Pumped hydropower – the green battery

Energy storage systems are the key to meeting Europe’s renewables targets, Robert Williams reports.

PumPEd hydRoPowER the green battery

For many years, a key challenge in the energy sector has been how to store energy for when it’s most needed. As we move towards relying on renewable energy, it becomes even more pressing to have alternatives, when “the sun doesn’t shine and the wind doesn’t blow”. It sounds straightforward but has proved remarkably difficult to address – which is why we still have to have back up renewables with electricity generated from oil, gas and nuclear power stations.

A huge amount of research work has been devoted to storing energy. Supercapacitators, lithium batteries, solid state batteries, hydrogen cells, there have been no shortage of options.

The European Commission sees renewable energy as playing a major role in fighting climate change, as well as being capable of providing Europe with affordable and secure energy. While solar and wind energy have received much attention – and are already significant in Europe’s energy mix – other renewable energy sources, such as hydropower, are likely to grow in significance.

This is partly because Europe’s 2020 target of 20 per cent of energy from renewables means adding an even greater amount of renewable energy, which some estimates put at between 35 per cent and 40 per cent

According to the International Hydropower Association, “hydropower is a versatile, flexible technology that at its smallest can power a single home, and at its largest can supply industry and the public with renewable electricity on a national and even regional scale.”

In 2016, hydro-electric power supplied 71 per cent of all renewable electricity generated, accounting for 16.4 per cent of the entire world’s renewable and hydrocarbon electricity generation. In the EU hydro accounts for over 14 per cent of all prime electricity, and 70 per cent of all hydropower is from five main countries - Sweden, France, Italy, Austria and Spain.

Storing hydro power

Norway is one country that could become, at least partially, the “green battery of Europe” by using hydropower plants to provide extra electricity. The existing network of hydropower plants could be developed to instantly boost power supplies across the continent. As the sources of energy change, power systems will have to become more flexible, so they can balance generation and consump-

tion. One way to introduce this flexibility into the grid is through pumped hydro storage.

Norway has 937 hydropower plants, which provide 96 per cent of its electricity, making it the sixth largest hydropower producer in the world - despite having a population of only 5 million.

Pumped hydro storage is the oldest kind of large-scale energy storage and works on a very simple principle – two reservoirs at different altitudes are required and when the water is released from the upper reservoir to the lower reservoir, energy is created by the downflow, which is directed through a turbine and generator to create electricity.

The water is then pumped back to the upper reservoir during periods of low demand. Pumped storage hydro provides one of the few large-scale, affordable means for storing and generating carbon-free and low-cost electricity. it is one of the most cost-effective utility-scale options for grid energy storage, acting as a key provider of ancillary services.

On average, European pumped storage plants are more than 30 years old, with two-thirds of them built between 1970 and 1990. It looks like conditions are ripe for new capacity construction.

Pumped storage generation offers a critical back-up facility during periods of unexpected peak demand or sudden shortfalls in supply, If we want to see this happening on a European scale, it is essential that we upgrade the continent’s ageing grid infrastructure, ensure that countries open up borders, increase interconnection and trade electricity on a single market.”

An alternative to building new dams is the Prosper-Haniel pit in the state of North Rhine Westphalia near the Dutch border. It has produced coal for almost half a century but is set to turn into a 200-MW pumped storage hydroelectric reservoir. It will act as a super-giant battery with enough capacity to power over 400,000 homes for up to 4 hours when needed.

Researchers from a number of German universities are working alongside private engineering companies and the government on the project. Once successfully up and running, this is something that could potentially be modelled and rolled out Europe-wide.

New grid systems

The construction of pumped storage facilities, be they dams or mines, brings other challenges to the fore, as the stored energy still needs to be distributed. This will require an increase in the capacity of interconnectors in Europe and new techniques to enable non-dissipative long-distance transportation of huge quantities of electricity.

A precondition for a pumped hydro storage boom is development of the power grids. In most cases, the existing grid structure is inadequate for absorbing and transporting the given amount of electricity to its storage location. For this reason, connections inside and between European countries must be expanded.

So, in tandem with new power stations is the development of the grid system, as the existing grid structure is not up to the task of absorbing and transporting the necessary amount of electricity to and from its storage locations.

For the Norwegian green battery, the crucial element is getting electricity out of Norway and to other parts of Europe, something that requires expensive undersea cables. The country is scheduled to connect with Germany by 2020, once the €1.5-2 billion NordLink cable is operational, and by 2021 with the U.K. through the €2 billion NSN Link.

Norway exports hydro power to the Netherlands and exchanges renewables with Sweden and Finland, and there are plans for similar green exchanges with Germany and the UK.

But the key project is with Denmark, a country that relies heavily on wind energy. Norway imports Denmark’s excess windgenerated power and sends hydro-generated electricity back when the wind isn’t blowing, allowing Denmark to rely on renewables for about 40 per cent of its electricity needs.

Energy storage and effective pan European distribution has a key role to play in the transition towards a carbon-neutral economy. By balancing power grids and saving surplus energy, it represents a concrete means of improving energy efficiency and integrating more renewable energy sources into electricity systems.

It will also help enhance European energy security and create a well-functioning internal market with lower prices for consumers. Ultimately, making this growth in storage capacities a reality throughout Europe - and beyond - is a task for innovators, grid operators and policymakers alike. n