Alternative Energy Demystified, 2nd edition

Stan Gibilisco

Explanations for Quiz Answers in Chapter 5

1. If you want to take advantage of sidehill construction and thermal mass for cooling purposes, you should build your home on a poleward-facing slope. The side with the most exposed exterior wall area, and with the greatest window area, will face downslope, toward the pole. Australia lies in the Southern Hemisphere, so poleward means southward. The correct choice is B.

2. If you want a direct wind-powered electric heating system to operate as if it gets its power from the electric utility, then you must provide the heating elements with the same voltage that the utility would provide. A voltage regulator (choice D) can accomplish that task. Storage batteries (choice A) and solar panels (choice B) have nothing to do with direct wind-powered systems; thermal mass (choice C) has no effect on the operation of the heating elements. The answer is D.

3. An evaporative cooling system draws outdoor air in through a water-soaked filter. The air emerges cooler because some of the water evaporates, drawing thermal energy from the air. The evaporated liquid water, in the form of vapor, moves into the interior living area along with the air. In effect, therefore, the system humidifies the air as well as cooling it. The answer is D.

4. The bearings among the moving parts of a water turbine have some friction. As the water drives the turbine, and as the turbine offers resistance to the flow of the water, the turbine produces a small amount of thermal energy that transfers to the stream water. Technically, that's a form of "pollution," although it's not significant on a residential scale. A water turbine doesn't produce any other form of pollution at all: no particulates, no greenhouse gases, and no toxic waste. The correct choice is B.

5. In most locations, the underground temperature rises as you go deeper than a few meters beneath the surface. That fact explains why deep mine shafts sometimes get so hot that they need sophisticated cooling systems to keep the workers from suffering from heat exhaustion! The correct choice is B.

6. You wouldn't want to build a subterranean home anywhere near radioactive mineral deposits, underground streams, or volcanoes. Any of those natural phenomena would make subterranean living unsafe. The correct choice is D.

7. With a moderate wind, a midsize residential wind turbine can produce approximately 12 kW of electric power, which translates into 12 x 3410 = 40,920 Btu/h. We can round that figure off to 41,000 Btu/h. The correct choice is C.

8. In a stream or small river with sufficient vertical drop and a fast flow of water, a good residential wind turbine can produce approximately 20 kW of electric power. That figure translates into 20 x 3410 = 68,200 Btu/h. We can round that figure off to 70,000 Btu/h. The correct choice is A.

9. A single silicon PV cell produces about 0.5 V DC in bright sunlight. If we connect six such cells in series, the voltages add, so we can expect to get approximately 0.5 V x 6 = 3.0 V DC. The answer is C.

10. The maximum amount of power that you can get from a PV panel varies in direct proportion to the total surface area of the array, assuming that all other factors hold constant. The correct choice is A.