Environmental Engineering Reference
In-Depth Information
the amount of power required to circulate the fluid streams from and to the ocean via the power
plant.
In 1979, a small closed-cycle demonstration plant mounted on a barge anchored off Keahole
Point in Hawaii generated 52 kW of gross electrical power but only 15 kW of net power, with
the difference being consumed in pumping losses. The heat exchangers were made from titanium
plate. The cool water polyethylene pipe was 0.6 m in diameter and drew water from a depth of
823 m. Currently, experiments are continuing with a 50-kW closed-cycle plant located on shore
at the Natural Energy Laboratory of Hawaii, with testing of heat exchangers that will be more
economical.
In 1981, Japan demonstrated a shore-based closed-cycle plant utilizing a fluorocarbon working
fluid. Cool water was drawn from a depth of 580 m. The gross and net powers from this plant were
100 kW and 31 kW, respectively.
In 1992, an open-cycle plant was tested at the Natural Energy Laboratory of Hawaii that
generated 210 kW of gross electrical power and 40 kW of net electrical power. The turbine rotor
for this plant weighed 7.5 tons.
There are several problems to be overcome if ocean thermal power systems are to become
practical. Fouling of the warm water supply pipe and heat exchanger by marine organisms, and
the corrosion of heat exchangers, needs to be eliminated. The mechanical power needed to pump
fluids through the system must be kept well below the gross output of the turbine. All components
of the system need to be constructed economically so that the capital cost per unit of net power
output becomes competitive with other types of renewable energy systems.
7.10
CAPITAL COST OF RENEWABLE ELECTRIC POWER
Under the new regulatory regime being instituted in some states of the United States in 2000, and
which perhaps will be extended subsequently to all of the states, the price of electricity paid by
consumers is the sum of several parts. One part is the price charged by the electricity producer for
electricity leaving the power plant. Other parts include the price for transmission by high-voltage
power lines and distribution networks to the consumer's location. One might say that the electric-
ity producer sells a product, electric energy (measured in kilowatt hours), while the transmission
and distribution utility sells a service, transmitting the electric energy to the customer. Individual
producers will compete to sell electric energy to consumers for the lowest price, but the trans-
mission and distribution system will remain a public utility monopoly whose price of service will
be regulated by public authorities. In a competitive market, electricity producers will price their
product to cover the costs of production, plus a profit for privately owned producers.
Most of the currently installed renewable energy systems in the United States generate elec-
tric power (see Table 7.1). These systems collect naturally available forms of renewable energy
and convert them to electrical power. The economic cost of doing so stems almost entirely from
the capital investment required to produce and install the equipment that accomplishes this energy
conversion. In contrast to fossil fuel power plants, where the cost of fuel and of operating and
maintaining the plant may equal or exceed the annualized capital cost, renewable energy plants
have small operating costs and, of course, no fuel cost. Because renewable energy plants have
higher capital costs and lower utilization than fossil fuel plants, their cost of producing electricity
is usually higher than that of fossil fuel plants.
