Energy Solutions to Air Pollution and Global Warming - Air Pollution and Global Warming: History, Science, and Solutions - page 334

resource. Although results for only 2 days are shown,
results for all hours of all days of both 2005 and 2006
(730 days total) suggest that 99.8 percent of delivered
energy during these days could be produced carbon free
from WWS technology (Hart and Jacobson, 2011). For
these scenarios, natural gas was held as reserve backup
and provided energy for the few remaining hours. How-
ever, natural gas reserves could be eliminated with
the use of demand-response measures, storage beyond
CSP, electric vehicle charging and management, and
increases in wind and solar capacities beyond those
used. In the last case, excess power not needed for the
grid would be used to produce hydrogen for industrial
processes and transportation. Such a use would reduce
wind curtailment (shutting down a wind turbine when
its electricity is not needed) and thus reduce overall
system costs.

13.8.4. Storing Electric Power at the Site
of Generation
Afourth method of dealing with variability is to store
excess energy at the site of generation, in batter-
ies, hydrogen gas, pumped hydroelectric power, com-
pressed air (e.g., in underground caverns or turbine
nacelles), flywheels, or a thermal storage medium (as
is done with CSP). Storage in hydrogen is particu-
larly advantageous because significant hydrogen will be
needed in a WWS energy economy for use in fuel cells,
aircraft, and high-temperature industrial processes.

13.8.5. Oversizing Wind, Water, and Sunlight
Generation to Match Demand Better
and Produce H 2 (g)
Oversizing the peak capacity of wind and solar instal-
lations to exceed peak inflexible power demand can
reduce the time that available WWS power supply is
below demand, thereby reducing the need for other mea-
sures to meet demand. The additional energy available
when WWS generation exceeds demand can be used
to produce hydrogen for heating processes and trans-
portation, which must be produced anyway as part of
the WWS solution. Oversizing and using excess energy
for hydrogen would also eliminate the current practice
of shutting down (curtailing) wind and solar resources
when they produce more energy than the grid needs.
Curtailment wastes energy; thus, reducing curtailment
and using the energy for other purposes should reduce
overall system costs.

13.8.3. Using Demand-Response
Management to Adjust Demand to Supply
Athird method of addressing the short-term variability
of WWS power, demand-response ,istouse finan-
cial incentives to shift times of certain electricity uses,
called flexible loads, to times when more energy is avail-
able. Flexible loads are electricity demands that do not
require power in an unchangeable minute-by-minute
pattern; instead, they can be supplied in adjustable
patterns over several hours. For example, electricity
demands for a wastewater treatment plant and for
charging BEVs are flexible loads. Electricity demands
that cannot be scheduled well, such as electricity use
for computers and lighting, are inflexible loads .With
demand-response, a utility may establish an agreement
with a flexible load wastewater treatment plant for the
plant to use electricity during only certain hours of the
day in exchange for a better electricity rate. In this
way, the utility can shift the time of demand to a time
when more supply is available. Similarly, the demand
for electricity for BEVs is a flexible load because such
vehicles are generally charged at night, and it is not crit-
ical which hours of the night the electricity is supplied
as long as the full power is provided sometime during
the night. In this case, a utility can use a smart meter
to provide electricity for the BEV when wind availabil-
ity is high and reduce the power supplied when wind
availability is low. Utility customers would sign up their
BEVs under a plan by which the utility controlled the
nighttime (primarily) or daytime supply of power to the
vehicles.

13.8.6. Storing Electric Power at Points of
End Use and in Electric Vehicle Batteries
Another proposed method of better matching power
supply with demand is to store electric power in the
batteries of BEVs and then to withdraw such power
when needed to supply electricity back to the grid. This
concept is referred to as vehicle-to-grid (V2G) (Kemp-
ton and Tomic, 2005a). The utility would enter into a
contract with each BEV owner to allow electricity trans-
fers back to the grid any time during a specified period
agreed upon by the owner in exchange for a lower elec-
tricity price. V2G does have the potential to wear down
batteries faster, but one study suggests that only 3.2
percent of U.S. light-duty vehicles, if all converted to
BEVs, would need to be under contract for V2G vehi-
cles to smooth out U.S. electricity demand if 50 percent