HONG KONG — Developing nations in Asia, it seems, are finally seeing the light.

In May, the Asian Development Bank started a major drive to promote solar power across the region. Last year, the Indian government approved an ambitious National Solar Mission, which seeks a huge increase in the country’s solar-energy capabilities. Bangladesh, with the support of the World Bank, is aiming to have one million remote rural homes supplied with solar panels by the end of 2012.

And in India, where nearly 40 percent of households have no access to electricity, companies like Selco Solar and Orb Energy have helped tens of thousands of families and small entrepreneurs purchase solar panels.

All worthy causes. So worthy and sensible, in fact, that you may well ask why on earth they did not take off much earlier.

The answer, as is so often the case, is political support — or, until relatively recently, the lack of it — and, inevitably, cost.