"My first home was a zero-energy home but my second is an energy-producing home," explains Prof Dr Soontorn.

An energy-saving home is a good start. Suggestions might include using fewer electrical appliances, architectural design to facilitate cooling and reduce heat, positioning windows and doors for optimum circulation of air, having large green areas, painting the house in light colours, and so on.

All are worthy strategies, but a bio-solar home leaves them in the shade when it comes to seriously saving costs. Developed by Prof Dr Soontorn Boonyatikarn, the bio-solar home can create, save and sell energy, while promoting a high quality of life.

The bio-solar home, located in Rangsit, was developed from his earlier energy-saving home, located in Muang Aek. "My first home was a zero-energy home but my second is an energy-producing home," he said.

The idea came to him when he observed a three-year-old mango tree that had grown and flourished from a seed discarded on the grounds of his property. Learning from this, he designed a home that could stand alone and produce essential resources including water and cooking gas for its residents.

"The bio-solar home is independent from external sources of electricity. It was designed with micro-climate modification with trees and plants covering the ground,s and a pond that can reduce the outside temperature, create outdoor activities for the family and increase the quality of life," he said.

In any case, he said, the budget for such a home had to be reasonable. "It must have a beautiful design, good security and the lowest maintenance cost."

Mr Soontorn's bio-solar home has an indoor area of 145 square metres and an outdoor area of 80 square metres. It took six months to complete in 2002-03 and is worth five million baht.

To produce sufficient electricity, a conventional energy-saving home needs costly solar cells, Mr Soontorn said.

"My bio-solar home has an indoor area of 145 square metres, requiring 6.2 kilowatts of electricity a day. That would cost about 22 million baht for 62 solar cell panels."

Instead, he turned to nature to save the energy needed. The house was designed and positioned in the direction where wind can pass through to keep the house cool, especially during daytime and in summer.

He said the bio-solar home consumed one-seventh of the energy used by an air-conditioning system in an ordinary home.

To create a structure that keeps out heat, foam insulation is used while the wall was made from an exterior insulation and finished system (EIFS).

Mirrors used around the house let the natural light pass through in order to reduce the use of artificial lighting. The mirrors can also cut down ultra-violet rays that are harmful to human skin and infra-red rays that generate heat.

With a carefully thought out bio-solar design in hand, Mr Soontorn needed to spend only 1.4 million baht for solar cell panels to produce enough electricity for use in the house. He was even able to sell some power back to the Metropolitan Electricity Authority.

"The house has both a 'buy-meter' for buying electricity in the daytime and a 'sell-meter' for selling electricity at peak load times during the night. This can help us obtain a return on our investment in the house within eight years, compared with 60 years," he said.

Another innovation by Mr Soontorn involved self-production of water and biogas for cooking.

Water from dew are drawn from the roof, which is angled at 10-15 degrees. The roof's surface was also coated with special paint to keep it cooler than the air temperature, leading to dew production. This resulted in 80 litres of water a day.

About 24 litres of water can be collected from air-conditioning systems each day and 40 cubic metres from rainwater collection. Water from bathing, car washing and the washing machine is also recycled for plant irrigation. This self-production and reuse of water can produce up to 9,000 litres per month for a family with three or four members.

Meanwhile, biogas for cooking is produced from wet garbage, waste and grass. Waste from the biogas process can be also used as fertilisers for organic vegetable production.

It was not surprising that Mr Soontorn's house won the Regional Technology Award in 2002-03 from the American Society of Heating, Refrigerating and Air-Conditioning Engineers.

Currently, he has two orders for his bio-solar home design in Bangkok and at least 10 in the provinces. But with a rise in the cost of some construction materials especially steel, the price of the house has increased by 18% to six million baht, he said.

He added that traditional Thai houses were actually the best home designs for the tropical climate, especially when they were situated in harmony with their natural environment. But since the environment has changed with a hotter climate, more noise and dust from outside, worse pollution and less security, traditional Thai houses are not suitable for city living.

"Some people think that a traditional Thai house is an energy-saving home. They put an air-conditioning system inside but it cannot help reduce heat inside the house," he said.