TPO12 Lecture 4　Environmental science
　　Narrator: Listen to part of a lecture in an environmental science class.

　　Professor: All right folks, let’s continue our discussion of alternative energy sources andmove on to what’s probably the most well-known alternative energy source---solar energy. The sun basically provides earth with virtually unlimited source ofenergy every day, but the problem has always been how do we tap this sourceof energy. Can anyone think of why it’s so difficult to make use of solar energy?

　　Student A: Because it is hard to gather it?

　　Professor: That’s exactly it. Solar energy is everywhere, but it’s also quite diffused. Andthe thing is the dream of solar energy is not a new one. Humanity has beentrying to use the sun’s light as a reliable source of energy for centuries. Andaround the beginning of the 20th century there were actually some primitive solar water heaters on the consumer market. But they didn’t sell very well. Anyof you wanna guess why?

　　Student A: Well, there were other energy choices like oil and natural gas, right?

　　Professor: Yeah. And for better or for worse, we chose to go down that path as a society.When you consider economic factors, it’s easy to see why. But then in the1970s, there was an interest in solar energy again. Why do you think thathappened?

　　Student B: Because oil and natural gas were...err...became scarce?

　　Professor: Well, not exactly. The amount of oil and natural gas in the earth was stillplentiful, but there were other reasons. It’s a political thing really and I’m gonnaget into that now. So what happened in the 1970s was oil and natural gasbecame very expensive very quickly, and that spurred people to start lookinginto alternative forms of energy, solar energy probably being the most popular.But then in the 80s, this trend reversed itself when the price of oil and naturalgas went down.Alright let’s shift our focus now to some of the technologies that have beeninvented to overcome the problem of gathering diffused solar energy. The mostbasic solution is simply to carefully place windows in a building, so the sunshines into the building and then it’s absorbed and converted into heat. Cananyone think of where this is most commonly used?

　　Student A: Greenhouses.

　　Professor: Yep, greenhouses where plants are kept warm and provided with sunlightbecause the walls of the building are made entirely of glass. But we do alsohave more complex systems that are used for space heating and they fall intotwo categories, passive and active heating systems.

　　Passive systems take advantage of the location or design of a house. For example, solar energy is gathered through large glass panels facing the sun.The heat is then stored in water-filled tanks or concrete. No mechanicaldevices are used in passive heating systems. They operate with little or nomechanical assistance.With active systems, on the other hand, you collect the solar energy at onelocation, and then you use pumps and fans to move heat from the collectorsthrough a plumbing system to a tank, where can be used to heat a home or tojust provide hot water.

　　Student B: Excuse me professor, but I’ve got to ask, how can solar energy work at night oron cloudy days?

　　Professor: That’s...Well...that is a really good question. As a matter of facts, science is stillworking on it, trying to find ways of enhancing energy storage techniques sothat coming of night or cloudy days really wouldn’t matter. That is the biggestdrawback to solar energy. The problem of what do you do in cases where thesun’s light is weak or virtually non-present. So the storage of solar energy, lotsof solar energy, is a really important aspect.

　　Student A: Does that mean that solar energy can only be used on a small scale, like heating a home?

　　Professor: Well actually, there have been some attempts to build solar energy powerplants. The world’s largest solar plant is located in Cremer Junction California.It can generate 194 megawatts of electric power, but that’s just a drop in thebucket. Right now the utility companies are interested in increasing thecapacity of Cremer Junction Plant, but only time will tell if it will ever developinto a major source of power for that region, considering the economic andpolitical factors involved.