Europe is planning to use hydrogen fuel cells to power cars and homes, as they are easier to store than electricity. This is seen as a realistic alternative to petrol engines and imported oil. Governments are increasing funding for hydrogen research, but it will take 15-20 years for fuel cell cars to become popular. The challenge is to find a way to store and transport hydrogen fuel in vehicles, and to build enough service stations. Europe aims to generate hydrogen from renewable sources, while the USA plans to use nuclear energy.