The very last episode in Neil MacGregor's history of humanity as told through the things that time has left behind. The director of the British Museum in London has spent the past year choosing objects from the museum's vast collection to represent a two million year story of humanity. Throughout this week he has been with objects that that speak of the great shifts in human organisation and thinking in the modern world. Here he describes the object that he has picked as his last; it's a solar-powered lamp and charger that he believes can revolutionise the lives of poor people around the globe. The portable panel can provide up to 100 hours of light after just 8 hours of direct sunlight. It can also charge mobile phones and help bring power to millions of people around the world who have no access to an electrical grid. Simple, cheap and clean - this is revolutionary technology for the future. Professor Nick Stern, the expert on the economics of climate change, describes the potential impact of new solar technology - and we hear examples of how the technology is being adopted in Africa and India. Neil explains why he has chosen a solar-powered lamp and charger as his final object - with examples of how it is already being used in rural Bengal and urban Kenya. Producer: Anthony Denselow