Ecotricity spent an average of £401.49 per customer on constructing renewable sources of electricity.
The second highest spender was ScottishPower, according to WhichGreen, which spent £102 per customer, followed by Centrica, which spent £38.
Meanwhile, EDF was responsible for spending £16.31 per customer on renewable, while npower spent just £4.38.
"In my opinion its a statistic that gets to the heart of the issues, cuts through the greenwash and spin of the Big Six and the small independents - it's the measure to me, of whether your deeds match your words," said Ecotricity founder and chief executive officer Dale Vince.
Ecotricity claims it invested £25 million in wind energy during 2007.
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