Projects 
The number of operational wind energy projects.

Turbines 
The number of operational wind turbines.

Onshore Capacity (MW)

The total installed capacity of onshore wind farms.

Offshore Capacity (MW)

The total installed capacity of all offshore wind farms.

Energy Produced (MWh/p.a.)

Calculated by multiplying the installed capacity in MW by the number of hours in a year (8760) and then multiplying this by BEIS’s longterm average load factor for (onshore + offshore) wind (30.1%) expressed as a fraction of 1 (e.g. 0.301). Source for capacity factors is Digest of United Kingdom Energy Statistics (DUKES) published annually by BEIS.

Homes Powered Equivalent (p.a.)

Calculated using the most recent statistics from the Department of Business, Energy and Industrial Strategy (BEIS) showing that annual UK average domestic household consumption is 3,900kWh.
RenewableUK calculates UK homes powered as: number of megawatts installed, multiplied by BEIS's "all wind" (onshore + offshore) load factor expressed as a fraction of 1, multiplied by number of hours in a year, divided by average annual domestic electricity consumption expressed in MWh.
As an example, using statistics available in July 2017:
15,905.185 MW installed capacity x 0.301 “all wind” load factor x 8,760 hours / 3.900MWh annual consumption = 10,753,373 homes powered equivalent

CO2 Reductions (p.a.) in Tonnes

RenewableUK uses BEIS’s carbon saving figure of 430g/kWh  see "A Comparison of Emissions Factors for Electricity Generation" Fuel Mix Disclosure on page 3  published by DECC in July 2013. Carbon reduction is calculated by multiplying the installed wind energy capacity in megawatts by the average (onshore + offshore) load factor as a fractional percentage of 1 (e.g. 0.301), multiplied by the number of hours in the year (8760), multiplied by the number of grammes of CO2 saved per kilowatt hour, divided by 1000 (to align the units, as grammes of CO2 is expressed in kWh). So for a generic 2MW turbine: 2 x 0.301 x 8760 x 430 / 1,000 = 2,267 tonnes of CO2 per year, assuming an average load factor (onshore + offshore) of 30.1%.

Load Factors

The load factor is the actual output of a turbine benchmarked against its theoretical maximum output in a year. The load factor is calculated by RenewableUK as a rolling average of the past five years using data (on an Unchanged Configuration Basis) from the Digest of UK Energy Statistics published by the Department of Business, Energy and Industrial Strategy in July.
 For onshore wind this is 26.6%
 For offshore wind this is 37.2%
 The load factor for all wind (onshore + offshore) is 30.1%, as used by government in its Digest of United Kingdom Energy Statistics (DUKES)
