Floating solar is usually discussed at utility scale — water-company reservoirs and flooded quarries — but the same idea fits a farm with a lined or embanked irrigation reservoir. The panels sit on the water instead of the land, the farm's biggest summer electrical load (the irrigation pumps) runs while they generate, and the reservoir keeps doing its job underneath. This guide covers how a floating array is built, what it produces, what the evidence says about evaporation and ecology, and the planning, reservoir-safety and grid checks to make before asking for a quote. The full review is summarised in does floating solar reduce evaporation?
SolarPanelsForFarms.uk is an independent guide, not an installer. Figures are sourced below; checked 6 October 2026.
How a floating array is built
A floating system has four parts: floats (usually moulded plastic pontoons that also form the walkways), panels mounted on them at a low tilt, a mooring system that holds the array in place — anchors on the bed, or lines tied back to the banks — and cables that carry the power to inverters and the grid connection on dry land.
The best-known UK example shows the scale involved. Thames Water's array on the Queen Elizabeth II reservoir in Surrey has a peak capacity of 6.3 MW from just over 23,000 panels, carried on more than 61,000 floats held by 177 anchors. It was expected to produce 5.8 million kWh in its first year, to help power the nearby water treatment works (WaterBriefing, 15 February 2016). That works out at about 920 kWh per kW of panels — close to what PVGIS gives for a low-tilt array in the south and east of England.
Why an irrigation reservoir is the farm candidate
- No land taken. A rooftop array needs a suitable roof and a ground-mounted array takes a field; a floating array uses a surface the farm already owns and manages.
- The output matches the load. Irrigation runs in late spring and summer. At a 10° tilt near Norwich, 53% of a year's output arrives from May to August and 74% from April to September (PVGIS), so a pump fed from the array uses its power as it is made.
- Evaporation. A 2024 review of 422 pieces of evidence (Rocha and colleagues, Lancaster University and UKCEH) found the strongest support — 114 pieces — for reduced evaporation or increased water savings from panel shading. For a reservoir filled under an abstraction licence, water kept is water that does not have to be pumped in again.
- Funding history. England's Improving Farm Productivity grant (round 2) paid up to 25% towards solar on farm-building rooftops or irrigation reservoirs. It closed to full applications on 31 July 2025, but it shows the reservoir case was recognised; see the current farm solar grant position.
What it generates
Floating arrays usually sit at a low tilt, which keeps the wind load down. PVGIS shows what that does to the year: a low tilt gives up some winter output but matches or beats a steeper roof in mid-summer.
| Month | 10° tilt (kWh per kW) | 30° tilt (kWh per kW) |
|---|---|---|
| Jan | 24.1 | 36.4 |
| Feb | 38.2 | 50.5 |
| Mar | 74.1 | 86.3 |
| Apr | 110.5 | 118.5 |
| May | 126.1 | 126.5 |
| Jun | 128.4 | 125.8 |
| Jul | 127.4 | 126 |
| Aug | 110.6 | 114.4 |
| Sep | 84.8 | 95.5 |
| Oct | 52.6 | 66.2 |
| Nov | 29.4 | 43.1 |
| Dec | 20 | 32.4 |
| Year | 926 | 1,022 |
PVGIS v5.3, south-facing, unshaded, 14% system losses, near Norwich (52.63°N), queried 6 October 2026. PVGIS does not model the cooling effect of water, which some studies report as a small gain.
So a 100 kW floating array at 10° near Norwich would produce about 92,600 kWh a year, with about 49,250 kWh of it from May to August. How much of that the farm uses itself — the irrigation pumps, packhouse or cold store — decides the return, because each unit used on site saves the full import price.
Planning permission
Permitted development for solar on farm and commercial premises in England covers two things: panels on a building (Class J of Part 14 of the General Permitted Development Order 2015) and one stand-alone array within a building's curtilage, limited to 9 square metres of panels with no dimension over 3 metres (Class K). A floating array on a reservoir is neither, so it normally needs a planning application — and the devolved rules for Scotland, Wales and Northern Ireland likewise cover buildings and small stand-alone arrays. Expect the council to ask about landscape and visual effects, glare, ecology and how the array is removed at the end of its life. See our planning guide for farm solar for how applications are assessed.
Reservoir safety
Reservoir-safety law applies to the reservoir, not the panels, but a floating array adds loads and fixings that the reservoir's engineer needs to know about.
- England: a reservoir that holds, or could hold, 25,000 cubic metres of water above ground level is a large raised reservoir. It must be registered with the Environment Agency, and qualified panel engineers supervise and inspect it.
- Wales: the threshold is 10,000 cubic metres; such reservoirs are registered with Natural Resources Wales.
- Scotland: reservoirs that can hold 25,000 cubic metres or more above the surrounding land must be registered with SEPA.
- Northern Ireland has its own reservoir-safety legislation.
Whatever the size, anchors set into an embankment, cables run over a dam crest, or weight added near a spillway are engineering changes. Agree them with the reservoir's supervising engineer before the design is fixed.
Ecology and water quality
The same 2024 review that found good evidence on evaporation is clear that "understanding of the ecological consequences for water bodies is very limited". Covering a reservoir changes light, temperature and mixing in the water underneath. For an irrigation reservoir that may be welcome — the review also notes the potential to reduce algal blooms — but it is a reason to cover only part of the surface, ask for an ecological survey, and agree monitoring as part of the planning consent.
Design checks for a farm reservoir
- ✓ Water-level range. An irrigation reservoir can be drawn down hard in a dry summer. The moorings must let the array fall with the water, and the floats must not ground on the bed or the liner.
- ✓ Liner protection. On a lined reservoir, bed anchors can puncture the liner; bank-side mooring lines avoid that.
- ✓ Wind and ice. Ask for the mooring design loads in writing, and for how the array copes with ice on the surface.
- ✓ Cable routes. Floating cable runs, the landing point and the route over or around the embankment.
- ✓ Access. Walkways for cleaning and inspection, including clearing bird droppings from the panels.
- ✓ Grid connection. 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.
Cost and tax
There is no official cost series for floating solar. DESNZ's statistics cover MCS-certified installations up to 50 kW, which are mostly rooftop, so a floating array is priced from itemised quotes: floats and moorings, panels and inverters, cabling to shore, the grid connection, and the planning and engineering work. Ask for each to be priced separately.
For tax, solar panels are special-rate plant. Most farm businesses can deduct the whole cost in year one through the £1 million Annual Investment Allowance — a partnership with a company as a member cannot claim it — and companies can take a 50% first-year allowance instead. See how capital allowances work for farm solar.
Floating, roof or ground?
Most farms should look at their roofs first: a roof array uses a surface that is already there and is usually permitted development. A floating array is worth comparing when the roofs are unsuitable or already full, when the reservoir sits close to the load and the grid connection, and when keeping water in the reservoir matters. Compare it with a field array in our guide to ground-mounted solar on farms, and with solar water pumps for livestock and irrigation if what you need is power for a pump rather than for the farm.
Floating solar — frequently asked questions
What is floating solar?
Floating solar mounts solar panels on buoyant floats moored on a reservoir, lake or flooded pit, with cables taking the power to an inverter on the bank. On a farm the usual candidate is an irrigation reservoir, because the water is already there and no field is taken out of production.
How much electricity does floating solar generate in the UK?
PVGIS, the European Commission solar model, puts a south-facing array at a 10 degree tilt near Norwich at about 926 kWh a year per kW of panels, with 53% of it from May to August. Thames Water's 6.3 MW array on the Queen Elizabeth II reservoir was expected to produce 5.8 million kWh in its first year — about 920 kWh per kW.
Does floating solar reduce evaporation?
The evidence points that way. A 2024 review by Lancaster University and the UK Centre for Ecology & Hydrology looked at 422 pieces of evidence; the strongest body of it (114 pieces) supported reduced evaporation, or increased water savings, from panel shading. The same review says understanding of the wider ecological effects is still very limited.
Do I need planning permission for floating solar?
Normally, yes. Permitted development for solar on non-domestic premises covers panels on a building (Class J) and one small stand-alone array of up to 9 square metres within a building's curtilage (Class K). A floating array on a reservoir is neither, so it needs a planning application.
Is there a grant for floating solar on a farm reservoir?
Not at the moment. Round 2 of England's Improving Farm Productivity grant paid up to 25% towards solar on farm-building rooftops or irrigation reservoirs, but it closed to full applications on 31 July 2025 and no further round has been announced. Most farm businesses can still deduct the whole cost in year one through the £1 million Annual Investment Allowance.
Does reservoir safety law apply to a floating array?
It applies to the reservoir. In England a reservoir that can hold 25,000 cubic metres or more above ground level must be registered with the Environment Agency and overseen by a panel engineer; in Wales the threshold is 10,000 cubic metres (Natural Resources Wales); in Scotland it is 25,000 cubic metres (SEPA). Anything anchored into or cabled over the dam should be agreed with the reservoir's engineer.
Sources
- European Commission JRC, PVGIS v5.3 (queried 6 October 2026): Norwich, 1 kWp, south-facing, 10° and 30°, 14% losses.
- WaterBriefing, "Thames Water installs Europe's biggest floating solar panel project" (15 February 2016).
- Rocha, Armstrong, Thackeray, Hernandez and Folkard (2024), "Environmental impacts of floating solar panels on freshwater systems and their techno-ecological synergies", Environmental Research: Infrastructure and Sustainability 4, 042002.
- gov.uk, "Reservoirs: owner and operator requirements" (updated 23 February 2024); Natural Resources Wales, "Register your reservoir"; SEPA, "Reservoirs".
- 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).