Only one UK energy supplier uses 100 per cent renewable energy, although various others claim to be green.
Data available on electricityinfo.org shows that Good Energy is the only firm offering its customers energy which is all generated from renewables.
Other companies which claim to offer green power, such as Ecotricity and Green Energy, don't even generate half of their power from renewables. And, while Good Energy makes no carbon emissions, the others do.
Green Energy, which has the second highest proportion of renewables, at 32 per cent, emits 0.136 kg carbon per kWh. Ecotricity sources roughly a quarter of its energy from each of nuclear, natural gas, coal and renewables and emits .316kg per kWh.
The worst performer on carbon emissions is Scottish Power, which burns coal for 55.2 per cent of its electricity.
Some of the firms are a long way off meeting government targets of 15 per cent of their supply coming from renewables by 2016.
Npower currently only gets three per cent of its energy from renewables, E.on gets 3.6 per cent, and both Utilita and British Gas get four per cent of their energy from renewable sources.
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