The electric power needs of a community are to be met by windmills with 40-m-diameter rotors. The windmills are to be located where the wind is blowing steadily at an average velocity of 6 m/s. Determine the minimum number of windmills that need to be installed if the required power output is 1500 kW.

Solar energy stored in large bodies of water, called solar ponds, is being used to generate electricity. If such a solar power plant has an efficiency of 3 percent and a net power output of 180 kW, determine the average value of the reuired solar energy collection rate, in Btu/h.

1 kg of ice from a freezer at -10◦C is placed in a bucket in the garden where the temperature is 20◦C. The temperature difference between the garden and the ice/water system is used to operate an engine. Calculate the maximum amount of work that can be done by this engine and its overall efficiency.

Large wind turbines with a power capacity of 8 MW and blade span diameters of over 160 m are available for electric power generation. Consider a wind turbine with a blade span diameter of 100 m installed at a site subjected to steady winds at 8 m/s. Taking the overall efficiency of the wind turbine to be 39 percent and the air density to be 1.25 kg/m³, determine the electric power generated by this wind turbine. Also, assuming steady winds of 8 m/s during a 24 hour period, determine the amount of electric energy and the revenue generated per day for a unit price of $0.09/kWh for electricity. The density of air is given to be p = 1.25 kg/m³. The electric power generated by the wind turbine is The amount of electric energy generated is The revenue generated per day is $ kWh. kW. K