- [Instructor] So in this lesson,
we're going to have a look at a special type of hydropower plant known as a pumped storage power plant. We've already looked at how various types of hydropower plant work, and this type is not much different from some of the others we've seen. However, it's got quite a
unique operating characteristic, which I'm gonna discuss
with you in a moment. So we can see we've got our water inlet, and that is on the opposite
side of this reservoir wall. Spin around so we can actually go down and have a look at the inlet. There's the inlet. We can see we've also got a gate, so we can close off the
water inlet to the penstock. We've then got our
penstock which comes down, comes all the way down the hill, and it's actually quite
a large head of pressure, or a large head, to have with
this type of power plant. Now, having a large to medium head is a characteristic of a
pumped storage power plant. What's unusual here is that
the penstock is split into two and feeds two separate turbines. Remember, you don't normally see that on power plants where you
have a medium to large head. Normally, one penstock
will supply one turbine. Now, I'm gonna go and have a look at the turbines and
generators from the outside, because I did actually
try and look earlier from inside, and it's quite cramped. We can see that we've
got a turbine runner, which is housed within this casing, and the water itself
comes from the penstock, you can see it coming in here. It's fed to the turbine runner, and then it's discharged
and it will go out through the draft tube and into the river. See if we can find the draft tube, and this is it here, and
on the opposite side, we also have another draft tube. So this is very similar, in a way, to some of the other hydroplants
that we've looked at, it's just that the head is much larger. If we've got a larger
head, then that means we can have either a Pelton type turbine or a Francis type turbine. We're not going to have
a Kaplan type turbine, because the head is simply too large. Pumped storage power plants, though, only utilize a Francis type turbine. They do not use Pelton
type turbines or Kaplan, and there's a very simple reason for this. Francis type turbines can be used to pump water back up the mountain. That means we can generate electricity when water flows down the mountain, and then we can pump
the water back up again to the upper reservoir, in order to refill the upper reservoir. But why would we do this? Why would we pump water back up and then let water back down again later? Well, a pumped storage hydropower plant is very similar to a battery,
except we're not storing chemical energy, we're actually storing the potential energy of the
water at a higher elevation. Let's imagine, for a moment, that it's a very sunny, windy day, and that means that we're generatin' a lot of electricity from
wind turbines and solar power. This also means that electricity is cheap, it's in abundance. So imagine we're paying
one cent per kilowatt hour, just to keep things simple. Now, it might be that the people operating this pumped storage
plant think that one cent per kilowatt hour is very cheap, and they'll buy the electricity in order that they can
power the Francis turbines and pump the water from
the lower reservoir, in this case a river, up
to the upper reservoir. And they'll do this all day, because it's been sunny all day, and there's also been a lot of wind, so we've got a lot of cheap electricity. When the upper reservoir is full, and this may take eight to 10 hours, maybe more, maybe less, we'll hold on to all of this stored potential energy. And what we'll do, we'll
wait until it's dark, and all of a sudden, all of
that abundant electrical supply that was provided by the
sun from solar power, and maybe the wind dies down as well. All of that abundant electrical
power will disappear. It will no longer be available
in the national grid. Now, because we have a free market, whenever we have something in abundance, it's not very valuable. Whenever something becomes
scarce, its value increases. And it's the same with electricity. So there's no longer an
abundance of electricity in the national grid, and it
may be that the grid operator is willing to pay two or
three cents per kilowatt hour that we sell to the grid. So if we open the valves and
the gates and everything else, and we allow the water to flow
down to our turbine runner, we can then begin to generate electricity. And because we've pumped so much water into the upper reservoir,
we may be able to do this for several hours or longer. As the water flows down and
we generate electricity, we're making money,
we're making a difference between what it cost to pump
the water up the mountain, which was one cent per kilowatt hour, and the price that we're getting now, which may be two or three
cents per kilowatt hour. In the past, the actual operation of the pumped storage plant
would be very regular. Because coal fired power stations and other thermal plants often
stay online day and night and do not cycle on and off
because they're not capable of that, especially not on a daily basis, there was an abundance of
power available at night, and these pumped storage
plants would come online at night time, and they would use some of this abundant electrical power to pump water up to the upper reservoir. And that was how things
stayed for about 30 years. In the morning, when
people started waking up and the electrical demand was very high, we would use pumped storage plants to deal with these peaks in
electrical power consumption. Remember, pumped storage
plants can come online very very quickly, typically
in less than a minute. So any large peaks that
we have in our grid, we can cover those using
pumped storage power plants. Now, this setup continued
for about 30 years. And then, we started getting
renewable energy sources becoming more and more onto the market. And I'm talking here mostly about wind turbines and solar power generation. Typically, PVs, or photovoltaics. When renewables came online,
the whole industry changed. The reason the industry
changed is because suddenly, there was an influx of power
available during the day. If we had a very sunny day, then there would be a
lot of power generated by all of these solar panels. If it was very windy,
there'd be a lot of power generated by all of these wind turbines. And all of a sudden,
instead of having to wait until night when the power demand dropped and pumped storage plants could actually purchase electricity at a better price, they were able to purchase
electricity at a cheaper price during the day time and at night, so the dynamic in the power
industry slightly changed. So at the moment, it's a very good time to own a pumped storage power plant. There's a lot more opportunity to make a profit than there
used to be in the past. I'm actually a big fan of
this type of power plant. They give the grid
operator good flexibility concerning frequency regulation
and voltage regulation of the grid, and they have a
high level of dispatchability. Remember, we can have
the entire plant online in less than a minute,
and that is very very fast compared to a coal-fired power station, which may take a day or two
days to come fully online. So a very unique and interesting
type of hydropower plant. Perhaps one of the most
interesting aspects of this type of power plant is
that we can store the energy. Remember, we can have an upper reservoir like the one we're looking at now, and we can store all of
that potential energy and turn it into electrical
energy on demand. That is a very unique feature
for this type of plant, and it's a very unique feature in the power plant industry, generally. The only problem with this type of plant is that you need very
unique geological features in order to have this type of plant. We need a difference in
elevation that is quite large, and you can see that
here, because the penstock is running all the way up
the side of the mountain. Sometimes, you'll actually
see these types of plants where the powerhouse
will actually be built into the mountain, that's not unusual. And the penstocks themselves will also be built into the mountain. So there'll be very
little of the power plant that you can actually see,
other than the upper reservoir at the top and the open air switchyard, which will be down at the bottom. Because you need an abundance of water and you also need these
geological features that allow you to bring the body of water from the upper reservoir
to the lower reservoir, with quite a large head between the upper and lower reservoir, you're very restricted on where you can actually have
these types of plant. Somewhere like Norway is ideal, because there they have very rocky and rugged terrain with a lot of water. A place like Switzerland is also ideal, they have hard rock,
they have deep valleys, they have a lot of
opportunity to capture water at higher elevation, and then to allow it to run down to a river and
pump it up and down on demand. Somewhere like the middle
of Germany is less ideal. The change in elevation per
square mile is rather low. You're more likely to get hills or plains than you are likely to
get these large mountains with sudden drops in elevation. Most of Europe has already exploited its pumped storage
capacity, and it's becoming more and more difficult to
build this type of plant for the same reasons as
with other types of plants. There are environmental
factors to consider. If you wanna build a pumped
storage hydroelectric plant in Central Europe, you're
gonna find it quite difficult, 'cause often these plants will
be located in remote areas. Sometimes, they may even be located in areas that are protected. Building an upper reservoir
like the one we're seeing now, is very very difficult to
get planning permission for. There are a lot of environmental agencies that will be against building
this type of installation within a wildlife area, especially
if the area is protected. Not only that, there are other factors that you need to consider. We go down to the bottom of
this 3-D model and spin around. You can see here, we've got things like electrical transformers,
open air switchyards, and generators and turbines. These items and machinery
require maintenance, which means you need to build
a road out to the plant. Again, this may be difficult
to get permission for. All of the machinery
associated with this plant may also need to be
environmentally friendly. What I mean here is that
the electrical transformer is often full of oil. This is an insulator,
and it's a requirement for very large transformers. Now, it's possible to
get biodegradable oils and fill the transformer up with these, but they are incredibly expensive. This is another factor
that you have to factor in when you're wanting to build
one of these power stations. Is the power station going to be within an environmentally protected area, and if it is, what does that
mean for all of the equipment and machinery that is gonna
be operating in this area? If, for example, we were
using oils and greases to seal the turbine runner space between the runner and the generator, what happens if some
of this oil and grease leaks into the water here, and
then starts going downstream? Again, you need to have biodegradable, environmentally friendly oil and greases. These also cost more money. So there are little things
that need to be taken into account with every
type of hydropower plant. There are always good large advantages, and there are always some disadvantages. But as I say, a very unique type of plant, one of the very few
that allows us to store and release energy on demand, but also one that requires very unique
geological features in order that it can be put into service. If you like this video, and would like to see more
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