As the sun sets over developing countries, more than a billion people are either plunged into darkness or forced to rely on polluting light sources such as kerosene.
While clean energy alternatives exist, switching to them has been slow and in Kenya, more than 80 percent of the country's 40 million inhabitants rely on kerosene, candles and torches as their main source of light.
But the development of an all-in-one solar electricity system that powers lights, radios and phones is revolutionising thousands of households and businesses.
Robin Forestier-Walker travels to Kenya's Rift Valley to see how innovative financing, distribution and product design is heralding a new era in solar lighting.
How it works: Geothermal electricity
The deeper you go into the earth’s core, the hotter it becomes.
Some of this vast energy is already harnessed by geothermal power plants which use steam from heated water deep underground to drive turbines and generate electricity.
Geothermal electricity plants are typically built near tectonic plate boundaries, where high temperatures can be accessed much closer to the earth’s surface.
But recent advances in technology mean that disused oil wells and even operating oil fields could be used to generate geothermal electricity.
A liter of light
Despite living in the sunny tropics, many people in the Philippines spend their days in darkness cramped together in make-shift homes with limited privacy and electricity.
However, a locally raised social entrepreneur and Liter of Light founder Illac Diaz has developed a green, cheap and simple method to illuminate homes – plastic bottles filled with water and bleach and installed into rooftops.
More than 350,000 people have already had the bottles fixed to their homes and the technology has spread to ten countries.
Russell Beard travels to the Philippines to meet Diaz and some of the people he is training to become Liter of Light installers so that they can earn a green living in their own communities.
earthrise can be seen each week at the following times GMT: Tuesday: 2230; Wednesday: 0930; Thursday: 0330; Friday: 1630; Saturday: 2230; Sunday: 0930; Monday: 0330; Tuesday: 1630.
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