Small wind turbine payback calculator: home and farm
Could a small wind turbine pay off at your home or farm? Enter your mean wind speed, hub height and site exposure, and we'll estimate what it would generate and save using a standard power curve.
Treat the answer as a best case, not a promise: small turbines often make less than predicted, especially near buildings and trees.
Your inputs
Fills in wind speed and prices. Then change anything.
EST example: a 6 kW pole-mounted turbine
EST: about £35,000 for 6 kW pole-mounted
Guernsey Airport 1981–2010: 12.5 knots at 10 m (Met Office)
Met Office stations measure at 10 m
Rougher ground slows and disturbs the wind compared with an airport mast
Our allowance for turbulence, downtime and power curves that fall short of the datasheet
From the turbine datasheet
Wind speed where it reaches full power (datasheet)
Farms with daytime loads can use more
Guernsey Electricity Standard tariff (GB cap: 26.32p)
Guernsey export rate not confirmed: 0 until you check. GB: Smart Export Guarantee, e.g. 12p.
Our placeholder: ask installers for a service contract price
Result
Adjust inputs to calculate
Breakdown
Cumulative net position over 20 years
Starts at minus the installed cost, then adds the yearly net saving after maintenance.
What your result means: the headline is the estimated net saving a year. If payback runs longer than the turbine's working life, it won't pay. Wind speed matters most of all, so if you're guessing it, try a lower figure too: a small drop in wind speed cuts output a lot.
Estimates for information only, not financial advice. Prices, grants and rates change, so check them with the supplier or installer before you decide. Get at least three quotes from MCS-certified installers. See our terms.
How we calculate
- Wind at hub height: reference speed × (hub height ÷ reference height)α × an exposure factor. α (wind shear) is 0.11 for coast, 0.16 open, 0.22 hedged and 0.30 built-up. The exposure factor is 1.05, 1.0, 0.85 and 0.65 respectively, allowing for the site being more sheltered than an open airport mast. Both are textbook-style assumptions; a site measurement beats them.
- Wind speed spread: a Rayleigh distribution with that mean, which is the usual assumption when only an average is known.
- Power curve: a generic curve: zero below cut-in, rising with the cube of wind speed to the rated power at the rated speed, flat to 25 m/s and zero above. Your turbine's certified power curve may differ.
- Generation: expected power × 8,760 hours × the real-world performance factor. Capacity factor = generation ÷ (rated kW × 8,760).
- Saving: on-site kWh × import price + exported kWh × export rate − maintenance and insurance. Prices are held flat.
Sources and last updated
All figures checked on 27 October 2026 unless stated. Every default can be changed.
| Figure | Default | Source (date) |
|---|---|---|
| Guernsey mean wind | 6.45 m/s (12.54 kn) at 10 m | Met Office: Guernsey Airport long-term averages (1981–2010): Guernsey Airport 1981–2010 averages, monthly means 10.2–15.3 knots (Aug lowest, Dec highest) |
| Turbine cost and size | 6 kW, £35,000 | Energy Saving Trust: Wind turbines (page last updated 20 May 2026) (updated 20 May 2026; savings about £650 a year in GB) |
| Guernsey import price | 26.01p/kWh | Guernsey Electricity Standard tariff (checked 3 Oct 2026) |
| GB import price | 26.32p/kWh | Ofgem price cap, 1 Oct–31 Dec 2026 |
| GB export | 12p/kWh | Octopus Energy: Outgoing Octopus |
| Shear, exposure, performance factor, power curve, maintenance | — | Our assumptions; change them. |
Frequently asked questions
How much does a small wind turbine generate?
It depends mostly on wind speed, because power rises with the cube of wind speed: a site with 6 m/s has roughly twice the energy of one with 4.8 m/s. On Guernsey's exposed airport averages (about 6.5 m/s at 10 m), our model gives a 6 kW turbine about 12,000 kWh a year at 15 m. A sheltered or built-up site may make a third of that or less.
Do roof-mounted turbines work?
Rarely well. The Energy Saving Trust says wind is less suitable for built-up or sheltered areas and that building-mounted turbines are typically around 2 kW. Buildings slow the wind and create turbulence, and UK field trials found many urban rooftop turbines produced only a small fraction of what was predicted.
Do I need planning permission?
In Wales and Northern Ireland you need planning permission. In England and Scotland some installations count as permitted development, but the rules are complex (EST, checked 27 Oct 2026). In Guernsey, ask the Development & Planning Authority before you buy. Noise and the distance to neighbours are usually the deciding issues.
Are there grants?
The Energy Saving Trust says there are currently no grants for wind turbines in GB. You may be paid for exported electricity under the Smart Export Guarantee if the turbine is MCS-certified.
More in the small wind turbine guide and the other home-energy tools. Your inputs stay in your browser; see our privacy notice.