Page 477 - A Comprehensive Guide to Solar Energy Systems

490 A CoMPrEhEnsiVE GUidE To solAr EnErGy sysTEMs

As shown in section 25.2, most renewable energy sources are capital intensive, and
operating costs can be small after initial capital expenditures are made. in economic
terms, costs for such energy sources are mostly fixed. For example, after incurring the cost
to install a solar panel, there is virtually no operating cost. The capital cost is the same
regardless of the how much sunlight the panel captures, and regardless of whether the
energy produced is actually useful at any given moment. The economic question then
becomes how much capital expenditure is necessary given anticipated production and
anticipated electrical demand. Extending this question to a portfolio of energy sources,
the objective is to minimize the total expense (including capital and operating expenses)
for energy production facilities that meet all demand conditions under all conditions of
ambient energy availability.
it is more expensive to collect renewable energy when ambient energy is limited. in the
Vermont example presented in section 25.4 below, average daily solar insolation during
the period of november–February is only 60% of the other eight months of the year. The
sun shines every day, and it is possible to collect some solar energy even on a cloudy winter
day. But meeting demand is more expensive when sunshine is limited, since more solar
panels are required to produce a given amount of electricity. other intermittent renew-
able energy sources have similar seasonal as well as daily variation. Total costs for renew-
able energy systems are driven not by average conditions, but by fixed capital investments
required for critical times when the renewable energy supply is low and/or the electric-
ity demand is high. The marginal cost of an energy resource represents the expenditure
(mostly capital expenditure) needed to deliver more energy at such a time.
Energy storage is an alternative to producing energy at each moment [5]. With stor-
age, energy produced now can be used later. Many energy storage technologies are avail-
able today [6,7]. Electrical storage options include batteries and capacitors; pumped water
storage, a hydropower variation; compressed air storage, for example, in underground
caverns; and energy stored as electrolytic hydrogen. Also, storage of thermal energy figures
prominently in some simulations of renewable energy systems [8,9]. Cost of energy stor-
age is in addition to production cost, and the financial characteristics of energy storage are
similar to those of intermittent renewables: most costs are for fixed capital expenditures,
and operating costs tend to be small.
Biomass represents solar energy that has already been stored by plants, and which can
be released on demand. Biomass can thus provide a complement to intermittent sources
like solar energy, with biomass combustion providing energy during times of insufficient
insolation. But in most industrialized countries, biomass (the predominant energy source
before the industrial revolution) is available in relatively small quantities compared to cur-
rent energy consumption. Fossil fuels represent similar ancient biomass energy, which can
be burned on demand. Though the focus here is on renewable energy, one application for
any residual fossil fuel use is to provide stored energy at times of low ambient energy avail-
ability. Total fossil fuel use is constrained to a quantity consistent with meeting climate-
change mitigation goals (a quantity that must eventually approach zero).