Using renewable energy such as wind energy or solar energy to generate electricity is great compared with traditional power generation methods, but they have a disadvantage that they cannot provide energy continuously and consistently. This means that if we want to make better use of them, we need batteries, an old and often new means of energy storage, to store some of the energy they produce for future use. Today, let's take a look at mechanical batteries that are different from traditional chemical batteries.

Nowadays, with the support of policies, new energy vehicles have come into our lives. However, not everyone likes the electrochemical batteries. They are very expensive and in fact not environmentally friendly.

Fortunately, we have other options, such as mechanical batteries, which use the potential energy or kinetic energy of objects rather than chemical substances to store energy.

Many mechanical batteries were designed long ago, but now they are making a comeback. Although we now propose that energy can be stored in a variety of new ways, those technologies that have been used for hundreds of years can still be used well, especially after the adoption of some modern science and technology for innovation.

Let's start with the place you may be familiar with: compressed air.

Since the invention of the first air pump in 1650, compressed air has been used to drive railway brakes and many construction engineering tools, such as nail guns and impact hammers.

Facts have proved that this idea can be expanded and used for energy storage.

First, a high-pressure compressor pumps air into a huge chamber, such as a salt cave or an abandoned basement. Then, when we need electricity, the compressed gas is released to run the power turbine. Because of its huge size, compressed air batteries can provide as much energy as power plants, up to 321 megawatts at a time. At the same time, they are also very cheap and have a short response time, about 12 minutes, less than half of the traditional fossil fuel generator. In addition, they can store energy for more than one year.

However, thermodynamics tells us that some energy converted into compressed air heat will dissipate into the wall of the room over time. And because the air will also become cold when it is depressurized, it needs to be reheated to avoid damaging the turbine. Therefore, part of the energy is lost, which means that the ratio between the input energy and the output energy in the compressed air battery is relatively low. Even modern compressed air facilities can only achieve 60% to 70% conversion efficiency. The conversion rate of chemical batteries below the top level is about 90%.

Engineers may be able to improve this, but for now, we still have other ancient mechanical battery technologies, such as railway energy storage.

Railway energy storage is basically a battery driven by gravity, which stores the gravitational potential energy of trains. The process is simple: the locomotive pulls the car uphill and can store more energy by adding more cars or higher car weight as needed. Then, when the train goes downhill, the gravitational potential energy is converted into electric energy through power recovery, which is often seen in new energy vehicles and even some electric vehicles. Since at least the 14th century, we have been using gravity to store energy, such as the mechanical turret clock driven by a heavy hammer.

Several types of modern gravity batteries have been proposed, but so far, the only large-scale gravity battery being developed is still on the hillside.

The capacity of the track battery is about 50 megawatts. Compared with the compressed air system, each battery has less storage capacity, but they also have many advantages. For example, we don't need a deep cave to hold all the energy, and railway energy storage can work at any place with a slope greater than 5%. And they have good conversion efficiency, about 78%. In addition, their startup response time is about five to ten seconds better than that of compressed air batteries.

However, this is still slower than flywheel energy storage.

Flywheel batteries use the kinetic energy of the flywheel rotating around the axis. Newton's law tells us that moving objects tend to maintain this way. These flywheels can store a large amount of energy in the form of kinetic energy. Then, we can obtain energy by slowing down, which is similar to power recovery.

The first flywheel battery specially designed for energy storage was developed in 1833 to drive the first self-propelled torpedo (1866). Compared with the previous two "batteries", flywheel batteries are not very useful in large power plant storage. Friction makes them lose up to 20% of their energy every day. However, modern flywheel batteries make them lighter and smaller by using high-tech materials, such as carbon fiber composites, which are suspended on superconducting magnetic bearings by rotating in vacuum, limiting the energy lost on friction, and making it possible to increase its speed and expand its storage capacity.

However, this also makes their manufacturing costs extremely high, especially when compared to compressed air or railway batteries. However, this technology is still worth investing, because its conversion efficiency can be as high as 90%, and the response time is in hundreds of milliseconds. And the flywheel battery can be used in such fields as server cluster, uninterruptible power supply system on the train, and hybrid racing due to its relatively small size.