Environmental Engineering Reference
In-Depth Information
and the variability inherent in their systems. The steps required to achieve
effective management for load and generation flexibility include:
• Energy efficiency and demand response
• Spatial and source generation diversity exhibiting complementary
profiles
• Ability to bring resources to market via transmission and timely
utilization
• Energy storage
• Smart grid electric utility data communications development to inte-
grate above steps
Note that energy storage is only one of these five steps intended to provide
flexibility to the energy system. However, energy storage is a key component
for ensuring flexibility and reliability with large penetrations of wind and
solar energy sources. Pumped hydroelectric systems (PHES), compressed air
energy storage (CAES), and other storage systems will facilitate the align-
ment of renewable generation with loads.
Baseload generation exerts the largest impact on emissions and furnishes
the largest portion of energy to a system. If renewable generation is to impact
electricity-driven emissions and diversity of supply in a significant way, it
must affect baseload generation. When renewable generation comes online
coincident with low demand, it will present a challenge because it may not
be possible to ramp down the baseload thermal generation systems and
require the curtailment of some form of generation. Storage, specifically via
PHES and CAES, can address difficulty in ramping rates and help correlate
generation and loads.
PHES and CAES take energy from the grid and return it at a later time
when it is needed. This raises an important question. What resource is
required to power a PHES or CAES facility? Such a resource is most efficient
if it is located near a site where a PHES facility pumps power or a CAES com-
presses air. Thus, when coal is on the margin, it will power a PHES facility;
wind on the margin will power a PHES facility. The more renewable energy
available, the greater the possibility of having a renewable energy resource
on the margin as the prime mover for a PHES facility. The larger the per-
centage of renewable energy resources, the more flexibility the system will
require. At lower penetrations of renewable resources, less storage is needed
and this increases the possibility that the storage will be powered by non-
renewable energy resources. At higher penetrations of renewable resources,
more storage will be required and this increases the chances that the stor-
age will be powered by renewable resources. Thus, storage is an important
issue for developing renewable energy and will reflect decreased emissions
by the rest of the system. Renewable energies such as wind and solar genera-
tion will benefit from storage as will traditional resources such as coal and
