Asolar thermal plant with energy storage capability is to be constructed at about a 40° latitude to provide the electric energy to a system whose 24-hr average load is 100 mwe during the winter. assume that the solar thermal power plant will have a 25% energy conversion efficiency; that the nighttime load is 40% of the total load; and that 10% of the energy that must be stored is lost. (a) determine the total land area (in km2) required for the reflectors (heliostats). (b) for comparison also determine the area (in km2) required for a fixed horizontal system. in both cases, it is believed that a parabolic reflector system can be set up so that the reflectors cover 45% of the land area on which they are placed. the reflected energy collected at 40° latitude in winter is 6 kw·hr/m2·day for a tracking system, and only 1.85 kw·hr/m2·day for a horizontal fixed system.

Na food processing facility, a spherical container of inner radius r1 5 40 cm, outer radius r2 5 41 cm, and ther- mal conductivity k 5 1.5 w/m · k is used to store hot water and to keep it at 100°c at all times. to accomplish this, the outer surface of the container is wrapped with a 800-w electric strip heater and then insulated. the temperature of the inner surface of the container is observed to be nearly 120°c at all times. as- suming 10 percent of the heat generated in the heater is lost through the insulation, (a) express the differential equation and the boundary conditions for steady one-dimensional heat conduction through the container, (b) obtain a relation for the variation of temperature in the container material by solving the differential equation, and (c) evaluate the outer surface tempera- ture of the container. also determine how much water at 100°c this tank can supply steadily if the cold water enters at 20°c.

Automobile fuel efficiency is often measured in miles that the car can be driven per gallon of fuel (mpg). heavier cars tend to have lower fuel efficiencies (lower mpg ratings). which variable (weight or fuel efficiency) is most naturally considered the explanatory (predictor) variable in this context?

Two resistors r1 and r2 may be connected either in series or parallel across an ideal battery with emf ε. we desire the rate of energy dissipation of the parallel combination to be 8.75 times that of the series combination. if r1 = 105 ω, what are the (a) smaller and (b) larger of the two values of r2 that result in that dissipation rate?