It seems the whole world's energy systems are in a bit of a
mess right now. Fossil fuel prices are very high, there are
some maintenance and reliability problems with generators too
with unexpected maintenance of, for example, nuclear power in
France and coal power in Australia. Plus throw in a few
extreme weather events, exacerbating the already big
problems most grids are facing and the world is looking for
solutions. One type of generation that has been having
fewer issues than the others is renewables. The price of the
wind blowing and sun shining remains free. And we do see a
lot of electricity grids with high proportions of renewable
energy are being shielded from the worst of these price
extremes. So this is a nice tailwind for the clean energy
transition for once. Economics and energy security both seem to
favor a fast transition to renewables. But as we all know,
the sun sets every night, some days are cloudy, and some days
and nights are not windy. If we're going to move away from
relying on volatile fossil fuels to fill in the gaps in renewable
electricity generation, we are going to want a way to store
electricity so we can smooth the difference in what we generate
on sunny and windy days with what's available on cloudy
windless days and weeks. That's why electricity storage is such
a hot topic these days. There seems to be no end to the
variety of new and old technologies being developed.
Using sand, concrete blocks, radioactive diamonds, and of
course the big one, lithium ion batteries. But over 90% of
current electricity storage is from a much less trendy storage
technology, pumped hydro, which is an energy storage solution
that's been around for over 100 years. And that's the topic of
today's video, I'm going to talk about how pumped hydro works,
its advantages and disadvantages, plus solutions to
some of its main issues and examples of existing and future
projects.
I'm Rosie Barnes, welcome to Engineering with Rosie. There
are currently about 10 terawatt hours of electricity storage in
the world, which sounds like a lot. But it's actually only
something like half an hour of storage based on global average
electricity usage. And estimates of the total amount of
electricity storage that we're going to need for a fully
renewable global electricity system range up to 10,000
terawatt hours. My opinion is we'll end up meeting a lot less
than that, because I think these estimates tend to underplay or
the other changes we're going to make, besides just trying to
make our new renewable grid look a lot like our old fossil fuel
one. So that would include things like flexible loads, aka
demand response and thermal energy storage, especially for
seasonal heating requirements. But anyway, I'm getting way off
track. Even with all that we're going to need a lot more
electricity storage in the future than what we have now.
And when most people think of electricity storage, I think
that they're thinking of lithium ion batteries. And if we go with
that high estimate of global energy storage needs, 990,000
terawatt hours is a lot of batteries to add, probably an
implausibly large amount. In fact, it's more than 300,000
times the world's current total. So lucky we've got pumped hydro
to help. So what is pumped hydro and how can we store electricity
in this way, you're probably already familiar with normal
hydro electricity, which is a way of converting the
gravitational potential energy of water into electrical energy.
This happens when water from a higher elevation is allowed to
flow down to a lower elevation, the falling water turns a
turbine which generates electricity. Traditionally, this
was done by either putting a turbine in a river and getting
electricity whenever the rivers flowing or by damming a river at
high elevation and then allowing water to flow through a turbine
located at lower elevation whenever you want electricity.
Pumped hydro simply takes a regular hydro system's
reservoirs, pipes and turbines and adds a pumping capability to
reverse the process. So you allow water to fall through the
turbine when you want to generate electricity. And when
you want to store it, you can power a pump and get the water
back up to the top. To calculate the amount of energy available
in the dam we use the equation for gravitational potential
energy. Mass times gravity times height, this will give the total
energy in joules which you can convert to megawatt hours or
gigawatt hours, or terawatt hours. For more familiar units
used in electricity supply and calculate the power needed to
divide energy by time. It's the same equation as in any kind of
gravity based energy storage system. And I covered a bunch of
the non-hydro types of gravity energy storage in a livestream a
little while ago. These all involve hauling heavy blocks up
to a height to store potential energy. So you can check that
out at this link. To increase the amount of energy stored, you
can either increase the height which for hydro is known as the
head, or you can increase the mass which for hydro is the
volume of water stored times its density. Generally water is
free, so the cost of additional energy storage is simply the
cost of making the dam wall a little bit higher. This is a
cheaper way to add energy than by say adding more concrete
blocks to a non-hydro gravity energy storage system. Or in the
case with a battery you need to add more cells in parallel. And
to increase the power of a hydro system. You can either add more
pipes and turbines or increase the size of the pipes and
hydro system is expensive and adding energy is cheap. This is
kind of the opposite of a lithium ion battery. So if we
just consider for now these two technologies, lithium ion
batteries suit high power, short duration storage needs, and
pumped hydro suits long duration storage needs. Currently, most
electricity grids are still getting their long duration
storage needs met by coal or gas. Fossil fuels, of course can
just sit there until you want to burn them. But as electricity
grids get more wind and solar power in them and less fossil
fuels, we're going to need longer durations of energy
storage than what lithium ion batteries can economically
provide. I mentioned at the start that hydro is already the
main source of energy storage around the world. But in terms
of recently added storage, lithium ion batteries are way
ahead. And a lot of people assume that we won't be adding
much new pumped hydro capacity in the future. And there are
some very good reasons for this. There are quite a few problems
with traditional pumped hydro that make it hard to expand
capacity much beyond what we have now. Problem number one is
financial. And this topic is slightly confusing because if
you look at cost estimates for batteries and pumped hydro,
you'll find that pumped hydro often comes out the cheaper
option. But reducing the cost of electricity storage to a single
number really misses a lot of important detail that matters
when you're trying to choose which storage technology you
need for a specific purpose. One aspect that's easily missed is
that the upfront cost of pumped hydro projects are usually huge.
And payback occurs over the extremely long lifetime of a
pumped hydro project. Dams just last for a really long time. So
when you calculate the cost of energy storage, you've got a
really big denominator and you end up with a cheap cost of
storage per megawatt hour or kilowatt hour, whatever, but you
still need to find those initial millions or billions of dollars.
And most private companies or even government these days, when
they're putting together a business case, they're not keen
to wait decades for a return on their investment. Usually you'd
want to see an investment payback period of more like five
years rather than 50. That's probably why the majority of
existing pumped hydro projects are government owned. The second
big issue is construction duration. Batteries can be put
on trucks and installed really quickly. Probably the most
famous example of this was the Tesla big battery installed at
Hornsdale Power Reserve in South Australia in 2017, which at that
time was the world's largest lithium ion battery. Elon Musk
had promised in a tweet, naturally, that Tesla will get
the system installed and working 100 days from contract signature
or it's free. And in fact, it was eventually commissioned 63
days after contracts were signed. And that was about nine
months after the tweet bet between Musk and Australian
entrepreneur Mike Cannon-Brookes. Pumped hydro
projects take longer. To use another Australian example we're
currently building new pumped hydro capacity by connecting to
existing dams in our Snowy Hydro scheme. No new dams needed to be
constructed just a big tunnel and hopefully eventually
there'll be some transmission to connect to the grid. And this
project is currently expected to take 10 years to complete and
this date has pushed out a little recently. The project
will take about 100 times as long to complete as the
Hornsdale battery though it will provide nearly 2000 times as
much energy storage. In fact, it will be more energy storage than
all of the utility scale of lithium ion batteries that
currently exist in the whole world. The third challenge of
pumped hydro is finding suitable locations, you need somewhere
with a good elevation difference between potential reservoirs and
if you're building new dams, you need to be okay with flooding
the valley and the risk of flooding anything downriver if
the dam ever fails. This is probably the main sticking point
for most people regarding pumped hydro. I enjoy skiing and
mountain biking in my free time and I have been lucky enough to
do those things in a lot of beautiful mountains around the
world. I have personally never come across an Alpine valley
that I thought would look better flooded. Although I will admit
that the artificial lakes created do tend to be lovely
once they're there. And another issue is that hydro projects
often involve flooding valleys that people had been living an
farming in, whose homes and farms are now covered by dam
water. I'm an energy transition engineer and I'm okay with the
idea of sometimes compromising local amenity for global
solutions. However, this is a huge problem for new hydro
projects. I think it's very hard to get community acceptance for
any big new projects that involve flooding a valley to
make a new dam and without community acceptance, it's very
hard to get anything big done. So those are in my opinion, the
three main big challenges with new pumped hydro projects,
upfront cost, construction timeframe and difficulty finding
appropriate sites. But those are all problems with traditional
hydro. And there are new ways of making a pumped hydro project
that mitigate all of those problems. These new ways are
off-river and modular pumped hydro. Off-river pumped hydro,
sometimes referred to as closed-loop, is not yet common
though the technology components are all very mature. It just
uses reservoirs, tunnels and pump houses similar to what
we've been using for over 100 years of traditional pumped
hydro. There are a few existing major off river pumped hydro
installations including Presenzano, Italy and
Tianhuangping, China. Usually the reservoirs are constructed
from scratch rather than building a dam and flooding a
valley so it might be in a turkey-nest dam perhaps using a
modular system to decrease cost and speed construction time or
if you've got a gulley at a suitable elevation you can add
an earth wall to hold water. And then there are a few proposals
I've heard to use pits left over after mining has been completed
in an area. There are a lot of advantages to the idea of
off-river pumped hydro. In many cases, the head can be two to
five times larger than traditional on-river systems
because the upper reservoir can be on top of a hill rather than
in a river valley. This is attractive because double the
head equals double the energy stored by the increase in cost
is a lot less than double. Off-river also means that
minimal flood control measures are needed because the
reservoirs can be deliberately placed away from water courses
that have enough catchment to cause serious flooding. And the
big one, there can be greatly reduced environmental impact, as
it usually doesn't disturb river flows and biodiversity. So all
of these factors can help to reduce cost and construction
times.
That's two of the three issues with traditional pumped hydro
addressed. What about the third, difficulty to find appropriate
sites for new pumped hydro. That is also much less of a problem
for off-river pumped hydro than traditional, you no longer need
to find rivers in steep terrain that you don't mind flooding,
you just need to look for places where there is a decent amount
of elevation gain over a fairly short distance. A good rule of
thumb is that you need at least 100 meters of head to have a
chance that the system can be cost effective. And as I
mentioned earlier, since you're not confined to rivers and
valleys, you can put the top reservoir on a hill, plenty of
100 meter high hills around. You might still be skeptical that
there are many suitable sites around the world where energy
storage is needed. When I'm working on energy storage
projects, I regularly hear from people that pumped hydro isn't
suitable in their region. The latest one was a comment just
actually today on LinkedIn from someone in the UK, saying they
expected to need hydrogen for long duration storage as they
weren't good sites or pumped hydro there. But it turns out
that good potential sites are more common than you might
think. Andrew Blakers' research group at the Australian National
University have used geographic information systems analysis to
automatically identify suitable sites around the world. They
screenned global GIS data to look for sites with possible
reservoir pairs with a large elevation difference and small
amounts of earthworks required to build the reservoirs and
short tunnel lengths to connect them. Based on this, they found
over 600,000 potentially feasible sites with a total
storage potential of over 20 million gigawatt hours.
According to their estimate of needed energy storage to support
a 100% global renewable energy system, that's about 100 times
more than the amount needed. Now this is just a preliminary
screening. They have attempted to avoid urban areas and
environmental protection areas, but they haven't assessed who
landholders are and whether they actually you know, want to use
that land for pumped hydro. And there will be other issues with
some of the sites as well. Still, because there are more
than 100 times that needed number of sites identified. That
means we could choose the most appealing 1% of sites and have
enough storage to support the whole global renewable energy
system and the geographic distribution of the sites is not
too bad either. Most regions where people live have pretty
good proximity to good potential pumped hydro sites. And if we
look at the example of the UK that we were talking about
earlier, you can see there are quite a few good sites there.
When you look at the map you can see a few bare spots though. And
when you correct for population, you'll see that Western and
Northern Europe followed by Western Africa have relatively
small amounts of energy storage potential per million people,
there's still more potential in those places than the about 20
gigawatt hours of storage energy and one gigawatt of storage
power per million people that Blakers' group has estimated
we'll need for a 100% renewable grid, but I would expect it's
likely that these regions will want to connect their
electricity grids to locations with more favorable pumped hydro
potential. And of course, many of these interconnections
already exist. So that's all the main issues with traditional
hydro addressed. Why then are we talking so much about lithium
ion batteries and not so much about pumped hydro. This is
because of the stage we're currently at in the energy
transition. With low amounts of variable renewable electricity
in the grid. There are still a lot of fossil fuels available to
fill in the long gaps in wind and solar generation. And so we
currently only need to fill short gaps and we heard at the
start that lithium ion batteries are currently the cheapest way
to do this. But as we move to more variable renewables in our
grids will need to add longer duration storage. So are we
starting to see this already?
The answer to that question is yes. Whilst we haven't seen a
lot of off river pumped hydro completed in recent years, there
are a lot of projects underway now. China are planning to
complete the world's largest pumped hydro energy storage
facility in 2025. Fengnin pumped storage power station and closer
to my home in Australia, construction is underway on the
two gigawatt 350 gigawatt hour Snowy Hydro 2.0 project though
that one doesn't fit all that neatly in the category of
off-river pumped hydro since it will connect two existing
reservoirs that are part of the original Snowy Hydro scheme that
has supplied all of mainland Australia's hydro electricity
since 1974. These reservoirs are on rivers that were dammed way
back then and it's in a national park. So the project doesn't
have all the environmental benefits that I talked about for
off-river projects. I personally feel a little conflicted about
that particular one as it does cause some environmental damage
to a location that's especially close to my heart. I may do a
video on just that project because I think it's a
Interesting want to talk about local versus global
environmental trade offs. So those are huge government funded
projects. But a lot of the potential for off river pumped
hydro will be in projects small and simple enough that non
government developers can take them on and there are a number
of projects like that in development, some of them are
advanced include K2 Hydro in Kidston, Far North Queensland,
it's a 250 megawatt two gigawatt hour project, which just started
construction in May 2021. With completion expected in 2024, and
Lewis Ridge is an off-river pumped hydro project currently
under development in Kentucky, USA that recently received its
permit in January 2022. It's located on a former coal strip
mine and will be 200 megawatts, 1.6 gigawatt hours. Its cost is
currently estimated at $1 billion, with a three to five
year construction timeframe. So pumped hydro is not the obsolete
technology that a lot of people assume it to be. For long
duration storage, and especially for really long duration
storage, it's hard to beat in terms of costs, and the main
disadvantages are pumped hydro can be avoided when you take it
off-river. I think we'll see a lot more of pumped hydro in the
coming years. So watch this space. One of the cool things
about gravity energy storage of any kind is that the physics
behind it is so basic. That's great because it's easy to check
for yourself the claims of any new gravity storage technology
or projects you just need to understand this basic physics
principle. If you've never studied physics in high school
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thanks to you for watching. I'll see you in the next one!