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 (30.9%) expressed as a fraction of 1 (e.g. 0.309). 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 3,781kWh.
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 2018:
19,261.180MW installed capacity x 0.309 “all wind” load factor x 8,760 hours / 3.781MWh annual consumption = 13,789,191 homes powered equivalent

CO2 Reductions (p.a.) in Tonnes

RenewableUK uses BEIS’s “all fossil fuels” emissions statistic of 460 tonnes of carbon dioxide per GWh of electricity supplied in the Digest of UK Energy Statistics (July 2018) p125 Table 5D (“Estimated carbon dioxide emissions from electricity supplied 2015 to 2017”).
Carbon reduction is calculated by multiplying the total amount of electricity generated by wind per year by the number of tonnes of carbon which fossil fuels would have produced to generate the same amount of electricity.
E.G. UKWED stated (as of 31.07.18) “Energy produced (MWh p.a.): 52,136,932”  therefore 52136.932GWh x 460 tonnes = 23,982,989 tonnes of carbon emissions saved.

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.
 onshore wind: 26.94%
 offshore wind: 38.36%
 BEIS "all wind": (onshore + offshore): 30.9%
 NB BEIS also states that the load factor for new build offshore wind is 47.3%  see "The Renewables Obligation for 2017/18" table on p12 "Load factors for each technology"
