POWER May 2020 - 41

RENEWABLE ENERGY
posed renewable energy installation. The
results of the modeling will change for
storage technologies that have different
performance characteristics.
Figure 1 shows the increase in required
solar energy generation and storage
as the RPS increases from 25% to
100%, assuming a typical solar profile
under ideal weather conditions with Li-ion
battery storage technology deployed. Not
only does the size of the required renewable
solar generation increase, but also
the necessary storage increases significantly.
The size of both the required solar
generation and storage will increase even
more when weather conditions are taken
into account, as will be shown.
The equipment sizes of a typical wind
generator with 25 mph wind and Li-ion
battery storage necessary to achieve various
RPSs are shown in Figure 2. Again,
not only does the size of the renewable
wind generation increase, but the necessary
storage also increases significantly
as the RPS ratchets up. Considering
less-than-ideal wind conditions will also
increase the required size of the wind
generation and storage facilities.
The Impact of Weather
As requirements for the use of renewable
energy such as solar and wind increase,
the power industry will become
increasingly dependent on the weather.
Historically,
utilities' weather concerns
were mainly limited to the grid's ability
to supply adequate power during summer
heat waves and winter cold spells,
and the effect winds have on power lines
during snow/ice storms, hurricanes, and
other weather-related events. Now, the
industry will have to consider the impact
of the frequency of cloudy and partially
cloudy days, as well as long-term wind
patterns and diminished wind events.
Figure 3 shows the impact of wind
speed on the necessary size for a wind
farm with a Li-ion storage facility. The
impact of generated wind power changing
by the cube of wind speed is clearly
seen in the 20-mph scenario. The impact
of cloudiness on the necessary size of
a solar farm and Li-ion storage facility is
shown in Figure 4. It can be clearly seen
that a renewable energy generation and
storage facility will have to be sized taking
into account the anticipated weather
conditions over the course of a year. The
power industry will be faced with studying
and understanding historic and anticipated
wind and cloudiness patterns at the
location in which the facility will operate.
The Impact of Energy Storage
Technologies
The power industry is not limited to
current storage technologies because
the incorporation of renewable energy
generation and storage is a long-term
game. Many RPSs increase over time,
and there is considerable energy storage
research and development currently
in progress. Utilities are faced with determining
which of these technologies
has the greatest economic and reliability
potential. Short-term decisions can be
made considering currently proven storage
technologies, but more economic
and reliable technologies can be part of
long-term plans. Of course, all storage
technologies ultimately utilized must be
demonstrated and proven reliable before
utilities can fully trust them.
There are various types of storage
technologies being considered for renewable
energy
storage
installations
including
gravity (pumped hydro, and
physical raising and lowering of blocks),
batteries (Li-ion and flow batteries),
chemical (electrolytic produced hydrogen),
thermal (molten salt, regenerative
stove, and phase change), and mechanical
(compressed air energy storage and
flywheel), among others. There are only
three storage technologies currently
thought to be proven and demonstrated
as reliable for incorporation into an electric
grid employing solar panels and wind
turbines. Although there may be differences
in criteria for proven and reliable,
the three are Li-ion batteries, gravity
pumped hydro, and flywheels.
However, each of these storage
2. This chart shows the required wind and
storage capacity needed to accommodate
four different RPS scenarios when constant
25-mph winds are modeled for a grid with a
maximum daily load of 200 MW. Source: The
Ledgemont Group
May 2020 | POWER
technologies has issues. For example,
pumped-hydro storage requires land for
reservoirs, which even if benign geology
is available, often faces governmental and
public approval challenges. Li-ion batteries
face heat removal challenges in large
facilities, and the economic impact of replacement
and disposal costs as perforwww.powermag.com
3.
This chart shows the calculated wind and
storage capacity required to accommodate
a 25% RPS under three different maximum
daily wind speed scenarios for a grid with a
maximum daily load of 200 MW. Source: The
Ledgemont Group
4. This chart shows the required solar and
storage capacity needed to accommodate
three different cloud cover scenarios under a
25% RPS for a grid with a maximum daily load
of 200 MW. Source: The Ledgemont Group
mance decreases over the life of facilities.
Flywheels are quite costly, and additional
hurdles exist for other technologies.
There are inherent technical risks the
power industry must consider as it investigates
the various storage technologies.
As with sizing, this can be quite
complex. Utility industry executives
should ask storage technology developers
whether the inherent technical and
scale-up risks have been addressed and
mitigated to the fullest extent possible
and what the economic consequences
could be, if expectations are not met.
The power industry may not possess the
in-house mechanical, chemical, thermal
and hydrologic expertise to evaluate the
wide range of storage technologies.
It is not possible to predict what storage
technologies will ultimately be the
economic and reliable technologies of
the future. At this time, the developing
technologies closest to commercialization
appear to be vanadium flow batteries,
and the physical lifting and lowering
of blocks. Other battery technologies are
at earlier stages of development.
The heating of molten salt directly with
electricity has not been adequately demonstrated
for use in conjunction with solar
panel and wind generated electricity,
even though molten salt has been used
for collection and storage in parabolic solar
tower plants. However, one such facility,
a government-funded 110-MW molten
41
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POWER May 2020

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