Science In Real Life

Welcome to Part II of the mini-series addressing power production, all about solar power in its many forms! If you could all just form a line in front of me, we can begin the tour. Please stay with the tour group at all times, we wouldn’t want you to get stuck under a dam. No flash photography is allowed – it scares the solar cells and then we have to bring out the UV lamps to calm them down again. Plenty of pictures of them on sale in the gift shop. And for all you would-be Don Quixotes, there will be no tilting at the windmills, ha ha. Can you hear me there in the back? Good, on we go.

The first thing you see, directly behind me, is the sun. Don’t forget to put on your special viewing glasses, you’ll find them tucked into the pocket of your program booklet. The sun is constantly radiating huge amounts of energy in all directions; it is this energy that we harness down here on Earth. Even though the Earth only gets about two billionths of the total energy the sun produces, it would be far more than enough to supply world’s needs if we could convert it efficiently. The sun produces energy from a complicated fusion process — see your program booklet for more details — which is why we in the biz say that a day without fusion is like a day without sunshine! Best of all, scientists think the sun won’t kill us all for another billion years or so. Everyone ready? On we go!

On your left you can see the Three Gorges Dam, currently nearing completion in the Hubei province of China and already producing more energy than any other power plant in the world. Like all hydroelectric facilities, Three Gorges produces electricity by using falling water to rotate the turbines of massive electrical generators. A question there in the back? Why of course this is solar power, young man! The sun is what lifted the water, via the water cycle. Evaporation from lakes and oceans causes condensation into clouds in the sky that yield precipitation into rivers that we use for energy generation. Although there are some concerns about the ecology of building dams, and of course safety, hydroelectric power has electricity flowing all over the world! Oh, I crack myself up sometimes. On we go.

Everyone watch your footing now! Here we are on the deck of a ship off the coast of Portugal. This is the Aguçadoura Wave Park, where three wave energy converters generate about 2.25 Megawatts of power. Each of the converters is segmented like a caterpillar, and as the sections compress, the ocean wave energy drives hydraulic pistons which push oil at high pressure to drive an electric generator. Now, if we could only figure out how to hook one of these up to a crowded football stadium we’d be all set. Waves, of course, are driven by the wind, which we can harness more directly in a place like *snap* this wind farm here in California. These wind turbines can immediately drive a generator by spinning in the wind. The sun drives the wind with all the consistency of New York City traffic, but in places such as this one it is steady enough to power machines that only look like they’re going to kill us all. And, on we go.

At last we come to the most well-known type of solar power: photovoltaic cells. Solar panels such as the ones on the roofs of these suburban homes convert incoming light directly into electricity using specially constructed semiconductors. Here we have a diorama to explain how this works: two prisons sit next to each other, their yards separated by a chain link fence. In a normal prison, each prisoner has a certain number of cigarettes and trades them freely without ever having too many or not enough. In the left hand prison here, though, a few prisoners who don’t make enough cigarettes have been transferred in. Now gaps in the cigarette flow move throughout the prison. In the right hand prison, a few prisoners who make too many cigarettes have been locked up. Extra cigarettes bounce around uselessly.

At the fence, cigarettes can move back and forth. You might think they would equalize, but the social dynamic of a prison is complex. Even though there are extra cigarettes floating around from the right prison, when one of them switches over, the prisoner near the fence still feels like he’s lost one. And when a prisoner near the fence on the left side lets a gap go, he feels like he has extra. There is, in short, cigarette overcompensation. Now, the guards are capricious and draconian arbiters of prison rules; when they tour the yard any prisoner they find with a cigarette immediately passes it to someone else and takes another after they’re gone. What this means is that every appearance of a guard frees up a cigarette-gap pair. Due to the cigarette overcompensation, the cigs flow left and the gaps flow right.

You will find in your programs a handy key for interpreting this in the context of a solar cell. Regular prisoners are silicon atoms, the odd ones are dopant atoms, cigarettes are electrons, gaps are … gaps, and the prison guards are rays of sunlight. When we connect the cell to a circuit, current flows. This type of arrangement is called a P-N junction, and it also appears in the use of semiconductors for computational circuits as a diode.

Well, we have at last reached the end of our tour. I hope you have a better understanding of some of the ways in which our favorite mass of incandescent gas powers the world around us. As a very wise man once said: Solar? I hardly knew ‘er!