article: Deep in the Nevada desert, thousands of mirrors arrayed in concentric circles face the sky, lit up by the sun. All this reflected sunshine is directed to the top of a 640 ft (195m) tower standing in their midst. It's an innovative power plant generating electricity, but not in a way you might expect. And it can carry on doing so even after the sun goes down. How? The concentrated light heats up liquid salt pumped to the top of the tower - the temperature reaches 566C (1,050F) - and this heat is then used to make steam to power an electricity generator in another part of the plant. "The issue with solar traditionally is it is an intermittent power source - you can only produce electricity when the sun is shining," explains Kevin Smith, whose company Solar Reserve built the Crescent Dunes plant. "But because we store the energy as heat, we can reliably produce electricity 24 hours a day, just like a conventional gas fired power station." The plant is one of a raft of sustainable energy storage solutions trying to address renewable energy's Achilles heel: its variability - ignoring tidal power's constancy. If we could store the electricity that sun and wind produce, we could tap into those stores when production dips. And this is the only way we're going to mount an effective challenge to the dominance of fossil fuels, experts say. Yes, tidal power is renewable and constant, but as yet, we haven't found commercially viable ways of tapping into it. Storage methods currently being used around the world include batteries, flywheels, geothermal plants, compressed air and hydrogen - even ice. But the the most popular method is hydro power - water pumped to the top of a mountain and then released to power turbines at the bottom. According to research company Navigant, global energy storage installations are going to rise from about 1,750 megawatts (MW) in 2016 to nearly 11,000 MW by 2020. "We are moving away from very large conventional power stations that produce electricity which is sent through the grid to consumers, to a system where power is produced in a much more distributed way," says IHS's Sam Wilkinson. "So storage is obviously a major focus, because it allows you to compensate for and correct for a lot of that fluctuating generation that comes from renewables." Our homes are increasingly being used for energy storage as well. Tesla's Powerwall, announced earlier this year, is just one of a crop of new storage batteries designed for domestic use. The US electric car manufacturer points out that the average household uses more electricity in the morning and evening than during the day, when solar energy is plentiful. So its battery charges during the day from solar roof panels, then powers the home in the evening. "Without a home battery, excess solar energy is often sold to the power company and purchased back in the evening [at a higher price]," Tesla argues. "The mismatch adds demand on power plants and increases carbon emissions," it adds. The same
summary: It could be a scene from a science fiction movie.