Why the barn roof is the best place to start
Of all the places to put solar on a farm, the barn roof is the easiest win. Modern steel-portal and Dutch barns offer large, unbroken, well-pitched roof spans with simple access and robust structures — so installation is cheaper per kWp than almost any other building type. Because the roof is already there, you avoid the cost of ground-mount foundations, fencing and long cable runs, and you keep your land in production. For most UK farms a barn-roof array is the lowest-risk, fastest-payback renewable investment available.
How many panels fit on a barn roof?
As a rule of thumb, every 6 m² of usable roof carries about 1 kWp (two to three modern 410–450 W panels). The table shows typical barn sizes, what they support and what they generate:
| Barn roof | System | kWh/yr, 30° roof near York | kWh/yr, 10° roof near York |
|---|---|---|---|
| 200 m² small barn | 30 kWp | 28,800 | 26,000 |
| 500 m² modern shed | 75 kWp | 72,000 | 65,100 |
| 1,000 m² large barn | 150 kWp | 144,000 | 130,200 |
| 1,500 m² grain store | 225 kWp | 216,000 | 195,300 |
Generation from PVGIS v5.3 (SARAH3, south-facing, 14% system losses, queried 26 September 2026). The two larger arrays are above 50 kW, which in England needs Class J prior approval. For costs, see the agricultural solar panel cost guide and pricing by system size.
"Free" barn solar panels — rent-a-roof and PPAs explained
Searches for "free barn solar panels" usually mean one of two things: a rent-a-roof scheme or a power purchase agreement (PPA). In both, an investor pays for and owns the system on your barn. You host it for 20–25 years and either receive a small roof rent or buy the electricity it produces at a discount to grid prices, with ownership often transferring to you at the end. The appeal is zero upfront cost. The catch is that the investor keeps most of the financial benefit — over the system's life you typically earn far less than if you owned it. For a profitable farm that can use the £1m Annual Investment Allowance, buying the system outright is usually the stronger play: you keep the full value of every kWh the farm uses. Ask for both routes to be modelled side by side so you can choose with real numbers in front of you. See our agricultural PPA guide for the full comparison.
Asbestos, structure and older barns
Many older farm buildings still have asbestos cement roof sheets. HSE says these roofs are always fragile and cannot bear weight, so panels should not be fixed straight onto them and nobody should work on them without fall protection. The sound routes are to overclad with non-asbestos sheeting attached to the existing purlins, or to remove and re-sheet before the array goes on; our guide to overcladding or re-sheeting an asbestos barn roof covers the duties and the choice. Steel-portal frames from the 1970s–90s need load calculations against the actual purlins (no generic templates), and listed or traditional stone barns fall outside Class J permitted development, so they need planning permission and usually listed building consent. For every other building on the farm, see our guide to solar on farm buildings.
Grants and tax relief for barn solar
- 🔴 Improving Farm Productivity grant (England) — paid 25% of eligible costs on rooftop solar; round 2 has closed and no solar round is open. The FETF's 2026 window closed on 12 May 2026. Full grants guide.
- 🟢 £1m Annual Investment Allowance — deduct the full cost of the system against profits in the year of purchase
- 🟢 Business rates — buildings used solely for agriculture are exempt; see solar panels and business rates
- 🟢 Smart Export Guarantee — roughly 4–12p/kWh (as at July 2026) for power exported from the barn
- 🟢 Wales, Scotland and Northern Ireland run their own schemes — check the current rules before planning around a grant
Barn solar panels — frequently asked questions
How many solar panels can a barn roof hold?
Roughly 1 kWp (about 2–3 panels) per 6 m² of usable south-facing roof. A 200 m² small barn takes ~30 kWp, a 500 m² modern shed ~75 kWp, and a 1,000 m² large barn or grain store 150–200 kWp. Size the array from your roof drawing and 12 months of half-hourly meter data, not a rule of thumb.
How much do barn solar panels cost?
Government data is the most reliable guide. DESNZ’s 2025/26 statistics put the median installed cost of a 10–50 kW solar system at about £1,262 per kW (MCS-certified installations in Great Britain, including VAT where applicable, excluding batteries), so a 40 kW barn roof would be roughly £50,500 at the median. The statistics stop at 50 kW, so for a larger barn compare at least three itemised quotes. England’s Improving Farm Productivity solar grant has closed; the £1m Annual Investment Allowance can relieve the full cost in the year of purchase.
Can I get free solar panels on my barn?
"Free" barn solar usually means a rent-a-roof or power purchase agreement (PPA): an investor funds and owns the system, you host it and buy the electricity it generates at a discount to grid prices, often with the system transferring to you after 20–25 years. You pay nothing upfront but keep less of the saving than owning outright. For most profitable farms, buying the system (with the Annual Investment Allowance) gives a better return — ask for both routes to be modelled side by side.
Can I put solar panels on an asbestos barn roof?
Not directly. HSE says asbestos cement roofs are always fragile and cannot bear weight, and advises against drilling through the sheets, so panels should not be fixed straight onto them. The usual routes are to overclad with non-asbestos sheeting attached to the existing purlins, or to remove the asbestos cement and re-sheet before the array goes on. Removing intact sheets on a small scale is normally non-licensed work, but a whole barn roof needs a proper risk assessment and plan of work.
Do I need planning permission for solar panels on a barn?
In England, rooftop solar on an existing agricultural barn is usually permitted development under Class J of Part 14 of the General Permitted Development Order: panels must not protrude more than 0.2 m beyond a pitched roof slope or rise more than 1 m above a flat roof, and must sit at least 1 m from the roof edge. Listed barns are excluded, and arrays above 50 kW need prior approval from the council. Ground-mounted schemes usually need full planning permission.