Last Updated: October 30, 2026
Quick Summary
Solar power return on investment is calculated by dividing the upfront installed cost by the annual net benefit, which combines avoided import costs on self-consumed kWh and Smart Export Guarantee income on exported kWh. A 100 kWp system costing £90,000 with a £13,500 annual benefit pays back in 6.7 years.
- A 100 kWp system needs roughly 500 square metres of clear roof and yields 850 to 950 kWh per kWp yearly in the North West.
- Warehouses typically self-consume 40 to 60 per cent of generation, while farms with batteries can reach 60 to 90 per cent.
- Capital allowances can let you deduct the full solar cost from taxable profits in year one through the Annual Investment Allowance.
- Battery storage pays when the gap between import and export rates is large enough to justify shifting surplus power.
- Book a free energy audit to get real roof area, shading and load profile figures for your own site.
Table of Contents
- The Four Numbers Behind Every Solar Power Return on Investment
- Upfront Cost, Generation, Avoided Cost, Export Income
- Step 1: Estimate Your Annual Generation in kWh
- Step 2: Value the Power You Use On Site
- Step 3: Work Out Your Commercial Solar Panel Payback Period
- How Capital Allowances for Solar Panels Change the Sum
- Solar Battery Storage ROI: Does Adding a Battery Pay?
- Three ROI Scenarios Compared: Warehouse, Farm, Home
- Booking Your Free Energy Audit and Feasibility Study
- Frequently Asked Questions
The Four Numbers Behind Every Solar Power Return on Investment
Solar power return on investment comes down to four numbers: what you pay, what you generate, what you avoid paying the grid, and what you earn from export. Get those right and the rest is arithmetic. Get them wrong and you will be quoted a payback figure that never materialises. A payback number without these four figures is just a guess. Below, we show you how to calculate each one, with a worked example for a 100 kWp roof.
- Upfront cost: the full installed price, including scaffolding, grid connection and commissioning
- Generation: annual output in kWh, based on roof pitch, shading and location
- Avoided cost: the unit rate you no longer pay for each kWh you use on site
- Export income: payments for surplus power through the Smart Export Guarantee
Miss any one of these and your payback period will be wrong, usually by years.
Upfront Cost, Generation, Avoided Cost, Export Income
Upfront cost is the total installed price of the system, not the panel price. Readers without capital can explore commercial solar with no capital investment. It includes mounting, inverter, cabling, scaffolding, commissioning and any grid connection work. This is the figure you divide everything else into.
Generation is the annual kWh your roof produces. It depends on panel count, orientation, pitch and shading. A south-facing roof at 30 to 40 degrees performs best; a flat warehouse roof needs tilted frames to match it.
Avoided cost is the simplest of the four. Every kWh you use on site saves you the import rate you would otherwise pay your supplier. As documented in Ofgem's guidance on business energy contracts, commercial unit rates vary widely by contract, so use your own bill, not an average.
Export income comes from surplus power. The Smart Export Guarantee requires large suppliers to pay for exported electricity, though rates differ between them (Smart Export Guarantee (SEG)).
Step 1: Estimate Your Annual Generation in kWh
Start with your roof's usable area and the panel wattage. A 100 kWp system needs roughly 500 square metres of clear roof. Then apply a realistic yield figure for the North West: around 850 to 950 kWh per installed kWp per year, lower than the south coast because of cloud cover. Optimising these generation estimates ensures that your installation contributes effectively to the broader strategy to lower home energy bills.
So a 100 kWp system generates roughly 85,000 to 95,000 kWh a year. Shading, soiling and inverter losses knock a few per cent off that.
You can sanity-check your own roof before committing to a survey. How much energy can your roof generate? gives you an instant estimate of roof area, panel count, annual output and projected savings from your address.
Watch out: yields quoted from sunny-climate case studies will overstate North West output. Always ask for a yield figure based on a local irradiance dataset.
Step 2: Value the Power You Use On Site
Not every kWh you generate is a kWh you avoid buying. Some is exported, some is lost. The split is called your self-consumption rate, and it drives the whole calculation.
A warehouse with daytime load and no battery typically uses 40 to 60 per cent of generation on site. A farm running grain drying or refrigeration through daylight hours can push higher. The rest goes to the grid at the export rate.
To value it, take your self-consumed kWh and multiply by your import rate. Then take exported kWh and multiply by your SEG rate. Add the two figures together: that is your annual benefit before any capital allowance relief.
Step 3: Work Out Your Commercial Solar Panel Payback Period
The commercial solar panel payback period is upfront cost divided by annual net benefit. That is it. No discounting, no complexity, just two numbers.
A Worked Example for a 100 kWp Roof System
Take a 100 kWp system on a Burnley warehouse roof. Suppose the installed cost is £90,000, generation is 90,000 kWh, self-consumption is 50 per cent, the import rate is 25p per kWh and the SEG rate is 5p.
- 45,000 kWh self-consumed × £0.25 = £11,250
- 45,000 kWh exported × £0.05 = £2,250
- Total annual benefit = £13,500
- Payback = £90,000 ÷ £13,500 = 6.7 years
That sits within the commonly quoted range of four to seven years for commercial systems. Change the self-consumption rate or the import rate and the answer moves a lot.
How Capital Allowances for Solar Panels Change the Sum
Capital allowances for solar panels improve the return, sometimes sharply. Solar PV installed on a commercial building may qualify for capital allowances, and in some cases for the Annual Investment Allowance, which can allow the full cost to be deducted from taxable profits in year one.
That does not change the cash payback, but it changes the after-tax return. A profitable limited company can effectively recover a substantial slice of the upfront cost through reduced corporation tax. Check current AIA limits and eligibility with HMRC's capital allowances guidance before you model it, and confirm with your accountant.
For a manufacturer paying corporation tax, this relief can shorten the effective payback.
Solar Battery Storage ROI: Does Adding a Battery Pay?
Solar battery storage ROI depends on one thing: whether the battery lets you use power you would otherwise export cheaply. A battery stores midday surplus and releases it in the evening, when your site is still drawing from the grid.
That arbitrage is worth the difference between your import rate and your SEG rate, multiplied by the kWh shifted. At 25p import and 5p export, each shifted kWh is worth 20p. Shift enough and the battery pays; shift too little and it does not.
Batteries can also provide backup power during grid outages, which matters for cold storage, livestock operations and any process that cannot stop. For a deeper look at payback periods and revenue streams, see our commercial battery storage ROI analysis.
Three ROI Scenarios Compared: Warehouse, Farm, Home
Different sites produce very different returns from the same technology. Here is how the three main cases compare.
| Scenario | Typical System | Self-Consumption | Payback Focus |
|---|---|---|---|
| Warehouse | 100-250 kWp | 40-60% | Daytime load, capital allowances |
| Farm | 30-100 kWp plus battery | 60-90% | Micro-grid resilience, SEG income |
| Home | 4-10 kWp plus battery | 50-70% | Import rate offset, export payments |
A farm with high daytime demand and a battery can aim for high self-sufficiency, which is where the strongest returns sit. A home system is smaller but benefits from the same arithmetic. Warehouse owners with complex roofs should ask for a structural survey before assuming viability.
Farm readers wanting the fuller picture can read our guide to renewable energy for agricultural businesses.
Booking Your Free Energy Audit and Feasibility Study
The calculation above only works with real numbers from your own site. A free energy audit gives you those numbers: actual roof area, shading, load profile and a modelled yield for your postcode.
We are MCS-certified installers, Sunsynk and SolaX approved, and Smart Export Guarantee registered. We also design farm micro-grid systems for clients across Lancashire and Yorkshire.
If you are looking for solar power return on investment advice in the Burnley area, a free survey is a sensible starting point. Make your business energy self-sufficient and book your free energy audit with Squirrel Energy today.
The gap between a solar project that pays back in five years and one that drags past ten is rarely the panels. It is the quality of the numbers behind the proposal. Squirrel Energy designs bespoke solar, battery and micro-grid systems for commercial, agricultural and domestic clients, with MCS-certified installation, Sunsynk and SolaX approved equipment, and Smart Export Guarantee registration. Get started with Squirrel Energy and turn your roof into a measured, defensible return.
Frequently Asked Questions
How do I calculate the return on investment for commercial solar panels?
Divide your net system cost by the annual financial benefit, then invert it for a percentage. Net cost is the installed price minus any capital allowances benefit. Annual benefit is the units you use on site multiplied by your import rate, plus Smart Export Guarantee payments on exported units. For a 100 kWp roof generating 85,000 kWh a year, using 70% on site at 25p per kWh and exporting the rest, the yearly saving runs to roughly £16,000 before any export income. Divide net cost by that figure to get your solar ROI percentage per year.
What is a realistic commercial solar panel payback period?
For well-sized commercial systems in the North West, payback commonly falls in the four- to seven-year range, depending on how much generation you consume on site and your current import rate. Systems with high daytime demand, such as cold stores, grain drying or manufacturing with day shifts, pay back faster because more units displace grid electricity. Systems with low daytime load rely more heavily on export payments and take longer. A feasibility study should model your half-hourly consumption before any figure is quoted.
How do capital allowances for solar panels affect the return?
Solar panels may qualify for plant and machinery capital allowances, and the treatment depends on the circumstances of each installation. That means you can often deduct the full eligible cost from taxable profits in the year of purchase, cutting your corporation tax bill and effectively reducing the net capital outlay. The exact treatment depends on your structure and whether the site is owned or leased, so confirm the position with your accountant before signing off the budget.
Does adding solar battery storage improve ROI?
It depends on your load profile and tariff. A battery raises the capital cost, so it only improves solar battery storage ROI when it captures value that would otherwise be lost: storing midday surplus for evening use, shifting load away from peak rates, or providing backup during outages. For a farm running irrigation or grain drying into the evening, the uplift can be strong. For a site that already uses most generation as it is produced, the extra spend may not clear its own payback within the battery's warranty life.
