Northern Ireland

NI firm's solar device is hot competition

John Willis of Willis Renewables
Image caption John Willis of Willis Renewables demonstrates the Solasyphon

A Northern Ireland company has won an Ashden Award for its innovative low cost water heating device.

Solasyphon allows the use of existing plumbing and substantially reduces the CO2 output of a water heating system.

John Willis recalls the moment he and his colleagues tested the idea for getting energy from a solar water heating panel to a domestic hot water system. They had invented Solasyphon.

"It was one of those moments when no words were spoken," he said.

"We knew instinctively that we'd invented something that provided a real step change in the way that solar energy is produced."

Roof panels

It is a simple heat exchanger that sits on the outside of a conventional hot water cylinder, the idea has now become a product selling around the world.

Hot water heated by the sun, using roof panels, is fed into the exchanger. The heat travels by a thermal siphon effect into the hot cylinder. It needs no pump or energy to move it.

A narrow vertical cylinder is connected to an existing hot water cylinder, needs just a single hole drilled into the cylinder and can be fitted in less than an hour.

It is then connected to solar water heating panels. The alternative is fitting an expensive new cylinder with additional plumbing. The old cylinder, although perfectly serviceable, is scrapped.

But would the Solasyphon retrofit perform as well as a modern purpose-built hot water cylinder?

To find out, Willis Renewable Energy Systems had the device tested at the Centre for Sustainable Technologies at the University of Ulster.

The results were impressive. Not only could the device almost match the apparently more advanced and expensive twin coil cylinders but the way it worked made it more practical.

When a hot water tap is turned on in a house, the water comes from the top of the hot cylinder.

The problem facing manufacturers of the purpose-built hot cylinders is having to heat the whole cylinder.

The heating coils are usually in the bottom of the cylinder.

The coil absorbs the same amount of energy from the sun but can only raise the cylinder's temperature slowly as it is trying to heat all the water.


The Solasyphon works in a different way.

It heats a little water at a time, just over a litre. This flows by a natural thermal siphon to the top of the hot cylinder.

Within a short time there is enough hot water at the top of the cylinder to have a shower or wash dishes.

The system works in the same way we use water in a house.

"If you take most home situations, you're drawing off hot water continuously throughout the day," Mr Willis added.

"It is exactly the way the Solasyphon stores energy.

"Compared to a conventional twin-coiled cylinder with the coils in the bottom of the cylinder, you're trying to heat a large volume very slowly over a long period of time.

"You're getting the same amount of energy but the way we're using it is much more related to the way it is used in the home."

The Ashden Award for Sustainable energy has already been won by those who developed smokeless stoves for Ethiopia or solar-powered education in Bangladesh.


"It is a very humbling experience to actually win the award," Mr Willis said.

"You're alongside other award winners who have these terrific little projects in remote parts of Africa and India.

"What I discovered from talking to these people is that we are all kindred spirits.

"They've all been presented in their own communities with an environment problem that they have overcome."

Made in Northern Ireland, Solasyphon has created new employment and its already selling around the world.

Pallets of the product sit in the company's reception awaiting collection and delivery to places as far apart as Poland and Canada.

It is estimated that so far the systems already fitted have saved more than 1300 tonnes of CO2 and a lot of copper cylinders.