Elizabeth Mukwimba, a 62-year-old farmer, stands in front of a solar light that's just been installed in her home, in northern Tanzania. The solar lighting system has been fitted by Off Grid Electric, a company dedicated to providing sustainable, affordable energy to people in developing countries as part of the UK's Energy Africa initiative. It means that she doesn't have to buy expensive kerosene anymore, her grandchildren can study at night and she can charge her mobile phone at home.