Solar energy advocates hit the road

Adelaide Advertiser
02/01/2008 Page: 19

IF you have ever blistered your bare feet on a hot road, you know how asphalt absorbs the sun's rays. Now, a Dutch company is siphoning the heat from roads and parking lots to heat homes and offices. As climate change rises on the international agenda, the system built by civil engineering firm Ooms Avenhorn Holding BV does not look as wacky as it might have 10 years ago when it was first conceived.

solar energy collected from a 180m stretch of road and a small parking lot helps heat a 70-unit, four-story apartment building in the northern village of Avenhorn. An industrial park of 14,864sq in in the nearby city of Hoorn is kept warm in winter with the help of heat stored during the summer from 3344sqm of pavement. The runways of a Dutch air force base in the south supply heat for its hangar. And all that under normally cloudy Dutch skies, with only a few days a year of truly sweltering temperatures.

The Road Energy System is one of the more unusual ways scientists and engineers are trying to harness the power of the sun, the single most plentiful, reliable, accessible and inexhaustible source of renewable energy - radiating to earth more watts in one hour than the world can use in a whole year.

But today, solar power provides just 0.04 per cent of global energy, held back by high production costs and low efficiency rates. Solar advocates say that will change within a few years. Other renewable sources have drawbacks. Not every place is breezy enough for wind turbines; waves and tides are good only for coastal regions; hydroelectricity requires rivers and increasingly objectionable dams; biofuels take up land needed for food crops. "But solar falls everywhere," says Patrick Mazza, of Climate Solutions, a consultancy group in Seattle, Washington.

Compared with other energy sources,"solar comes out as the one with the real heavy lift. It's the one we really need to get at." Ooms' thermal energy system is too expensive and inefficient to solve the world's energy problems. In fact, it was a spin-off of investigations into reducing road maintenance.

A latticework of flexible plastic pipes, held in place by a plastic grid, is covered over by asphalt, which magnifies the sun's thermal power. As cool water in the pipes is heated, it is pumped deep under the ground to natural aquifers where it maintains a fairly constant temperature of about 20C. The heated water can be retrieved months later to keep the road surface ice-free in winter. The same system pumps cold water from a separate subterranean reservoir to cool buildings on hot days.

Though it doubles the cost of construction, the system's first benefits are a longer life for roads and bridges, fewer ice-induced accidents and less need to repave worn surfaces. "We found we were gathering more energy in summer than we needed, so we asked a building contractor what we could do with the extra energy," says commercial manager Lex Van Zaane. The answer was to construct buildings near the tarmac and pipe hot water under the floor. The water usually is not hot enough on its own, and must go through an electricity-powered heat pump for an extra boost.

The installation cost is about twice as much as normal gas heating, but the energy required is about half of what would otherwise be needed. That translates into lower monthly heating bills and a 50 per cent saving in carbon emissions.