The array of electricity-generating cells covering more than 100 square metres should allow the centre, at Machynlleth in Powys, to finally end any dependence on fossil fuels and become totally reliant on renewable resources.
It had been getting 10 per cent of its electricity from a diesel generator which also supplied heat, with nearly all of the remainder coming from a wind turbine and hydroelectricity. With the advent of the solar roof, sunshine should now provide more than one-third of the centre's electricity through the year.
Founded more than 20 years ago, it covers a seven-acre site, has 14 permanent residents and is visited by 90,000 residents each year who come to learn about green technologies and lifestyles.
The cost of photovoltaic cells is falling, but they are still uneconomic compared with conventional electricity supplies. However, if they are installed at the same time as a roof is constructed or renewed - as one integrated whole - that makes the proposition much more attractive. The cells take the place of tiles.
Paul Trimby, the centre's solar design consultant, said Britain had only six photovoltaic roofs compared to more than 1,000 in Germany.
''As the costs become comparable with conventional building cladding and roofing materials, solar power will allow buildings to generate their own power," he said.
''They will sell it to the national grid when they have a surplus and buy electricity back when they have a deficit.''
The system used at Machynlleth costs pounds 80,000, and was funded with help from the Department of Trade and Industry and a European Union grant aimed at advancing renewable energy technologies.
The roof will be carefully monitored for several years, to see whether it generates as much power as it should - the peak output is 13 kilowatts - while performing the more conventional task of keeping out the rain.Reuse content