«The need for storage depends on various factors»

Author: Silvia Zuber

Even when there’s little wind, rainfall or sunshine – the demand for electricity will still have to be met after the energy transition. This can be achieved using a range of storage technologies that perform different functions within the energy system.

In the interview

Dr Stefan Oberholzer
Dr Stefan Oberholzer

Head of the SFOE photovoltaics research programme

Mr. Oberholzer, why does the electricity supply have to adapt flexibly to demand?

Stefan Oberholzer: Generally speaking, ensuring the stability of the grid requires that the supply of electricity always equals demand. The energy transition presents us with new challenges: wind and sun don’t always supply electricity when we need it. This variability results in the need for greater flexibility, i.e. the ability to respond during periods of fluctuating electricity consumption or power generation to keep the system in balance.

Is it possible to forecast this variability?

Only to a certain extent. If the sun doesn’t shine even when the weather forecast says it will, we can’t simply ramp up electricity generation to meet increasing demand. It’s easier to even out seasonal effects by taking advantage of the different production profiles of renewable energies. Water and solar power is more readily available in the spring and summer, while wind levels increase in the autumn.

Is it possible to offset the disadvantages of renewable energies?

The Swiss electricity grid plays a key role in offsetting the disadvantages. There’s no point increasing local production capacities if there are no grid connection options to transport the electricity generated from renewable energies. If we look beyond the Swiss borders, it’s clear what needs to be done: a report published by the International Energy Agency at the end of 2023 states that the restructuring and expansion of distribution and transmission grids will have to double globally by 2040. Otherwise, it will be impossible to achieve the desired level of electrification with renewable energies and meet the climate targets. The situation is similar in Switzerland.

Are there other options?

We need to find ways of ensuring that, when it’s possible to produce electricity, we can store reserves for use at other times when demand is high and production is low. These storage systems could be housed in private residences, commercial buildings or energy supply companies.

Overview of storage technologies

To be able to store energy, it first needs to be converted from one form to another. The stored energy is then converted back again so that it can be released as electricity.

Examples of different types of energy storage systems:

Mechanical storage systems
Mechanical storage systems

such as pumped storage power plants

Chemical storage systems
Chemical storage systems

such as power-to-hydrogen

Electrochemical storage systems
Electrochemical storage systems

such as batteries

How many storage units would be needed?

The actual need for storage or storage capacity depends on grid expansion, the type and quantity of electricity generation, and the management of demand. In Switzerland, a great deal has already been done in this area. In 2019, the «Electricity Grid Strategy» improved the framework conditions for grid conversion and expansion, and therefore also for optimisation and further development.

The Electricity Supply Act paves the way for the use of suitable storage facilities throughout the electricity system. Storage system operators are the owners of their flexibilities by law, which allows them to offer the storage facilities where it benefits the system the most. In particular, self-consumers are given incentives to use their considerable flexibility potential and can thus generate extra income.

When it comes to electricity storage, most of us think of batteries. What other technologies are available?

Well, batteries play a big role in storing electricity and will play an even bigger one in the future – be it mobile batteries, such as those used in electric vehicles, or stationary batteries. Based on the scenario that 100% of electricity will be produced using renewable energies, the Finnish LUT University assumes that 60% of Europe’s total energy storage will be provided by batteries by 2050.

In principle, various systems are available for storing electricity: pumped or gravity storage systems, which are mechanical storage systems; batteries, which are electrochemical storage devices; or capacitors, which are electrical storage devices that store charges and the associated electrical energy in the form of an electrical field, usually for a short period of time. You also have power-to-gas or power-to-hydrogen, which are chemical storage systems that can be used to store energy over longer periods of time; or power-to-heat, which is a thermal storage system.

Do these technologies have different functions within in the electricity system?

The challenge is obviously to meet the demand for energy on any given day, so the storage technologies need to be able to cover everything from periods with no wind to dark winter days or dry spells. That’s why it makes sense to use a range of different technologies.

Storage hydropower plants play a key role in seasonal balancing, while decentralised battery storage systems are more useful for grid stabilisation and daily balancing. Electrolysers that convert renewable electricity into hydrogen for storage can also play a balancing role in the electricity system.

Decentralised battery storage systems are suitable for grid stabilisation and daily balancing. Water reservoirs will continue to be very important at the highest grid level.

Dr Stefan Oberholzer

What role does storage play in the transmission system?

Water reservoirs will continue to be very important at the highest grid level. According to the Confederation’s somewhat outdated report on energy storage in Switzerland, the energy stored in pumped storage systems, i.e. the energy recovered by these storage systems, will more than double by 2050. However, other storage systems in combination with sector coupling will also play a role in the transmission system. Sector coupling generally refers to the connection of the «energy sectors» of electricity, gas, heat and transport. The idea is to align the technical systems, infrastructures and markets in these sectors more closely to establish a comprehensive, intelligent energy system. The storage options in the different sectors can also play a role in the transmission system, for example in the provision of ancillary services.

When it comes to sector coupling, we’re thinking large scale. What about storage in households?

Around one in every three single-family houses with a photovoltaic system was equipped with a battery storage unit in 2022. However, in future, it won’t be necessary for every household to have a storage unit to ensure sufficient flexibility.

For grid operators, it is also important that the decentralised storage systems can be operated as «grid-friendly» as possible. The use of bidirectional charging with electric vehicles or the establishment of local electricity communities that are connected to the distribution grid will undoubtedly increase the potential uses for storage systems.

Which storage technologies will become more important in the future?

I think that batteries will be vitally important, although this doesn’t mean that other forms of storage, such as seasonal thermal storage in conjunction with a grid-connected heat supply, will not play an important role. No matter which storage technology is used, the simplest and most efficient way to move away from fossil fuels is to increase electrification.


Silvia Zuber
Silvia Zuber

Project Manager

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