Nearly 20 years ago, Andrew Bissell was relaxing in his living room in the Edinburgh area. He and his wife, Susan Lang-Bissell, had just sold their medical imaging startup and were contemplating their next move. “Do we retire or do we go again?” Bissell told TechCrunch. During this reflective period, Bissell came across a science magazine article discussing climate change. The article predicted a sea level rise of between 30 cm and 1 meter by the century's end. This startled Bissell, who realized that such a rise would submerge the ground floor of his beachfront home.
This realization led him to think about the millions of homes worldwide that would face a similar fate, a prospect he found unacceptable. Instead of joining Greenpeace, he and his wife decided to take action by founding Sunamp. Collaborating with a lab at the University of Edinburgh, they developed a technology to store solar power as heat for household heating or hot water—an innovation known as a thermal battery.
The core of Sunamp’s thermal battery includes sodium acetate trihydrate (SAT), a food flavoring found in salt-and-vinegar potato chips, water, and tiny amounts of crystal habit modifiers. SAT has long been used in hand warmers, which operate by heating the substance until it dissolves into a supersaturated solution. Upon triggering, SAT recrystallizes, releasing heat. This heat storage and release process was effective but needed improvement for long-term use.
Over time, the salt in SAT settles out and inhibits recrystallization. To counteract this, Sunamp integrated a form of acrylic as a crystal habit modifier, ensuring the SAT maintains its optimal configuration repeatedly. “It’s both weird and exciting,” Bissell remarked, noting that this innovation allows the compound, named Plentigrade, to sustain up to 40,000 heating cycles, equating to over 50 years of daily use.
The objective is to utilize surplus renewable energy, charging the thermal battery when solar power is abundant or electricity rates are low, due to high wind activity. During periods without wind or sunlight, the battery discharges, delivering heat as SAT crystallizes. Sunamp has already gained traction in the United Kingdom and Italy and is planning expansion into other Western European countries and the U.S. The company is currently raising a Series B round, with revenues reportedly in the “tens of millions range.”
Their first mainstream product is a compact heat battery designed for domestic hot water, catering to households with limited space for a hot water tank. “Globally, maybe half of homes can afford the space to put a hot water tank in,” Bissell noted, “We’re for the other ones, the ones that can’t afford that space.”
