Rated power 0.75 Power output (MW) 0.5 FIGURE 10.13 Power curve for a typical wind 0.25 turbine. This unit has a rated Cut-in Rated Cut-out power output of 1 MW, which speed speed speed it achieves at its rated wind speed of 15 m/s. The cut-in O 5 10 15 20 25 30 35 speed is 5 m/s, and power Wind speed (m/s) generation ceases at the cut- out speed of 30 m/s.1. As used today, are hydropower, wind, and biomass truly renewable energy sources? Answer separately for each. 2. Hydroelectric dams can, surprisingly, result in significant greenhouse gas emissions. What's the source of these emissions? 3. Why can't a wind turbine extract all of the wind's kinetic energy? 4. Why is the power curve in Figure 10.13 so steep in the region below the rated speed? 5. Tailpipe emissions of VOCs are lower for ethanol than for gasoline, but overall VOC emissions are higher with ethanol fuels. Why? 6. What accounts for the difference between gross and net primary productivity? 7. By what factor must the wind speed increase in order for the power carried in the wind to double? 1. Hydroelectric dams can, surprisingly, result in significant greenhouse gas emissions. What's the source of these emissions? 2. Why can't a wind turbine extract all of the wind's kinetic energy? 3. Why is the power curve in Figure 10.13 so steep in the region below the rated speed? 4. Tailpipe emissions of VOCs are lower for ethanol than for gasoline, but overall VOC emissions are higher with ethanol fuels. Why? 5. What accounts for the difference between gross and net primary productivity? 6. By what factor must the wind speed increase in order for the power carried in the wind to double