According to some estimates, about 0.2-0.5 percent of the world's land surface is covered with roads. And that ratio should increase by 60% by 2050. There is an amazing amount of space reserved for roads, and in fact they are mostly used only for transport. What if you make them generate energy? China is building one of the world's first solar tracks. Could solar-lined highways be the power plants of the future?
One of the advantages of fossil fuels over renewable energy sources is energy density. The reason is quite simple: fossil fuels are renewable energy that accumulates over millions of years. Oil, coal, natural gas - these are all energy reserves that were created from plants (and the animals that ate these plants) and accumulated solar energy for thousands of years through photosynthesis. It turns out that fossil fuels are more energy intensive than using solar energy in real time.
Simply put: Fossil fuels require a lot less land to generate energy than solar panels.
One of the biggest obstacles to using renewable energy sources is the physical space required to service these sources. And our ever-increasing energy consumption makes it all a problem. Primary energy - the total amount of energy consumed by humans from all sources - includes fossil fuels and renewable sources. In 2016, we consumed 478 TW of primary energy, and this number is growing every year.
For example, if you want to meet all of our energy needs with corn bioethanol, which has an energy production density of 0.2 watts per square meter (one of the worst among biofuels), you need about 2 x 1015 square meters of land to grow corn. Unfortunately, this is more than four times the Earth's surface area.
Opponents of renewable energy use this example to show that renewable energy infrastructure is simply not possible. But this is an exaggeration; the energy density for solar array arrays can reach 20 W / m2 or even more, and the Earth's surface is quite enough for this. It is also worth noting that the energy produced by solar panels is in the form of high quality electricity.
Since moving away from fossil fuels means using electricity instead of burning fuel, which is often more efficient, we would consume less primary energy in a world without fossil fuels; Fossil fuel power plants are not 100% efficient, and some lose up to 70% of their primary energy when converted to electricity. However, the scale of renewable sources that could replace traditional energy sources will require a lot of land.
It is only natural that many people consider road networks as an option.
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Considering that the land is already covered with roads, the environmental damage will be quite low. Such power plants will not suffer from the remoteness problems that we might face in the Sahara; for repair and maintenance it will be enough to reach them … by road. Add LEDs and markings, road signs, lights and borders will appear. One might even dream that one day cars will receive energy wirelessly, simply by traveling on such roads.
It would seem that this is completely impossible. But no, solar roads have a lot of support from governments and companies.
In China, they decided to enclose 2 kilometers of solar panels in a sandwich between transparent asphalt and a layer of insulators. And this is the very last attempt to do something. Solar Roadways, an Idaho-based startup, has already raised $ 2 million for development on Indiegogo. Scott Bryusov, founder of the company, unveiled a backyard prototype road that could supply half of the US's energy needs. Unfortunately, Solar Roadways will have to attract more investment and overcome the skeptical barrier. David Biello noted in an article in Scientific American that "glass for such roads must be tempered, self-cleaning and capable of transmitting light to batteries even in dire weather conditions - such glass simply does not exist."
The Chinese method uses a new transparent asphalt instead of glass and solves the problem of materials scientists, as it can withstand 10 times more pressure than conventional asphalt. Building solar roads is not a matter for one person or one country; prototypes were created in the Netherlands - the SolaRoad bike path, and in France - it seems like they even built the first solar road. Such projects have already been generating energy for several years, so the idea is, in principle, feasible. Unfortunately, there is a huge gap between “in principle realizable” and “practical”.
For example, the price. There is an estimate of Scott Bryusov's Solar Roadways, the cost of replacing American roads with solar ones will be $ 56 trillion, so no crowdfunding will cover the costs (unless everyone on the planet pays for the Bryusov case). There is a consensus in any government on infrastructure investment, but solar roads are unlikely to be funded unhindered. The Chinese solar road costs $ 458 per square meter, while the Bryusov road costs $ 746. Better, but not much.
Obviously, any real solution to our energy crisis must be radical and massive. Similar drastic schemes to turn the Sahara into a giant solar panel or suck carbon dioxide out of the atmosphere will also be worth trillions of dollars.
But along with the cost, there is also a very important question of whether this will work as a solution to the energy crisis. Roads were not always built in optimal locations for solar panels, and they may not be at the ideal angle for solar panels. If cleaning solar panels in the Sahara from dust is a problem, then keeping roads functioning and clean at the same time can turn into a technician's nightmare. It is difficult to understand why placing panels parallel to the road would not be cheaper or better.
And the prototypes themselves …
A prototype road in the Netherlands was reported to perform "better than expected," generating "70 kilowatt-hours per square meter per year." But 70 kWh is not much. If you want to charge your car on such a road, 1 square meter will give you 500 kilometers a year in your Tesla; however, the average car runs 15,000 kilometers a year, so those 500 kilometers will be a drop in the ocean.
What about the energy density problem? Scaling up the Dutch prototype will result in a density of 8 watts per square meter. If you spend 56 trillion on solar roads, you cover about 7.5 x 1010 square meters with panels and get 600 GW of electricity. Not bad - about the same amount of energy consumed by the United States per day. But for 56 trillion one could think of something better.
The drive to build a solar road in China is symbolic in its own way. The country is looking for innovative energy solutions. Who knows, maybe one day solar roads will become cheap and efficient enough to become a reality. At worst, this project will distract us from finding better solutions. At its best, the road will receive another appointment.
Ilya Khel