Amid the gloomy news of the worsening impact of climate change is a bright spark: the dramatic fall in the cost of solar energy. This source of clean and renewable energy could help power the world without emitting greenhouse gases.

Solar energy has traditionally been more expensive to use than carbon-intensive coal or oil. But in recent years solar power has become much cheaper, and energy experts say its cost could match that of conventional fuels in the next few years in some areas.

Solar cell prices have fallen from $76 per watt in 1977 and about $10 in 1987 to just 74 US cents in 2013. Between 2006 and 2011, Chinese cell prices fell 80 percent from $4.50 per watt to 90 cents per watt. Among the reasons for this fall are a drop in the price of the main raw material, polysilicon (because of oversupply), increasing efficiency of solar cells, improvement in manufacturing technology, economies of scale and intense competition.