“The problem is that sometimes when we need energy, there is no sunshine or there is no wind,” Penn State University Petroleum and Natural Gas Engineering Professor Arash Dahi Taleghani explained. That plain fact is one of the oldest and most infuriating problems with renewable energy intermittency. Though sunlight and wind have become a reality in the world’s energy market, they are as good as discovering means of storing surplus energy for utilization when nature is on holiday. A breakthrough innovation by Penn State scientists comes at a time that can shift the paradigm on which renewable energy can be stored and, in the process, solve some of the environmental challenges of stranded oil and gas wells.
Compressed Air Energy Storage or CAES is not new, but because of the problem of cost, cost effectiveness has never taken center stage. The method is simple excess energy from renewable sources compresses air in underground caverns. During times of peak energy usage, pressurized air is released and utilized to drive turbines and generate electricity. The only downside is that conventional CAES plants are energy hungry and expensive. Taleghani and his group at Penn State created a new system that couples CAES with geothermal energy with significantly increased efficiency for the system.
The technology relies on the geothermal heat of hot rocks in wells’ reservoirs. Geothermal heat is an added boost if naturally heated compressed air is employed. Hotter temperatures produce increased air pressure to store more energy. This geothermal CAES technology, the research further adds, is 9.5% more efficient, a paradigm shift from what technology can do. “Without taking advantage of the geothermal setup, you could not get enough encouraging numbers,” said Taleghani. By numerical simulation modeling, the team concluded that by incorporating CAES plants in the abandoned shut in wells, air temperature was increased by 160°C and pressure by 0.5 MPA, both of which are major issues for maximum storage of energy. Not only is the concept technologically advanced, but it also resolves another vexing issue: environmental risk due to abandoned gas and oil wells.
The United States Environmental Protection Agency conservatively estimates 3.9 million abandoned wells in the United States. Stranded wells, therefore also tens of thousands of poorly plugged ones, emit methane, a very potent greenhouse gas, into the atmosphere and into water contamination. Reline these wells with energy storage has the twin benefit of updating two fronts closing them off to leaking and leveraging existing infrastructure to augment renewable energy plans. “If we use existing wells, we are basically hitting two birds with one stone,” explained Taleghani. “First, we are sealing these wells. That stops any potential leaks. And then if we are repurposing these wells for energy storage, we are still using the infrastructure that is in place in these communities.” The humanness of doing it this way is also pleasing.
Almost all but most of the non productive areas are fossil containing, and when the company became bankrupt, the towns lost all to maintain their economies. Reusing of the wells can reactivate local economies through the generation of employment opportunities in energy storage and maintenance. “It can potentially maintain employment in the area and allow communities to be part of the energy future,” supplemented Taleghani. This is also consistent with Penn State’s Recet mission, as it seeks to convert fossil energy infrastructure into renewable energy infrastructure. The proposal also eliminates the hindrance of the significant capital investments associated with the drilling of new wells for CAES systems.
Observe that by utilizing existing wells, operators save up front costs by considerable amounts, but this will accelerate the technology even quicker for industry operators. “This improvement in efficiency can be a game changer to justify the economics of compressed air energy storage projects,” Taleghani said. Coupled with lower cost, this increase in efficiency means that it is theoretically possible to observe large scale usage of geothermally supported CAES systems. Energy storage is central to stabilizing the grid as the globe transitions toward cleaner sources of energy.
Having excess renewable energy and producing it where and when needed, technologies such as CAES reduce the variability of wind and solar energy. As Taleghani rightly observed, “That’s why it’s very important to have some storage capacity to support the grid.” Penn State research, funded by the U.S. Department of Energy, offers an intriguing solution spanning the economics feasibility gap with the sustainability green factor. Although the concept is still in the infancy stage, it is hard not to appreciate the benefit derived from geothermal supported CAES systems.
Through the utilization of redundant existing oil and gas wells, this new process not only offers the promise of energy storage from renewable sources but also circumvents environmental concerns and resuscitates towns. While the world is seeking pragmatic solutions to its energy requirements, this two way process can be a template for sustainable development. Journal of Energy Storage research results are a clarion call to research more into what is possible with the reuse of existing infrastructure to energize a greener world.
