According to the Energy Information Administration: In 2022, the United States had about 23 GW of total pumped-storage hydroelectric generating capacity in 18 states, and 5 states combined had 61% of that total: California 17%; Virginia 14%; South Carolina 12%; Michigan 9%; and Georgia 8%. Pumped storage systems work by pumping water uphill or up gradient and letting it flow downhill by gravity to provide hydroelectric power when needed. It takes more energy to pump the water up gradient than the hydroelectric power produced so these systems consume more energy than they produce. Thus, pumped storage hydro is not truly a “source” of energy, but a method of energy storage. These systems are typically charged by pumping up gradient during off-peak periods of energy consumption and their energy is typically dispatched during peak periods of energy consumption. In the U.S. pumped storage hydro makes up about 94% of utility-scale energy storage capacity and 99% of all energy storage. Globally, pumped storage hydro (PSH) makes up 94% of all energy storage with the ability to store an estimated 9000 gigawatt hours (GWh) of electricity. This amounts to 158GW of capacity. Thus, the U.S. has about 14.5% of global PSH capacity. There are about 43 PSH facilities in the U.S. that can store 553 GWh of electricity. Global capacity is forecasted to rise to about 240GW by 2030. Both globally and in the U.S. there is an abundance of sites where new PSH can be built if needed. Most of these are in mountainous and hilly areas with significant gradients and topography that allow the construction of upper and lower reservoirs.
Source: Closed-Loop Pumped Storage Hydropower Resource Assessment for the United States: Final Report on HydroWIRES Project D1: Improving Hydropower and PSH Representations in Capacity Expansion Models. May 2022. Closed-Loop Pumped Storage Hydropower Resource Assessment for the United States. Final Report on HydroWIRES Project D1: Improving Hydropower and PSH Representations in Capacity Expansion Models (nrel.gov)
Source: Pumped Storage Tracking Tool. International Hydropower Association. Pumped Storage Tracking Tool: International Hydropower Association
Source: A Review of Technology Innovations for Pumped Storage Hydropower. April 2022. Vladimir Koritarov, Jonghwan Kwon, Quentin Ploussard, Patrick Balducci. HydroWires. U.S. D.O.E. A Review of Technology Innovations for Pumped Storage Hydropower (anl.gov)
The first
pumped storage plant was built in Zurich, Switzerland in 1891 on the Limmat
River. In the U.S. the first PSH plant was built in 1929 in Connecticut. The
two main types of pumped storage hydro are Open-loop: where
either an upper or lower reservoir is continuously connected to a naturally
flowing water source such as a river and Closed-loop: where an
‘off-river’ site produces power from water pumped to an upper reservoir without
a significant natural inflow.
Fixed-Speed PSH, Adjustable-Speed PSH, Ternary PSH,
Quaternary PSH, and Small, Modular PSH
According to the DOE: “Most existing PSH plants in the world use traditional fixed-speed (or single-speed) technology. They employ a synchronous machine as motor-generator, which operates in sync with the grid frequency. This is also the case with most other generating technologies, as they typically employ synchronous machines to generate electricity. While other technologies use synchronous machines only as generators, PSH plants use them as both motors and generators. The synchronous machine is used as a motor when the PSH unit operates in the pumping mode, consuming the electricity from the grid to pump the water into the upper reservoir. The same synchronous machine is used as a generator when the water is released from the upper reservoir, reversing the direction of rotation, to generate electricity for the grid.”
Due to
electricity demand changes, particularly a drop in demand at night, there is often
a need for baseload power plants to keep running at normal output. One way to
do this is to have PSH plants pump water upgradient at night. Adjustable-speed
PSH plants can provide this needed additional nighttime load. Additionally,
adjustable PSH can provide frequency and voltage regulation while in pumping
mode. Adjustable PSH plants have been built in Japan, Europe, and a few other
countries but not yet in the U.S., although some have been proposed. There are more
than 20 in operation globally. They are slightly more expensive to build and
operate than fixed-speed PSH plants.
Ternary technology uses three components: a motor-generator, a separate turbine, and a separate pump, which are designed with “hydraulic short circuit” capabilities when the pump and turbine are operating simultaneously in the same direction. The pump and turbine can be disconnected with a clutch. There are a couple of different configurations. These configurations offer very good operational flexibility, particularly in pumping mode. More flexibility in the full range of pumping mode offers superior frequency and voltage regulation capabilities. However, construction and operating costs are higher.
With quaternary
PSH, in addition to a separate pump and turbine there is a separate motor and
generator. That makes four parts, thus quaternary. This technology employs two
shafts. While CAPEX and OPEX costs are higher yet, the operational flexibility
is optimized in both pumping and generating modes.
Small, modular
PSH is focused on reducing costs by utilizing standardized off-the-shelf
equipment and components which can allow for modular PSH designs that can be
built and deployed quickly. Most proposed designs are small at 10MW or less but
can be banked together into multiple units as sites allow. These are typically
closed-loop designs.
PSH Regulatory and Environmental Challenges
The biggest challenges to new PHS designs are 1) revenue uncertainties; 2) long
and complicated permitting and licensing requirements and times; 3) environmental
issues – these are more common with open-loop PSH. Closed-loop PSH has less
environmental impact and the reservoirs are normally void of fish and aquatic
life. They can repurpose abandoned mines and brownfield sites; and 4)
regulatory issues – like permitting issues, these can be addressed by
redesignations and streamlining timelines.
PSH Ancillary Services
All energy storage provides excellent ancillary services
for the power grid. PSH can provide those services continuously for a longer
period of time. According to the International Hydropower Association (IHA):
“Pumped hydro offers services such as system inertia,
frequency control, voltage regulation, storage and reserve power with rapid
mode changes, and black-start capability. All of these are vital to support the
ever-growing proportion of variable renewables.”
“Pumped hydro excels at long discharge duration and
its high power capacity will be crucial in avoiding curtailment, reducing
transmission congestion, and reducing overall costs and emissions in the power
sector.”
“In addition, pumped hydro enjoys several distinct
advantages over other forms of energy storage due to its long asset life,
low-lifetime cost and independence from raw materials.”
Levelized Cost of Storage (LCOS) is Expected to
Improve for Chemical Batteries but LCOS for PSH Will Always Be Better at
Durations Longer Than 8-12 Hours
The costs of different
kinds of energy storage are compared by a metric known as levelized cost of
storage (LCOS) which is calculated similarly to levelized cost of electricity
(LCOE). According to a 2019 paper in Joule: while PSH has enjoyed a lower
levelized cost of storage in the past, it is expected to stay at a similar LCOS
while lithium-ion and vanadium flow batteries are expected to drop in price
with the LCOS becoming better for those technologies. However, with unexpected
rises in lithium prices due to demand the LCOS reduction process has slowed.
Thus, the paper’s prediction of lithium-ion and vanadium flow storage
overtaking PSH by 2025 may be delayed. Duration of discharge and annual cycle
requirements complicate the comparisons. PSH offers superior long-duration
storage compared to the others. It can support seasonal changes in wind and
especially solar output much more effectively. That gives it a value difficult
to assign in LCOS/LCOE models. It is difficult to assign discount rates to each
tech in economic modeling. Basically, as the 2020 Clean Technica article
points out, comparing storage technologies like lithium-ion, sulfur flow, and
vanadium flow to PSH, is dependent on time, or duration.
The graph shows that at durations of 4 hours or less lithium-ion
has the lowest LCOS but as that duration is increased PSH and sulfur flow get
cheaper and cheaper relative to lithium-ion. The 4-hour duration time is not a
limitation but a breakeven duration time for lithium-ion to
compete with longer-duration storage technologies. The author expects market
forces like economies of scale to eventually increase that breakeven duration
time to ultimately increase to somewhere between 8-12 hours. LCOE of PSH,
however, is considered to be as low as it will ever get. Even with that
limitation, PSH is expected to remain much more economical at durations longer
than 8-12 hours. PSH also has a low levelized lifecycle cost. Compared to PSH,
chemical batteries are much more resource-intensive. Chemical batteries require significant
amounts of minerals. While lithium tech has the highest energy density among
chemical batteries, the cost of lithium is higher than the costs of vanadium or
sulfur. However, due to the lower energy densities of the latter two, more of
those materials are required.
Advantages of Closed-Loop Pumped Storage Hydro
Closed-loop
PSH relies on pumping to and/or from man-made reservoirs rather than existing
surface waters such as rivers or lakes. One advantage to this is that some of
the siting and permitting challenges can be circumvented. This will vary by
project and initial and periodic filling needs.
A January 2021
paper in Joule: Global Atlas of Closed-Loop Pumped Hydro Energy Storage assesses that globally there are “616,000 potential sites identified with
combined storage potential of 23,000 TWh.” The authors used digital
elevation models to identify potential sites where paired reservoirs consisting
of an upper reservoir and a lower reservoir, could be constructed. Typically,
the reservoirs are connected via a tunnel where the pumps pump the water up and
the turbine converts the flowing water to electricity. The potential sites were
ranked according to the capital cost of storage, which is basically the cost to
construct the two reservoirs.
Closed-Loop Pumped Storage Hydro has the Lowest
Emissions Intensity of All Energy Storage Technologies
A new paper in
Environmental Science and Technology: Life Cycle Assessment of Closed-Loop
Pumped Storage Hydropower in the United States, written by Daniel Inman,
Gregory Avery, Rebecca Hanes, Dylan Hettinger, and Garvin Heath, all of NREL’s
Strategic Energy Analysis Center, concludes that closed-loop PSH has the lowest
carbon emissions intensity/lowest global warming potential of all energy
storage technologies. NREL notes that they compared pumped storage hydropower
against four other technologies: compressed-air energy storage (CAES),
utility-scale lithium-ion batteries (LIBs), utility-scale lead-acid (PbAc)
batteries, and vanadium redox flow batteries (VRFBs). They note that PSH and
CAES are designed for long-duration storage, while batteries are designed to be
used for shorter time durations. NREL reports: “In examining pumped storage
hydropower, the researchers modeled their findings based on 39 preliminary
designs from 35 proposed sites in the contiguous United States. The average
closed-loop pump storage hydropower facility was assumed to have a storage
capacity of 835 megawatts and an average estimated 2,060 GWh of stored energy
delivered annually. The base scenario also assumed the electricity mix would
entirely come from renewable technologies.” It should perhaps be pointed
out again that longer-duration storage can store and discharge large amounts of
renewables for a much longer time period and thus, it offers superior seasonal
storage for variable renewables. Another way to say this is that longer-duration energy storage technologies such as PSH offer more energy services
than chemical storage. One might even say that they can provide a kind of
baseload storage service vs. a kind of intermittent storage service provided by
a shorter-duration technology. The base case considers different sources of
emissions including materials (mainly steel and concrete), electricity,
transportation, and fuel.
The paper concludes that closed-loop PSH has a global
warming potential of slightly less than half that of lithium-ion battery tech and
considerably less than half that of vanadium redox flow battery tech,
compressed air storage, and lead acid battery storage.
Innovations in Pumped Storage Hydro
While in
general it is thought that LCOS for PSH won’t get any cheaper there are
potential innovations that could change that conception, especially under
certain situations. The U.S. Dept. of Energy’s HydroWires published a study in
April 2022 that evaluated 12 technology innovations for PSH including the
following:
• Small PSH with reservoirs of corrugated steel and
floating membranes;
• PSH using submersible pump-turbines and
motor-generators;
• Geomechanical PSH;
• Hybrid PSH and wind plant;
• Integrated PSH and desalination plant;
• Underground PSH using tunnel-boring machines for
storage excavation;
• Underground mine PSH;
• Open-pit mine PSH;
• Hybrid modular closed-loop scalable PSH;
• Pressurized vessel PSH;
• Thermal underground PSH; and
• High-density fluid PSH.
The study is focused on innovations that provide construction
cost savings and reduce construction time while acknowledging that these
technologies are at different technology readiness levels (TRLs). The most
promising PSH technologies were found to be submersible pump-turbines and
motor-generators, geomechanical PSH, open-pit mine PSH, and hybrid PSH
technologies. The study also considered adding PSH capabilities to existing
hydroelectric dams and innovative new construction methods, including new
excavation techniques and modular dam construction methods. Using mines for PSH
takes advantage of past mining as
previous excavation.
Source: A Review of Technology Innovations for Pumped Storage Hydropower. April 2022. Vladimir Koritarov, Jonghwan Kwon, Quentin Ploussard, Patrick Balducci. HydroWires. U.S. D.O.E. A Review of Technology Innovations for Pumped Storage Hydropower (anl.gov)
This study is
very interesting and perhaps will be the subject of another post in the future.
References:
Hydropower explained: Where hydropower is generated. Energy
Information Administration. 2023. Where hydropower is generated - U.S.
Energy Information Administration (EIA)
Closed-loop
pumped hydro least likely storage tech to contribute to global warming: NREL.
Kavya Balaraman. Utility Dive. August 22, 2023. Closed-loop pumped hydro least likely
storage tech to contribute to global warming: NREL | Utility Dive
News
Release: NREL Analysis Reveals Benefits of Hydropower for Grid-Scale Energy
Storage. National Renewable Energy Laboratory. August 17, 2023. News Release: NREL Analysis Reveals
Benefits of Hydropower for Grid-Scale Energy Storage | News | NREL
Life
Cycle Assessment of Closed-Loop Pumped Storage Hydropower in the United States.
Timothy R. Simon, Daniel Inman, Rebecca Hanes, Gregory Avery, Dylan Hettinger,
and Garvin Heath.
Environ. Sci. Technol. 2023, 57, 33, 12251–12258. Life Cycle Assessment of Closed-Loop
Pumped Storage Hydropower in the United States | Environmental Science &
Technology (acs.org)
Closed-Loop
Pumped Storage Hydropower Motivations and Considerations. National Hydropower
Association. Closed-Loop Pumped Storage Hydropower
Motivations and Considerations - National Hydropower Association
Lithium-Ion
Energy Storage Cost Vs. Pumped Hydro Or Flow Battery Cost Are Dependent On Time.
Nate Brinkerhoff. Clean Technica. April 25, 2020. Lithium-Ion Energy Storage Cost vs.
Pumped Hydro Or Flow Battery Cost Are Dependent On Time - CleanTechnica
Projecting
the Future Levelized Cost of Electricity Storage Technologies. Oliver Schmidt,
Sylvain Melchior, Adam Hawkes, Iain Staffell. Joule. Volume 3, Issue 1, 16
January 2019, Pages 81-100. Projecting the Future Levelized Cost
of Electricity Storage Technologies - ScienceDirect
Global
Atlas of Closed-Loop Pumped Hydro Energy Storage. Matthew Stocks, Ryan Stocks, Bin Lu,
Cheng Cheng, Andrew Blakers. Joule. Volume 5, Issue 1, 20 January 2021, Pages
270-284. Global Atlas of Closed-Loop Pumped
Hydro Energy Storage - ScienceDirect
Closed-Loop
Pumped Storage Hydropower Resource Assessment for the United States: Final
Report on HydroWIRES Project D1: Improving Hydropower and PSH Representations
in Capacity Expansion Models. May 2022. Closed-Loop Pumped Storage Hydropower
Resource Assessment for the United States. Final Report on HydroWIRES Project
D1: Improving Hydropower and PSH Representations in Capacity Expansion Models
(nrel.gov)
A
Review of Technology Innovations for Pumped Storage Hydropower. April 2022. Vladimir
Koritarov, Jonghwan Kwon, Quentin Ploussard, Patrick Balducci. HydroWires. U.S.
D.O.E. A Review of Technology Innovations
for Pumped Storage Hydropower (anl.gov)
Pumped
hydro: Water batteries for solar and wind power. International Hydropower
Association. Pumped storage hydropower
Pumped
Storage Tracking Tool. International Hydropower Association. Pumped Storage Tracking Tool:
International Hydropower Association
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