"Solar panels for greenhouses" covers two very different jobs. A commercial grower with a hectare of glass wants to cut a large electricity bill without costing the crop any light. A gardener with a 6 by 8 foot greenhouse wants a fan, a watering pump or some frost protection without running a cable from the house. The physics is the same for both — panels make most of their power in summer and very little in December, and anything that shades the crop costs yield — so this guide covers both, starting with the commercial case.
SolarPanelsForFarms.uk is an independent guide, not an installer. Figures are sourced below; checked 7 October 2026.
The commercial sector is small in area and large in value. UK growers had 866 hectares of protected vegetables — crops under glass or polythene — in 2025, worth £431 million, including 79,000 tonnes of tomatoes (Defra, Horticulture Statistics 2025). AHDB's GrowSave programme notes that, as a proportion of business variable costs, energy costs can be considerable, particularly in protected cropping.
Where the panels go on a greenhouse site
| Location | Light for the crop | Planning (England) | Verdict |
|---|---|---|---|
| Packhouse, store or workshop roof | No effect | Usually permitted development (Class J); prior approval above 50 kW | The first choice on most sites |
| Ground mount beside the glass | Little or none if sited north of the glass and far enough away | Planning permission (Class K covers one array of 9 m² or less) | Good where land is spare and the grid connection is close |
| Opaque panels on the glass | Large loss — 82% under the panels in one trial | Class J covers roofs, but the structure must be checked | Rarely worth the yield cost |
| Semi-transparent panels or PV glazing | Smaller loss; depends on the product | As for any roof | Mostly trial stage for crops |
| Polytunnel | Shades the crop | — | Film on hoops is not built to carry panels; use a nearby roof or the ground |
A glasshouse frame is designed to carry glass, wind and snow, not a second layer of equipment, so any proposal to fix panels to the glasshouse itself needs a structural engineer's sign-off before anything else. Packhouses, cold stores and workshops often have solid roofs on steel frames, which is why they are the normal home for the array. On older sheds the roof covering matters as much as the frame: see solar on asbestos roofs before planning an array on fibre-cement sheets.
How much light do solar panels take from the crop?
Two pieces of research set the scale. In a trial reported by Cossu and colleagues at the University of Sassari (Applied Energy, 2014), half of a greenhouse's roof area — its south-facing slopes — was replaced with 68 kW of crystalline panels. Over a year the light reaching the crop fell by 64% compared with the same greenhouse without panels: 82% directly under the panels and 46% under the remaining clear cover. The trial was in Italy, which has far more sun than the UK to spare.
What that light is worth was quantified in a 2006 review led by Leo Marcelis (Acta Horticulturae 711). The common rule of thumb — 1% more light, 1% more yield — turned out to be close for most crops but not exact: each 1% of light added 0.7–1% to the yield of fruit vegetables (tomato, cucumber, sweet pepper), 0.8–1% to lettuce and radish, and 0.6–1% to roses and chrysanthemums. The review also found the relative effect of light is greater at lower light levels — which describes a UK winter, when a glasshouse has the least light to give away.
Put together, an array that takes even a modest share of the light off a heated crop can cost more in lost produce than it saves in electricity. That is the arithmetic behind keeping panels off the glass. Semi-transparent and wavelength-selective panels aim to change it: see how transparent solar panels work for where that technology is.
When a greenhouse uses electricity, and when solar makes it
Solar output in the UK is heavily seasonal. PVGIS, the European Commission's solar model, gives this month-by-month output for a south-facing array at 30° in the Vale of Evesham:
| Month | Output (kWh per kW of panels) |
|---|---|
| Jan | 34.5 |
| Feb | 50.2 |
| Mar | 83.2 |
| Apr | 111.5 |
| May | 123.3 |
| Jun | 123.2 |
| Jul | 124 |
| Aug | 110 |
| Sep | 91 |
| Oct | 63.2 |
| Nov | 40.6 |
| Dec | 29.9 |
| Year | 985 |
PVGIS v5.3 (SARAH3 data), near Evesham (52.09°N), 1 kW, free-standing, south-facing, 30°, 14% system losses, unshaded, queried 7 October 2026. The same settings give 1,111 kWh a year near Thanet in Kent, 1,012 in the Lea Valley (Cheshunt) and 987 near Cottingham in East Yorkshire.
Near Evesham, 48.8% of the year's output arrives from May to August and only 15.8% from November to February. That decides which greenhouse loads solar can carry:
- Good match — summer and daytime loads: irrigation and fertigation pumps, air circulation and cooling, cold stores, grading and pack lines, and the climate computer and controls.
- Poor match — winter and night loads: heating, and supplementary crop lighting, which is needed most in the darker months when an array makes least. These need the grid, CHP, a heat pump on grid power, or stored energy from elsewhere.
A site that already runs a CHP engine needs its own modelling, because the engine and the array may both be supplying daytime electricity. Ask the installer to model the two together from your half-hourly meter data rather than from annual totals.
Sizing an array for a glasshouse business
Take a 250 kW array on packhouse roofs in the Vale of Evesham. On the PVGIS figures above it would generate about 246,000 kWh a year — about 120,000 kWh from May to August and under 39,000 kWh from November to February. Whether that is a good investment depends on how much of it the site uses as it is generated, because a unit used on site saves the full import price, while an exported unit usually earns less than that.
- ✓ Start from half-hourly data. The daytime base load on a summer weekday is the number that sizes the array.
- ✓ Add a battery only for a reason. A battery can move midday surplus into the evening, when packing or lighting runs; see battery storage for farms for how to test whether it pays.
- ✓ Check the grid connection early. Anything above 16 A per phase (3.68 kW on a single phase) needs a G99 application, approved before equipment is ordered; see how farm grid connections work.
- ✓ Price from itemised quotes. There is no official cost series for arrays above 50 kW, so compare panels, inverters, mounting, cabling, grid works and any structural work line by line.
Water is the other summer load that solar handles well. If the site pumps from a borehole or a reservoir, see solar water pumps for irrigation; if it has an irrigation reservoir with no roof nearby, floating solar is worth comparing.
Heating: what solar can and cannot do
AHDB's GrowSave notes that protected horticulture often needs a large heating capability, which usually makes up most of a business's energy needs — and heat is needed most from November to March, the months when an array makes least. Near Evesham a south-facing array averages about 1 kWh a day for each kW of panels in December, against about 4.1 kWh a day in June. No realistic roof area closes that gap for a heated crop.
Solar can still help with heat indirectly. A heat pump runs on electricity, and in spring and autumn an array can supply part of what it uses; a battery or thermal store can carry a little of the day's output into the evening. But midwinter heat for a commercial crop comes from boilers, CHP, biomass or heat pumps on grid power, and the business case for solar should be made on the electrical loads in the list above, not on heating.
Planning permission and the grid
In England, panels on the roof of a building other than a house or flats — a packhouse, store or workshop — are usually permitted development under Class J of Part 14 of the General Permitted Development Order 2015. They must not stand more than 0.2 metres proud of a pitched roof or 1 metre above the highest part of a flat roof, must be at least 1 metre from the roof edge, and cannot go on a listed building or scheduled monument. Arrays above 50 kW need the council's prior approval on design and external appearance, in particular glare for neighbours. There has been no capacity cap since 21 December 2023.
Ground-mounted panels beside the glass are different: permitted development (Class K) covers only one stand-alone array within the curtilage of a non-domestic building, with no more than 9 square metres of panels, no dimension over 3 metres and a height limit of 4 metres. Anything bigger needs a planning application. Wales, Scotland and Northern Ireland have their own rules; see our planning guide for farm solar.
Grants and tax
England's Improving Farm Productivity grant (round 2) paid 25% towards solar on farm-building rooftops or irrigation reservoirs, but it closed to full applications on 31 July 2025 and no solar round is open. Wales, Scotland and Northern Ireland run their own schemes; see what farm solar funding is open by nation. For tax, solar panels are special-rate plant: most farm and horticulture businesses can deduct the whole cost in year one through the £1 million Annual Investment Allowance, and companies can take a 50% first-year allowance instead — see capital allowances for farm solar.
Small greenhouses: what a solar panel can and cannot run
For a garden or allotment greenhouse the useful question is how much energy a panel makes, day by day. On the PVGIS figures above, a 100 W panel near Evesham, facing south at 30°, averages about 0.41 kWh a day in June and about 0.1 kWh a day in December.
- Ventilation fans: a good match, because the fan is needed when the sun is out. A fan rated at 20 W running for eight hours uses 0.16 kWh. The RHS warns that plant damage can occur once temperatures build up beyond about 27°C. Automatic vent openers, which work by wax expanding in a cylinder, need no electricity at all.
- Watering pumps, sensors and controllers: small loads that a panel and a small battery handle easily in the growing season.
- Lighting: fine for working light; supplementary light for plants in winter needs far more energy than a panel makes in December.
- Heating: not realistic. An electric heater rated at 2 kW uses 2 kWh every hour it runs — about twenty December days' output from a 100 W panel. The RHS's frost-free target is 4°C; insulating with bubble plastic, which it says cuts out about ten per cent of the light, and a thermostat-controlled heater on a mains supply do more. See whether solar greenhouse heaters work, and how a passive solar greenhouse stores the sun's heat instead.
Questions to ask an installer
- ✓ Which roofs will carry the array, and has a structural engineer checked them?
- ✓ Will any part of the array, at any time of year, shade the glass? Ask for the shading study.
- ✓ What share of the output will the site use itself, month by month, on your half-hourly data?
- ✓ How does the design work alongside any CHP, heat pump or battery already on site?
- ✓ Is the project permitted development, or does it need prior approval or a planning application?
- ✓ Has the G99 application been made, and what does the network operator's offer say?
Solar panels for greenhouses — frequently asked questions
Can you put solar panels on a greenhouse roof?
You can, but opaque panels on the glass take light the crop needs. In an Italian trial, covering half of a greenhouse roof with panels cut the light reaching the crop by 64% over a year. On a commercial site the panels are better placed on packhouse and store roofs, or on the ground where they will not shade the glass. Semi-transparent panels that let most light through are still largely at trial stage.
Do solar panels reduce crop yield in a greenhouse?
Only if they shade the crop, and then the loss can be close to proportional. A 2006 review led by Leo Marcelis found that each 1% of extra light raised the yield of fruit vegetables such as tomato, cucumber and sweet pepper by 0.7% to 1%, and of lettuce and radish by 0.8% to 1%; the effect is larger at low light levels, which is the UK winter.
How many solar panels do I need to power a greenhouse?
Work from the loads, not the floor area. A commercial site sizes the array from its half-hourly meter data so that most of the output is used on site. For a garden greenhouse, a fan rated at 20 W running for eight hours uses 0.16 kWh, and PVGIS puts a 100 W panel near Evesham at about 0.41 kWh on an average June day, so on an average June day one such panel covers it.
Can solar panels heat a greenhouse in winter?
Not on their own. Near Evesham a south-facing array averages about 1 kWh a day for each kW of panels in December, while an electric heater rated at 2 kW uses 2 kWh in every hour it runs. Winter heat for a commercial glasshouse comes from boilers, CHP, biomass or heat pumps; for a garden greenhouse, insulation and a thermostat-controlled mains heater do more than any panel.
Do I need planning permission for solar panels at a glasshouse site?
Panels on the roof of a packhouse, store or other non-domestic building in England are usually permitted development under Class J, subject to height and edge limits, with prior approval from the council on design and glare for arrays above 50 kW. A ground array beside the glass needs planning permission unless it is a single array of no more than 9 square metres (Class K). A panel on a garden greenhouse falls under the householder rules instead.
Are transparent solar panels an option for greenhouses?
Not yet at commercial scale for most growers. A 2021 North Carolina State University study grew lettuce under light filtered to match semi-transparent organic solar cells, with no real loss of growth, but the researchers were still waiting for a manufacturer to produce the cells at scale. Transparent PV glazing is sold for roofs, facades and canopies, but its output per square metre is lower than an ordinary panel.
Sources
- European Commission JRC, PVGIS v5.3 (queried 7 October 2026): Evesham, Thanet, Cheshunt and Cottingham; 1 kW, south-facing, 30°, free-standing, 14% losses.
- Cossu, Murgia, Ledda, Deligios, Sirigu, Chessa and Pazzona (2014), "Solar radiation distribution inside a greenhouse with south-oriented photovoltaic roofs and effects on crop productivity", Applied Energy 133, 89–100.
- Marcelis, Broekhuijsen, Meinen, Nijs and Raaphorst (2006), "Quantification of the growth response to light quantity of greenhouse grown crops", Acta Horticulturae 711, 97–104.
- North Carolina State University study of lettuce grown under light filtered to match semi-transparent organic solar cells, Cell Reports Physical Science (2021), as reported by Vegetable Growers News, 15 April 2021.
- Defra, Horticulture Statistics 2025 (updated 25 June 2026); AHDB, GrowSave.
- RHS, "How to heat a greenhouse efficiently" and "Greenhouse: ventilation and shading".
- The Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 14, Classes J and K (legislation.gov.uk).
- gov.uk, Improving Farm Productivity grant round 2 guidance; Capital Allowances Act 2001 (as cited on our grants and capital allowances pages).