Student Energy Research Spotlight: Compressed Air Energy Extraction
By LT Michael Johnson
Energy is a hot topic in the world today. Transitioning from fossil fuels to resilient energy sources, such as solar and wind, has become a major focus within the power generation industry and in the Department of Defense. Increased energy independence is of strategic importance due to emerging grid dependence on networks, which are susceptible to cyber-attack.
Wind and solar are great for this movement but have the typical drawbacks associated with these energy sources. When peak power is produced with Solar (noon to mid-afternoon), the demand is the smallest. Wind tends to be the best generator at night, but demand is small then as well. Traditional thinking lends itself to using batteries and by extension, capacitors to store this excess energy. Unfortunately, existing battery technology does not provide large amounts of storage space for the energy required. Large battery banks, the size of buildings, would be required to store the energy required for a small area during high demand. Storage of energy outside of batteries also allows for more options to diversify energy storage.
Compressed air storage and infrastructure is already in place throughout the country. Gas stations have compressed air stations to inflate tires and auto shops have compressed air systems in place for air tools. All ships have compressed air systems on board for a multitude of purposes. Compressed air systems are easy to install and maintain and are very user friendly, typically just plug and play once installed.
The design uses low pressure air to power a small air motor to generate voltage to recharge a super capacitor. Voltage is sensed on the capacitor and the air motor is periodically cycled to maintain. This use could allow for smaller battery or capacitor banks with more intermittent recharging rather than a large bank to hold stored energy over a long period. Further, as this air motor runs on low pressure air, an air reserve at high pressure would be able to last quite a while.
The Navy could put this system to use in many applications, from shore to sea. Ashore, this could be used to help sever the Navy’s dependence on the existing power grids around the installations, providing power to buildings or vital equipment. At sea, with emerging weapons such as the rail gun and the directed energy weapons, this system could be used to minimize the impact to the ship’s existing electrical system. Using already installed air systems, this could be an addition to offset charging requirements to battery/capacitor banks being used to power loads with high electrical demand. This is scalable and mobile, only weighing about 35 pounds. Using all commercially available and inexpensive materials (the most expensive part is the air motor at $1000), this system is also very cost effective and easily implemented into existing arrangements.
In a world where energy resilience is essential, the Navy is helping to lead the transition into the various options using widely available existing technology.
