Fourth Power

The falling cost of renewable power from wind and the sun will eventually make it possible to decom­mis­sion every coal- or gas-powered electrical plant. The only big roadblock is that wind and solar energy are inherently variable. To meet electrical demand when the sun isn’t shining or the wind isn’t blowing, we’ll need grid-scale storage technology that costs less, and stores power longer, than today’s lithium-ion batteries. That’s what Fourth Power is building. At the company’s megawatt-scale demon­stra­tion facility outside Boston, molten tin, pumped by an innovative all-ceramic pump, will carry heat from grid power into large graphite blocks — where it will be stored until needed, then turned back into electricity using thermophotovoltaic cells.