Supplemental material for the Feature Article "Home photovoltaic systems for physicists" PHYSICS TODAY, July 2008, page 42.
Thomas W. Murphy Jr
Ordinary gasoline stores an extraordinary quantity of energy compared
with many alternatives. A lead–acid battery, for instance—currently the cheapest
alternative for storing electricity in residential-scale photovoltaic systems—stores
only 1/500 the energy that can be obtained from an equal mass of gasoline. A gallon of gasoline can
provide about 36 kWh of energy, more than a typical house uses in a day. To produce that amount of energy
via photovoltaic panels illuminated with 5 peak-equivalent Sun hours per day would theoretically
require 72 100-W panels. Actually, 100 100-W panels is a more reasonable estimate after
one takes into account such practical limitations as inefficiencies in transporting and storing
charge and power losses associated with the high operating temperatures of the PV panel.
One saving grace is that electrical applications tend to be far more efficient
than the thermodynamic processes associated with gasoline consumption. All the same, the comparison
given here highlights the difficulty we will face in replacing our precious gasoline with renewable
sources.
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