Balancing the grid is hard. There has always been waste in the system because running into deficit could cause total collapse. However, there are people looking for good solutions. The grid previously relied on peaker plants, burning fossil fuels during high demand times so most of the time it only what was needed was run.
Those plants, in combination with stored hydropower, composed the entire system of dealing with energy fluctuation. With continued advances in clean energy, solutions for both long and short term power storage have been examined, with a keen eye on making it cheaper and easier to store power for later use. Whether only for high demand times, or to balance out larger trends, energy storage provides a powerful aid in converting the grid to clean energy and combating intermittency.
Energy storage is an efficient way to balance the grid. Typically, when power companies respond to up-ticks in demand, there is some delay as fossil fuels take time to reach peak efficiency. However, most forms of energy storage are available in an instant and allow us to explore at a deeper level the renewable systems that are creeping up. We will never have sunshine at night and we need to account for that.
Currently the United States has 23 gigawatts of storage capacity, 96 percent of which is in pumped hydroelectric. This was mainly implemented in the 60s and 70s because nuclear power plants had no ability to scale up or down, and were a huge investment. In order to balance differences in demand across the day, water could be pumped uphill during low demand times, such as at night, and then be allowed to flow down during periods of higher demand, complementing the base-load.
Now there is a similar, but an exaggerated problem. Rather than having stable production and stable demand, we now have unstable production and unstable demand. Nowhere is this clearer than California, which has some of the largest numbers for solar energy production in the country. While this has been good for California for many reasons, it has resulted in a phenomenon called the "Duck Curve," which is based on the demand that has to be produced from sources other than solar throughout the day. There is a massive ramp up in other forms of production that have to be performed every day. Right now, the ramp up is dealt with fossil fuels, but it would be much better if the other power storage options were implemented.
A storage technique with a large amount of background knowledge is compressed air. We have long used air motion to produce power (wind turbines) and are extreme experts in compressing air (tires), so it seems natural to use the two in conjunction to store power. While this is not the most efficient way to store power, it has been quite refined, since it uses already developed technology. There are currently two commercial facilities which compress air for energy storage, with more being planned.
One of the main advantages of compressed air is the nearly limitless recharge-discharge cycles. While other forms of storage have a limited life, which adds to cost, compressed air's cost lays almost entirely in setup cost. A small amount of the costs result from power loss, but almost none for maintenance. This means that the longterm viability of air storage looks good. The high cost may be prohibitive in the current environment, but as we continue to invest in energy storage, more long term options may prove attractive.
Just as compressed liquid hydrogen can be used to power cars, it can also be used at a larger scale to complement the grid. By producing pure hydrogen, and compressing it, we can store a lot of power at a fairly efficient ratio. Similar to compressed air, this is a technology that has had a lot of time for refinement. Chemists and various engineers have been extracting hydrogen from water for a long time, and the physics of compressing it are well understood. For the same reason it makes sense to use as car fuel, it makes sense to use for grid storage. It is energy dense and can be utilized using relative cheap infrastructure.
One potential issue is that it might not make sense to only use during peak times. The hydrogen may prove a valuable commodity, and not just a grid level energy storage technique, harming viability for this technique to combat the issues with renewables.
One other way of utilizing grid power now so you don't have to later, is heating and cooling. By creating ice or molten salts, you can use energy now for heating or cooling that would usually be used later, whether at an industrial or individual level. This would require homes to be equipped to understand the dynamics of the grid and utilize power accordingly. Many areas are already on this path, equipped to have variable electricity prices, so it is not unlikely that this will complement any other future power storage technique.
The next couple of techniques all rely on turning grid power into potential energy. By raising matter against gravity, energy is used that can later be reclaimed by having downward motion turn some sort of generator. These are all in the vein of pumped hydroelectric power, which is by far the biggest current contributor to United States' energy storage. Besides solar power, essentially all the power in the grid gets added through movement; kinetic energy being turned into electrical energy. We are very good at making this sort of power, and also fundamentally understand that when we lift something up, it comes down with force. Because these concepts are so fundamental to our understanding of power, it is logical that most of our storage would come from these techniques.
There is no doubt that hydroelectric is an extremely effective and useful way for us to store our power. Water is heavy and is relatively easy to move. Moreover, dams produce power passively, in addition to serving as a storage technology. However, there are two good reasons we may be at our peak for hydroelectric storage.
First, we have built up most places where it is convenient to use hydroelectric. In order for this method to be effective, you need fresh water, as salt water causes many complications. All the ideal spots to put a dam and utilize hydroelectric (and its storage potential), have already been claimed. These spots are being utilized, otherwise, we wouldn't have anywhere near the 23 gigawatts of storage we do, but there just aren't too many more feasible ones.
Second, in the remaining spots, it could prove environmentally disastrous to build up. When a dam is built, the supply of sediment to the areas downstream is cut off. This means that all the life in the ecosystem that relies on that sediment, whether for a home or to balance ion levels, will have a much harder time functioning. In the 60s and 70s, these were issues people cared less about, but now the natural ecosystem is very much in the public conscious.
Trains are an underutilized resource in the lifting something up and letting it come down arena. We have many railways in the United States that do not currently serve any purpose. We didn't take away the tracks when we moved to highways, we just stopped utilizing them. By moving a train uphill and letting it roll down, powering a generator in the process, we can extremely efficiently store power. It doesn't make sense to build more railways, but any future storage solution will definitely include railways as part of their technique. The infrastructure is already there, it makes sense to utilize it.
One of the most interesting and promising techniques of energy storage is also one of the simplest. Lifting concrete blocks and letting them drop down has very little loss, and costs very little to set up. It is one of the cheapest ways to store power and has a very long life span. It also uses waste resources, just requiring any heavy thing with enough integrity to lift. It is basically as simple as it seems, and it works in any conditions and with any grid.
Image credit to: Quartz
Flywheel storage involves spinning a wheel up in an extremely low resistance environment, and then when the energy is needed, using that spin to produce power. They are generally within a vacuum, and therefore have very low wear and tear. They have a very rapid response, with the spin up and down directly related to the energy in and out. They are not too expensive to set up on the small scale, however they do not scale up very well, with the average flywheel only storing a few kilowatts of power. At neighborhood level, they could definitely play a role, but at the grid level, they have limited potential.
The most obvious area of energy storage for the future is batteries. Batteries are the only item in the list that are rapidly decreasing in price, so it is likely that they will play a large role in the future of energy storage. Batteries have the lowest input/output loss of any item on the list, so the main constraints are upfront cost and limited lifespan. Currently, a large scale battery storage solution is present in Australia, but due to the current lack of urgent need, and dropping price, there is limited investment in batteries as a grid level technology. However, batteries are used in many things besides grid storage, so research and development investment show no sign of slowing.
Car batteries in electric cars could provide a potent medium for adding storage to the grid in the near future, and helping to adjust for the demand production difference. Electric cars will likely only be used for some portion of the day, and for the rest of the day they will have large battery capacity not doing much. If vehicles are integrated with homes, they could be charged at times of high production, and discharged when needed. If electric vehicles form the abundance of transportation as many predict them too, this could be the most important energy storage method of the future.
It is likely that no one solution will dominate energy storage in the future. Each of these techniques could play their role, and more technology will doubtlessly be developed. Right now, we are managing the duck curve and there is little incentive to meaningfully transition to more costly storage techniques. However, as time goes on and renewables continue to decrease in price, our interest in these techniques will skyrocket. In order to solve the problems related to solar and wind, we need to research these technologies, and luckily lots of smart people with interesting ideas are working hard to make energy storage a reality.
Title image credit to: Washington Times