When Debabrata Dutta, a senior technical manager with Wipro Technologies, and wife Arunima finally settled down in Kolkata — after postings in the US and Bangalore — what they wanted was a home that combined the luxury of a bungalow with the security of a housing complex. They got both, with a bonus: being part of India’s first solar housing project.

Today, the couple are the proud owners of a “dream house” in Rabirashmi Abasan — christened thus by Chief Minister Buddadeb Bhattacharjee himself, for rabirashmi means sunrays.

The housing complex comprises 25 plush bungalows priced at Rs 43 lakh to Rs 45 lakh each for a built-up space of 1,700 sq ft. As Arunima says, they don’t mind paying extra for the “green” bonus.

The brainchild of the West Bengal Renewable Energy Development Agency (WBREDA), Rabirashmi has been developed on a 1.76-acre plot in New Town Kolkata by Bengal DCL — a joint venture of the West Bengal Housing Board and Development Consultants Ltd. The construction was undertaken by Mackintosh Burn.

What is interesting is that it is perhaps the first project in the country where residents push power — generated in their rooftop solar photovoltaic panels — into the grid of power utilities. If they are “power surplus”, they can supply it to the state power utilities and the balance is adjusted to their total consumption of electricity. In this “net metering concept”, consumers pay only for the net energy consumption (calculated on how much they consume from power utilities and how much they push into the grid).

WBREDA is in-charge of general maintenance for the first year while each installation — be it the heater, inverter or solar lights — comes with a five-year guarantee.

There are several other features which make the housing complex every environmentalist’s dream, and has already drawn curious and interested delegates from the UK, the US and Thailand.

* The architecture is based on a “Solar Passive Concept” — buildings are oriented to receive the southern breeze while the cavities of walls have “puff insulation” that keeps extreme temperatures at bay. This means it is warm indoors during winters and cool during summers, almost dispensing with the need for air-conditioners. Plus, the windowpanes of the community centre are transparent photovoltaic panels which double up as windows.

* A “Grid Interactive Solar PV” means the buildings and community centre are connected with a “grid” or supply network of power utilities, says S P Gon Chaudhuri, Director, WBREDA.

* The complex’s own hydro-pneumatic water pump starts working when there is a reduction of pressure inside the pipes caused by opening of taps, flushing cisterns etc. The pump has a varying frequency so that it operates only up to the speed which is needed to get full pressure, thereby saving energy. It operates at maximum capacity only when all the taps are opened.

* Each bungalow has own “power plant” on the rooftop, comprising a solar photovoltaic panel with a capacity of two kilowatts. Household gadgets and electric installations can run on solar power during the day. Post sunset, with the generation dwindling, the system automatically switches to conventional electricity.

* The PV system also has an in-built power back-up system, which stores around 3 kilowatts of power. So, in case of an emergency at night, say during power cuts, one can switch to the back-up to harness stored power. An inverter helps the “switchover” post-sunset. All residents have been advised to opt for LEDs and CFLs.

* Each house is fitted with a solar heater on the rooftop connected to kitchen and bathrooms. The small water tank in the solar heater has a thermal insulation which provides round-the-clock hot water supply.

* There is a swimming pool heated by solar energy.