【听力】为何不用太阳能电池板覆盖沙漠？

NB: This may not be a word-for-word transcript.

Why Don’t We Cover the Desert with Solar Panels?

Dan Kwartler

Every day, the sands of the Sahara Desert reach temperatures up to 80° Celsius. Stretching over roughly nine million square kilometers, this massive desert receives about 22 million terawatt hours of energy from the Sun every year. That’s well over 100 times more energy than humanity consumes annually. So, could covering the desert with solar panels solve our energy problems for good?

Solar panels work when light particles hit their surface with enough energy to knock electrons out of their stable bonds. On their journey back to stability, these electrons produce electricity. However, there’s a limit to how much power panels can generate. Solar panels can only interact with certain wavelengths of light, making it impossible to convert over half the sunlight they receive. And even light particles they can convert often bounce off them without ever hitting an electron.

But thanks to clever scientists and engineers and substantial government investment, solar panels are generating more electricity than ever. Anti-reflective coatings and patterns on the panels’ surface create more opportunities for incoming light particles to hit electrons. These techniques have increased commercial solar panel efficiency from the low-teens to 25%, with experimental models reaching up to 47%. What’s more, solar has gotten 89% cheaper over the last decade, thanks in part to global supply chains for other technologies that use the same materials. Together, these factors have made solar power the cheapest source of electricity on Earth.

Countries including India, China, Egypt, and the US, have already taken these new panels into the desert. Their massive solar farms range from 15 to 56 square kilometers, and when the sun is high in the sky, these plants can provide energy for hundreds of thousands of local residents. But these farms also get extremely hot. Light that solar cells don’t convert or reflect is absorbed as heat, which reduces a panel’s efficiency. And the cooling systems employed by many farms can use huge amounts of energy powering fans or moving water to maintain optimal temperatures. Even with these systems, solar panels in the desert absorb far more heat than the natural sandy environment. This hasn’t been a problem on the scale of existing solar farms. But if we tried to cover the Sahara, this effect could create massive changes in the region’s climate. Constructing solar farms already disrupts local ecosystems, but a plant of this scale could dramatically transform the desert landscape.

Thankfully, solar panels aren’t our only option. And some of the largest solar plants in the world are trying a new approach: giant mirrors. Morocco’s Noor Power Plant, which will eventually cover roughly 30 square kilometers of the Sahara, is a concentrated solar power plant. This design reflects light onto a receiver, which converts that energy to heat, and then electricity. These mirrors still create a dangerous temperature shift for local wildlife, but they have less potential to transform the landscape. And since it takes time for the materials being heated to cool off, these plants often continue producing electricity past sunset.

Whether they use panels or mirrors, industrial solar farms are often easy to fit into existing energy infrastructure. However, getting their electricity beyond local power grids is much more difficult. Some countries are working on ways to connect electric grids across the globe. And many farm store energy in massive batteries, or convert their electricity into clean gas that can be used later. But right now, these techniques are still too expensive and inefficient to rely on. Worse still, industrial renewables can share some of the same problems as fossil fuels, relying on destructive mining operations and carbon-emitting global supply chains.

Fortunately, solar can exist on many scales, from industrial solar farms to smaller installations that power individual buildings and rural communities. These projects can supplement energy use or provide a passive source of energy for regions off the grid. And since solar panels rely on a few simple components, they’re quick to install and relatively easy to update. In fact, it’s this flexibility that enabled solar to become so cheap and ubiquitous over the last decade. So if we want to keep up with humanity’s rising energy use, we’ll need answers both big and small.