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  (Source: Flickr)
Researchers have found four new methods of harvesting solar energy from roadways

University of Rhode Island researchers are looking to obtain solar energy found in heat radiating off roadways in large cities and use it to illuminate signs, power streetlights, heat buildings and melt ice. 

K. Wayne Lee, leader of the study and professor of civil and environmental engineering at the University of Rhode Island, along with his team, have studied different ways to harvest solar energy from cities, and concluded that there are four different approaches they can take to do so. 

"We have mile after mile of asphalt pavement around the country, and in the summer it absorbs a great deal of heat, warming the roads up to 140 degrees or more," said Lee. "If we can harvest that heat, we can use it for our daily use, save on fossil fuels, and reduce global warming."

The first approach is to divide highways by wrapping flexible photovoltaic cells around the top of Jersey barriers, which would provide electricity to illuminate road signs and power streetlights. Also, photovoltaic cells could be set in the roadway between the Jersey barrier and the rumble strip. 

"This is a project that could be implemented today because the technology already exists," said Lee. "Since the new generation of solar cells are so flexible, they can be installed so that regardless of the angle of the sun, it will be shining on the cells and generating electricity. A pilot program is progressing for the lamps outside Bliss Hall on campus."

The second approach is to insert water-filled pipes under the asphalt and have the sun warm the water. This method will eliminate the need to salt bridges when they're icy because the heated water will be piped underneath bridge decks melting the icy as it passes. The warm water could also be used to help with heating and hot water needs at nearby buildings much like geothermal heat pumps

A third idea would be to generate a small amount of electricity using a thermo-electric effect. This works by connecting two types of semiconductors to form a circuit that links hot and cold spots, which could then produce electricity. Thermo-electric materials could be inserted into roadways to defrost roadways. 

The final approach is to replace asphalt roadways completely with roadways made of durable electronic blocks that have LED lights and sensors as well as photovoltaic cells within them. The blocks would be capable of illuminating roadway lanes, provide warnings when maintenance is needed and generate electricity. While the use of these road blocks would be helpful in harvesting solar energy, it costs $100,000 just to build a driveway with them. 

"This kind of advanced technology will take time to be accepted by the transportation industries," said Lee. "But we've been using asphalt for our highways for more than 100 years, and pretty soon it will be time for a change."

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Just for reference
By Solandri on 11/10/2010 7:05:51 AM , Rating: 5
The U.S. has about 4 million miles of roads.

If you figure a minimum 2 lanes 12' wide with 3' shoulders, that's 30' in width. 4 million miles * 30 feet / 5280 feet/mile = 22,727 square miles.

Total land area of the U.S. minus Alaska is just under 2.9 million square miles. So if you figure a good percentage of the roads are wider than 30', you're talking about ~1% of the land area of the lower 48 being covered with roads.

Sunlight hits the earth at ~800 W/m^2 measured normal to the rays. Figure 12 hours night, factor in movement of the sun and average 40 degree latitude, say 1/3rd of the days are cloudy, you're looking at an average 130 W/m^2. 22,727 square miles would thus receive on average 7652 gigawatts of solar energy.

If you could put something in all the roads which collects just 1% of the solar energy hitting them (c.f. commercial PV panels are about 15% efficient), you'd still be getting 76.5 GW. That's over 37x the generating capacity of Hoover Dam. It works out to 671 million MW-h/year, which is 17% of the US' annual 3.873 billion MW-h/year electricity consumption.

And that's for 1% efficiency. This is an idea which seems implausible when you first hear about it. But once you factor in the staggering amount of road surface area we have, its potential impact on our energy consumption could be huge. The catch is making it affordable.

RE: Just for reference
By Paj on 11/10/2010 8:06:57 AM , Rating: 2
I enjoyed reading that. Yeah, it would be cool if one of these solutions gets to a decent price point.

With regards to the thermoelecric effect, I read something about using it to generate electricity from the very deep oceans (where its very cold). Has anyone been trying this, or is it unfeasibly complicated/expensive? Anyone have any more info about it?

RE: Just for reference
By kattanna on 11/10/2010 12:05:26 PM , Rating: 3
or for the same price we could get 6,336 nuclear reactors costing $10 billion a piece that would provide at least 6,336 GW but more likely 12,000 GW

and then we get into maintenance

which makes turning roads into solar cells even more comical

WARNING: math..

22,727 SQ miles turns into 633,592,396,790 sq ft
a generous drive way at 20' X 50' equals 1,000 sq ft

633,592,396,790 sq ft divided by 1,000 sq ft times $100,000 equals


divide that by $10,000,000,000 per reactor and you get

6,336 nuclear plants

RE: Just for reference
By Zoomer on 11/10/2010 12:26:24 PM , Rating: 2
What about having the roadways and sidewalks heated by the waste heat of these plants? We could reduce or even eliminate cooling towers, as well as the massive amounts of water they require.

It'll save a ton of labor, discomfort, energy (powered plows/shovels), not to mention keep roads in better condition by preventing water from freezing in them.

RE: Just for reference
By JediJeb on 11/10/2010 2:22:02 PM , Rating: 2
Umm but what will we use for cooling in the summer?

RE: Just for reference
By ekv on 11/10/2010 2:43:53 PM , Rating: 2
Now you're getting into the co-generation power cycle. Here's a small example.

Real-world (power) plant efficiency gets up to something like 75-85%

Of course, simply heating the sidewalk or roadway to melt ice would be considered kind of a waste of the "power" being generated. But I suppose if someone is willing to pay for it ... that'd kind of settle the argument 8)

Lol @ the last approach
By tbhuang2 on 11/9/2010 8:31:26 PM , Rating: 2
The last approach is the least realistic energy harvesting-related proposal I've ever heard. It's not even worth considering, given the current cost, performance, efficiency, and durability of semiconducting materials and manufacturing processes.

By today's standards, getting the first approach implemented is already a stretch. Flexible electronics are based on either organic TFTs, which have pretty poor electronic properties, or from devices still in the research stage, and even then their efficiencies are not competitive [1]. Flexible photovoltaics still have a way to go to catch up to their more rigid, but more efficient counterparts.

Energy harvesting still has a long way to go before we see government entities actually wanting to use them (i.e. when they are cheap).

[1] J. Yoon et al., "Ultrathin silicon solar microcells for semitransparent, mechanically flexible and microconcentrator module designs", Nature Materials, 7 (2008), 907-915.

RE: Lol @ the last approach
By FITCamaro on 11/9/2010 9:12:33 PM , Rating: 3
Not to mention the one about the Jersey border.

I mean its growing way too fast to keep up. It'll be in South Park in three days.

RE: Lol @ the last approach
By lelias2k on 11/10/2010 1:44:26 AM , Rating: 2
While it might still be unrealistic, it's a great idea and it's already being developed:

Whether or not it will ever become reality...

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