# How Much Carbon Dioxide Does a Wind Turbine Save?

A typical modern wind turbine has a capacity of two megawatts (MW) and is expected to avoid emissions of over 1,880 tonnes of CO2 in an average year.

Calculations

The simplest formula to estimate the amount of energy generated by any electricity generating station is:

(Power x Time) x Capacity factor = Energy (electricity) generated

The units of energy normally used are megawatt hours (MWh) and kilowatt hours (kWh) but sometimes Joules (J), Kilojoules (kJ) or Megajoules (MJ).

• Power = the rated capacity of the generating station
• Time = the number of hours in a year
• Capacity factor = an adjustment to take account of the fact that no power station operates at full output all year round

A wind turbine’s output varies with the wind speed and an average modern wind turbine has a capacity factor in the range of 25-30%. This figure should not be confused with the amount of time a wind turbine is generating energy which is much higher (approximately 75%).

Example

Here is a worked example for a 2MW (2000kW) wind turbine over a year:

• Power = 2,000kW
• Time = 24 hours x 365 days = 8,760 hours
• Capacity factor = 0.25 (25%)

Energy = (2,000 x 8,760) x 0.25 = 4,380,000 kWh

The electricity generated by a wind turbine reduces the need to generate electricity from other sources.  In the UK these other sources will almost certainly be fossil-fuelled, i.e. coal, oil or gas.

Carbon dioxide emissions reductions

Electricity generated by long term marginal plant results in average emissions of 430gCO2/kWh of electricity generated (DEFRA environmental reporting guidelines – April 2008).

4,380,000 kWh of clean energy displacing electricity generated from this generation mix will result in the displacement of 1,880 tonnes of CO2 ((4,380,000 x 430)/1,000,000) per 2MW wind turbine over a year.

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