Engineering news
Scientists at Brunel University have designed a hybrid roofing system which has the potential to halve energy bills in new homes.
The patented system harnesses a mixture of technologies to pre-heat domestic hot water for radiators, baths and showers while also generating electricity. More than half of domestic energy use in the UK is to heat water.
Dr Hussam Jouhara of Brunel’s Institute of Energy Futures, who led the British team which developed the system, said: “As a professional engineer with a long-term research interest in heat pipes I could see many advantages in applying this technology to a renewable energy system.”
The system uses heat pipes which are found in high tech devices from PCs to the International Space Station where they prevent it from melting in the heat of the sun on one side and freezing in the vacuum of space on the other.
The system is a solution to a major technical issue with solar cell or photovoltaic (PV) panels used to generate electricity. The reason is that the more intense the sunlight the more electricity the cells will produce but only a fraction of the sun's energy can be turned into electricity.
Jouhara said: “Until now there was no system which fully addressed all the technical and practical issues that face making an entire building’s roof a solar-powered generator of both heat energy and electrical energy.
“So the sunnier it is the more of that unusable energy hits the cell which, in turn, heats it up. As PV cells heat up their electrical generation ability is degraded. Heat pipes, in this case, constructed in flat panels 4m x 400mm, will whisk that away to heat domestic hot water.”
In proof of concept tests, PV cells cooled by Jouhara’s methods outperformed identical panels by 15%. Rather than being wasted, almost the full spectrum of energy from the sun is harnessed by the panels.
The system also addresses a wide range of practical issues in installing solar panels in new properties. “What was needed was an engineered, systems approach,” said Jouhara. “Our solar panels are PV coated for the most southerly-facing aspect of the roof and are designed to clip together as a weather-tight roof as simply as clicking together laminate flooring.
“When we constructed our test roof using standard “off-the-shelf” roof trusses, tradesmen were able to quickly and easily screw together the panels with no extra guidance than a simple set of written instructions.
The heat pipe technology also turns the biggest downside of integrating solar panels into conventional roofs into a positive. Jouhara said: “Currently the panels would get hottest in the summer and roofs need to be designed to dissipate that heat. Simply insulating the house below is not a good solution as that simply traps it driving up the PV panel temperature and further lowering its performance. With our system there is no waste heat.”
The solar roof is now undergoing extensive further trials at the Building Research Establishment (BRE) in Watford where a prototype is powering a standard UK three-bedroom detached house.
Already there has been one unexpected finding. Jouhara said: “Our flat heat pipes are so efficient that they can actually capture the energy from early morning dew evaporating off the trial roof."