How does large-scale energy storage work?
It’s Fun Fact Friday and today we’re going to take a look at energy storage. Power demands fluctuate throughout the 24 hour cycle, creating the need for adjustments in supply. Many traditional power generation methods produce a consistent amount of energy, creating a surplus during times of low need, like in the late night and early morning, and a shortage during times of high need, like in the afternoon and evening. Human activity patterns mean renewable energy is especially vulnerable to peak demand, since solar and wind are both strongest during the day, but peak power needs are usually around 7 pm. Let’s take a closer look at why energy storage solutions are needed, how energy storage works, some of the technologies already in use, and some of the new technologies in the pipeline.
Why is energy storage needed?
You might be wondering why we can’t vary output of the conventional energy generation methods to meet demand. Most traditional energy generation methods from nuclear and fossil fuels are either incapable of adjustment and generate fixed amounts of power, or take too long to increase or decrease output due to their sheer size. For example, nuclear power plants generate electricity 24 hours a day, with no option to turn the flow up or down. They also never shut off, so power production is constant and they may not meet peak demand in the afternoon and evening, and likely overproduce in the early hours of the morning when electricity needs are low.
Energy storage methods help balance power demand with power generation from different sources, allowing this low cost power to be stored and retrieved as needed for peak demand times. Some fossil plants may be able to increase or decrease production, but the scale of these plants mean that increasing and decreasing output is too slow to help. Renewable sources only produce at certain times. Wind blows the hardest in the early afternoon, although at higher altitudes where newer, larger wind turbines operate, it may blow harder at night. Solar generation is at its peak in the middle of the day and early afternoon as well, with no generation at night. Energy storage can fill in the gaps between all of these power generation methods, helping to respond to changes in demand rapidly, something other forms of power generation can’t do.
Grid-scale battery system. Image Credit: Windpower Engineering
For some communities, power generation isn’t up to the grid, but to themselves or smaller microgrids. The farther you are from the electrical grid, the more important energy storage becomes. Homes away from the grid are more susceptible to power outages and disruptions than homes in cities, and may go longer without power during a disaster. Islands and microgrids are often disconnected from the main grids entirely, meaning they need energy storage to guarantee power availability.
How does energy storage work?
The topic of energy storage is becoming more popular, especially with lithium ion batteries in cell phones, cars, and even at grid-scale, but people have stored energy since the dawn of the electrical grid. The first energy storage was simply fossil fuel plants that could scale up and down with demand, the energy stored within the coal, natural gas, or other fuel used in the plants. This worked at smaller scales, but the ever growing amount of energy consumed today requires more storage. With the enormous increase in power demand and a combined focus on renewable energy, other storage solutions have come into widespread use, but at their core, all of the solutions simply store energy now to be used later. There are two main methods: mechanical storage, which uses water, air, or other materials to store energy, and other methods, such as batteries.
What are the methods for storing energy?
Pumped hydro is one of the oldest and most common methods for storing energy on a massive scale. In total, the United States has 23 gigawatts of storage capacity, and according to the Union of Concerned Scientists, or UCS, “Pumped hydroelectric storage accounts for about 96 percent of this total storage capacity, most of which was built in the 1960s and 1970s to accompany the new fleet of nuclear power plants.” Due to the inability of nuclear power to regulate output, a large scale solution was needed to make use of wasted power at night and retrieve it during peak demand. It starts with two large water reservoirs, picture a lake on top of a hill and a lake at the bottom, with a pump in the middle. At night, when power demands are low, the nuclear plants power pumps that recharge and move water from a low reservoir to a higher reservoir. The next day, during peak demand times the water can be discharged to the lower reservoir, generating power. This is an excellent solution that allows for precise power generation and easy adjustment of just turning the faucet on and off. The downsides to this method are the vast expense of building the facility and the potential harm to the environment, especially when hydroelectric power comes from a dam rather than pumped hydro storage. Hydroelectric power is generated through building a dam on a river, creating a reservoir or lake behind it. Water flow through the damn can be regulated as need to generate electricity.
Pumped storage hydropower. Image Credit: Energy.gov
Compressed air is another form of mechanical energy that uses the elastic potential of air to store power. During non-peak times, air is compressed using electricity and pumped into underground caverns. When power is needed, the air is released and mixed with natural gas in a combustion turbine, utilizing only a third of the natural gas that would normally be used to generate electricity. Since this method requires an underground reservoir, they are location specific, and in fact, only two plants exist: one in Germany and one in Alabama. They were built in 1978 and 1991, respectively. Companies are proposing building more plants around the United States, but none have yet been built.
Hydrogen is an interesting technology for storing energy, using electricity to generate hydrogen that is then stored for use as a fuel. Some new wind farms incorporate hydrogen production directly into their plans with technology in development to create hydrogen at the turbines, possibly even inside the turbines themselves. Hydrogen is created via electrolysis and can then be used to power ships or as a clean burning fuel for electricity generation.
Thermal Energy Storage
Thermal storage generates electricity by capturing power from the sun for later use. According to UCS, “Concentrating solar plants can capture heat from the sun and store the energy in water, molten salts, or other fluids. This stored energy is later used to generate electricity, enabling the use of solar energy even after sunset.” There are projects out west in operation and in planning for California, Arizona, and Nevada. The Rice Solar Energy Project will power 68,000 homes around the Blythe, California area using a molten salt storage system. This type of energy storage can even function as an end-use system to freeze ice at night, which can then be used the next day to help air condition homes. There is even a pilot program to store energy in residential water heaters.
Crescent Dunes thermal solar plant near Las Vegas. Image Credit: Science Alert
Flywheel Energy Storage
Flywheels take power drawn from the grid to spin the rotors very fast, storing the power as rotational energy. A fairly simple design, a flywheel is a large cylinder inside which is a rotor in a vacuum. When the power is needed, the rotor uses its inertial energy to generate electricity back to the grid. There are a lot of upsides to flywheels: they are compact, last a long time, and require very little maintenance. Because of their small size, they can be located near consumers of power that need them. The only downside is that most of these devices hold kilowatts of power, but this can be overcome with “flywheel farms” that can store megawatts. The largest flywheel farm in the United States is Beacon Power’s Stephentown Flywheel Energy Storage Plant in New York, with a capacity of 20 MW.
Flywheel energy storage. Image Credit: Better World Solutions.
Batteries are a technology that everyone is familiar with, from flashlights and cell phones to laptops and electric cars. Grid-scale batteries are just heating up and “There are many different types of batteries that have large-scale energy storage potential, including sodium-sulfur, metal air, lithium ion, and lead-acid batteries. There are several battery installations at wind farms; including the Notrees Wind Storage Demonstration Project in Texas, which uses a 36 MW battery facility to help ensure stability of the power supply even when the wind isn’t blowing”, according to UCS. The electric vehicle industry has been a huge driver of new battery technology, causing sharp increases in battery performance with decreases in costs. EVs can even act as supplements to the grid through battery discharge.
Stacked Block Energy Storage
Energy Vault has developed stacked block technology, a brand new method that works similarly to other mechanical methods of energy storage, and was inspired by pumped hydro. Cranes stack 35 ton bricks into a tower hundreds of feet in the air, storing the energy in the elevation gain. Energy is discharged by lowering the blocks back down to the ground. The first small scale prototype was built in 2018 followed by the current full size version completed in July 2020. Software development and testing are being performed as of late 2020. The towers are expected to have a capacity of 20 to 80 MW and a continuous 4-8 MW discharge for 8-16 hours. They are already honing their technology to develop a new system that could generate multi-GWh of storage capacity.
Stacked block energy storage. Image Credit: Energy Vault.
There are many methods to store energy, with improvements on old and new technologies on the horizon. As the world consumes more energy and at the same time seeks to become more energy efficient, storage will play an increasingly important role. New technologies like anti-solar may be able to help with nighttime demand by turning residual heat into power at night, but are not ready for mainstream use. This type of technology is also brand new and currently operates at 25% of the efficiency of solar, so more robust energy storage solutions are still needed as power needs around the world continue to grow.
The team at OneStep Power is excited to see the new technologies that keep the power flowing. Your energy could be coming from nuclear, gas, wind, hydro, thermal, flywheels, or even stacked blocks! So, this Fun Fact Friday we’ll leave you with a question: do you know where your energy comes from?