How can you store electricity?

On a technical level, you cannot store energy as soon as you generate it. It first needs to be converted into a different form. This is achieved by means of a transformation cycle that converts the flow of electrons into chemical, mechanical or thermal energy.  Only when you actually need the electricity, is it then released again.

Each storage method has its own unique properties and three main factors are then crucial in that regard:

• Its efficiency: the ratio between the energy stored and the energy recovered.
• Its energy density: the amount of energy you can store per volume or weight.
• The discharge time: how fast or how slowly the energy is made available again.

At a glance

Here is a brief summary of the various storage methods. Click on a technology to go directly to the detailed explanation:

Tip: This article provides an overview of all the available technologies. Are you mainly looking for specific ideas for your home? If so, skip straight to our practical summary at the bottom.

Using a battery

A battery works on the basis of a ‘reversible’ chemical reaction. This means that the reaction can take place in two directions:

Using a capacitor

A capacitor does not store electricity in chemical form as in a battery, but temporarily captures an electrical charge between 2 metal plates. A capacitor is the "sprinter" amongst storage technologies.

Capacitors have a number of typical characteristics:

• Lightning-fast: A capacitor can be charged and discharged extremely quickly, just like the flash on a camera that releases all of its energy in one go.
• Short-term peaks: A capacitor is an ideal way of responding to sudden peaks in the electricity network or to give electric vehicles an ultra-short "boost" during acceleration.
• Limited storage: A capacitor has only a very small storage capacity. A capacitor is able to get a machine off to a powerful start, but isn't suitable to power your home all evening long.

Using hydrogen

You can also store electricity by converting it into gas. Using surplus electricity, water is split up into oxygen and hydrogen (by means of electrolysis). The resulting hydrogen gas can then be stored under pressure in tanks, just like a giant battery.

When the energy is needed again, the hydrogen is combined with oxygen:

• In a fuel cell, the electricity is generated directly.
• In a motor, the gas drives a generator that produces the electricity.

Though this is a powerful way of storing large quantities of energy for a long period, its efficiency is still low. Too much energy is actually lost during the two-way conversion (electricity to gas and back again). As a result, this type of storage is primarily a solution for industrial use at the moment and is less suitable for powering homes.

Using pumps and turbines

One of the most widely used method in the world (in Belgium, it is used at the Coo power plant). In this system, water from a lake located at a lower level is pumped uphill to a reservoir situated at a higher altitude. Later on, whenever demand for electricity arises, the water flows back down again. Along the way, it drives a turbine and an alternator, which together generate electricity. This system is already used on a large scale today as a means of addressing fluctuations in renewable energy.

Using pressure accumulation

Compressed gas is stored in a sealed space with waterproof walls. Once you let the gas escape again, it drives a turbine. That turbine then drives an alternator that produces the electricity. This system is also primarily suitable for large-scale energy storage.

Using a gravity pit

Under this principle, a heavy piston is hauled upwards out of a 500-metre-deep pit using an electric motor. When that mass is released, it will fall back down to the bottom. Due to its weight, water is compressed and transported, driving an electric generator. This is how stored energy is converted into electricity.

Gravity-based storage is an interesting concept, but at the present time, it mainly takes the form of a niche solution or a demonstration project.

A train on an inclined track

This principle is rather like winding up an old-fashioned mechanical watch. A weighted train drives up a 10-kilometre long slope with a gradient of 7%. On its way down again, the weight of the train causes a generator to turn, thereby generating electricity.

With a flywheel

A flywheel is a heavy, rotating mass (a wheel or cylinder, etc.) that is brought up to speed by a motor. As it slows down, the wheel dries a generator that produces electricity.

Using a water reservoir

The most familiar way of generating energy at home is using hot water. Surplus electricity is used to heat up the water reservoir of your central heating system or boiler. By doing this, you are converting electricity directly into usable thermal energy.

Using sand

In addition to water, sand can also be used to store heat, even at very high temperatures. In Finland, for example, this technology is already being used on a fairly large scale. A 'sand battery' can store heat for months at a temperature of around 500 degrees Celsius. Surplus solar energy and wind energy generated during the summer can therefore be used to heat entire districts during the winter.

Though technologies such as sand batteries or hydrogen panels will be widely used in the future, they are not yet sufficiently well developed to be used in the cellar of your home. So what can you actually do as a private individual or as a co-owner of a property?

• A home battery: This is the most familiar route. In the evening, this is an ideal way of consuming the solar energy generated during the day, even though the cost of the investment is still considerable.
• An electric car (V2G): Do you have an electric car? If so, you may already have an enormous battery on wheels that is capable of supplying your home in the future.
• Thermal storage: The simplest and least costly method. By operating your electric boiler or heat pump in a smart way, you can store energy in the form of hot water.