Hydroelectric Pumping Compressed Air Energy Storage (PHCAES) is a new system that can deliver stored energy at two to three cents per kilowatt hour. This cost, much lower than that of lithium batteries, is similar to the proven technology Pumped Hydro Energy Storage (PHES). Although it has many similarities to PHES, PHCAES has significant advantages over PHES, including lower capital costs and much less floor space required.
Like PHES, PHCAES uses a ground-level water tank and power plant. The difference is in the pressure tanks. While PHES uses a high altitude water tank to create water pressure, PHCAES uses a depleted underground well (gas / oil / water) which contains a water tank as well as high pressure air to create its water pressure. PHES and PHCAES pumps pump / reverse the flow of water between the surface water tank and their respective high pressure tanks through a power plant to store or generate electricity. See the numbers below.
PHCAES water tanks rejected:
Charged PHCAES water tanks:
The investment costs will be lower for PHCAES as this system uses an existing well compared to building a large elevated water reservoir for PHES. PHCAES stores energy at a much higher pressure, therefore requiring a surface water reservoir five times smaller than PHES for the same amount of stored energy.
As the air pressure increases during charging with the PHCAES system, a small amount of heat is created. The heat produced is much less than the heat created by standard open compressed air systems (isochoric compression vs adiabatic compression). This small amount of heat reduces the efficiency of the round trips and increases the cost, but the increase is offset by the investment cost savings.
The use of wells for storage is well known. For example, in the United States, 4.8 billion cubic feet of natural gas are currently stored at pressures between 500 and 3,000 psi in approximately 17,000 underground oil / gas wells, aquifers, and salt formations. The volume of liquids that a well can hold, as seen in fracturing liquids, is also well known. These underground reservoirs already exist, are inexpensive to operate, and occupy virtually no land space.
If the 2.7 million abandoned oil and gas wells in the United States were used for PHCAES, they could store 60,000 gigawatts of electricity. This energy storage is enough to store one hundred percent more than six hours of the electricity produced per hour in the United States today. This storage does not include aquifers, which would add significantly to the total. In addition, energy can be stored for much longer than the four hour energy storage window typical of lithium batteries.
PHCAES will provide an attractive electric energy storage solution as the world shifts from fossil fuels to intermittent renewables like wind and solar. With its potential low cost of two to three cents per kilowatt hour and its many possibilities for low cost underground sites, it could make the transition easier and faster.
Our company, PowerXpro *, LLC, does not have the ability to commercialize the patent pending PHCAES technology. We are looking for an interested person to take over the whole project. Our goal is to see the project come to fruition for the good of the world, rather than for big profits.
If you are interested, please contact Bob Cantrell, President of PowerXpro LLC, at bob.cantrell @gmail.com.
*This item is supported by PowerXpro. All graphics provided by PowerXpro.
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