vgbe energy journal 10 (2022) - International Journal for Generation and Storage of Electricity and Heat

New storage technologies in the energy market
––
Storage peak capacity in [MWh]:
Maximum amount of energy that can be
stored in the energy storage
––
Peak power output in [MW]:
Maximum discharge load to the grid
––
Peak power consumption while charging
in MW:
Maximum energy charging load from the
grid
––
Mean time to deliver Primary or Secondary
Frequency Control (load response
time):
Some types of energy storage offer “instant”
energy, some others require a startup
time, e.g. conventional power plants
must start and synchronize the turbine
before load can be delivered, while hydro
power storages open the gates and the energy
is almost instant, given the generators
are already synchronized at that time.
––
Charge/discharge cycles (n) / wear and
tear / ageing:
––
Several types of storage age over charging
cycles or time. This can be seen as degradation
of batteries or wear and tear in
thermal storage.
––
Requirement to fully charge/discharge after
n cycles:
We should avoid to fully charge/discharge
electro-chemical batteries, while some
types of thermal storage require full
charging/discharging on a regular basis
to recover the full capacity.
––
Changeover time from charging discharging
and from discharging charging:
––
E.g., Thermal storage requires switchover
times, since usually several dampers
and valves must be opened or closed.
Steam processes require a complete startup
process before the turbine can be synchronized.
With good control concepts
those changeover times can be reduced
or even eliminated, in case there can be
an overlap between charging and discharging.
Effectively this means that we
manipulate the working point of one
mode.
The same applies to mechanical storage
technologies like compressed air energy
storage (CAES), liquified air energy storage
(LAES) or pumped hydro storage.
Specific parameters for batteries or capacitors:
––
C-Rate as relation of power [MW] to storage
capacity [MWh]
Environment:
––
Environmental, Social, Government
(ESG) impacts (resources/mining/energy):
Which materials are required? Where and
with which labor conditions are they
mined? Are the components environmentally
friendly? Can they be recycled? How
much energy is required to produce those
energy storages? And where (which technology)
does it come from?
––
nominal efficiency η: MWh out / MW hin
The nominal efficiency varies vastly over
the different kind of energy storages.
Thermal storage with a steam cycle is limited
as described by the Carnot process,
but also chemical storage has thermal
losses, electrolyzers produce heat, converting
H 2 to Ammonia or Methane also
produces heat, mechanic storage produces
frictional losses, etc. All sums up to the
nominal efficiency.
––
Storage loss: Energy Loss over time:
––
Energy storage may have losses over time.
Losses can occur due to radiation, chemical
reactions, thermal losses, mechanical
losses, leakages, etc.
––
Energy density (MWh/m³ or MWh/m² or
MWh/kg):
––
Where shall the energy storage be erected?
How much real estate is available?
How much volume can be used? Are there
weight limitations?
Financial:
––
Heat and/or electrical storage:
Which revenue stream shall be served?
E.g. thermal storage can be used for thermal
use only or combined with cycle processes
for electricity and/or district chilling
(with combination of absorption chillers).
Is the target primary frequency
control or is a seasonal storage required?
(See next chapter)
––
Scalability:
Can the energy storage be (easily) extended
in regards of load and/or capacity?
––
Capital Expenditures (CAPEX):
Cost to build the storage
––
Operational Expenditures (OPEX):
Cost to operate and maintain the storage.
––
Levelized costs of storage (LCOS):
Combination of CAPEX, OPEX charging
and discharging price
––
Cycle Efficiency as combination of nominal
efficiency and storage loss over time as
mentioned under “Environment”
Other considerations
Energy Storage needs to serve a certain purpose,
so the previously mentioned categories
can be used to find the right product. In
many cases, not a single storage solution fits
all and often a combination of different
measures leads to the most suitable solution.
For example, load control means not
only producing load but also consuming
load in a controlled manner, therefore, load
consumption also can contribute to the load
control. Keeping the control devices in control
range can be achieved by shifting load
setpoints between the contributors in the
grid, e.g., charging batteries to induce consumption
to the grid so that a steam turbine
can leave minimum load. Also there is a high
potential due to sector coupling, or a thermal/mechanical
coupling, where thermal
storage is combined with CCPPs for a hybrid
operation to reduce CAPEX/OPEX. Battery
driven electric vehicles could be used as
short-term storages. Since a number of conventional
power plants will be shutdown (or
even just temporarily), converting such
power plants to add revenue even when
not in power generation mode may be a relevant
option. Concepts for such conversion
may be including thermal storage into an
existing steam cycle, converting power
trains to (hybrid) synchronous condenser
units with or without adding a flywheel
(mechanical storage to provide inertia to
the grid), adding battery energy storage systems
and / or super capacitors for more flexibility
electrically. Siemens Energy provides
solutions for all of those concepts, assists
in finding the optimum energy system
design for a specific site and integrates
the respective solution. Since energy storage
sites are most likely unmanned, integration
to the grid / remote connection and cyber
security become an issue. Eventually,
when scaling this down, it also leads to including
smart home devices / intelligent
prosumers (producer and consumer). More
households install energy storages and electric
mobility is on the rise. Therefore, the
charging / discharging eventually must be
integrated into the grid control strategy. In
virtual power plants, new financial models
may also become valid including blockchain
based payments, certificate trading and
more.
The extensive topics of microgrids, virtual
power plants, ... will be discussed in a separate
article.
Summary and result
In this article we discussed different types of
energy storage that are currently seen on the
market with their properties, advantages,
and disadvantages. However, this comparison
will never be complete: new technologies
are evolving, and existing technologies
are improving but also requirements change
over time. The storage market is democratizing
as more private households install battery
storage, more industries discover the
benefits of peak load shaving, conventional
power plants extend the primary and secondary
frequency support with storage, and
much more.
Investors must focus on their own use cases,
and some external use cases could extend
the business models even further. As
one example, the optimization targets
change, when the plant operators not only
optimize their local plant operation but
also look at energy trading on the spot market.
Most battery storage systems in small
to middle sized companies or private households
(=prosumers) start charging, when
the solar energy production exceeds the
house load and they start discharging, when
the house load exceeds the solar energy production.
But it would make more sense, if
the solar panels on the roof (and the battery,
too, if it is not empty) support the grid in the
32 | vgbe energy journal 10 · 2022