To me, it's the most important technology humans need to develop in our battle against

climate change. Solar and wind technologies have reached maturity and are capable of providing

more than enough energy for all of humankind for a fraction of the cost of older fossil

fuel power, and before I hear the same old argument in the comments, no they aren't

cheaper because of subsidies. In 2017 the fossil fuel industry received

subsidies totalling 447 billion dollars worldwide, dwarving the 128 billion renewables received.[1]

Despite renewables providing a larger share of new capacity installations in 2017 at around

75% of total new electricity generation capacity. [2] Renewables are cheaper, cleaner and sustainable.

That's why countries are investing in renewables, that's the point of subsidies, it's government

funding for economy sustaining infrastructure. The faster we can transition the better. Countries

will become less reliant on constant imports of fossil fuels from war ravaged regions,

will create new jobs in the renewable industry, and because we are looking down the barrel

of a climate crisis that is going to send the world into chaos if we don't address it

now. The primary factor holding renewables back today is this energy storage problem.

Lithium ion batteries and other novel battery technologies are rapidly becoming the forerunners

to form the brunt of our energy storage needs, while hydrogen looks poised to seize long

duration energy storage applications. However, in all of this analysis, we have glossed over

the oldest and most dominant form of energy storage. A simple method of energy storage

that converts electricity to potential energy by pumping water to an elevated reservoir,

where it can later be released to drive an impeller turbine when the electricity is needed.

Pumped hydro is one of the oldest technologies still in use in our modern day electricity

grid. It's a rugged, long-lived and mature technology that provides an incredibly valuable

service to grids across the world for more than a century. There have been calls around

the world to increase our energy storage capacity in this tried and tested technology. However,

as we will find out, it's not quite as simple as investing in the infrastructure.

To learn more about this essential technology, I visited Turlough Hill, Ireland's first

and only pumped hydro station. Construction began on this landmark infrastructure project

in 1968 and after 6 years of laborious excavation the final components of the generators were

installed and became operational in 1974. Since then Turlough Hill has provided valuable

load shifting services for the Irish electricity grid, requiring just one overhaul of its facilities

in 2012, 38 years into its operation. That is an impressive life cycle.

Historically, Turlough Hill has taken thermal power generation from coal, oil and peat fueled

stations, which could not be turned off at night, and released that power during the

day when needed most.

However, today it has become a valuable resource as Ireland rapidly increases it's wind power

generation. Helping the country to gradually decommission those heavily polluting fossil

fuel plants and replacing them with wind. Ireland, with it's windy position on the

edge of the Atlantic, has prime real estate to begin growing it's offshore and onshore

wind resources and with the help of energy storage, become a net exporter of energy.

To its neighbours in the UK and wider Europe.

However, the question I find myself asking, is how many Turlough Hills would Ireland need

to fully convert to renewables?

To understand the scale of the task at hand, let's imagine a 1 cubic metre cube of water.

We can raise its energy by increasing its height. We can calculate the increase in energy

using the equation for gravitational potential energy, which is simply the mass of the object

multiplied by the acceleration due to gravity multiplied by its height. Here we are defining

height as the difference in height between our starting point and end point.

The mass of a 1 cubic metre of water is 1000 kilograms, so with every 1 metre gain in height,

we add 9810 joules of energy. We will convert to watt hours here as it's a more commonly

used unit. 9810 joules equals about 2.725 Watt Hours. That's not a lot.

That could run a 100 watt lightbulb for just 98.1 seconds, but we can't convert that

energy perfectly. Turlough Hill is about 80% efficient, so that would be closer to 78.5

seconds. If we raised it to 286 metres, the head of Turlough Hill, that 1 cubic metre

block of water could power that same light bulb for 22,451 seconds, or about 6.2 hours.

We of course couldn't drip feed water like this through a generator over nearly 6 hours.

Let's see how the power station buried deep within this mountain works. To get there we

drove down this tunnel. It felt like we were entering some villain's lair from James

Bond. The tunnel is 600 metres long and the granite rock was blasted out of the mountain

using explosives until the desired location of the internal cavern was met.

Here they cleared a cavern 28 metres high. 23 metres wide and 82 metres long to install

the four 73 megawatt generators deep inside the mountain. [3]

Animation 2a The cavern cross section looks like this.

We enter the cavern here on the upper level where the pony motors are located. These are

electric motors which take electricity from the grid to spin impellers located on the

lower level, which pumps water uphill. When we need to generate electricity this valve,

also on the lower level, opens to allow water to flow through the impeller. This now rotates

impellers in the opposite direction and drives the generator, located just under the pony

motor. This is a single machine that is capable of both pumping water and generating electricity.

There is no control over the rotational speed here. It's a fixed speed generator. Locked

to the grid 50 Hertz Frequency. However, there are wicket gates between this valve and the

impeller which limits the flow rate into the impeller and allows the generator to be throttled

down to 5 megawatts. This is an important feature that allows Turlough Hill to quickly

ramp it's production up or down with grid demands. It also features a compressed air

evacuation system that allows the impeller chamber to be quickly emptied of water using

a blast of compressed air. This allows the impeller to quickly reverse direction without

the resistance of the water impeding it. Allowing Turlough Hill to quickly switch from generation

to pumping.

At maximum flow rate, water rushes through the machine at 28.3 cubic metres per second.

For a total of 111.3 cubic metres per second if all four 73 megawatt generators are used.

That is an ungodly rush of water. One hundred and eleven metric tonnes of water, every second.

At this flow rate the 2.3 million cubic metre upper reservoir would be drained in a little

over 5 and a half hours.

When this valve opens to the water pressing down on it with the force of 29 atmospheres

you can feel the ground beneath you shake. I was in the drive shaft access room during

generation and the power behind it was truly awe inspiring. This massive chunk of steel

rotates at 500 revolutions per minute, driving the rotors to rotate inside the magnetic stators

to generate 73 megawatts of power. That's an enormous quantity of water and electricity.

It felt like the entire mountain was shaking around me.

Together these four generators can provide 292 MW of power.

Capable of providing about 4.8% of Ireland's total electricity needs at its peak demand

of about 6000 MW, which occurs at about 5.30 pm every day.[4]

This is truly a massive battery that helps Ireland immensely in smoothing out it's

erratic wind generation. Over the last month, this is what wind generation in Ireland looked

like. [5] Going to a maximum of 4249 megawatts over 80% of Ireland's maximum demand, to

a minimum of 300 megawatts, just 5% of maximum demand. Thankfully, Ireland's grid operator

has become incredibly skilled in forecasting wind generation using weather data. This graph

shows the actual wind generation and this is the forecasted generation.

This ability to predict what power will be available ahead of time allows Ireland's

grid operators to predict when quick response generators, like Turlough Hill and natural

gas power plants, will need to kick in and take up the slack.

Going forward though, we will want to completely eliminate this natural gas generation. So

let's look at the average natural gas generation in Ireland, and figure out how much pumped

storage would be needed to replace it.

This will be a little imprecise and won't account for many scenarios, but we can get

a general idea of the challenge that awaits us.

I started by downloading the generation data from the Irish Grid dashboard website and

found the average generation for the past month, which came out to 4840 megawatts.[6]

Over that period roughly 50% of power generation came from fossil fuels. So, let's say we

need 2420 megawatts of power generation.

That would require 8.3 more pumped hydro stations like Turlough hill to satisfy at any one moment,

but the problem is, Turlough Hill can only run for 5.3 hours at peak generation.

This power generation would need to be available 24 hours a day, so we are going to need 4

to 5 groups of 8 pumped hydro stations available to come online at different periods of the

day. That would require about 37 stations of equivalent size.

Now keep in mind that Ireland is a relatively sparsely populated country. New York City

has a larger population than the entire island of Ireland. 37 facilities like this for such

a small population is a massive undertaking. If we were to create one massive reservoir,

with the same head as Turlough Hill, that reservoir would need a volume of 85 million

cubic metres. That is roughly the same volume of Ireland's 9th largest lake, and trying

to find space for that on top of large hills and mountains isn't easy.

Finding suitable sites for pumped storage is difficult. Extremely difficult. We need

not one, but two reservoirs capable of holding massive volumes of water separated by a meaningful

height, at least 200 metres, but the horizontal distance between the two reservoirs needs

to be relatively short, as a long passage between the upper and lower reservoir will

result in greater energy losses due to friction and viscous fluid effects. The cost of boring

the tunnels between the reservoirs will also be higher.

Typically the cut off point is defined by a ratio of head height to horizontal distance.

Anything greater 1:10 is usually deemed uneconomical. [7] So a 200 metre head could have a maximum

horizontal distance of 2 kilometres between the reservoirs.

Turlough Hill has a head to height ratio of about 1:5.

Next, the site needs to be relatively close to population centres to avoid transmission

losses or expensive purpose built high voltage transmission lines to connect to a distant

grid.

We also need a supply of fresh water. Which is a much larger logistical issue than people

anticipate. Freshwater resources are valuable and interfering with them often comes with

environmental concerns. Even with a closed loop storage system, like Turlough Hill, where

water is just swapped from one reservoir to the other without an outflow. This water can

evaporate over time. Thankfully it's rarely sunny and rains so often in Ireland that any

evaporation is more than replaced by ground water gathered by the lower reservoirs catchment

area.

Because finding suitable sites for pumped hydro storage is difficult, we have designed

algorithms [8] that scour over databases of map data looking for suitable sites, and there

are plenty of proposed sites currently vying for planning permission or already under construction,

but there isn't enough to satisfy our total energy storage needs.

Ireland has just one active site seeking permission to begin construction. The estimated cost

of the facility will be 948 million dollars and will use a disused strip mine as it's

lower reservoir. [9] It now has EU backing, but still hasn't begun construction a decade

after first being proposed. The combination of high initial capital cost and environment

concerns often block the few suitable sites we can find. This progress is too slow.

To this end, some companies are looking to fix these problems. A pumped storage facility

that used salt water instead of fresh water would open some locations where freshwater

is scarce.

A seawater pumped storage facility was tested to limited success in Japan [10], but that

experimental facility eventually closed due to lack of demand for the electricity.

This could open many new possibilities, and would be particularly valuable for places

like California, where fresh water is a very valuable asset and solar energy is abundant.

One such facility was proposed in County Mayo in Ireland on this large flat topped mountain

directly next to the sea. A flat topped mountain of this size could house a massive upper reservoir

and simply use the Atlantic ocean as it's lower reservoir.

Others, like Quidnet Energy, are looking to instead pump water into underground rock layers

under pressure, which would then be released to drive a generator when needed.

Pumped storage is a reliable and long lasting energy storage method. It's not going anywhere.

It is coming under pressure from competition from cheaper batteries that don't require

massive 1 billion dollar investments, but it's ability to store energy for longer

durations will ensure its continued use.

One energy storage method isn't going to fix this problem. We are going to see a world

where multiple methods are used.

This graph, taken from a fantastic paper on levelized cost of storage, shows the mix I

see be utilized by 2050. [11]

A combination for several forms of batteries for fast frequency response and short duration

load shifting, with pumped hydro being used for longer duration storage from 12 to 72

hours, while hydrogen being the only feasible option for longer duration storage.

There won't be just one solution that solves this energy storage crisis. This problem is

going to need a holistic analysis of the grid and it's needs.

Electricity generation is just one aspect of how humans need to adapt to a more sustainable

existence on this planet. We have a long way to go in our quest to avoid a climate disaster.

This video was created in partnership with Bill Gates, inspired by his new book “How

to Avoid a Climate Disaster”, which approaches this problem with the exact holistic analysis

I mentioned above. You can find out more about how we can all work together to avoid a climate

disaster with the link below.