Worldwide about 1.5 million people die annually from indoor pollution due to lighting and cooking.
It is the health benefits that sell the more expensive panels together with the promise of a much brighter source of light than paraffin lamps so users can work and make money after dark, or read and educate themselves or their children.
The Solar Electric Light Company (SELCO) has supplied solar powered electricity to 75,000 households over the past 12 years in India, where 60 percent of households lack electricity.
Their standard solar panel, replacing three smoky paraffin lamps, costs $250, equal to at least 12 months' income for many rural households, said SELCO Managing Director Harish Hande.
Customers can spread the cost over five years, and microfinance creditors collect payments as often as weekly from those who struggle to put money aside.
One downside is that large parts of Karnataka get monsoon rains for about 4 months a year and people complain that solar systems are not effective in cloudy conditions.
Another is that SELCO's small profits are making it difficult for the company to compete with salaries offered by Bangalore's Internet industry and expand outside its core Karnataka state, said Hande.
Many wealthier suburbs in Karnataka cities and towns have terraces of houses with solar water heaters -- a more basic and widely available technology which heats water but doesn't supply electricity, unlike the solar PV panels.
MANUFACTURING BOOM
SELCO cuts costs by making fluorescent light bulbs and designing solar panels itself, but the panels are still more expensive than the more heavily subsidised oil lamps.
So when will costs come down?
Rapidly developing countries like China are joining a silicon solar cell manufacturing boom, helping to pare the price of the alternative technology and simple, economy panels could soon be affordable even to the rural poor, said Chu.
"Very inexpensive solar cells could be used by off-grid people to charge appliances that don't use a lot of power but make a world of difference," he said, listing life-enhancing items such as radios, mobile phones, water purifiers and bright, efficient lamps called light emitting diodes (LEDs).
The World Bank last month announced a private sector competition to devise the best-value, low carbon light source for poor households in Africa, as a way to flag up what it estimates is a $17 billion African market in off-grid lighting.
UK-based solar company G24 Innovations this month started production of a low-cost, non silicon-based solar panel, which it says it will supply into the LED market in developing countries from next year.
