Sunamp turned the hand-warmer's phase-change gel into a heat battery in 650 homes

A hand-warmer works by phase change: click a metal disc and a gel crystallises, releasing heat; dunk it in hot water to recharge. East Lothian firm Sunamp, led by former Edinburgh University academic Andrew Bissell, spent eight years scaling that principle into 'heat batteries' — cells holding a heat exchanger immersed in phase-change material — after Bissell noticed that energy use is mostly heat, yet storage effort goes almost entirely to electricity.

In a Sunamp cell, solar panels melt the gel; when a hot tap opens, cold water flowing through the heat exchanger prompts the material to solidify, handing its heat to water instantly, cycle after cycle. The hard part was formulation: Sunamp screened a huge number of candidate materials with the Diamond Light Source synchrotron in Oxfordshire, a facility no small business could normally access, through a partnership with Edinburgh University arranged by Interface, a publicly funded body that has introduced over 2,500 Scottish businesses to academic partners.

By June 2017 the units were installed in 650 Scottish homes, providing heat and hot water for about half the cost of gas. One homeowner, Joan Maclean, reports her previously 'really cold, cold house' now gets hot water effectively free. The formula — an alkali-soluble polymer with tweaks and additives — is, the BBC noted, not far removed from a salt-and-vinegar crisp flavouring.

Scale the hand-warmer's phase-change gel into stackable heat cells: solar heat melts it; cold tap water triggers instant re-solidifying, releasing hot water.

The storage medium is cheap, rechargeable chemistry, not an exotic battery — thousands of cycles per cell.

It stores heat directly, skipping the lossy detour through electricity that dominates storage thinking.

The synchrotron screening let a tiny firm find a formulation that defeated corporations for decades.

Proof came from ordinary homes, not labs: 650 installations at about half the cost of gas.

A simple idea still lives or dies on formulation: a publicly funded matchmaker pairing a sub-30-person firm with university chemists and a national synchrotron beat decades of failed corporate R&D.

As of June 2017 Sunamp's heat batteries were in 650 Scottish homes at about half the cost of gas heating; growing demand had attracted investors and the company was seeking larger premises. Sunamp also makes blue 'cold batteries', and its third employee was an Edinburgh postgraduate who joined to become its materials scientist.