新托福考试必备：新托福TPO（1-24）听力原文文本TPO12

　　Professor
　　All right folks, let’s continue our discussion of alternative energy sources and
　　move on to what’s probably the most well-known alternative energy source---
　　solar energy. The sun basically provides earth with virtually unlimited source of
　　energy every day, but the problem has always been how do we tap this source
　　of 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. And
　　the thing is the dream of solar energy is not a new one. Humanity has been
　　trying to use the sun’s light as a reliable source of energy for centuries. And
　　around 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. Any
　　of 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 the
　　1970s, there was an interest in solar energy again. Why do you think that
　　happened?

　　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 still
　　plentiful, but there were other reasons. It’s a political thing really and I’m gonna
　　get into that now. So what happened in the 1970s was oil and natural gas
　　became very expensive very quickly, and that spurred people to start looking
　　into 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 natural
　　gas went down.

　　Alright let’s shift our focus now to some of the technologies that have been
　　invented to overcome the problem of gathering diffused solar energy. The most
　　basic solution is simply to carefully place windows in a building, so the sun
　　shines into the building and then it’s absorbed and converted into heat. Can
　　anyone think of where this is most commonly used?

　　Student A
　　Greenhouses.

　　Professor
　　Yep, greenhouses where plants are kept warm and provided with sunlight
　　because the walls of the building are made entirely of glass. But we do also
　　have more complex systems that are used for space heating and they fall into
　　two 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 mechanical
　　devices are used in passive heating systems. They operate with little or no
　　mechanical assistance.

　　With active systems, on the other hand, you collect the solar energy at one
　　location, and then you use pumps and fans to move heat from the collectors
　　through a plumbing system to a tank, where can be used to heat a home or to
　　just provide hot water.

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

　　Professor
　　That’s...Well...that is a really good question. As a matter of facts, science is still
　　working on it, trying to find ways of enhancing energy storage techniques so
　　that coming of night or cloudy days really wouldn’t matter. That is the biggest
　　drawback to solar energy. The problem of what do you do in cases where the
　　sun’s light is weak or virtually non-present. So the storage of solar energy, lots
　　of 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 power
　　plants. 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 the
　　bucket. Right now the utility companies are interested in increasing the
　　capacity of Cremer Junction Plant, but only time will tell if it will ever develop
　　into a major source of power for that region, considering the economic and
　　political factors involved.