Civil Engineering Reference
In-Depth Information
12
Stand-Alon
e System
The major application of the stand-alone power system is in remote areas
where utility lines are uneconomical to install due to terrain, the right-of-
way difficulties or the environmental concerns. Even without these con-
straints, building new transmission lines is expensive. A 230 kV line costs
about $1 million per mile. For remote villages farther than two miles from
the nearest transmission line, a stand-alone wind system could be more
economical. The break-even distance for pv systems, however, is longer
because the pv energy is four to five times more expensive than wind energy
at present.
The solar and wind power outputs can fluctuate on an hourly or daily
basis. The stand-alone system must, therefore, have some means of storing
energy, which can be used later to supply the load during the periods of low
or no power output. Alternatively, the wind or pv or both can also be used
in a hybrid configuration with diesel engine generator in remote areas or
with fuel cells in urban areas.
According to the World Bank, more than 2 billion people live in villages
that are not yet connected to utility lines. These villages are the largest
potential market of the hybrid stand-alone systems using diesel generator
with wind or pv for meeting their energy needs. Additionally, the wind and
pv systems create more jobs per dollar invested, which help minimize the
migration to already strained cities.
Because power sources having differing performance characteristics must
be used in parallel, the stand-alone hybrid system is technically more chal-
lenging and expensive to design than the grid-connected system that simply
augments the existing utility system.
12.1
pv Stand-Alone
The typical pv stand-alone system consists of a solar array and a battery
connection as shown in
Figure 12-1
.
The array powers the load and charges
the battery during daytime. The battery powers the load after dark. The
