Environmental Engineering Reference
In-Depth Information
are
hours in a year. If you live in Dallas, Texas, for
example, you are between the
and
hour con-
tours so your effective output is about
% of peak and
you will produce
kilowatt-hours of electricity for
every kilowatt of peak capacity installed. This map is for
stationary
flat plate collectors like those for California
'
s
million solar roofs. In California,
Figure
shows that
the average number of hours of collection is
.
per
year, so the energy delivered averaged over the year is
only
% of the capacity.
The time of peak demand in most places in the world is
in the daytime when solar systems are most effective. PV
systems can make an important contribution to reducing
greenhouse gas emissions, but without energy storage
there is no way to generate electricity from sunlight on a
large scale during the day and store it for use at night.
Small systems typical of residences can use simple battery
systems for night time storage, but PV solar is not yet
suitable for base-load power
(solar
thermal electric
systems can store energy
more on this later).
Typical systems for single residences have
-
to
kilo-
watt capacities and cost about
$
per kilowatt (the
estimate of the California Public Utilities Commis-
sion). A
kilowatt system in California starts out at a cost
of
$
. For this system the present federal credit is
per
watt, but no longer does so. What started out costing
$
%or
$
. California used to give a rebate of
$
.
nets out after all the credits at
$
. With an
interest rate of
% and a
year lifetime, electricity will
cost about
cents per kilowatt-hour in California. With
all the rebates the payback time is typically about
years.
California has expensive electricity in the daytime, so solar
