Around the world billions of dollars axe being invested in clean-energy technologies of one sort or another, from solar arrays and wind turbines to electric cars. But there is a problem lurking in the power grid that links them together. Green sources of power tend to be distributed and intermittent, which makes them difficult to integrate into the existing grid. And when it comes to electric cars, a study by America's Pacific Northwest National Laboratory (pnnl) found that there is already enough generating capacity to replace as much as 73% of America's conventional fleet with electric vehicles-but only if the charging of those vehicles is carefully managed. In order to accommodate the flow of energy between new sources of supply and new forms of demand, the world's electrical grids are going to have to become a lot smarter.
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