Environmental Engineering Reference
In-Depth Information
Problem 7.9
If incident solar radiation averages 700 W/m
2
for 8 hours, estimate the area
A
of 80% efficient
heliostats needed to provide 10 MW of electrical power (as in Solar One). Assume that the efficiency
of converting solar heat to electric energy is 35%.
Problem 7.10
Calculate the land area in km
2
that would be needed for a solar thermal power plant delivering
1000 MW of electrical power under the following conditions: The concentrating mirrors receive
700 W/m
2
; each concentrating mirror and its platform require a land area twice the area of the
mirror itself; the efficiency of converting solar heat to electric energy is 35%.
Problem 7.11
An earth satellite photovoltaic power system is oriented toward the sun to intercept the solar
irradiance of 1367 W/m
2
. (a) If the photovoltaic cell efficiency is 17%, calculate the electrical
power output per unit of surface area. (b) If 90% of the solar irradiance is absorbed by the cell,
calculate the heat flow rate, per unit area, radiated to space that is needed to maintain the cell at
a fixed temperature. (c) If this radiant heat flow is that of a black body (
T
4
, where sigma is the
Stefan-Boltzmann constant [see Table A.3] and
T
is the cell absolute temperature), calculate the
cell temperature.
σ
Problem 7.12
If solar irradiation is 700 W/m
2
and the efficiency of a photovoltaic cell is 10%, calculate the area
(in m
2
and ft
2
) of a PV cell needed to run simultaneously—and without a grid or battery backup—a
typical refrigerator, toaster, TV, and stereo set. Use electric power consumption data from your
own appliances or from the literature.
Problem 7.13
A single-story retail store wishes to supply all its lighting requirement with batteries charged
by photovoltaic cells. The PV cells will be mounted on the horizontal rooftop. The time-averaged
lighting requirement is 10 W/m
2
; the annual average solar irradiance is 150 W/m
2
; the PV efficiency
is 10%; the battery charging-discharging efficiency is 80%. What percentage of the roof area will
the photocells occupy?
Problem 7.14
Calculate the power produced per m
2
of wind turbine disk area for a wind velocity of 20 miles
per hour, assuming a power coefficient
C
p
of 0.5 and an air density of 1.2 kg/m
3
. Calculate the
diameter of a wind turbine that would supply 1 MW of electrical power under these conditions.
