Andrew Byrnes, sitting with me outside a Palo Alto cafe on Monday, lights a candle—in this case, a small Sterno-type can designed for warming food—and fills a tiny pot sitting on a rack above the flame with water. About 10 seconds later, a green light on an attached USB cable begins glowing, and Byrnes plugs in his iPhone. The phone immediately begins charging.
That is how you charge a phone with candlepower, something Byrnes’ San Francisco-based company, Stower, wants people to be able to do during their next power outage. And it’s pretty simple, especially for someone like me who grew up on old school emergency preparedness and still has a tendency to check the drawers for candles when a big storm is predicted.
Stower’s tiny charging system, the Candle Charger, launched on Kickstarter today for $65; it’ll be available late this year or early next at retail for $100. It produces a steady 2.5 watts of USB charging for the 6 hours that standard Sterno can burns, though any candle that can fit under the pot, even votive candles, will work. That’s enough to fully charge a typical smartphone in three hours, Byrnes says. (And you can use the water it heats to make a cup of tea to drink while waiting for your phone to charge.)
The Candle Charger produces electricity using a thermoelectric generator. This device, based on a bismuth telluride semiconductor, takes advantage of the difference in temperature between the area close to the flame and the area near to the water in the pot, which stays cooler. Diffusion of electrons between the hot and cold sides of the semiconductor generates a voltage.
By carefully designing the way different materials are incorporated in the device, Byrnes says Stower’s products can keep generating power indefinitely, as long as there is a heat source underneath and water in the pot. He says the company also put a lot of design effort into conditioning the power output to directly charge smartphones, finally figuring out a reliable way to do so using low-cost analog circuitry. “Our magic is being able to charge phones reliably from a variable power source,” he says.
This isn’t Byrnes’ first foray into charging by fire. I first met him and Stower cofounder Adam Kell two years ago at a showcase for Stanford University’s Business Association of Stanford Entrepreneurial Students (BASES). They were demonstrating Flamestower, a gadget designed to turn any pot on any cooking fire into a charger. At the time, the two were graduate students studying materials science at Stanford. Before entering grad school, Kell had been working on silicon wafer technology at a clean tech startup, and Byrnes had been involved with utility scale wind and solar energy projects. But Byrnes wanted to work on technologies with more of a direct connection to the consumer. The need for charging mobile devices during power outages was an obvious place to start for Byrnes, who was a Florida resident during Hurricanes Katrina and Wilma.
The Flamestower charger works with most campfires and camping stoves, packed for travel (left) and ready to charge (right).Photo: Tekla Perry
Flamestower hit retail shelves last year, and is now available for $99 at Sportsman’s Warehouse and other outdoor equipment outlets in the United States and Canada. The company is working with Grupo EBIS to build the technology into its Eco-Stove clean-burning cookstoves being distributed in Central America, and with French telecom giant Orange to develop a version of the technology for use in Africa.
But Byrnes thinks the Candle Charger will have a much broader market than Flamestower, since it can be easily used indoors, and it fits compactly on a shelf or in an emergency kit until needed. Though people in developed countries have become more and more dependent on cellphones, power has become less reliable, he says: according to Department of Energy statistics power outages in the United States have been on the rise since 2000.
The company is guaranteeing that Candle Chargers ordered on Kickstarter will ship in December—a bit too late for this year’s hurricane season.
Tekla S. Perry is a senior editor at IEEE Spectrum. Based in Palo Alto, Calif., she's been covering the people, companies, and technology that make Silicon Valley a special place for more than 40 years. An IEEE member, she holds a bachelor's degree in journalism from Michigan State University.