 Providing sufficient food, water and energy to allow everyone to lead decent lives is an enormous challenge. Energy is a means, not an end, but a necessary means. With 6.7 billion people on the planet, more than 50% living in large conurbations, and these numbers expected to rise to more than 9 billion and 80% later in the century, returning to a world that relies on human and animal muscle power is not an option.  The challenge is to provide sufficient energy while reducing reliance on fossil fuels, which today supply 80% of our energy (in decreasing order of importance, the rest comes from burning biomass and waste, h 