Tapping the Power of 100 Suns
Napoleon’s dictum no longer applies: These days, an army marches not so much on its stomach as on its batteries. Without them, soldiers can’t see in the dark, work their radios, or determine their positions. But even the best storage batteries—accounting for one-fifth of the load in a typical infantryman’s 45-kilogram pack—can’t last the week or so that field soldiers require. The same problem is coming to afflict the rest of us, as we become ever more dependent on our smartphones and GPS navigation.
While we wait for better batteries we must find new ways to recharge the ones we have when we’re far from a wall socket. What we need is a really good, portable photovoltaic system, one that can take in a huge gulp of sunlight and convert most of it into electricity. Such an advance could also help drive down the cost of solar electricity in sunny climes around the world and prevent great quantities of carbon emissions.
The most promising effort to create such superefficient photovoltaics began in 2005, when Doug Kirkpatrick, a veteran of the optics industry, kick-started the Very High Efficiency Solar Cell (VHESC) program for the U.S. Defense Advanced Research Projects Agency (DARPA). He wanted a way to build modules from solar cells that would convert a full 50 percent of the solar energy they receive into direct current. That’s a jaw-dropping number when you consider that in 2005 the best laboratory devices were still shy of 40 percent efficiency and were improving by less than one percentage point per year.