“We think storage will be absolutely necessary to enable the deployment of solar across the grid at extremely high penetrations” – Eric Carlson, SolarCity
The expansion of renewable energy projects in North America presents an unprecedented opportunity for Edison Power Constructors and other PLH companies. There is a massive amount of new infrastructure needed to build these projects and connect them to the grid while maintaining optimal power availability.
The adoption of renewable energy comes with unique challenges. Renewable power sources produce varying outputs, depending on the conditions nature provides that day. Renewable energy cannot be stored and used the same way traditional fossil fuels are. How can a country become independent of fossil fuels when renewable energy production varies in ways that are out of our control? Grid level energy storage is the solution, and the United States is a world leader in its implementation.
Types of Grid Energy Storage
Renewable energy production rates don’t usually line up with peak and off peak energy usage. Below are some of the most promising technologies which can store energy produced during off peak hours for later use.
Compressed Air Energy Storage
There are two main types of compressed air energy storage
Constant Volume Air Storage
Constant volume means the storage space doesn’t change. This could be an empty mined cave, storage tanks, pipelines etc. Air is pumped into the storage container with a compressor, and then released with a turbine to recapture the energy. The pressure in this type of storage changes based on how much air is compressed or decompressed from the chamber. There are pressure limitations on this type of storage based on the limits of the chamber, compressor and turbine.
Constant Pressure Air Storage
Constant pressure storage has the same pressure in the air container, but the container’s volume changes based on how much air it contains. This type of storage is placed a few hundred meters below water at a constant depth to maintain a constant pressure. One benefit of this type of system is that all the air can be used because pressure is constant if it is full or almost empty. This air energy storage technique tends to be more expensive than constant volume due to the container’s cost and its need to be deep underwater.
One challenge associated with compressed air energy storage is that when air is compressed, energy is released in the form of heat. In order to make this storage solution as efficient as possible, the heat must be stored or prevented from escaping the container. Another concern with this type of storage is tank failure. Over time, tank structural integrity can degrade, leading to failures and dangerous explosions. This method has been shown to be 60-90% efficient.
Battery Power Storage
Batteries are the ultimate solid power storage solution, especially for the grid. There are countless battery technologies which continue to be developed in the search for the perfect power storage device.
In the past, lead-acid batteries were primarily used for power storage due to their price and stable technology. Lithium ion is beginning to pass up lead acid in every way though. New lithium ion technology is cheaper, has more life cycles, weighs less, is smaller, charges faster, wastes less energy and needs less maintenance. Because of these advancements, lithium ion is better in almost every way.
In recent years, the mass production of lithium ion batteries has led to their price dropping faster than even the most optimistic predictions. Because of this, along with technology improvements, the majority of new grid storage projects (over 90%) are going to use lithium ion technology.
Tesla has taken grid lithium storage one step further by creating lithium ion battery packs mounted in homes, capable of powering an entire house. This battery pack can store power from solar panels and wind turbines, or charge when utility rates are low for use during peak hours. This type of technology has the potential to mitigate risk within the grid by better distributing energy storage. This type of distributed technology can lead to extraordinary resilience within the power grid.
Hydrogen Power Storage
Hydrogen power storage has been a dream of clean energy advocates for decades. Renewable energy can be used to produce hydrogen from either natural gas or fuel cells. Once hydrogen is produced, it would be stored in tanks and then converted back to energy using fuel cells or combustion.
There are many benefits of hydrogen fuel, including its conversion to water once combusted. Scientists have been researching ways to make hydrogen production more energy efficient, but there is still a ways to go before it can compete price and efficiency wise vs batteries. The efficiency of hydrogen storage is around 20-24% which makes this storage solution uneconomical on a large scale.
Hydroelectric Energy Storage
Hydroelectric energy storage does exactly what hydroelectric dams do, but in reverse. When there is extra energy being generated during off peak times, it can be used to run pumps, pumping water up into a reservoir for later conversion back into energy. This method is relatively efficient with 70% to 85% efficiency.
While this method is efficient, it requires unique geological features which are not common around many power plants. This method requires two reservoirs at considerably different heights close to the power plant. If a hydroelectric dam exists at the site, there is still a significant amount of work and money required to build the upstream pumps.
The United States is leading the way when it comes to grid energy storage. Currently we have 418 MW between over 250 projects. As renewables continue to expand their market share, grid scale energy storage will continue to expand as well. Edison is excited for this unique transition and prepared to build the next generation of quality, environmentally friendly electric infrastructure.