All the big local builders have flagged their presence here, and so have a number of reputed national ones. But there's one recently completed development that's truly revolutionary.

This is Rabi Rashmi Abasan, India's first "solar housing complex". Piloted by the West Bengal Renewable Energy Development Authority (WBREDA), the 26 villas in this complex are a showcase for the exciting possibilities that BIPV -  building integrated photovoltaic - technology offers for residential projects of a similar nature.

BIPV refers to solar panels integrated into the architecture -  mostly into the roof, the facade or the glazing - that convert the sunlight to which they are exposed through the day into electricity.

According to Lyn Toh, spokesperson for SunTechnics India, the firm that supplied the hardware at Rabi Rashmi: "BIPV makes a building highly energy-efficient and reduces carbon emissions, while ensuring basic functions of standard building elements, such as water tightness, light transmittance and thermal insulation."

BIPV is all the rage in the West. Indeed, it makes a lot of sense in a world that's fast running out of oil and coal -  the two, extremely polluting sources of energy that have powered industrialisation.

According to S P Gon Choudhuri, director, WBREDA, BIPV constitutes around 15 per cent of the around 5,000 mega watts of installed capacity of solar power, and is growing at 50 per cent annually.

So each house in Rabi Rashmi will generate 2.2 kwh - which will account for 40 per cent of the power needed to run the standard household electrical appliances. Whenever these are not being used, the power generated will be fed into the grid.

In addition, each house has a solar water heating system which is good enough to supply 100 litres of hot water every day. The design of the houses uses elements of "solar passive architecture" to keep the house cool in summer.

Essentially, this means ensuring cross ventilation so that the cool breeze from the water bodies to the south can circulate through the house, and making the most of natural light. "The houses are carbon neutral," says Gon Choudhuri.

BIPV sounds great, but like all good things it has downsides too - primarily the high cost of installation. As Toh says, "The cost of an installed BIPV system can vary from $12-20 per watt peak, or even higher, depending upon the complexities of installation or type of solar modules. The payback will significantly depend upon the local utility's willingness to buy the green energy at a preferential feed-in tariff [the rate at which the power utility buys the power from the producer]. This is what drives the urban PV market the world over, and we envisage that it is going to happen in India as well in the years ahead."

At Rabi Rashmi, the cost of each house - around Rs 45 lakh - was quite a notch higher than similar developments in the vicinity.

Says Debabrata Dutta who's bought one of the houses, "We were given an estimate that we were paying about Rs 6 lakh more for all the BIPV paraphernalia, which was okay because we would be paying far less for our electricity and recovering the cost in a few years."

As for maintenance, WBREDA has contracted SunTechnics India and Mackintosh Burn, the civil contractor for the project, to help the residents' association for five years.

Given the costs, the maintenance and all that, it takes some amount of push by government to make people turn to such technologies. That's been the experience in the West where a number of European countries, the US and Japan offer financial incentives to encourage the adoption of BIPV, whether as subsidies on the cost of installation or as a generous "feed in" tariff.

The West Bengal government's contribution in this regard has been two-fold. It put in around Rs 50 lakh, which went into the street lighting, the landscaping and so on. Of the rest of the total project cost of around Rs 12 crore (Rs 120 million), Rs 11.5 crore (Rs 115 million) came from the sale of the houses. "In that sense," says Gon Chaudhuri, "Rabi Rashmi was a completely commercial project."

But the government has also stepped in with a feed-in tariff of Rs 5.60 per kilowatt hour, which is the peak slab for domestic power in the state.

"There is a benefit of Rs 7 per kilowatt hour to the residents," the WBREDA director calculates. Incidentally, West Bengal, he adds, is the only state in the country which allows domestically generated solar power to be fed into the grid. "No other state allows this."

But as Lyn Toh of Suntechnics says, "We must realise that switching to solar is not just about payback. It is also about taking that all-important first step towards securing your own energy source and about making a 'green' choice."

Already Gon Choudhuri says DLF and a few local builders have signed MoUs with WBREDA to build similar houses in the state, and officials from the Centre and other states are trooping down to Rajarhat to check out Rabi Rashmi.