Years ago, when the phrase “Global Warming” began gaining popularity, we started batting around the idea of replacing asphalt and concrete surfaces with solar panels that could be driven upon. We thought of the “black box” on airplanes: We didn’t know what material that black box was made of, but it seemed to be able to protect sensitive electronics from the worst of airline crashes.
Suppose we made a section of road out of this material and housed solar cells to collect energy, which could pay for the cost of the panel, thereby creating a road that would pay for itself over time. What if we added LEDs to “paint” the road lines from beneath, lighting up the road for safer night time driving? What if we added a heating element in the surface (like the defrosting wire in the rear window of our cars) to prevent snow/ice accumulation in northern climates? The ideas and possibilities just continued to roll in and the Solar Roadway project was born.
And here’s some numbers –
Now let’s talk strictly about numbers for energy:
Engineers love numbers. They (the numbers, that is) generally bore people to death, but at times they are necessary for understanding. One of the biggest questions that has been asked is simply, “Can we really generate enough pollution-free electricity to power our businesses and homes?” The calculations below are presented to answer this very important question.
First, the “givens”: In the 48 contiguous states alone, pavements and other impervious surfaces cover 112,610 square kilometers-an area nearly the size of Ohio-according to research published in the 15 June 2004 issue of Eos, the newsletter of the American Geophysical Union. Continuing development adds another quarter of a million acres each year.
Let’s do some conversions: 112,610 square kilometers equals 43443.54 square miles. The report was done ten years ago, so that means an additional 2.5 million acres have been turned into impervious surfaces. That’s an additional 3906.25 square miles, so all told, we have 47349.79 square miles of impervious surfaces. Let’s make a conservative assumption that a full 1/3 of that number accounts for rooftops of homes and businesses, which we’re not currently interested in.
That leaves us with 31,250.86 square miles of roads, parking lots, driveways, playgrounds, bike paths, sidewalks, etc., to work with.
If these impervious surfaces were replaced with Solar Road Panels, how much electricity could we produce?
In labs, solar cell efficiency has exceeded 44-percent, but they’re not cost feasible yet. For our calculations, we looked up commercially (and cost competitive) available solar panels.
Sunpower Labs is shipping E18 series panels with 18.5% efficiency, so let’s go with what is currently available.
For our calculations, let’s use the following (conservative) assumptions:
– We use solar cells that have an 18.5% efficiency
– We average only 4 hours of peak daylight hours per day (4 x 365 = 1460 hours per year)
Sunpower offers a 230 Watt solar panel rated at 18.5% efficiency. Its surface area is 13.4 square feet. If we covered the entire 31,250.86 square miles of impervious surfaces with solar collection panels, we’d get:
((31,250.86 mi²) x (5280 ft / mi)²) / (13.4ft²/230W) =
((31,250.86 mi²) x (27,878,400 ft² / mi²)) / (13.4ft²/230W) =
(871,223,975,424 ft²) / (13.4ft²/230W) = 14,953,844,354,292 Watts or over 14.95 Billion Kilowatts
If we average only 4 hours of peak daylight hours (1460 hours per year), this gives us: 14.95 Billion Kilowatts x 1460 hours = 21,827 Billion Kilowatt-hours of electricity.
In 2009, we received a contract from the Federal Highway Administration to test some of our theories and to build a crude prototype Solar Road Panel. One of the tests that we conducted was “real world” solar collection.
When you install a roof-top solar panel, you have to take into account where you are installing it. The farther north you live, the more you have to angle your panel toward the equator (or more accurately, the sun above the equator) to gain maximum efficiency.
We did our testing in January and February in northern Idaho. Here we have worst case scenario: our measurements were taken in the dead of winter (sun is at its lowest point of the year) an hour south of the Canadian border at latitude 48.19 degrees. The farthest northern point in the contiguous 48 states is 49.38 degrees near Lake of the Woods, Minnesota. That’s 82 miles farther north than our location. Conclusion: we would be hard pressed to find a worse time and place to conduct this experiment!
At our northern position (48.19 degrees North), the optimal solar gain angle for our solar panels is 72 degrees. Brownsville, Texans would want to angle their solar panels at 26 degrees. So our southern roads will naturally produce much more electricity than their northern counterparts, as solar intensity maps show.
Unfortunately, we can’t angle roads or parking lots. Roads go up and down hills, have banks on curves (going both left and right), and have a typical three percent “crown” (on both sides) to allow stormwater runoff. It’s a pretty safe assumption to figure that the national average angle of roads is zero degrees.
We tested two identical solar panels. We mounted one at the recommended 72 degrees for our location and leveled the other one with the horizon (zero degrees) to simulate an average road. We installed a monitoring system to track the data 24/7.
Although the tilted solar panel produced more energy as expected (an average of almost 31 percent more than its horizontal counterpart), we were surprised to see the phenomenon of the horizontal solar panel producing more energy than the tilted panel on certain overcast days. It appears to be similar to getting sunburned on a cloudy day: sunlight is still present, but it is scattered, so the horizontal solar panel is more likely to pick up the scattered photons than the solar panel aimed at the southern horizon.
For fairness, let’s subtract 31 percent from our totals since we can’t angle roads and parking lots:
21,827 Billion Kilowatt-hours x 0.69 = 15,060 Billion Kilowatt-hours
Another thing we learned – through experimentation – was that our 1/2-inch textured glass surface reduced the amount of energy produced by solar cells by 11.12-percent. Subtracting that from the total, we still have 13,385 Billion Kilowatt-hours. And remember: this is the amount of power calculated for a latitude near the Canadian border. The number would be much larger if calculated for the southern states.
While we found no evidence that moonlight or the light from shining stars at night produce energy in solar panels (a common question), we found that headlights did. Although it would be very difficult to measure accurately due to distance, speed, hi/low beams, etc., we found that a small solar panel placed flat on the ground about 10 feet in front of a vehicle with its high beams on produced electricity in otherwise total darkness. So it appears that vehicles driving on the surface at night will be providing a service as well as reaping the benefits.
According to the Energy Information Administration, the United States (all 50) used 3,741 Billion Kilowatt-hours of electricity in 2009 (EIA Electricity Overview, 1949-2009). It’s easy to see that the
Solar Roadways could produce over three times the electricity that we currently use in the United States.
The “lower 48” could produce just about enough electricity to supply the entire world. And once again, remember: these calculations are made with very conservative numbers using north Idaho as a reference point, which is one of the worst case scenarios in the U.S. where latitude is concerned (OK, we have to concede to Alaska!).
What does this do for greenhouse gases?
As best we can tell, it is estimated that approximately half (different agencies provide different estimates, but the average is about 50-percent) of the greenhouse gases that are causing global warming come from the burning of fossil fuels (primarily coal) to generate electricity. The Solar Roadway therefore has the ability to eliminate half of the greenhouse gases currently being produced.
Another 25-percent comes out of our tailpipes. A Solar Roadway is an electric road that can recharge electric vehicles (EVs) anywhere. We’re talking with companies that make mutual induction plates to charge EVs while they’re driving (the “receiver” plate gets mounted beneath the EV and the “transmitter” plate is installed in the road). The Solar Roadway could charge the EVs while they’re traveling, which would increase their range. With an infrastructure in place that will make EVs finally practical, people would likely start trading in their internal combustion engine vehicles for EVs. Eventually, we’d have eliminated an additional 25-percent of greenhouse gases.
Summary: the Solar Roadway has the ability to cut greenhouse gases by up to 75-percent!
One of the great features of the Solar Road Panel is that much of it can be reused. Some components like the solar cells, capacitors, and LEDs will wear out and have to be replaced, but much of the panel is reusable. If we began manufacturing today with 18.5% efficient solar cells, and the panels lasted 20 years before the need for refurbishing, the latest (20 years from now) efficiency solar cells would be installed and the same Solar Road Panel would produce even more power than before. This will allow the Solar Roadway to keep up with the increase in electricity demand over the years.
In addition, the Solar Roadway replaces our current aging power grid. The Solar Roadways carry power – not from a centralized point like a power station, but from the power-producing grid itself along with data signals (cable TV, telephone, high-speed internet, etc.) to every home and business connected to the grid via their driveways and parking lots. In essence, the Solar Roadways becomes a conduit for all power and data signals.
Final thoughts: elimination of the fossil fuel plants will take away about half of the CO2 emissions that are known to be contributing to the climate crisis. Providing a means to recharge all-electric cars anywhere along the roadside or even while driving will open the door for the elimination of the internal combustion engines, which account for most of the other half of the CO2 emissions. With internal combustion engines now obsolete, our dependency on oil – foreign or domestic – will finally be over with.
Unlike current road systems, a Solar Roadway will pay for itself over time. No more contributing to the climate crisis. No more power outages (roaming or otherwise). Safer driving conditions. Far less pollution. A new secure highway infrastructure that pays for itself. A decentralized, self-healing, secure power grid. No more dependency on foreign oil.
The real question may be:
What will be the cost if we don’t implement the Solar Roadways?
“You cannot escape the responsibility of tomorrow by evading it today.” ~ Abraham Lincoln
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