Pumped storage electricity: sustainable energy - and then some.

As the UK moves from fossil fuels to renewable energy sources, pumped storage electricity could become an essential part of our future energy supply. 

Yes, it’s a “clean” form of energy. (And that’s something we love about it). But that’s not its only attraction. 

What is pumped storage electricity?

Imagine two lakes, one nestled in the valley and another perched high on a hilltop. These aren't ordinary lakes—they're a giant, water-powered battery.

During quiet times on the electricity grid, when power is plentiful and cheap, powerful pumps spring to life. They draw water from the lower lake and push it uphill, filling the higher reservoir. Think of this as charging a battery – the higher reservoir stores all that excess energy in the form of potential energy.

But then, as the day progresses and homes need more electricity for lights, TVs, ovens and so on, the power demand spikes. Now it's time to release that energy stored in the higher lake. 

The water up on the hilltop is “released”.  It rushes back downhill, turning giant turbines as it flows. These turbines spin powerful generators, and just like that, electricity flows back into the grid, meeting the surge in demand.

This is the essence of pumped storage. It's like a massive rechargeable battery, balancing the ups and downs of electricity supply and demand. It can help to store energy from sources like solar and wind power, even when the Sun sets or the wind dies down.

So, the next time you think of a battery, don't just picture a small cell in your phone, think of those two lakes, quietly storing and releasing vast amounts of energy, keeping the lights on - and help keep our energy grid stable.

What is pumped storage electricity similar to?

In many ways, pumped storage electricity is similar to hydroelectric power. This may be something you learned about at school, where the water used to drive the turbine is held in a single reservoir behind a dam and that reservoir is usually “topped up” naturally by rainfall, rivers flowing into it. 

How is pumped storage different?

Hydroelectric power’s reliance on the natural flow of water to generate electricity makes it more susceptible to things like drought and other water supply changes. Pumped  electricity generation isn’t so reliant. This is what makes it more reliable.

And of course pumped storage hydropower can help us when other renewable sources of electricity are struggling to meet demand (for example in the summer when it is generally less windy¹).

Pumped storage and energy efficiency.

We’ve already talked of pumped storage as a giant water-powered rechargeable battery –  and it’s worth saying that it’s incredibly good at its job. 

.Now, it's not perfect. Just like when you charge the battery on your phone: some energy is always lost (as heat). Pumped storage plants usually get back about 70-80% of the energy they put in. In the case of pumped storage, energy is lost as friction, driving the turbines and so on.

That might sound a little low, but it's important to compare apples with apples.

Batteries, those shiny superheroes of portable energy, usually do a bit better on efficiency, getting closer to 80-90% of energy returned. But, they're also much more expensive, especially when you need to store energy to power whole towns.

And compared to traditional power plants, pumped storage stands strong. Coal and gas plants waste a lot of energy as heat. It even holds its own when compared to solar and wind power, which are the champs at turning natural energy directly into electricity.

The real strength of pumped storage lies in its massive scale and staying power. It can store enough energy to keep lights on for hours or even days. That's why it's so important for balancing the grid, ensuring we always have enough electricity, even when the Sun sets or the wind calms down.

It's also incredibly flexible. It can respond to changes in energy demand very quickly², making it ideal for balancing out the ups and downs of renewable energy generation.

How much pumped hydro energy can be stored?

We’ve touched upon the potential of pumped storage to vast amounts of energy. This makes it a crucial player in the UK's energy transition. 

The amount of energy stored depends on factors like:

• The size of the reservoirs (how much water they hold).

• The height difference between the two reservoirs (more height = more potential energy).

But for a real world example, let’s take a look at the Dinorwig Power Station in Wales, which is the largest pumped hydro energy storage facility in the UK. It has a huge storage capacity and can store approximately 9.1 GWh (gigawatt-hours) of electricity. 

To give you an idea of what this means, that's enough to power about 2.27 million average UK homes for an hour.

And Dinorwig is just one example. The UK has several smaller pumped storage plants, and there are even larger-scale projects in development.

Help towards a sustainable future.

Of course, because pumped storage produces no carbon emissions, it's a great way to reduce our carbon footprint. And in fact it can be used to store the renewable energy generated by wind and solar power, which can help keep carbon emissions down.

Pumped storage acts like a bridge between the unpredictable nature of renewables and the constant demand for electricity. It soaks up the excess power when nature is generous (the wind is blowing and the Sun is shining) storing it away. Then, when the Sun sets or the wind dies down, it unleashes that stored energy, preventing the need to turn to those polluting coal plants. So how exactly does it do this?

During the day, when the energy from solar and wind is more available we can use any excess energy to drive the powerful pumps to push water uphill to the reservoirs. 

So this excess energy from wind and solar is saved, now held high in those hilltop lakes like water in a giant battery.

And then, when there are times when that renewable energy is less plentiful, pumped energy comes into its own. 

Years ago, in a situation like this, where power demand remains high and renewable energy sources struggle to meet that demand, it might have meant firing up coal power plants – a burst of energy, but one that spews carbon into the atmosphere.

But now, when demand outstrips the renewables, the water in our upper reservoir rushes back downhill. It roars through turbines, spinning generators with the force of stored sunlight and wind. Electricity surges back into the grid, the clean energy meeting the evening's needs.

Helping us make the transition.

Pumped storage is a key player in the fight against climate change. It helps us squeeze every drop of power out of our renewable resources, ensuring a reliable flow of clean energy even when nature takes a break.

But by helping us to create a more stable energy grid as well as reduce our reliance on fossil fuels, pumped storage electricity will be crucial to the UK's transition to a clean and sustainable energy future.