As technological obstacles to the efficient use of solar energy diminish, economic and political challenges remain to its widespread adoption by the poor.
"The sun occupies centre stage, as it should, being literally the original source of all energy," said India's prime minister, Manmohan Singh, describing an action plan for India's national strategy on climate change, in June 2008.
He promised India would pool "scientific, technical and managerial talents with financial sources to develop solar energy as a source of abundant energy to power our economy, transform the lives of our people and change the face of India".
In principle, solar energy is a near-perfect solution for the energy needs of developing countries. It is universally and freely available, particularly near the equator, where many developing countries are found.
Solar energy is the ultimate renewable energy resource, at least within the timescale of human existence. Its use doesn't deplete reserves, or emit much carbon dioxide to the atmosphere, making it the ideal response to the challenge of climate change.
Unlevel playing field
Until recently, the major barrier to solar energy's uptake lay in the low efficiency — and relatively high cost — of converting it into a usable form. But scientific breakthroughs are rapidly eroding this barrier. Photovoltaic technologies, which use chemical reactions to turn sunlight into electricity, are advancing rapidly, as are the batteries used to store electricity until it is needed.
As conversion and storage costs fall, solar technology's potential for serving poor communities will inevitably rise. In India, the long-term costs of using solar-powered lamps are already considerably cheaper than traditional lighting fuelled by kerosene.
If the economic playing field were a level one, this combination of strong need/demand and falling costs would be sufficient to guarantee solar energy's rapid dissemination across the developing world.
But, unfortunately, the playing field is not level. The capital costs of solar devices remain considerable, particularly to the poor. And government subsidies for energy produced from non-renewable sources — intended ostensibly to keep prices affordable — have too often also distorted the market in the interests of conventional energy suppliers.
All this means that the spread of solar energy, particularly to the rural communities that stand to benefit most from it, is far slower than it should be.
Under a solar spotlight
This week, SciDev.Net highlights the technological opportunities and the social and political challenges surrounding solar power for the poor, in a series of opinion and feature articles.
A background article sets the scene, summarising the scientific and technological options for harnessing solar energy, and their many uses — from solar electric fencing to solar wifi (see Solar power for the poor: facts and figures).
Three opinion articles highlight regional perspectives on getting solar technologies to the poor.
Banji Oyelaran-Oyeyinka, from UN-HABITAT in Kenya, calls on African governments to build the continent's capacity to develop and produce the technologies itself by investing in solar innovation, production and demand (see Africa: Time to go solar).
Vishaka Hidellage, from Practical Action in South Asia, echoes this call for government support, highlighting the need for subsidies and infrastructure to make solar energy available to the poor in her region (see Solar power for the poor needs government support).
Meanwhile Huang Ming, head of Himin Group in China and Yidong Gong, China news editor for SciDev.Net, argue that, in China, it is not only financial support that is needed but also a shift in focus — away from producing photovoltaics for export markets towards developing solar thermal energy to meet domestic energy needs (see China should support solar thermal energy research).
Subsidies can certainly help make solar power more affordable. But there are other financial mechanisms that work too. Pinaki Roy and Katherine Nightingale describe how funding options — in particular microfinance — are helping South Asians access and acquire solar technologies (see Financing solar power for the poor).
Politics of power
One of the frequently-overlooked achievements of last December's climate conference in Copenhagen was the agreement on a Green Climate Fund. This is intended to raise and distribute about US$30 billion a year for the next three years to help developing countries expand their use of renewable technologies and integrate these into development plans (See Climate accord offers some grounds for hope, say analysts).
The fund reflects growing acceptance that developing renewable energy sources — particularly solar— is crucial to raising the world's poor out of poverty in a way that is environmentally sustainable.
But governments' failure to reach a global commitment to reduce carbon emissions underlines how energy policy is, and always has been, highly political. Powerful interests (which can include those of consumers in the developed world) often have as much influence on policy as technological opportunities.
If solar energy is to contribute effectively to sustainable development, it must be an integral part of community-based innovation strategies. And these must simultaneously promote local needs and contest conflicting external forces. Hopefully our selection of articles demonstrates some of the ways in which this can be achieved.