gap project portfolio » Applied Exergy


Project Title: Thermal Approach to Grid Energy Storage (TAGES)

Principal Investigator: Dr. Hailei Wang, Oregon State University

Company Contact: Bailey McCallum, CEO, Applied Exergy

Description: A remarkably simple and cost effective energy storage system can be realized by using waste (or otherwise low-grade) heat. This approach to energy storage is poised to open up new areas for waste heat utilization, energy recovery, and enhanced power plant operations. The concept uses inexpensive, bulk storage of frozen water slush and conventional technology to store energy from the grid. But unlike currently existing cold storage technologies meant to relieve air-conditioning loads, this thermal approach reconstitutes the electrical energy and places it back onto the grid. Because it is thermally based, integration with existing power plants and HVAC systems is straightforward. Very low-grade heat in the range of 40 to 80 degrees C can be utilized to boost round trip efficiency into the 70 to 90% range, depending on conditions. Because of the versatility afforded by thermal storage, the concept presented here should be considered scalable platform technology useful across many areas of application - it is referred to in the following pages as TAGES, which stands for Thermal Approach to Grid Energy Storage. Up to the present time there has been no significant linkage between low-grade heat utilization and energy storage. We have shown how practical electrical energy storage can be directly coupled to low-grade heat where the potential benefits are many. The linkage of these two areas is through an innovative system that resembles the Rankine cycle with imbedded thermal energy storage. The conventional thinking in this area has been that such an approach is impractical. However, a new concept recently developed at Oregon State University has dispelled the idea that electrical energy cannot be efficiently stored in a thermal manner at moderate conditions. Cost metrics for this new approach are currently being developed, but Pacific Northwest National Laboratory has conducted an early cost analysis at the 10 MW/50 MW-hr level. The analysis gave an attractive cost structure for the system. This new approach is versatile and can be applied in many ways to power generation when sited at a location having access to low-grade heat. Possible applications include:

  • Utilizing waste heat to efficiently store base load energy for use at peak demand times.
  • Storing renewable energy at any time and making it dispatchable.
  • Storing energy at a conventional power plant during times of intermittent renewable power generation to avoid cycling the plant.
  • Recovery of energy in steam plumes and providing energy storage capability while recovering water.
  • Integrating with carbon capture systems to utilize waste heat for energy storage.
  • Integrating with data centers, refineries, pulp and paper mills, and other industrial sites for storing off-peak energy for use at peak times.
  • Sited at geothermal facilities to store electrical energy during the night and place it on the grid during the day for enhancing revenue generation.

Since receiving their ONAMI Gap grant, Applied Exergy has received an Oregon BEST Commercialization Grant to Help Advance Grid-Scale Energy Storage Technology. (Link:

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