Imagine storing summer heat.

Renewable energy has always been about the art of the possible, turning the obvious and plentiful into a reliable source of clean fuel. If the wind, waves and even the almighty sun can be harnessed for generation, almost anything else can be captured, too.

For one group of researchers, heat could be the next big source of power.

Scientists at the Swiss materials science and technology institute, Empa, have been developing a technique to capture solar thermal heat in the summer and store it for use during winter. The scientists have taken a process involving the use of concentrated sodium hydroxide (NaOH) and turned it on its head.

Otherwise known as lye or caustic soda, the salt-based compound is very corrosive and is used in a variety of applications, such as the manufacture and processing of soaps, rayon, paper, explosives and cotton fabric, bleaching, metal cleaning and electroplating.

NaOH also has the unique property of generating heat when mixed with water. The scientists have exploited this property and reversed it for the purposes of storing energy. They developed a device that introduces heat into a diluted solution of NaOH. The chemical reaction causes the water to evaporate, and the remaining substance captures the heat that has been introduced. That substance can be stored for months, and when water is reintroduced to it, the stored heat will be released again.

The Swiss researchers developed a system using the same pipes used in instant water heaters. The NaOH solution travels down the exterior of a spiral pipe in the device. Inside that pipe runs water that has been heated by solar collectors. The solution absorbs that heat through the pipe and expels its own water vapor. It can then be stored in tanks for months until winter when the process can be reversed.

Empa is now searching for industrial partners to help build a compact system for heating homes.