Lab 10. Solar and Wind Power

Transcription

1 1 Name Lab 10. Solar and Wind Power INTRODUCTION Sunlight can be used to create heat or generate electrical power. This is referred to as solar energy. It is a clean form of energy production, which doesn't pollute the environment, as some other forms of energy production do. A common way to capture solar energy is the use of photovoltaic cells. Photo- means "light," and voltaic means "producing electricity." Photovoltaic cells thus produce electricity when they are exposed to light. This technology was pioneered by NASA in the 1950 s for the US space program for use on satellites and other spacecraft. Photovoltaic (PV) cells usually contain two layers of different materials called semiconductors. When light hits these two layers, electrons are dislodged, begin to move, and one of the layers becomes positively charged, and the other becomes negatively charged. This is similar to a regular battery, which has a positive end and a negative end. When a wire connects the two ends, they produce an electric current. In this way, when the two layers of material in a solar cell are exposed to light, they create an electric current. Each individual solar cell only produces a small amount of electricity and can be used on small devices such as calculators or watches. However, individual cells can also be daisy-chained by connecting them together to create a solar panel to produce more electricity. For example solar panels can be put on the roofs of buildings or they can be arranged in larger arrays in open areas where they can feed into an electrical grid. How much electricity? The amount of electricity that we can produce using solar panels obviously depends on the amount of sunlight that strikes the panels. Major factors in producing electricity include: 1) Panel area: the larger the panel, the more electricity we produce

2 2 2) Sunlight intensity: peak electricity is produced if the sun is directly overhead and there are no clouds in the sky. 3) Sunlight duration: peak electricity is produced during the summer when the days are longest and the sun is brightest. 4) Geography: equatorial regions (such as the tropics) receive more sunlight per year, desert or dry areas have fewer clouds. The Southwestern US (Arizona, New Mexico) are the best locations for sunlight intensity and duration but the Southeastern US is good too. Any area can utilize solar panels especially where other energy sources are not feasible (such as outer space and the South Pole in the summer) but panels will most rapidly pay for themselves in areas with more sunlight available. Answer these questions: 1) Is Knoxville a good place for solar panels? Explain your answer by citing specific reasons. 2) Briefly describe how solar panels work. 3) Name 3 devices besides calculators and watches that could operate with only solar cells powering them 4) What is the difference between a solar cell and a solar panel? Advantages & Disadvantages Solar energy is a relatively clean and renewable power source. It can also be portable. When one is backpacking in the wilderness or travelling far from power grids, solar power can provide a means of powering electronic equipment. Another advantage is, of course, the lack of pollution created by solar energy production. Disadvantages include: solar energy can only be generated during the daytime or on sunny days so that batteries are needed to store excess energy produced during peak times. Or an alternate source of energy can be used such as wind power or geothermal energy. In addition, desert ecosystems may be disturbed by large solar arrays. As of 2011, solar energy produced less that 0.1% of the energy used in the U.S. EXERCISE I: MEASURING SOLAR POWER Lab equipment: Your TA will provide you with portable solar meter. This is a device that measures solar radiation in WATTS per sq meter (W/m 2 ). Locate the sensor on the top of the meter. If 1 meter = 3.28 feet then 1 m 2 = ft 2 Procedure: 1) Turn on the solar meter. What is the reading? W/m 2 (always write units) 2) NOTE: your readings will fluctuate so you should take an average for all readings. Record these indoor readings: Pointing toward the window W/m 2 Pointing directly at an indoor light W/m 2

3 3 3) Take the solar meter outside and make readings in different locations outside the building. Be sure and measure the solar power: In the shade W/m 2 In sunlight pointing exactly at the sun W/m 2 In sunlight pointing away from the sun W/m 2 Calculations (SHOW all work) 1) Estimate the area of floor space in your lab room m 2 (remember that 1 meter = 3.28 feet) 2) If you had a solar panel on your roof that was the size of your lab room area, how much electricity could you produce if your roof was in the SHADE? Important: solar panels are only about 10% efficient. This means that the produce about 10 W of electricity for each 100 W of sunlight!!! 3) If you had a solar panel on your roof that was the size of your lab room area, how much electricity could you produce if your roof was in the DIRECT SUN? 4) Assume your roof has an area of 1300 sq feet (= 121 sq meters). This is about the average home roof area. How much electricity would you produce in direct sun? If your average home electricity use at any given moment is about 1,000 W, what percentage of your electricity could you produce with your panels in direct sunlight?

4 4 WIND POWER Wind is a form of solar energy. Winds are caused by the uneven heating of the atmosphere by the sun, the irregularities of the earth's surface, and rotation of the earth. Wind flow patterns are modified by the earth's terrain, bodies of water, and vegetative cover. Wind energy is a free, renewable resource, so no matter how much is used today, there will still be the same supply in the future. Wind energy is also a source of clean, non-polluting, electricity. Unlike conventional power plants, wind plants emit no air pollutants or greenhouse gases. Wind Turbines Wind turbines have large blades that turn in the moving air and power an electric generator that supplies an electric current. Thus, a wind turbine is the opposite of a fan. Instead of using electricity to make wind, like a fan, wind turbines use wind to make electricity. The wind turns the blades, which spin a shaft, which connects to a generator and makes electricity. There are 2 basic kinds of wind turbines: 1) household scale which can power individual homes, and 2) industrial scale which are several stories high and can power hundreds of homes. EXERCISE II: MEASURING WIND POWER Lab equipment: Your TA will provide you with portable wind meter to measure wind speed. Procedure: 1) Carefully remove the top from the meter to expose the moving blades. 2) Turn on the meter and be sure that wind speed is measured in MPH. 3) Turn on the electric fan 4) Measure the maximum wind speed in front of the fan. Be sure that your wind meter is vertical and upright in front of the fan and take measurements for at least 2 minutes. Record MAXIMUM wind speed that you measured: MPH Calculations (SHOW all work) 1) Using the Table below, calculate the amount of electricity (per square meter of swept area) that would be produced by the maximum wind speed created by the fan:

5 5 Note that the unit is per sq meter of swept area. This means that if you have a turbine with a blade that is 3 meters long, then the swept area is roughly 28 sq m (the area of a circle is pi*radius 2 ). 2) What would be your total electricity production for your wind turbine? 3) Let s say you want to add wind power to your house so you buy a wind turbine that has rotors that are about 4 m long so your swept area is about 50 sq m. In E. TN you can find some areas that have an average wind speed of 9.8 mph. A) Using the chart above, calculate how many kwh per year your turbine will produce (on average)? B) The typical American home uses about 1,000 kwh per year. What percentage of your total household electricity will your turbine with 4 m blades produce? C) Assuming you are paying 12 cents/kwh to the utility company, how much money are you saving with your wind turbine?

6 6 D) Assuming you paid $6,000 to install your wind turbine system (with tax breaks included), how long will it take you to recover your investment? GEOGRAPHY OF WIND POWER In the map below, the darker the area, the higher the average wind velocity (wind power potential). Please answer the following based on the map below: 1) Name 3 states with the highest wind potential? What is the reason for such strong winds? 2) Which parts of Tennessee have the highest wind potential? What is the reason for the strong winds?