Nearly 20 years ago, Andrew Bissell was sitting in the living room of his Edinburgh-area seaside home. He and his wife, Susan Lang Bissell, had just sold their medical imaging startup, and he was thinking about the future.
“Am I retiring or am I going to go back?” Bissell told TechCrunch.
Around that time, he was leafing through a science magazine when he came across an article about climate change that predicted sea levels could rise by between 30 centimeters and 1 meter by the end of the century.
“Wait a minute,” he said to himself, “if that were to happen, our living room on the first floor of our house would flood twice a day, and if that were to happen to hundreds of millions of homes around the world, that would be unacceptable.”
Instead of joining Greenpeace (“that's not our job”), he and his wife founded SunAmp, and working with a lab at the University of Edinburgh, they came up with a way to capture solar energy and store it as heat, which could be used to heat homes and provide hot water – a so-called thermobattery.
At the core of SunAmp's thermal battery are three compounds: sodium acetate trihydrate (SAT), a food flavoring used in salt-and-vinegar potato chips, water, and a sprinkling of what's called a crystallization modifier. SAT has been used in hand warmers for many years; hand warmers are made by heating the substance until it dissolves in a supersaturated solution. When activated, the SAT recrystallizes, releasing heat in the process. This reaction can be reversed, allowing the SAT to store heat for later use, but not indefinitely. Eventually, the salt precipitates out of solution and will no longer recrystallize.
To extend the life of the SAT, Sunamp uses a type of acrylic as a crystal habit modifier, helping to guide the SAT into the right configuration over and over again. “It's weird and exciting. It's weird that it happens, but what's exciting is that [SAT] “It just gets worse and worse over time and stays that way,” Bissell said, adding that the material, which SunAmp calls PlentyGrade, can last up to 40,000 heating cycles, or more than 50 years of daily use.
The goal is to use excess renewable electricity to charge the thermal battery when sunlight is plentiful or the wind is blowing and prices are low. At night or when the wind stops, the battery discharges, releasing heat as the SAT crystallizes.
Sunamp already has a presence in the U.K. and Italy, and is working on expanding into other Western European countries and the U.S. The company is in the process of raising Series B funding, which Bissell said will generate revenue in the “tens of millions of dollars range.”
The startup's first widely available product is a compact heat battery for home hot water heaters, targeted at customers where space is at a premium. “Globally, maybe half of homes have the space to put a hot water tank,” Bissell says. “We're there for the rest who don't have that space.”