We all rely on energy. When it comes to clean energy, solar and wind are proving to be our greatest alternative to fossil fuels. However, when it comes to solar and wind power, a common question asked is what happens when the wind isn’t blowing and the sun isn’t shining? Is clean energy really dependable? These are all good questions. The answer lies in how we bridge the gap between the time energy is produced and the time when energy is used – aka energy storage.

To start, we’d like to define energy. The simplest scientific definition of energy is that energy can exist in different forms: heat, light and motion –  to name a few. Energy can also be grouped into two categories: potential and kinetic. Energy cannot be created or destroyed but it can be converted from one form to another. For example, in a traditional power plant the chemical energy in coal or natural gas is heated to become thermal energy, which boils water to produce steam that moves turbine generators. Chemical energy is turned into electricity to provide your phone battery with power.

Chemical battery storage has provided a means to store the unused energy, but also comes with its own environmental shortfalls. Proper disposal of chemical batteries is expensive. Perhaps we can store energy without chemical batteries by leveraging technology of the past.

Mechanical batteries store energy in the form of motion or potential energy with no chemicals and no carbon emissions. Sounds like some kind of tomorrowland fantasy, right? What if I told you that not only do methods for mechanical energy storage exist right now but that most of them have been around for decades and one of the most promising ways to store energy predates just about every other human-made technology. Did you know that in the early 1800s the flywheel, basically just a wheel on an axel, was used to store energy? In fact, storage energy flywheels have been around since at least 4000 BC, debuting as the Potter’s Wheel. This mechanical battery consists of a heavy accelerating mass on a wheel rotor with a shaft connected to a motor generator. As a wheel accelerates to high speed all that energy gets stored as rotational energy. When you need that energy you can switch to generation mode, extracting some of that rotational energy and creating electricity from the slowdown.

When it comes to energy storage, large scale flywheels have the same basic principles. Around 1940, a Swiss technology company developed a functional alternative to buses and trolleys using flywheel technology, aka. the Gyrobus. Instead of diesel or electricity fuel, a huge flywheel would be spun up at every stop while passengers loaded and unloaded creating enough energy to propel the bus to the next stop; a truly groundbreaking technology for the time.

Today, NASA is exploring flywheel technology for satellites and other applications due to its high energy density, long life, reliability and efficiency compared to other energy storage options. When compared to traditional lead acid cells which have energy densities around 30-to-40-Watt hours per kilogram, a flywheel-based battery can reach energy densities three to four times higher at around 100-to-130-Watt hours per kilogram. You may think that a flywheel stops quickly, but figures show that typical energy capacities range from 3 kWh to 133 kWh, with a storing efficiency of up to 90%. On top of that, flywheels unlike chemical batteries do not produce any waste or emissions.

Recently deployed flywheel storage banks show improvement in using flywheels as standalone energy storage. A couple of examples are the frequency regulation plants such as the Beacon Power 20 MW flywheel energy storage plant in Stephentown, New York using 200 flywheels built in 2011 and a similar 20 MW system at Hazle Township, Pennsylvania built in 2014. Along with those, Amber Kinetics Inc. has an agreement with Pacific Gas and Electric (PG&E) for a 20 MW / 80 MWh flywheel energy storage facility located in Fresno, CA with a four-hour discharge duration.

While all that sounds great, flywheels are not entirely foolproof. Current flywheel technology requires electricity to accelerate the flywheels. Although fully mechanical options are in development, the challenge remains to overcome issues due to mechanical stress and fatigue limits. As the future unfolds, newer building materials and technological developments such as vacuum chambers, magnetic bearings and lighter carbon fiber material could help offset some of these disadvantages and increased energy efficiency. That could also make the technology incredibly expensive but with one of the highest energy density ratings of any currently explored option.

Would you consider changing your energy storage devices? Are you keeping up with the advancements in energy storage and their market adaptation?

What’s up next? In our next article, we’ll continue to discuss historical technologies as we explore the future of energy storage. In the mean time, check out some of our other recent insights and don’t hesitate to reach out to anyone of our team members to learn more. We’re excited to hear from you!