Where our numbers come from
Here’s how we calculate the figures for our wind park pages...
Amount of electricity generated by a wind park
For operational wind parks we provide the average figure for the amount of electricity produced since the site started generating.
For new wind parks that are entering the planning system, we use a standard method for calculating how much electricity the site could produce.
We do this by multiplying the total rated capacity (how many MW 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 produced by the Department for Energy and Climate Change. This approach is recommended by the Advertising Standards Agency.
For example, a wind farm 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
To work out how many households could be supplied by a wind park we divide the amount of energy generated in a year by 4,152 kWh, which is the amount of electricity consumed by an average household.
This figure is published by the Department of Energy & Climate Change as part of their Sub-National Energy Consumption Statistics and is the average domestic figure for Great Britain.So for the scenario of two 2.3 MW windmills outlined above:
11,169,637 kWh generated per year / 4,152 kWh average consumption level = 2,690 homes
Tonnes of carbon dioxide
Wind energy replaces the output from coal and gas 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 430g of carbon dioxide into the atmosphere. This is a standard ‘emissions factor’ referenced by many bodies including RenewableUK and The Advertising Standards Agency and refers to the CO2 emissions that could be saved during a year of turbine operation; 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 430g CO2 per kWh = 4,802,943,910g
CO2 = 4,802,944kg
CO2 = 4,803 tonnes 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. We review the data on this website annually with the next update scheduled for December 2014 (we have to wait for DECC to publish new data for average UK electricity consumption). In a perfect world a planning application would be passed before the information had a chance to change, but we’re not all perfect!
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