LONDON, — Heat storage tanks that can cut energy used for heating by 50%-70%, and are becoming an increasingly profitable investment as energy prices shoot up.

"The heat tank is basically a battery for heat," said Trefor Evans of First Light Energy Ltd., the company currently launching its heat tanks in the U.K. following their success in Germany, following a presentation at the Nemex exhibition at the NEC in Birmingham.

Such high energy savings can be achieved thanks to the thermal properties of paraffin wax, used to capture as much as 10kWh in a storage tank with dimensions of 2x1x1m. As the paraffin melts it takes in large amounts of heat -- melting down paraffin requires around four times the amount for melting ice. The heat is then released when it cools and returns to the solid state.

For air and water heating, this means that almost all the heat generated is used. Storing excess heat also means that boilers can be fired much less frequently, increasing efficiency. As boilers typically take five to six minutes to reach peak efficiency, intermittent firing wastes much energy.

By reducing the number of boiler start-ups by 90%, a heat storage tank can also dramatically reduce the production of soot and other pollutants.

But the highest savings of 70% tanks are achieved when the tanks are used in conjunction with solar systems.

"All the heat produced on a sunny day is stored, and can be used when it is necessary," Trefor Evans explained.

The tanks are also ideal for use with air and ground-source heat pumps, he said -- "basically any renewable energy source that produces heat."

While an insulated hot water tank initially at 80 degrees will cool by roughly ten degrees overnight, a heat tank storing thermal energy as latent heat will only lose one degree in the same conditions.

Rising energy prices are good news for heat tanks, increasing their economic viability together with continuous technological development.