Energy grids fluctuate throughout the day as demand and production increase and decrease. Usually, during peak hours, demand for electricity is close to or exceeds the production capacity at that time. During off hours, usually in the night, production capacity far exceeds what is being drawn from the grid. This results in a natural unsteadiness to the energy grid and experts have been experimenting with ways to make sure that the lights always stay on.
One of the most common ways that energy is stored in large scale for the grid is through pumped hydro electric storage dams. The Taum Sauk reservoir is one of these types of "physical batteries" that essentially stores excess energy through potential energy in water mass. When there is excess power, water is pumped to the high elevation of the reservoir. When there is too little power, water is released thus generating electricity again. While this is a current solution, it is only suitable in the perfect geographical location.
One California company has come up with another solution, the Advanced Rail Energy Storage System, or ARES for short.
[Image Source: ARES]
This technology is essentially a land based train that takes excess electrical energy and stores it through potential energy gained in large train masses. In rudimentary terms, it's the equivalent of pushing a large rock up a hill when you have the energy so you can push it down later when you need more energy.
ARES technology uses rail cars that essentially carry extremely heavy blocks of concrete to the top of a hill or specific grade. The rail cars can be powered by electricity off the grid during off-peak hours when there is little demand. During peak hours, the rail cars are then released from the top of their grade to move down the hill, transferring potential energy into electrical energy through regenerative braking.
While the technology may seem too simple to work, the company claims an 80 percent efficiency rate of energy input to energy output through storage. Each car can deliver constant power for up to 8 hours.
The company has put together several test systems including a 268-meter track in California. The Nevada Public Utilities Commission has tasked ARES with constructing the grid energy system in the mountains of Nevada in order to stabilize their grid.
While it may sound absurd, in only a few years, Nevada's electrical grid may be stabilized by a fleet of automated trains weighing 300 tons each. The company has specifically designed the system to work best on a grade of 7.2%. This allows the best transfer of energy from potential to kinetic while also allowing the trains to maintain stability. When each 300-ton train moves down the slope, it can provide 50MW of power to help stabilize the grid. In total, the track for the Nevada system will stretch 9.2 kilometers through the desert with an elevation differential of 640 meters (2100 feet).
[Image Source: ARES]
One of the most advantageous qualities to the energy system is the low cost compared to other energy storage techniques. The company states that it can be implemented for half of the cost of the cheapest electrical energy storage system. The system also requires no external input in the form of fuel or water, it purely operates from the energy coming from the grid. These qualities are impressing many electrical companies across the world and have taken a fairly rudimentary design and turned it into a possible universal solution
The concept of physical batteries storing excess electricity through potential energy is one that currently leads the large scale energy storage techniques. With the emergence of electric cars, Elon Musk and other leading minds believe that the future of maintaining a steady grid my lie in all of our cars batteries. By allowing the energy grid to draw power from our cars during night time charging hours, it may allow every electric car to essentially function as a small battery helping the overall infrastructure maintain level output. In order for this system to practically work, however, the entire energy grid would need to be redesigned for 2 way flow and certain constraints would need to be set in place around how and when power can be taken from a car's battery.
All in all, between electric cars and concrete gravity sleds, the power grid is becoming significantly better managed.