It has been fitted out with an array of solar panels to provide electricity, is about to get a special geothermal system to heat its water, and is expected to be the first house in the state to meet exacting “leadership” standards set by the national Green Building Council.

The 20 room, eight bathroom mansion in the upmarket Nashville suburb of Belle Meade shot to notoriety this spring, when a local right wing group revealed that it “consumed more electricity every month than the average American household uses in an entire year”.

The Tennessee Center for Policy Research disclosed that last year the former Vice-President’s home used more than 221,000 kilowatt hours of power, more than 20 times the national average. And, it added, its monthly consumption had actually risen by 14 per cent since the release of his blockbuster film, An Inconvenient Truth.

On average, it concluded, Gore spent an average of $1,359 a month on electricity and another $1,080 on gas – amounting to some $30,000 a year – on the 10,000 square foot building, which is more than four times the size of the average American home. Critics also charged that he flew frequently by private jet.

The revelation came the day after he had received an Oscar for his film. Standing beside fellow eco-campaigner, Leonardo DiCaprio, he had told the audience that going green was “not as hard as you might think”, adding: “All of us can do something in our own lives to make a difference”.

The Center – which calls Gore a “global warming alarmist” – said that he should get “a gold statue for hypocrisy” to go with his Oscar. And commentators were quick to highlight exhortations to “use energy more efficiently at home” on the film’s website.

To some extent, the criticisms were unfair. The group omitted to mention that, for at least the past 18 months, Al Gore and his wife, Tipper, have been paying more for their electricity, so as to be part of a special scheme that only provides electricity generated by the sun, wind, and from methane given off by waste. And for over three years they have offset their carbon emissions by giving money to renewable energy projects around the world.

Gore’s office added that they drove a hybrid car, and were engaged in a “renovation” programme to try to cut the house’s gargantuan energy consumption. They also use commercial flights except when travel commitments make this impossible, when they hire a private plane for the occasion.

Now 33 solar panels have been installed on the mansion’s roof, and are expected to generate 6,570 kilowatt hours of electricity a year. The Gores have been trying to put them up for nine months, but until April were blocked by local planning laws – dating from 1938 – which forbad them. A new ordinance now allows them so long as they cannot be seen by neighbours. The panels will still only enable them to get a relatively small proportion of their power from the sun – but they are now also installing an Australian-developed geothermal energy system to provide all their heating and hot water from rock 300ft under their home, which both Gores also use for their offices.

They have also just completed installing the best insulated windows available, have fitted energy efficient compact fluorescent light bulbs and energy saving light switches, and upgraded their boiler, among other measures.

They are aiming to get official certification from the country’s top rating system, Leadership in Energy and Environmental Design, run by the US Green Building Council. This sets such exacting standards that it has so far certified only 6000 homes across the entire United States and almost all of these are new ones, designed to be green. Adapting an old building, like the Gore’s home, is very much harder, and few have been recognised.

Jay Hall, the programme’s Acting Director, told the Independent on Sunday, “It’s an old house and getting it right is quite a challenge. But the Gores’ project is very aggressive and I think it will probably make it to certification”.

“If it succeeds,” he added, “it will be the first home, old or new, to be certified in the state of Tennessee”.

Drew Johnson, President of the Tennessee Center for Policy Research says “the renovations are obviously in direct response to our finding that he is a hypocrite on the issue of global warming”.

Gore retorts that “the plan has been in the works for a long time”, adding “the only thing that has changed is that we are more public about it because of the misleading attack by a global-warming denier group.”