What is a mechanical battery? And why do we still need them over electric batteries?

Question

Basically the title.

In: Engineering

Answer 1

I think that you’re referring to chemical batteries when you say “electric battery”. The rest of this post is written under that assumption.

There are lots of ways to store energy, then release it later as electricity. Chemical batteries are popular nowsdays for their portability and relatively high energy density, but they have some problems. The chemicals aren’t good for the environment (and recharging is only a partial solution). They wear out over time, becoming less and less effective. They’re actually relatively heavy for their size, which isn’t a problem when they’re very small but it limits how large you can make them.

*Most* mechanical batteries work at larger scales than chemical batteries. One of the classic examples involves large water tanks at the top of a hill overlooking the river. You charge the batteries by pumping water into the tanks when the river is running high and strong. When the flow ebbs (or at other times when power is scarce), you can release the water slowly, using it to spin electric turbines and generate electricity. You can store and release more energy with this system than you could without chemical batteries, and you can do it without the nasty chemicals. The drawback is that it has to be very large, but you can’t really make chemical batteries large enough for this purpose anyway.

But mechanical batteries *can* be made smaller, up and to a point. [The GravityLight was an example of this](https://deciwatt.global/gravitylight). In this case, you charged the battery by lifting a weight: as the weight slowly fell, it would spin a turbine to generate electricity to power the light for 20 minutes. The goal behind this design was cost and robustness: it didn’t become less effective over time, and it didn’t need new batteries or fuel periodically. The whole system is still larger than a chemical battery, but it could be made “small enough”.

These systems aren’t perfect, but neither are chemical batteries. All technology involves trade-offs of some kind, and depending on the situation, sometimes mechanical batteries beat chemical, and sometimes the reverse is true. It’s all just a matter of figuring out what works best for the job.