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Supercritical carbon dioxide (sCO₂) is a fluid state of carbon dioxide when it exceeds its critical temperature and critical pressure. In this state, it assumes properties intermediate between those of a gas and a liquid, and in fact loses the distinction between gas and liquid phases. Its high density manifests itself in an equipment set with a very small footprint. sCO₂ is a non-flammable, minimally toxic, non-corrosive, thermally stable working fluid. 

Properties of supercritical CO₂ allow for:

• Flexible cycle that can integrate with wide variety of heat sources from exhaust heat recovery (low-speed diesels, gas turbines, or industrial processes) to high temperature advanced nuclear and CSP applications.  
• Compact, closed-loop system with minimal operating & maintenance support required
• Competitive thermal-to-electric power conversion efficiency with typically lower capital cost vs. steam or ORC technologies
• sCO₂ can interact more directly with the heat source, eliminating the need for a secondary thermal loop, and further reducing the total installed cost of the system.
• Simple, single phase, single pressure high temperature heat exchange

Echogen’s proprietary sCO₂-based Pumped Thermal Energy Storage (PTES) system delivers safe, reliable, low-cost, low-impact, and scalable long duration energy storage (LDES). Technology that will unlock the transition to affordable and reliable baseloaded renewable energy. Our system offers:

• Generation capacity of 50-200 MW for durations of 8 to 100 hours 
• Variable charging rates depending on application requirements
• Significant cost and performance advantages relative to competing LDES technologies – expected mature overnight capex between $175-250 / kWh (100 MW with durations of 10-16 hrs) and round-trip efficiency (RTE) up to 60%. For a 24-hour system, we expect costs at $137/kWh
• Energy densities of up to 250 MW-hr / acre.

Using CO₂ as the working fluid a closed loop charge cycle takes electricity from the grid and generates a thermal resources. In the generate cycle, these thermal resources are then used to generate electricity.

Thermodynamic Cycles Transform Heat to Electricity

1. Charging cycle: heat pump uses electrical power to transfer heat from cold reservoir to hot temperature reservoir, storing thermal energy for later use
2. Generating cycle: heat engine uses the energy stored in the hot thermal reservoir to generate electrical power, returning low temperature heat to the cold reservoir

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Echogen is well-positioned to leverage its recent advancements and partnerships to meet the increasing demand for reliable, safe, and cost-effective long-duration energy storage solutions, essential for supporting the transition to renewable energy and the expansion of data centers and AI infrastructure

• In Sep. 2023, US DOE Office of Clean Energy Demonstrations (OCED) awarded $50M to Westinghouse / Golden Valley Electric Association (GVEA) / Echogen to deploy a 1.2 GWh utility-scale PTES project in Alaska
  
  • On Jun. 20, 2024, OCED announced the start of Phase 1 to fund a detailed FEED study
• Formed a strategic partnership with Westinghouse Electric Company to deploy PTES technology globally
• Initiated the FEED study for the 1.2 GWh GVEA project in Alaska
• Announced the first PTES project in Europe in partnership with Westinghouse and Vodohospodárska Výstavba (VVB) in Slovakia
• Engineering for a 1.0 GWh project at a retired coal power plant in NY starts in December 2025

The term “waste heat,” refers to the thermal energy produced by machines, electrical equipment, and industrial processes that escapes into the environment unused. Often this waste heat can be recovered and used for other purposes.

The most common uses for waste heat are:

• Recycling heat back into the existing manufacturing process
• Transferring the waste heat from one process to another within the facility
• Converting heat into electrical (or mechanical) power [Waste Heat to Power (WHP) or Waste heat to Mechanical Drive (WH2MD)]

Waste Heat to Power (WHP) creates electricity by heating a fluid at high pressure, then expanding the fluid through a turbine to drive a generator. Classic systems use steam as a working fluid, but Echogen uses sCO₂ due to its beneficial properties.

1. Liquid CO₂ pumped to supercritical state   
2. CO₂ preheated at recuperator
3. Recovered waste heat added at waste heat exchanger
4. High energy CO₂ expanded at turbine drives generator
5. Useful heat left over after the expansion is used to preheat the CO₂ in the recuperator
6. CO₂ is condensed to a liquid at condenser

The greatest potential source for WHP generation is in the industrial sector. In the United States, the industrial sector remains one of the largest consumers of energy, accounting for approximately 30% of total energy use. Of this, an estimated 20% to 50% is lost as waste heat through exhaust gases, cooling water, and heat lost from heated products and equipment. [Waste Heat...of Energy]

Recent assessments estimate that 1,500 to 3,000 trillion British thermal units (BTU) of waste heat are discharged annually from industrial processes. This low-grade heat (typically under 300°F or 149°C) represents a significant untapped energy resource. If recovered efficiently, it could yield over $50 billion in annual economic opportunity and significantly reduce greenhouse gas emissions. [Title (Use...aceee.org] [Demonstrat...in the ...]

The U.S. Department of Energy has updated its estimate of recoverable electric generating capacity from industrial waste heat to 15 gigawatts (GW). This includes waste heat from industries such as cement, steel, aluminum, glass, chemicals, petroleum refining, and natural gas pipelines. [Waste Heat...t is Power]

sCO₂ heat engines are highly effective at converting heat to electricity over a wide range of applications. Echogen has developed and continues to refine innovative sCO₂ heat engines for fossil-fired power generation, Concentrating Solar Power (CSP) and advanced nuclear power systems. The higher temperatures used in Gen IV nuclear reactors, combined with the high efficiency, lack of reactivity with reactor coolants and flexible operating temperatures of sCO₂ heat engines enable safe, low-cost conversion of nuclear heat to electricity.

Echogen has a strong IP portfolio with 90 issued patents (39 US) and 37 pending patents (18 US)

Echogen’s founders originally licensed a NASA technology, a CO₂ absorption heat pump, and developed further intellectual property and patent-pending applications that extended the heat pump technology to a WHP engine.

Echogen’s first prototype, completed in 2007, was a version of the absorption heat pump using carbon dioxide and a preferred secondary fluid. Echogen then converted the heat pump to a WHP engine, reducing to practice a first approach to the power generation cycle. A second prototype system, completed in early 2009, used pure carbon dioxide and proved that a transcritical cycle heat engine could be built to produce electricity from waste heat for commercial applications, and established a development pathway for first production units.