How Energy Is Produced - The Renaissance of Renewable Energy - page 73

Source Technology Capacity factor (%)

Domestic pellet heating 13-29

Municipal solid waste 80-91

Anaerobic digestion 68-91

Geothermal Electricity 60-90

Heat 25-30

Ocean energy Tidal 22.5-28.5

Wave 25-40

Note: Plants that operate around the clock, such as nuclear or fossil fuel plants, have
generating capacities much higher than those that can only supply electricity when the
sun shines or the wind blows.
Sources: McGowin ( 2008 ) , Bain ( 2011 ) , Bruckner et al. ( 2011 ) , Arvizu et al.
( 2011a ), Kumar et al. ( 2011 ) , ETSAP ( 2010 ), Lewis et al. ( 2011 ) , Smil ( 2012 ).

Base Load and Peak Load
Over the course of twenty-four hours, our homes and our bodies experience ebbs and flows
of energy consumption. In the evenings, homes are a hive of activity, as parents fuss to
make dinner, children squirm while trying to finish their homework, the washing machine
does its thing, and grandma knocks out an email on an arthritic keyboard. During the night,
the household's energy expenditure dips low, represented by the nasal purr of the fridge
and some throaty snoring from the master bedroom. In the morning we wake up a bit later
than the central heating does, and new energy demands kick in.

Electricity utilities cope with these variations in two ways. First, they create what are
called load profiles. These are graphs showing variations in demand for electricity (or
electrical load) within a particular network or by particular consumer groups over time (see
Figure 4.2 ) . Luckily, electricity demand patterns are quite predictable, so power utilities
can plan how much electricity to generate at any given time. As we have seen, electricity
is very difficult to store in large quantities, so excess electricity is likely to go to waste.