From 1990 onwards, gas-turbine generation has taken the lead. It is cheap, clean and easy to site. It needs no fuel store, uses less water than coal-fired or nuclear generation, and produces no waste. Gas turbines have also paved the way for other smaller-scale generators. Traditional water and steam power kept scaling up because a bigger unit made cheaper electricity. For microturbines, gas engines, Stirling engines, flow batteries, fuel cells, wind turbines, microhydro and marine energy, biomass power, solar thermal and photovoltaics, what counts is scaling up the number of units: the more you make, the cheaper their output, with rapid learning curves. Some also deliver both electricity and heat from the same fuel, boosting efficiency and reducing emissions. Generation from wind, water and sunlight uses no fuel and produces no emissions.