Solar cookers have been around for over 200 years now. Their use is limited because of shortcomings related to cooking time and a very basic problem of cooking dinner.

Two professors at Jodhpur have come up with an improved version of a solar cooker, which they claim addresses the problems.

But critics have reservations about the improvised cooker. Solar cookers work on the principle of converting sunlight to heat, which is used for cooking.

Broadly, they come in three designs -- box, panel and concentrating cookers. Reflective surfaces such as mirrors or aluminium foils are used to convert light into heat energy.

The researchers, who focussed on box cookers, found their model fared better than existing ones in terms of collecting light energy and retaining high temperature in the cooking chamber.

In the new model, the researchers added four extra mirrors to the basic cooker. The glass panel, horizontal in the basic design, was tilted to face the sun directly. The cooker can now fit in a window and food can be loaded from the front and not the top, as was done in the basic model.

A number of experiments were carried out using the basic and improved version of the cooker. Temperature in the cooking box was recorded over a day.

The scientists observed the new design achieved a higher temperature than the basic cooker, thus decreasing cooking time. Temperature in the new cooker remained higher in the evenings than the basic design. This implied that the cooker can keep meals warm for a longer time.

To simulate cooking twice a day, the authors experimented with food-loads that were kept and removed twice a day. One load was kept at 11 am and the other placed at 3 pm. Here too they found that their design fared better. Their work was published in the March 2008 issue of Renewable Energy (Vol 33, No 3).

Grey areas

Size is a problem. "Extra mirrors may get better results but they make the cooker bulky and increase the possibility of damage," says Sankha Subhra Datta of Jalpaiguri, West Bengal, who designs solar cookers.

U S Mirdha, lead author of the paper and a professor at Jai Narain Vyas University, Jodhpur, says the size of the cooker can be ignored as long as the cooker performs better than the conventional ones.

"We have improved the design by splitting the top lid and by adding one more cooking chamber," says Mirdha.

The researchers are working on improving the design. They say the cost of the new cooker will be Rs 3,000-4,000 compared to Rs 1,800-2,500 -- the price of conventional solar cookers.

Tom Sponheim of Solar Cookers International, a non-profit organisation based in the US, says the reflectors may be a problem in windy countries like India. With extra mirrors, and hence more heat, food might get burnt, especially if the quantity is small, he says.

Ajay Chandak of Dhule, Maharashtra, says box cookers are not a practical option in today's times. "Extra mirrors may decrease cooking time by an hour from about two-and-a-half hours but it is still not acceptable. Life these days needs faster gadgets and box cookers are still not fast enough," says Chandak, the founder of Prince, a volunteer-based group that promotes use of renewable sources of energy.

He recommends concentrating cookers instead, which take about 30-40 minutes of cooking time.