Environmental Engineering Reference
In-Depth Information
DID YOU KNOW?
Solar energy can be used for making brackish or saline water potable. Without
using electricity or chemicals, wastewater can be treated. Obtaining salt from
seawater is also one of the oldest uses of solar energy.
a module or array, the greater amount of electricity will be produced. Photovoltaic
modules and arrays produce direct-current (DC) electricity. They can be connected
in both series and parallel electrical arrangements to produce any required voltage
and current combination.
c
oncentrating
s
olar
P
ower
Concentrating solar power (CSP) offers a utility-scale, firm, dispatchable renewable
energy option that can help meet a nation's demand for electricity. CSP plants produce
power by first using mirrors to focus sunlight to heat a working fluid. Ultimately, this
high-temperature fluid is used to spin a turbine or to power an engine that drives a
generator that produces electricity. Concentrating solar power systems can be classi-
fied by how they collect solar energy: linear concentrators, dish/engine systems, or
power tower systems (NREL, 2012b).
•
Linear concentrators
collect the sun's energy using long rectangular, curved
(U-shaped) mirrors. The mirrors are tilted toward the sun, focusing sun-
light on tubes (or receivers) that run the length of the mirrors. The reflected
sunlight heats a fluid flowing through the tubes. The hot fluid is then used to
boil water in a conventional steam-turbine generator to produce electricity.
The two major types of linear concentrator systems are parabolic trough
systems, where receiver tubes are positioned along the focal line of each
parabolic mirror, and linear Fresnel reflector systems, where one receiver
tube is positioned above several mirrors to allow the mirrors greater mobil-
ity in tracking the sun.
•
Dish/engine systems
use a mirrored dish similar to a very large satellite
dish. The dish-shaped surface directs and concentrates sunlight onto a
thermal receiver, which absorbs and collects the heat and transfers it to
the engine generator. The most common type of heat engine used today in
dish/engine systems is the Stirling engine (conceived in 1816). This system
uses the fluid heated by the receiver to move pistons and create mechanical
power. The mechanical power is then used to run a generator or alternator
to produce electricity.
•
Power tower systems
use a large field of flat, sun-tracking mirrors known as
heliostats to focus and concentrate sunlight onto a receiver on the top of a
tower. A heat-transfer fluid heated in the receiver is used to generate steam,
which, in turn, is used in a conventional turbine generator to produce elec-
tricity. Some power towers use water/steam as the heat transfer fluid. Other
