Solar skyline

Homes around the world may soon sport dramatic-shaped roofs designed to catch the sun

UK city skylines are famous for funky architecture, but soon homes across this country and the rest of the world could all have bold designs to boost the energy production of rooftop solar panels.

Researchers from Oxford University are developing optimal roof shapes for directing the Sun’s rays on to solar cells. The shape will differ depending on the location, so the roof of a UK home will look different to one in, say, Brazil.

‘What we find with our computer models is the further north we go the more shallow the roof tends to be,’ said Malcolm McCulloch, the principal investigator of the one-year project. ‘The roofs all look paraboloid-ish. They have some quite odd features on them, but they look quite attractive.’

McCulloch compared the roofs to Spanish architect Antoni Gaudí’s unique Barcelona buildings that integrate natural organic shapes such as parabolic arches and hyperboloid structures.

He said the researchers should have a basic prototype by next year and the roofs could be constructed on new homes within the next three years.

McCulloch began in electrical engineering but gradually moved into sustainable engineering in 2002. Since then he has had an interest in solar concentrators which use Fresnel lenses to take a large area of sunlight and direct it towards a specific spot by bending the rays of light and focusing them.

The team hopes to design an effective concentrator to work with small and large solar energy applications. ‘You need about three per cent of the world’s surface to generate all the world energy needs from solar energy,’ said McCulloch. ‘You are looking at an area of about 1,000 sq km so it’s an absolutely massive scale.’

With typical large solar energy applications, McCulloch said the most effective concentrator system is one that tracks the Sun from east to west. Another follows the Sun in all four cardinal directions. ‘The downside about tracking concentrators is they have moving parts, which means maintenance becomes a big issue. Also, it can be difficult to integrate those solar concentrators into every solar cell.’

The team is developing a concentration system that will work effectively without tracking the Sun. ‘All we need to do is get half the efficiency of tracking concentrators, and it will open up whole new areas of applications,’ said McCulloch. His team is working on some ‘exotic’ algorithms to devise computer models of roof shapes that will get reasonable and economic solar concentration levels .

‘There is a universal truth that photocells cost about £3/W to install,’ said McCulloch. ‘We’re looking for about a third of that’

He is in contact with architects. ‘We know what the shape would look like but we don’t know exactly what the materials would look like,’ he said.

Fresnel lens solar concentrators are made with optically clear material such as glass or polycarbonate, while alternatives like reflective panels are often made of aluminium.

‘We would be looking at potentially making our concentrators out of much thinner film because it doesn’t have to be mechanically rigid and able to move,’ said McCulloch.

One potential choice is aluminised Mylar, a product from DuPont often used generically to refer to polyester films or plastic sheets. When pasted on to cardboard, paper-mache, tinned or galvanised iron, or thin aluminum sheets, the aluminised Mylar can be fabricated into inexpensive and practical solar concentrators. ‘It’s good if it’s used as stationary concentrators, but not if it’s moving,’ said McCulloch. ‘They’re also very cheap to make.’

When the results of the research comes through next year, the group will begin looking for industry partners to help it bring the concept to fruition.