Solar road path to the future or road to nowhere?

According to some estimates, in the order of 0.2–0.5 percent of the world's land surface covered by roads. And this ratio is expected to increase by 60% by 2050. Amazingly a lot of space devoted to roads, but they are mostly just for transportation. What if to make them produce energy? China is building one of the first in the world solar traces. Can a highway covered with solar panels to become energy stations in the future?

One of the benefits of fossil fuels against renewable energy sources is energy density. The reason is simple: fossil fuel is a renewable energy that accumulated over millions of years. Oil, coal, natural gas are all energy reserves that were created from plants (and animals that eat those plants) and accumulated solar energy over thousands of years through photosynthesis. Turns out, fossil fuel is more energy intensive than the use of solar energy in real time.

In short: fossil fuel requires much less land to produce energy than solar panels.

One of the biggest obstacles to renewable energy is the physical space required to service these sources. And our ever-growing energy consumption makes all this a problem. Primary energy — total energy consumed by humans from all sources — includes fossil fuels and renewable sources. In 2016, we consumed 478 TWh of primary energy, and this number is growing every year.

For Example, if you want to provide all our energy needs at the expense of corn ethanol, which has a density of energy production in the order of 0.2 watts per square meter (one of the worst among biofuels), to about 2 x 10¹⁵ square meters of land to grow corn. Unfortunately, this is more than four times larger than the area of the surface of the Earth.

The Opponents of renewable energy use this example to show that renewable energy infrastructure is simply impossible. But this is an exaggeration; the energy density of arrays of solar cells can reach 20 W/m² or more, and that the surface of the Earth is enough. It is also worth noting that the energy produced by solar panels is in the form of high-quality electricity.

Since giving up fossil fuels means the use of electricity instead of burning fuel, which is often more efficient, we would consume less primary energy in the world without fossil fuel; fossil-fuel efficient not 100%, and some lose up to 70% of the primary energy when converted to electricity. However, the scale of renewable energy sources that could replace traditional energy sources, will require a lot of land.

It is natural that many people consider the road network as an option.

Given the fact that the earth is already covered with roads, the environmental damage will be quite low. Such plants will not suffer from problems of remoteness that we would face in the Sahara; for repair and maintenance will be enough to get to them... on the road. Add LEDs and will be markings, road signs, lighting and borders. You can even dream that one day cars will receive the energy wirelessly, just by driving on such roads.

It would Seem that this is completely impossible. But no, the solar roads have a lot of support from governments and companies.

In China, I decided to make 2 kilometres of solar panels in a sandwich between the transparent asphalt and a layer of an insulator. And this is the last attempt to do something. Solar Roadways, a startup from Idaho, has already attracted $ 2 million in development on Indiegogo. Scott Bruce, founder of the company, presented a prototype of a road created in the back yard, which could provide half the energy needs of the United States. Unfortunately, the Solar Roadways will have to attract more investment and to overcome the skepticism barrier. David Biello noted in an article in Scientific American that "glass for such roads shall be hardened, self-cleaning and capable of transmitting light batteries even in terrible weather conditions — this glass simply does not exist."

The Chinese method uses new transparent glass instead of asphalt and solves the problem of material scientists, since the withstand 10 times more pressure than conventional asphalt. The construction of solar roads is not a matter for one person or one country; the prototypes created in the Netherlands — SolaRoad bike path, and in France — it seems like even the first solar road was built. Such projects already generating energy for several years, so the idea in principle is realizable. Unfortunately, between the "in principle feasible" and "practical" is a huge gap.

For Example, price. Estimate Solar Roadways Scott Bryusov, the replacement cost of American roads the sun will reach 56 trillion dollars, so no crowdfunding will not cover the cost (if only everyone on the planet will not be thrown off the case Bryusov). In any government there is a consensus that investment in infrastructure, but hardly Sunny roads freely will receive funding. Chinese solar road costs $ 458 per square meter, and Bryusov — 746 dollars. Better, but not much.

Obviously, any real solution to our energy crisis must be radical and massive. Similar radical schemes to transform the Sahara into a giant solar panel or sucking carbon dioxide from the atmosphere will also be evaluated in the trillions of dollars.

But along with cost, there is another very important question about whether it will work as the solution to the energy crisis. The roads are not always built in the optimal locations for the solar panels, and they may not be at the ideal angle for such. If cleaning the solar panels in the Sahara dust is the problem, keeping the roads clean and functioning at the same time can become a nightmare technology. It is difficult to understand why the placement of the panels parallel with the road will not be cheaper and better.

And the prototypes...

A prototype of a road in the Netherlands, as reported, is working "better than expected", generating "70 kilowatt-hours per square meter per year". But 70 kWh is quite a bit. If you want to charge on a road a your car, 1 square metre will provide you with a mileage of 500 kilometers per year for your Tesla; however, the average car runs 15 000 km per year, so these 500 miles will be a drop in the bucket.

What to do with the problem of energy density? The Dutch scale of the prototype will lead to a density of 8 watts per square meter. If you spend 56 trillion on the sun road, you will cover about 7.5 x 10¹⁰ square meters of panels and get the 600 Gigawatt of electricity. Good — about as much energy to absorb US for the day. But over 56 trillion we could come up with something better.

The Desire to create solar roads in China in its own way symbolic. The country is looking for innovative energy solutions. Who knows, perhaps one day solar roads would be cheap enough and efficient enough to become a reality. In the worst case this project will distract us from searching for the best solutions. The best — the road will get another appointment.