback periods for UK business solar — from 10 kWp to 500 kWp+
Get Your Free Quote →Quick Answer
How do I calculate commercial solar savings for my business?
To estimate commercial solar savings: multiply your system size (kWp) by 1,050 (UK average kWh/kWp/year) to get annual generation. Multiply by your self-consumption rate (typically 60-80%) and your electricity unit rate (typically 26-28p/kWh) to get annual savings. Add Smart Export Guarantee income (3-6p/kWh on exported surplus). A 100kWp system generates approximately 105,000 kWh/year, saving £22,000-£28,000/year at 80% self-consumption.
Commercial Solar Calculator: Size, Cost & Savings
Choosing the right commercial solar system starts with the numbers. This calculator page gives you industry-standard estimates for system size, installation cost, annual generation and financial return — whether you run a 5,000 m² warehouse, a multi-site retail estate or a rural agricultural holding. Use the sizing guide below to estimate your system, then request a site-specific quote from an MCS-certified installer.
Quick Solar Cost Estimator
By Monthly Electricity Bill
| Monthly Bill | System Size | Est. Cost | Annual Saving |
|---|---|---|---|
| £500–£1,000 | 20–30 kWp | £16k–£22k | £5,000–£7,500 |
| £1,000–£2,000 | 30–60 kWp | £22k–£40k | £8,000–£15,000 |
| £2,000–£5,000 | 60–150 kWp | £40k–£95k | £15,000–£38,000 |
| £5,000–£10,000 | 150–300 kWp | £95k–£175k | £38,000–£75,000 |
| £10,000+ | 300 kWp+ | £175k+ | £75,000+ |
Estimates based on 75% self-consumption, 28p/kWh electricity rate.
By Roof/Ground Area
| Available Area | System Capacity | Annual Output | CO₂ Saved/yr |
|---|---|---|---|
| 200 m² | 20 kWp | 17,000 kWh | 8.5 tonnes |
| 500 m² | 50 kWp | 42,500 kWh | 21 tonnes |
| 1,000 m² | 100 kWp | 85,000 kWh | 42 tonnes |
| 2,000 m² | 200 kWp | 170,000 kWh | 85 tonnes |
| 5,000 m² | 500 kWp | 425,000 kWh | 213 tonnes |
Assumes south-facing roof, 10–15% tilt, 850 kWh/kWp/yr yield.
How to Size a Commercial Solar System
Commercial solar sizing is a three-stage process. First, establish your actual consumption pattern — not just total annual kWh, but when you use electricity. A business consuming most power 9am–5pm Monday to Friday will self-consume 70–80% of generation. A business with heavy overnight or weekend loads may self-consume only 40–50% and benefit from battery storage.
Second, assess your roof or ground area. South-facing pitches at 30–35° deliver peak output. East–west splits of a flat roof (two rows at 10–15° facing opposite directions) deliver 85–90% of south performance but spread generation across more of the day. Ground-mounted systems on brownfield land or car park canopies have no roof constraints.
Third, check grid export capacity with your DNO. Systems above 16A per phase (roughly 11 kWp three-phase) require G98 or G99 notification. Large systems above 50 kWp often require a formal G99 application with protection settings, anti-islanding relays and potentially a grid reinforcement contribution. Your installer handles all DNO submissions.
Commercial Solar Cost by System Size (2025/26)
| System Size | Typical Capacity | Installed Cost | Annual Yield | Payback Period |
|---|---|---|---|---|
| Small office/retail | 10–30 kWp | £8,500–£22,000 | 8,500–25,500 kWh | 6–9 years |
| Medium commercial | 30–100 kWp | £22,000–£68,000 | 25,500–85,000 kWh | 5–8 years |
| Large industrial | 100–250 kWp | £68,000–£155,000 | 85,000–212,500 kWh | 5–7 years |
| Major warehouse/factory | 250–500 kWp | £155,000–£290,000 | 212,500–425,000 kWh | 4–7 years |
| Utility-scale roof | 500 kWp+ | £290,000+ | 425,000+ kWh | 4–6 years |
Costs include MCS-certified installation, inverters, mounting, cabling, DNO application and commissioning.
100 kWp System: Full Financial Model
The 100 kWp rooftop system is the most common commercial installation in the UK — large enough for a significant financial return, small enough to fit a single warehouse or factory roof without complex grid upgrades. Here is a full 25-year financial model based on current market data:
| Metric | Figure | Notes |
|---|---|---|
| System size | 100 kWp | Approx. 200 panels |
| Installed cost | £70,000 | Including VAT at 0% |
| Annual generation | 85,000 kWh | South-facing, UK average irradiance |
| Self-consumption rate | 75% | 63,750 kWh used on site |
| Export | 25% | 21,250 kWh sold to grid |
| Electricity rate saved | 28p/kWh | £17,850/year |
| SEG export income | 7.5p/kWh | £1,594/year |
| Total Year 1 benefit | £19,444 | Before AIA tax saving |
| AIA tax saving (19%) | £13,300 | One-off, year 1 |
| Simple payback | 5.8 years | Including AIA |
| 25-year total saving | £486,100 | At 5% electricity price inflation |
| 25-year ROI | 594% | Net of all costs |
| CO₂ saved over 25 years | 1,062 tonnes | 42 tCO₂/yr × 25 |
Projections assume 0.5% annual system degradation, 5% annual electricity price increase.
Get a Site-Specific Quote
Our installers provide detailed financial models based on your actual consumption data, roof survey and grid capacity. Most quotes delivered within 5 working days.
free-quote →Regional Solar Yield Comparison
Solar irradiance varies significantly across the UK. The South West and South East receive the highest annual radiation; Scotland and Northern England receive less but still deliver strong commercial returns. System sizing should account for local peak sun hours:
| Region | Peak Sun Hours/Day | 100 kWp Annual Yield | 100 kWp Annual Saving |
|---|---|---|---|
| South West England | 4.0–4.2 | 85,000–90,000 kWh | £23,800–£25,200 |
| South East England | 3.9–4.1 | 83,000–87,500 kWh | £23,200–£24,500 |
| East Anglia | 3.8–4.0 | 81,000–85,000 kWh | £22,700–£23,800 |
| Midlands | 3.6–3.9 | 77,000–83,000 kWh | £21,600–£23,200 |
| North West England | 3.4–3.7 | 72,500–79,000 kWh | £20,300–£22,100 |
| Yorkshire / North East | 3.4–3.7 | 72,500–79,000 kWh | £20,300–£22,100 |
| Scotland | 3.1–3.5 | 66,000–74,500 kWh | £18,500–£20,900 |
| Wales | 3.5–3.8 | 74,500–81,000 kWh | £20,900–£22,700 |
Based on PVGIS irradiance data for south-facing 15° tilt systems.
Battery Storage: Adding the Numbers
Adding battery storage to a commercial solar installation increases upfront cost by £20,000–£80,000 depending on capacity (30–200 kWh), but improves self-consumption from 70–75% to 85–95%. The financial case strengthens further for businesses on time-of-use tariffs, where morning and evening peak rates exceed 35p/kWh.
| Battery Capacity | Typical Cost | Self-Consumption Uplift | Extra Annual Saving | Battery Payback |
|---|---|---|---|---|
| 30 kWh | £18,000–£22,000 | 5–8% increase | £1,500–£2,500 | 8–12 years |
| 60 kWh | £30,000–£38,000 | 8–12% increase | £2,500–£4,000 | 8–12 years |
| 100 kWh | £45,000–£58,000 | 10–15% increase | £3,500–£5,500 | 9–13 years |
| 200 kWh | £80,000–£100,000 | 12–18% increase | £5,000–£8,000 | 10–15 years |
Tax Incentives That Improve Your ROI
Two tax mechanisms significantly improve commercial solar ROI. The Annual Investment Allowance (AIA) allows businesses to deduct 100% of the capital cost from pre-tax profits in the year of installation — a 19–25% reduction in net cost depending on corporation tax rate. A £100,000 installation effectively costs £75,000–£81,000 after AIA.
The Smart Export Guarantee (SEG) requires Ofgem-licensed energy suppliers to pay for surplus electricity exported to the grid. Current SEG rates range from 5p to 15p/kWh depending on supplier. On a 100 kWp system exporting 25%, this generates £1,500–£4,500/year in passive income for 25+ years.
- ✓Annual Investment Allowance (AIA): 100% first-year tax deduction on full capital cost
- ✓Smart Export Guarantee (SEG): 5–15p/kWh paid for every exported unit
- ✓0% VAT on commercial solar panel supply and installation
- ✓Enhanced Capital Allowances: additional incentives for energy-efficient equipment
- ✓Industrial Energy Transformation Fund (IETF): grants for high-energy manufacturers
Step-by-Step: Getting a Commercial Solar Quote
Once you have a rough system size from the calculator above, here is how to move from estimate to installed system:
- 1.Submit a quote request — your name, site address, monthly electricity bill and roof description. Takes 2 minutes.
- 2.Initial desktop survey — installer reviews satellite imagery, grid map and electricity data. Same day.
- 3.Site survey — structural engineer visits for roof assessment, shading analysis and load profile review. 1–2 days.
- 4.Detailed proposal — full system design, financial model, DNO route and timeline. 5–7 days.
- 5.Installation — typically 3–10 days on site depending on system size.
Frequently Asked Questions
How do I calculate how many solar panels I need for my business?
Divide your annual electricity consumption (kWh) by 850 to get an approximate system size in kWp. A business using 100,000 kWh/year typically needs an 80–120 kWp system. Your installer will refine this using roof orientation, shading analysis and load profile data.
What is the payback period for commercial solar panels in the UK?
Most commercial solar installations achieve payback in 5–8 years. Systems with battery storage typically add 1–2 years. 100 kWp rooftop systems for businesses with high daytime consumption often pay back in under 6 years at current electricity prices.
How much does a 100 kWp commercial solar system cost?
A 100 kWp commercial rooftop system typically costs £65,000–£90,000 fully installed in 2025–2026. Costs vary by roof type, location, inverter specification and scaffolding requirements. DNO application fees (G99) add £500–£2,000 depending on grid capacity.
How much will commercial solar panels save my business?
A 100 kWp system generating 85,000 kWh/year saves approximately £22,000–£28,000 annually at current electricity rates (26–33p/kWh). Additional SEG export income of £1,000–£3,000/year applies for surplus energy. Total 25-year financial benefit typically exceeds £600,000.
Can I claim tax relief on commercial solar panels?
Yes. Commercial solar installations qualify for 100% Annual Investment Allowance (AIA) in the year of purchase, up to the AIA threshold (£1 million in 2025/26). This reduces your corporation tax bill in the first year, significantly improving the financial case.
What size solar system does a warehouse need?
A 10,000 m² warehouse typically installs 200–400 kWp depending on roof space and consumption. Annual generation of 170,000–340,000 kWh can offset 60–100% of electricity bills for warehouses with heavy refrigeration, lighting or conveyor loads.
How accurate is the commercial solar calculator?
Our calculator uses industry-standard irradiance data (3.5–4.2 peak sun hours across UK regions), typical system performance ratios of 0.78–0.82, and current grid prices. For budgeting purposes it is accurate within ±15%. A site survey will provide a precise quote.
Ready to Find Out Your Exact Savings?
Use our free quote service to get a detailed financial model specific to your site — including real electricity consumption data, roof survey results and a firm installation price.
get-free-quote-now →Calculator estimates are indicative. Actual savings depend on site-specific factors including consumption profile, roof orientation, shading, grid connection and electricity tariff. All installations by MCS-certified contractors.
Making Your Solar Calculator Results Work Harder
Once you have your calculator output, the next step is translating the numbers into a financial decision. The key metrics to focus on are: (1) simple payback period — when total savings equal total cost; (2) IRR — the equivalent annual investment return; (3) 25-year NPV — total discounted value created.
For most UK commercial businesses, a solar system that generates a payback of under 7 years and an IRR above 12% represents a better risk-adjusted return than alternative capital investments. Many well-designed commercial solar projects deliver 5-year paybacks and 18-22% IRR when Annual Investment Allowance tax relief is factored in.
| Decision Metric | Target Value | Notes |
|---|---|---|
| Simple payback | Under 7 years | Typical commercial average: 5 years |
| IRR | Above 12% | AIA-adjusted: typically 18-25% |
| 25-year NPV (6% discount) | Positive by Year 5 | Usually 2-3x initial investment |
| Self-consumption | Above 65% | Target 75-85% with load management |
What Affects Your Calculator Result Most
The single biggest variable in any solar financial model is electricity price. Most calculator tools use national average commercial rates (typically 24-28p/kWh), but your actual tariff may differ. Half-hourly metered businesses on Flexible or ToU tariffs face peak rates of 35-50p/kWh during 4pm-7pm — meaning self-consumed solar during peak hours is worth significantly more than the calculator's flat-rate assumption.
Self-consumption rate is the second key variable. A 75% self-consumption assumption may be conservative for a factory running two shifts or a logistics site with continuous operations, but optimistic for an office building that's empty from 6pm Friday to 8am Monday. Get your half-hourly smart meter data and share it with your installer to get a more accurate model.
Commercial Solar Sizing Quick Reference
| Annual Bill | Recommended Size | Annual Saving | Net Cost (after AIA) | Payback |
|---|---|---|---|---|
| £10,000-£20,000 | 20-30kWp | £5,000-£8,000 | £11,000-£17,000 | 2-3yr |
| £20,000-£50,000 | 50-100kWp | £13,000-£28,000 | £22,000-£55,000 | 2-3yr |
| £50,000-£150,000 | 100-250kWp | £28,000-£68,000 | £47,000-£116,000 | 2-3yr |
| £150,000-£400,000 | 250-500kWp | £68,000-£135,000 | £116,000-£222,000 | 2-3yr |
| £400,000+ | 500kWp+ | £135,000+ | £220,000+ | 2-3yr |
Savings based on: 1,050 kWh/kWp annual yield, 75% self-consumption, 27p/kWh unit rate, 4p/kWh SEG export. AIA at 25% Corporation Tax rate. All ex-VAT.
Get a precise calculation for your specific premises
Our solar sizing tool uses your actual energy bills, roof dimensions, satellite irradiance data and current electricity tariff to produce an accurate 25-year financial model — not a rough estimate.
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