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A surge in investment in solar power is bringing down costs of the alternative energy source, but affordability problems still dog hopes for the 1.6 billion people worldwide without electricity.
Supporters believe a solar era may be dawning, boosted by Western funding to combat oil "addiction" and climate change.
But there are few handouts in developing nations where it could be argued solar power is more relevant.
The InterAcademy Council said efforts to curb climate change must target vast numbers of people who lack basic energy.
In the Indian state of Karnataka, private firms, backed by state subsidies, have been pushing solar power for households in towns and cities. The picture is very different for off-grid rural Indian communities, which until now were dependent on kerosene, or paraffin lamps for lighting.
"There are some solar PV programmes that provide a ... limited capital subsidy. It's not at a scale that makes it viable. Solar PV is still really expensive ... more expensive than kerosene," said J.P. Painuly, senior energy planner at Risoe National Laboratory in Denmark.
The Solar Electric Light Company (SELCO) has supplied solar powered electricity to 75,000 households in India, where 60 per cent of households lack electricity.
Their standard solar panel, replacing three smoky paraffin lamps, costs US$250 ($328), 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.
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.
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 Professor Steven Chu of the University of California, Berkeley. "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 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 US$17 billion ($22.42 billion) African market in off-grid lighting.
UK-based solar company G24 Innovations has started production of a low-cost, non silicon-based solar panel, which it will supply into the LED market in developing countries from next year.
