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Energy Storage – What is it and Is it the Holy Grail of Solar

Energy storage is a vital component of modern solar systems for a simple reason: most people don’t use energy at the same time they generate it. Being able to store energy for a long time is vital to most modern conveniences, from air conditioning to car engines. 

Solar Energy Storage

While solar energy storage isn’t the holy grail of solar all by itself, it is a part of the ideal solar energy system. Here are some of the current ways to store solar energy and which situations they make the most sense for.

How Does Energy Storage Work?

Energy storage is a straightforward process where generated energy becomes captive in some way. This isn’t always direct as electricity. Rather, many energy storage systems convert the energy to another type of potential power while it’s in storage, then change it back before releasing it.

The most common types of energy storage are chemical, mechanical, and thermal systems.

Each energy storage system has several qualities that help define how appropriate they are for a particular situation. Many larger locations have some mix of short-term and long-term energy storage to meet different needs.

Storage Efficiency

We don’t have a 100% efficient energy storage system. We always lose some of the energy while storing it, but more efficient systems are generally better. Getting more power from the same amount of work is a key aspect of a great solar system.

Various kinds of Lithium-Ion Batteries

Most people use lithium-ion batteries [1] to store solar energy, which works well thanks to a mix of effectiveness and affordability. High-efficiency storage is almost always better for any purpose.

Storage Capacity

This isn’t the same thing as storage efficiency, which measures what percent of the electricity you generate that you can store. Capacity is the total amount of energy you can store within a system, and we usually express it as either kilowatt-hours or megawatt-hours.

Power Capacity

This term sounds confusingly close to storage capacity, but it’s a separate quality. Power capacity is how much energy a system can release at any time, and it usually has the same sorts of ratings as storage capacity.

This isn’t usually a big deal if you’re only powering one or two small appliances with solar power, but it becomes much more crucial if you want to run an entire house or commercial facility with solar energy.

Why Does Solar Energy Storage Matter So Much?

Energy storage matters for several reasons beyond the simple convenience of being able to use energy when you want it, not when you generate it.

The first reason is that it helps balance energy loads. Solar power is somewhat inconsistent in most areas, and that’s not even taking into consideration nighttime hours. Storms and cloud cover can sharply reduce the effectiveness of solar systems, and worse, grid operators might have to disable some of their generators to help match demand.

Solar energy systems help address this by creating power when demand is lower, then releasing it when demand is higher. This applies both to small, single-home systems and industrial power generation.

Solar storage is also an excellent way to firm electricity generation. This term refers to covering for quick short-term changes in generating effectiveness, such as clouds passing overhead. By releasing energy as needed, solar energy storage can help each generator provide a consistent amount of electricity. That’s much better for the overall power grid.

Finally, solar power provides resilience for systems and can work during more significant power disruptions. This allows us to keep using essential and sometimes life-saving equipment with no external help.

None of these are possible without solar energy storage.

The Types of Energy Storage

While most people immediately think of batteries, the truth is that those aren’t even the primary method of storing energy, much less the only option. Here are the primary systems in use today.

Pumped Hydropower

Schematic to show Pumped Hyrdo-Power Storage

This is one of the most common energy-storage systems currently available. It’s hard to do on a home scale unless you have a lot of space to install the systems, but cities and states often use this for their primary power grid.

The philosophy behind pumped hydropower[2] systems is simple. Large pumps use electricity to move water up a hill and into a storage reservoir, with enough capacity to be helpful. Reservoirs can be almost any size, but bigger is usually better. Evaporation is a minor concern, but modern systems can help minimize that.

When demand goes up, regulators can start letting water back down. This flowing water turns wheels or other systems that can generate electricity for immediate use.

Ultimately, this system turns electricity into kinetic force for moving the water uphill, then into a mix of kinetic power and gravity when the water comes back down. Outside of evaporation, pumped hydropower is especially useful because it can hold energy indefinitely, rather than slowly leaking it out over time the way some other systems do.

Pumped hydropower is also outstanding for overall capacity. It offers a low cost of storage for each gallon the reservoir can hold, and the larger the reservoir, the cheaper each megawatt-hour of energy becomes.

The main thing that holds pumped hydropower back from being almost everywhere is the long payback period for the initial investment. Building proper reservoirs and generators costs quite a lot and needs to be done in areas that won’t hurt the environment, so private investors are often reluctant to fund it.

Electrochemical Storage

Electrochemical Storage

This is the energy storage system that most people are familiar with. Despite the idea of storing “electricity” in batteries, the truth is that most batteries cause chemical reactions when you store energy inside them, and that’s how the energy gets stored.

Releasing energy from the battery reverses the chemical reaction, outputting power based on the battery’s specifications. Most people use lithium-ion these days, but specialized applications may also see nickel, lead-acid, or sodium batteries as the top choice.

Electrochemical storage is excellent for small-scale applications, including household and vehicle needs. However, it’s too expensive for large-scale energy storage. The scarcity of resources and cost of holding energy make electrochemical storage a poor choice for city or state-scale needs.

Outside of the cost, electrochemical storage is also relatively inefficient. Batteries charge well when they’re nearly empty, but charge slower as they get closer and closer to being full. That makes them uncomfortably inefficient, especially if you’re trying to store as much energy at home as possible.

These two problems of cost and inefficiency are the primary reasons that electrochemical storage is not the “holy grail” of energy storage for solar power. They may be good enough for households and small-scale use, but we need something better.

Flywheel Storage

Fly-Wheel Storage

Now here’s a method of energy storage that most people aren’t too familiar with. Flywheels[3] are a mechanical energy storage system where power goes in to start turning the wheel, possibly through magnets or other systems.

These are a great way to store power fast and also to extract it quickly as needed. Most flywheels store more energy when they turn faster, so the speed is a primary component. Floating them on magnets and putting them inside vacuum-sealed chambers can almost eliminate friction, making them incredibly efficient as well.

However, flywheels lose energy quite quickly when you stop them. Maximum effectiveness can pull out all of their stored energy in just one second, while lower energy generation can spread it out over 60 seconds.

In short, installing enough flywheels to power an entire household at night has problems with the amount of space needed, plus the costs of installation. In other words, despite the possibilities, flywheels face significant challenges for most practical-use scenarios.

The one thing that helps them remain promising is the fact that the flywheels themselves have essentially unlimited recharges as long as you don’t exceed their threshold for durability. Batteries often wear out over time, so systems that you can reuse indefinitely are much closer to the holy grail of solar energy storage.

Compressed Air Storage

Compressed Air Storage

Compressed air is another unusual storage system, albeit one with a lot of potential in certain applications. The basic concept is similar to pumped water storage, with electricity pumping air into tight containers to store it as kinetic energy. This pressure can be released to drive wind turbines and produce electricity as needed.

Compressed air isn’t quite a great system all on its own. It’s hard to get containers that are large enough and tight enough to store a lot of power over long periods, though it’s certainly not impossible.

The reason compressed air storage works is that it’s often possible to integrate it with another system, especially ones with moving parts that go through the air. If a forward motion pumps water, a backward motion might be able to pump air. Storing energy in two ways with one repeated motion can be more efficient, and that’s our main goal here.

Hydrogen Fuel Cell

Hydrogen Fuel Cell Storage

If there’s any realistic holy grail for solar energy storage, this is probably it. Solar power is a great way to produce fuels for various purposes, especially through some mix of hydrogen, oxygen, and carbon dioxide. This is a major principle behind the use of hydrogen fuel cells[4], which are significantly more effective than traditional internal combustion engines.

Solar fuels aren’t technically unlimited, but in most cases, they use resources that are so abundant that we’re not going to run out of them in any realistic scenario. This is especially true if we can both split and recombine atoms in the same amounts, ending with about the same amount of material as we started with.

One of the major advantages of solar fuel cells is the fact that they have outstanding storage efficiency, storage capacity, and power capacity. Less waste is always better, and the fact that we can use solar fuel cells that run mainly on water (or byproducts of water) makes them considerably better for the environment.

The main challenge now is making solar fuel cells that are practical on smaller scales. These can be quite difficult to power small devices with, for example, although they work well on anything car-sized or bigger. If we can make these more practical, they may well replace traditional power generators and battery systems.

Cheating the Law of Thermodynamics

We (probably) can’t cheat the laws of thermodynamics, but we can get close with smart applications of energy storage systems. This is especially true for minimizing costs.

For example, great insulation can keep even large areas warmer or cooler much more effectively. Cooling an area in the middle of the night, when electricity demand and costs are lowest, can minimize the amount of energy required to reach a temperature goal. With good insulation, the area can stay close to that temperature throughout the day.

This is drastically more efficient than letting the area heat up, then trying to cool it off later in the day. In effect, cheating is understanding the most efficient way to reach a particular goal, then setting things up accordingly.

The Ultimate Principle of Energy Storage

Past all of the details, energy storage comes down to one simple principle: anything that moves can be used to generate or store energy. This applies to everything from spinning turbines to pumping air and water. Efficient generation is all about using natural forces as much as possible because those functionally won’t run out of power.

New materials and construction techniques can improve the efficient use of energy, allowing you to get more from the same amount of electricity. By improving generators, storage systems, and the things we use, we can get more efficient in different ways and see better results.

Frequently Asked Questions

Here are some common questions that people have about solar energy storage.

  • Is Solar Energy Storage Worth It?

In the broader sense, yes, solar energy storage is worth it. We went into extensive detail on that above.

However, the answer can get trickier depending on your needs. The main question here is whether you can generate enough power to be worth storing. If you’re not storing and using that power, there’s no need to go to the cost and trouble of installing a storage system.

  • How Much Do Solar Batteries Cost?

The cost of solar batteries varies, depending on factors like the type of battery and their size. Many home storage systems are several batteries strung together, rather than a single large battery.

In realistic terms, costs can range from around $200 for a small battery to over $15,000 for a larger system that could power a small store or business. Anything larger than this usually goes straight to energy generation for emergencies instead of on-demand storage for anything more than short periods.

  • How Long Do Solar Batteries Last?

Solar batteries have different lifespans depending on how much you use them. Typically, greater use means shorter lifespans. This can be an issue if you’re storing and using power every day.

Most modern batteries will last somewhere between five and fifteen years. Modern solar power systems can last for up to 30 years, so realistically, you’ll probably end up replacing your batteries at least once or twice during the lifespan of your system. Keep that in mind when you’re collecting bids for it.

  • Will Solar Panels Work in the Rain?

Some panels can. These aren’t especially widespread yet, but recent inventions known as hybrid solar panels [6] can also generate electricity from the force of falling rain. This takes advantage of the fundamental principle above, which is that anything moving can generate power.

These panels aren’t quite as efficient in the rain as they are in sunlight, but every bit helps when you’re trying to maximize the amount of power you generate. The most important consideration here is that rain often falls at night when solar panels can’t otherwise work. Transforming rainwater into electricity can help provide steadier power, especially in rain-heavy areas.

Unfortunately, rain is also inconsistent in some areas, so this isn’t a perfectly reliable system. However, technology like this is increasingly practical and affordable, so it will probably become an integral part of future solar power systems.

Incidentally, gutter-based generators could become a way to get more use out of falling rain. Placing several simple turbine generators in downspouts on roofs can provide quite a lot of supplemental power for an existing solar system.

  • How Much Energy Storage Do Houses Need?

That depends on where you live. The average household uses a little less[7] than 11,000 kilowatt-hours annually. Some parts of the country use more electricity, while others are useless. How much time you spend at home heavily affects overall energy use.

In practical terms, this means that most houses need about 25 solar panels to cover their energy use. You may not need to add any energy storage at all, though. If your area lets you feed excess power into the grid, they’ll handle that for you. If you’re going totally off-grid, expect to shell out several thousand dollars for solar energy storage.

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