Energy Storage Crucial to Renewable Energy Success

27 February 2017
Posted by Megan Ray Nichols.

In 2016, the U.S. consumed 10.16 quadrillion British thermal units (Btu) of renewable energy, according to the U.S. Energy Information Administration. That number is expected to rise to 10.934 quadrillion Btu by 2018.

Many have hailed renewable energy resources, such as wind, solar, hydropower and geothermal power, as the answer to the question of how to reduce our carbon emissions and slow climate change, while also providing affordable, adequate energy to consumers.

Others say renewables are not nearly reliable enough to solve our energy problems. After all, the sun only shines during the day, and the wind blows in random intervals. What will we do if we’re relying on wind energy and demand is high on a day without much wind?

One part of the solution to this issue is energy storage. Scientists continue to research, develop and deploy various technologies that store energy when there’s excess and release it into the grid when needed. For example, a wind farm can store the energy it creates during the night when demand is low, then release it into the grid during peak demand hours the next day.

Here are five energy storage technologies, and the pros and cons of each.

Batteries

Developing a better battery for energy storage has been a major goal of the energy industry for the past few years. There are different types of batteries used for energy storage. These include lithium-ion, lead-acid, metal air, and sodium-sulfur.

The development of electric vehicles has led to significant improvements in energy storage batteries. A variety of companies make batteries for both utility-scale and residential energy storage.

Batteries are a suitable energy storage solution because they’re efficient, clean and can provide stored energy very quickly. They can also be located either at generation facilities or closer to energy consumers.

While the cost of batteries has been falling, they’re still not as cheap as some other storage technologies. Some people worry that installing them at the large scale necessary for our electric grid will not be economical.

Compressed Air

Compressed Air Energy Storage (CAES) technology compresses air and stores it in an underground container. When electricity is needed, the pressurized air is realized and heated, which causes it to expand. This expansion drives a turbine and generates power.

CAES is a relatively new technology still in development, but funding for research and development is growing. Some energy is lost through heat during the process, making it less efficient than some other energy storage methods.

However, proper maintenance, operation, and storage can increase efficiency. Researchers are currently working on ways to save that energy and use it to heat air later in the process. CAES can help renewables to better navigate fluctuating demand and better compete with fossil fuels for a lower price than many other methods. 

Pumped Hydroelectric

Hydroelectric storage is one of the most developed and widely used energy storage techniques.

A pumped hydro system contains two reservoirs, one at a higher elevation and one that’s lower. Water is stored in the higher reservoir and when power is needed it’s released into the lower reservoir, turning turbines and generating electricity as it goes.

With an efficiency of around 75 percent, this method is one of the most efficient storage methods available. The fact that it’s already been well-developed gives it another advantage over other storage technologies, at least for now. It is also relatively affordable and is suitable for large-scale use.

One downside is that energy is not instantly accessible when it’s needed. Another is that it must be used at specific sites, ones with two areas at different elevations for the two reservoirs.

Cryogenic

Cryogenic energy storage, also known as liquid air energy storage, cools air with electricity until it reaches a liquid state. This liquid air is stored in a tank and, when power is needed, is turned back into a gas by waste heat or ambient air. This gas then turns turbines and creates electricity.

Cryogenic energy storage works similarly to pumped hydro, but its location requirements are much more flexible. This means it can be located near power users. It also works well on a large scale and for long duration uses.

Alone, this system is not as efficient as some others, but using waste heat and cold in the process can improve its efficiency. The system is also relatively new, although it uses components of other, more established systems. This means it is not as well-developed as some other energy storage methods, but it may improve in the future.

Thermal

The second most-used energy storage technique in the U.S. is thermal storage. Thermal storage keeps energy at a temperature that will be useful somewhere down the line.

For example, one method involves using excess energy produced at night to freeze water into ice. During the next day, the cold acts as-as air conditioning.

In another system, solar energy is used to create molten salt. That heated salt is then used to create steam, which drives a turbine and generates power.

Other examples include heated water, rocks, gravel or concrete slabs.

Thermal heating methods are often relatively cheap and efficient, as well as environmentally friendly. They also work in a variety of places, including at the generating site and where the demand is.

One disadvantage is that some methods are less useful at certain times of the year. For example, air conditioning isn't needed in the winter, so ice energy storage systems aren’t used.

What's in store for energy storage?

Right now, engineers are utilizing a combination of different energy sources - battery, compressed air, hydroelectric, cryogenic and thermal - based on the location of the power system, to store the excess energy produced during renewable energy production to address current issues with emissions, security, distribution and peak demand.

Energy storage is one of the most promising sectors of the energy industry. It’s developing a broad range of possible solutions that have the power to improve our electrical grid, especially when paired with the power of renewable energy resources.  While our current solutions have their respective drawbacks, they are nonetheless impressive technologies. Plus, engineers keep experimenting with new techniques and technologies to improve the system.  

In the future, we could get our energy from microbes that convert methane into fuel or space-based solar power.  The industry is already discussing transitioning from traditional power plants to virtual power plants. Only time will tell which of these technologies gain popularity, but one thing is for certain, the potential for energy storage is a vast as the methods to produce that energy.

Comments

Heating uses an annualised 60% of household energy where I live in Sydney and a lot more than that in winter. A well insulated house would need to have stored perhaps 20 or 30kWh of energy for central heating on a cold, cloudy winter's day. This would be too expensive a storage method if implemented using batteries (more than $570 per kWh for a Lithium battery).

However there is a solution which radically reduces the overall cost by reducing the amount of battery storage required.

The solution is to store energy for heating as heat. Hot water storage (45 to 90 Celsius operating range) can store 52 kWh per 1000 litres, water is cheap ($2 / 1000 litres) so most of the cost is the tank. This can be a cheap unpressurised tank for hydronic heating or a normal mains pressure tank for the domestic hot water service. The tank needs to be well insulated of course but insulation is cheap.

Hot water running through wall-mounted radiators is used all over the world for central heating. Hot water at 90 Celsius is too hot to use in wall mounted radiators so a tempering valve mixes in cold water to reduce the temperature but this does not involve any energy loss.

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