Where our numbers come from

Here’s how we calculate the figures for our wind and solar park pages...

Amount of electricity generated by a wind or solar park

For operational wind and solar parks, we provide the average figure for the amount of electricity produced since the site started generating.

For new wind and solar parks that are entering the planning system, we use a standard method for calculating how much electricity the site could produce. 

For wind, we do this by multiplying the total rated capacity (how many megawatts of windmill are on the site) by the total number of days in a year (365.25 – the quarter day allows for leap years), by the number of hours in a day (24) and the capacity factor for that particular site calculated using NOABL wind speed data. This approach is recommended by the Advertising Standards Agency.

For example, a wind park with two turbines, each with a capacity of 2.3 MW will have an overall capacity of 4.6 MW, so to calculate how much electricity that wind farm could generate in a year, we also need to know the capacity factor from NOABL data, say it’s 27.7%:

4.6 MW x 365.25 days x 24 hours x 27.7 per cent capacity factor = 11,169,637 kWh (units of electricity)

= 11,170 MWh

= 11.17 GWh or 11.17 million units of electricity

Number of households

Wind parks

To work out how many households could be supplied by a wind park we divide the amount of energy generated in a year by 3,860 kWh, which is the amount of electricity consumed by an average household. 

This figure is published by the Department for Business, Energy and Industrial Strategy (BEIS) as part of their Energy Consumption Statistics and is an average domestic figure for Great Britain. This figure often decreases each year as households use less electricity. Ofgem have a figure of 3,100 for a typical domestic household.

For the scenario of two 2.3 MW windmills outlined above:

11,169,637 kWh generated per year  / 3,860 kWh average consumption level = 2,893 homes. Using Ofgem’s figures this could be 3,851 homes.

Sun parks

For planning applications and our own advertising, we calculate how many homes our sunmills will power. Rather rather than using wind data, we use an average load factor for solar photovoltaics determined by BEIS. This load factor was 11% when using the average over the last 5 years.

A 5MW (or 5,000 kW) project, could produce 4,821,300 kWh/year – calculated by multiplying 5,000 kW x 365.25 days (including leap year allocation) x 24 hours x 11% load factor.

When dividing 4,821,300 kWh/year by the average household figures above, the result is 1,555 homes using the Ofgem figures and 1,662 using the BEIS figures.

Tonnes of carbon dioxide

We also work out how many tonnes of carbon dioxide could be saved by building the site. Wind and solar energy replaces the output from fossil fuel power stations because these are the ones that are switched on and off to adjust the UK’s power supply to meet demand.

Each kWh of electricity from this mixed bag of fossil fuel generation releases 208g of carbon dioxide into the atmosphere. This is a standard ‘emissions factor’ referenced by the BEIS Digest of UK Energy Statistics 2019 report, and refers to the CO2 emissions that could be saved during a year of turbine operation. The carbon dioxide within our grid mix has reduced over the years with more renewables coming online – great news! It does not refer to the lifecycle emissions involved in construction and operation. 

For our model 4.6 MW wind park

11,169,637 kWh generated per year x 208g CO2 per kWh = 2,323,284,496g

CO2 = 2,323,284g

CO2 = 2,323 tonnes of CO2

The carbon dioxide within our grid mix has reduced over the years with more renewables coming online.

For a 5MW sun park

If the same calculation is used for solar energy, a 5MW solar park could produce 4,821,300 kWh per year x 208g CO2 per kWh = 1,002,830,400g

CO2 = 1,002,830kg

CO2 = 1,002 tonnes of CO2

Therefore, a 5MW solar park could save 1,002 tonnes of CO2.

Variation in published figures

It should be noted that the figures presented on this website may not correspond exactly with those previously published in a planning application. At the time of submission, the figures in a planning application are based upon the most recent evidence available. Due to the nature of the UK planning process an application may take many years before it is finally resolved, and over this period the figures contained are not subject to revision. Once operational we use the generation data to provide an average, and this is updated each year.

Reasons to switch

Al Gore

"As more and more people understand what's at stake, they become a part of the solution, and share both in the challenges and opportunities presented by the climate crises."

Al Gore