Every 10 years or so, roads need to be dug up and replaced. Next time, tuck a power station inside.
Theres something very appealing about solving our energy needs by utilizing raw materials we already have in abundance, and we do have plenty of freeways and parking lots. Why not make them sources of energy? The Dutch are designing roads that can literally clean up pollution and we are about to put up solar power arrays along the sides of freeways in Oregan.
Now, lets put all that solar heated asphalt to work as well, to heat water. Hot water flowing from an asphalt energy system could be used “as is” for heating buildings or in industrial processes, or could be passed through a thermoelectric generator to produce electricity.
A research team at Worcester Polytechnic Institute is developing a solar collector that could turn roads and parking lots into ubiquitous—and inexpensive–sources of electricity and hot water. The research, undertaken at the request of Novotech which holds a patent on the concept of using the heat absorbed by pavements is being directed by Rajib Mallick, associate professor of civil and environmental engineering, who says there are many advantages to using the solar energy in roads.
"For one, blacktop stays hot and could continue to generate energy after the sun goes down, unlike traditional solar-electric cells. In addition, there is already a massive acreage of installed roads and parking lots that could be retrofitted for energy generation, so there is no need to find additional land for solar farms."
Now, you may be saying, but who wants to dig up all those roads?
Apparently, we already do. "Roads and lots are typically resurfaced every 10 to 12 years and the retrofit could be built into that cycle." says Mallick. "Extracting heat from asphalt could cool it, reducing the urban heat island effect. Finally, unlike roof-top solar arrays, which some find unattractive, the solar collectors in roads and parking lots would be invisible."
The tests were conducted on slabs of asphalt in which were embedded thermocouples, to measure heat penetration, and copper pipes, to gauge how well that heat could be transferred to flowing water. The highest temperatures are found a few centimeters below the surface. This is where a heat exchanger would be located to extract the maximum amount of energy. Experimenting with various asphalt compositions, they found that the addition of highly conductive aggregates, like quartzite, can significantly increase heat absorption, as can the application of a special paint that reduces reflection.
Many countries are encouraging increased use of solar hot water technology. Worldwide installations grew 14 percent in 2005, led by China with almost 80 percent of today’s worldwide market. On a per-person basis, Israel leads the way with 90 percent of all homes taking advantage of the technology. Worldwide, solar hot water capacity reached 88 gigawatts-thermal (GWth) in 2005, with 46 million houses equipped with systems.
The United States currently has 1.6 GWth of solar hot water capacity installed, or 1.8 percent of global capacity. Hawaii, with a strong rebate program, installed almost half of the 9,000 new systems in the U.S. in 2006. California, Florida, and Arizona each installed about a thousand systems in the same year.
Passive solar water heating like this is not a new idea. The first Solar water heater was invented in 1891. In the nineteenth century, no easy way existed to heat water. People generally used a cook stove for this purpose. Wood had to be chopped or heavy hods of coal lifted, then the fuel had to be kindled and the fire periodically stocked. In cities, the wealthier heated their water with gas manufactured from coal. Still, the fuel didn't burn clean and the heater had to be lit each time someone wanted to heat water. If someone forgot to extinguish the flame, the tank would blow up. To add to the problem of heating water, in many areas, wood or coal or coal-gas cost a lot and many times could not be easily obtained.
To circumvent these problems, many handy farmers or prospectors or other outdoors men devised a much safer, easier, and cheaper way to heat water - placing into the sun a metal water tank painted black to absorb as much solar energy as possible. These were the first solar water heaters on record.
Of course, back then we did not realize that in a century or so, we would be blessed with an abundance of nice warm blacktop, the perfect spot for our national solar water heating system.