Are you one of those people who starts stressing out when their phone battery drops below 50%?

Or do you like living on the edge, regularly seeing a single  digit number up in that corner? Either way, you probably think  about energy storage a lot.

But probably not as much as the people who are responsible for maintaining  our municipal power grids. There’s a huge variation in how much energy gets used at certain times in certain places. And whether you’re storing energy to power a city or your iPhone, it requires batteries.

Typical batteries store energy in the chemical bonds within materials, usually a set of metals. To get this energy out, other  materials in the battery chemically react with these metals to  remove some of their electrons, which are then used to generate electricity. Hence the name electrochemical batteries.

But if we get creative, we can store energy using way more and potentially way weirder methods. Like using water, rocks, and even soil! So let’s break down 5 weird ways to store energy. [♪INTRO] The first example on our list today is called pumped storage hydropower.

Or, more informally, water batteries. As you might have guessed, water  batteries store energy in water, and they do this through the power  of gravity. Here’s how it works: We start off with a large reservoir of water.

When we want to store energy,  we pump the water from this reservoir up to another reservoir  on higher ground using a turbine. Because we had to fight against  gravity to get that water up there, it now holds energy in a form called  gravitational potential energy, which is kind of like an energy IOU with gravity. When we want to use this energy, we cash in this IOU by having gravity take over and letting the water flow back  down to the lower reservoir.

All that moving water is used to spin  a turbine and generate electricity. Water batteries are usually ginormous in scale, both in terms of physical size and in terms of how much energy they can store. And as long as the top  reservoir is fully enclosed, these batteries can basically  store energy for forever without any loss due to evaporation or leaks.

This means they’re often used in  the power grid to store backup energy in case of emergency, like  storms or equipment failures, or just when demand gets a little too high. Also, if the grid has inconsistent energy sources, like solar or wind power, water batteries can save any excess energy for later like when it’s dark or, you know, not windy. In fact, water batteries are so good at storing backup energy they’re used almost everywhere.

More than 90% of grid energy storage in the world uses water batteries! And right now, the largest is located at the Fengning power plant in northern China. Physically, the upper reservoir  can hold 45 million cubic meters of water, which is enough to fill  around 18,000 Olympic swimming pools.

That amount of water translates to  about 40 gigawatt-hours of energy, which is enough energy to meet  340,000 people’s needs for a week. But as gigantic as Fengning seems,  there’s another water battery under construction in Australia  that should shatter this record. This project, called Snowy  2.0, is an expansion upgrade to the existing pumped-hydro  power plant called Snowy.

Snowy 2.0 is supposed to begin operation in 2029, and is designed to store nine  times more energy than Fengning. That brings it to a storage  capacity of 350 gigawatt-hours, which is enough for 3 million people for a week. Now, it’s worth noting that water batteries aren’t a perfectly efficient  form of energy storage.

You expend a lot of energy pumping  the water into that upper reservoir that you don’t get back out when  you let the water flow back down. For example, over the course of one year, the plant at Fengning uses  about 8.7 terawatt-hours of energy to generate about  6.6 terawatt-hours of energy. That translates to an  efficiency of 76%, which isn’t amazing for a water battery,  but it’s certainly not terrible.

And anyway, I’d rather have an  inefficient backup than no backup at all. Water batteries aren’t the only way  we can store energy using water. Another way turns the concept  of water batteries upside down.

This technology, called geomechanical storage, stores energy by pumping water 300 to 600 meters underground into pockets between rocks. The pressure from the water  pushes against the rocks, slightly deforming them, and it’s within this  deformation that energy is stored. To retrieve the energy, we  release the pressurized water out of the ground and, once  again, use it to spin a turbine.

Like water batteries, geomechanical  storage is intended for large-scale grid applications,  serving as backups for blackouts or energy supplements for inconsistent  renewable energy sources. This tech is also fairly new.  One company called Quidnet Energy has been working over the past several years on a megawatt-hour-scale commercial storage system. Recently, they demo’d storing  35 Megawatt-hours of energy for six months, enough energy for  300,000 people for a week.

Quidnet predicts that their final system will have an energy efficiency of around 50%. While that number might sound like a major downgrade from Fengning’s 76%, the technology’s selling point is that it’s much easier and cheaper to  install than water batteries. You know what’s also cheaper  than building a battery big enough to support a city’s worth of people?

Making a YouTube video about those batteries. But only by comparison, so here’s an ad: Since you watch SciShow, I know you’re the kind of  person who loves engaging with new ideas and learning  outside of a classroom. And that’s what makes Brilliant so great too.

Brilliant helps you strengthen your math skills, with lessons in Proportional  Reasoning full of examples that are relevant to your  life, from recipes to payments. And you’ll be actively  learning all this stuff because they’ve packed 357 exercises into just 30 lessons. You definitely won’t be falling  asleep in a lecture hall.

To learn for free on Brilliant  for a full 30 days, go to brilliant.org/scishow, scan the QR code onscreen, or click on the link in the description. They’re also giving you unlimited  daily access to everything on Brilliant with 20% off an  annual Premium subscription. Thank you to Brilliant for  supporting this SciShow video.

An energy storage technology  that’s further along than those water-plus-rock batteries  are thermal batteries, which store energy in the form of heat. To do this, we first generate heat by operating what is essentially a giant toaster, running an electric current through a  highly resistive material. The heat this generates is  used to warm the thermal battery to a blazing hot  temperature, which can range from around 500 to 1700 degrees Celsius depending on the material we’ve chosen.

Also, to prevent that heat from escaping, we also need to insulate this  hot material really well. When we want to access that stored energy, we just open the insulation, or blow air across the hot material to carry the heat away. This hot air can then be used to do work, such as heating a space  directly, or turning water into steam that can then be used  to, yet again, spin a turbine.

Why does everything come back to turbines? For their heat-storing materials, thermal batteries typically use  bricks, rocks, sand, or molten salts. These all have a high specific heat capacity, meaning they can absorb a ton  of energy before getting hot, allowing thermal batteries to  pack more energy into less space.

Because thermal batteries  naturally output energy as heat, they work best for industrial  manufacturing processes that can directly use that  heat, such as furnaces or kilns. And in such cases, thermal batteries can operate with very high  efficiency, like around 95%. Meanwhile, if we want to turn the  released heat back into electricity, things get a little bit more complicated.

As I said earlier, we could  do this with a steam turbine. But this only works for the batteries  operating at lower temperatures. Above 1500 degrees Celsius, turbines literally start falling apart from the heat.

So instead, some researchers are looking into a technology called thermophotovoltaics, or TPVs. This technology basically works like solar cells, but instead of turning sunlight into electricity, it turns infrared radiation into electricity. Which our sun also emits, but TPVs are focused on more down-to-Earth sources.

The efficiency’s still fairly low, though. One of the best prototypes  still only hits about 44%. But even without a great way  to turn heat into electricity, thermal batteries are still  operating in the real world.

Today, the largest operating thermal battery is in the Ouarzazate Solar Power Station in Morocco. It can store 2800 Megawatt-hours  of energy using molten salt… which I should probably clarify is not, like, regular table salt, but a mix of other salts. Which are not just inedible, but  can be hazardous if swallowed.

So sadly, no. You can not use  this battery as a salt lick. But heat isn’t the only way to store energy.

We can also crank the temperature all the way down and make ice batteries. To do this, we first freeze water  or some other liquid into ice. We then use that ice to cool a place down.

To extend the ice’s reach, we  can also use it to cool a liquid that then gets sent off to  circulate somewhere farther away. Now technically, we aren’t  really storing energy here, at least not in the same way  I’ve talked about previously. Because when we freeze stuff,  we’re actually pulling energy out of the material, not pumping  it in to be accessed later.

We can still colloquially refer  to this system as “energy storage” because we’re doing work to make  ice now so we don’t have to do the work again later when we actually  want to make something colder. To get the best ice batteries, we  want to use materials that have a high latent heat of fusion, which  means they require a lot of energy to physically switch from being a  liquid to a solid, or vice versa. That way, the ice can provide a larger “cooling energy” stockpile to draw from later on.

Many ice batteries rely on good ol’ H2O, water. But pure water famously freezes at the relatively low temperature of 0 degrees Celsius. Since an ice battery also needs to  maintain this temperature to work, you might want to use something  with a higher melting point, like paraffin wax.

Meanwhile, other ice batteries use salt hydrates, which is basically just a  fancy way of saying you’ve got a bunch of salt crystals with water molecules incorporated into them, rather  than a bunch of salty water. While some salt hydrates freeze  at higher temperatures than water, they also tend to freeze and melt unevenly, which hurts their effectiveness as ice batteries. Plus, all that salt can corrode  the battery’s equipment, which isn’t great unless you’re an HVAC company looking to put some planned  obsolescence into your tech.

But with all that said, ice  batteries are still helpful for making our A/C needs more manageable. At night, we can stockpile ice  when electricity is cheaper to use. Then, during the day, when  electricity costs are at a premium, we can rely on the ice for cooling instead of drawing electricity to power the A/C.

So not only do ice batteries save us money, but they also help keep our power grid happy by reducing the strain on  it during peak usage hours. And yes, ice batteries are also  out there in the real world, though they’re not super common. One example system is at 11  Madison Avenue in New York City.

Every day, the building freezes  227,000 kilograms of ice, enough to fill three city buses. That ice equates to “storing”  22.5 Megawatt-hours of energy, enough to last 193,000 people for a week. And just like the molten salt battery, I do not recommend sticking your  tongue against the ice block, even if it’s one made of just water.

Nor do I recommend licking the final  energy storage system on this list. Remember the very beginning of this episode when I said energy can be  stored in chemical bonds? Well our final piece of tech takes advantage of this type of energy again.

But this time, we’ve got microorganisms  to help us get the energy out, and a microbial fuel cell or microbial battery. In microbial batteries, microorganisms  such as bacteria, algae, and fungi digest biomass by stripping  electrons off the biomass’s atoms. These electrons are then directly  used to generate electricity.

The “biomass” in these batteries  is typically soil or wastewater. And with wastewater, we get the added bonus of reducing our giant piles of, well, waste! So yeah, don’t lick the sewage battery…   Unlike the energy storage  systems I’ve covered so far, microbial batteries put out way less power.

Instead of sustaining an entire city’s  worth of people for several days, or even a single building, they work  best for smaller scale applications, like powering irrigation switches that  control water sprinklers on farms, or powering sensors for  measuring wastewater pollution. But researchers are working on ways to boost how much power a microbial battery can pack. Some are testing different architectures, some are looking for new materials.

One state-of-the-art microbial  battery described in a paper from 2024 achieved a power density of 10  milliwatts per square centimeter, which is about 100 times less than  a top-tier wireless phone charger. But let’s let ‘em cook. Maybe  one day, we’ll be living in a world where you can buy your  own microbial fuel cell… Feed it like a sourdough starter, give it a name like your sourdough starter….

And then you can thank it when it saves you after you realize your phone is at 3%. [♪OUTRO]