Electricity from the sun is cheap and clean but the solar cells we see on our rooftops could be much more efficient. Henry Snaith of Oxford PV has developed a new material which helps solar roof panels extract more energy from the solar spectrum. Tom Heap visits Henry's lab and joins Dr Tamsin Edwards to consider the carbon-cutting potential of a new generation of solar energy. Producer: Alasdair Cross Series made in partnership with the Royal Geographical Society