Environmental Engineering Reference
In-Depth Information
Utilities also take advantage of the law of supply and demand, and charge different rates
depending on the level of demand.
Figure 4.2.
Typical daily load profile on a hot summer's day in California. Industry and
agriculture tend to use electricity in a more uniform way; commercial use tends to peak
during central hours, while residential demand peaks in late afternoon when most
appliances are in operation. While the aggregate demand evens out the individual peaks
somewhat, the daytime load is still twice the night-time load.
Source:
Lawrence Berkeley
National Laboratory.
The second way utilities adapt to fluctuating demand is by generating power in different
types of facilities: base-load and peaking plants. Base-load plants are those facilities that
meet a region's continuous power demand, and they generate power at a relatively constant
rate.Nuclearandcoal-firedplantsaremostcommonlyusedtosatisfybasedemand.Among
renewables,geothermal,biogas,andbiomassplantsarealsosuitableforthispurpose.Since
they are designed for maximum efficiency and operate almost continuously at high output,
base-load plants have the lowest costs per unit of electricity.
Peaks (or spikes) in demand are handled by smaller, more responsive plants. These are
typically natural gas and hydroelectric plants that can be switched on and off very quickly
in case of sudden unplanned demand, such as during heat waves (when there is a spike
in air-conditioning demand) or when base-load plants break down. Peaking plants may
operateforafewhoursaday,orevenjustafewtimes peryear,andthepowertheygenerate
commands a higher price per kilowatt hour than base-load power.
Stages of Technology Development
As we have seen, conventional power plants come in a variety of shapes and sizes, and
fulfil different needs within the energy market. However, the core principle upon which
they operate has not radically changed since James Watt's day, as heat is generated to boil
water, and the resulting steam is converted into mechanical energy. Of course, we have
discovered many new fuels in the last two centuries (including an entirely new type of fuel,
uranium), and in the last hundred years we have added a further link to the conversion
chain: electricity. However, these days, the really exciting developments are taking place in
the renewables sector. It is here that the imaginations of modern-day Edisons have room to
roam.
