If you've 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 doesn't look as wacky as it might have 10 years ago when it was first conceived.
Solar energy collected from a 200-metre stretch of road and a small parking lot helps heat a 70-unit, four-storey apartment building in the northern village of Avenhorn. A 160,000-sq.-ft. industrial park in nearby Hoorn is kept warm in winter with the help of heat stored during the summer from 36,000 sq. ft. of pavement. The runways of a Dutch air force base 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 Seattle consultancy group.
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," he said.
Ooms' thermal energy system is too expensive and inefficient to solve the world's energy problems. It was actually a spin-off of a method to reduce 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 for repaving.
"We found we were gathering more energy in summer than we needed, so we asked ... what we can do with the extra energy," said commercial manager Lex Van Zaane. The answer was to construct buildings near the and pipe hot water under the floor.
The water usually must go through an electric-powered heat pump for an extra boost, Van Zaane said. The installation cost is about double that for normal gas heating, but the energy required is about half of what would otherwise be needed. That translates into lower heating bills and a 50 per cent savings in carbon emissions.