Repurposing fossil fuel plants as storage facilities: an update from E2S Power

10 May 2023

E2S Power, a company established four years ago with the objective of transforming fossil-fuelled power assets into clean energy storage facilities is delivering a 250 kWh thermal energy storage pilot to India Power Corporation.

The pilot unit for India, which was designed, built, and tested at E2S Power’s facility in nine months, has successfully passed factory acceptance tests and will be delivered to site in the first half of 2023. The collaboration between E2S and India Power, in one of world’s most important energy markets, has the potential to contribute significantly to India’s renewable energy growth and energy transition.

Avoiding stranded assets

India’s government is targeting 500 GW of renewable generating capacity by 2030, and around 50 GW of coal capacity is expected to be decommissioned in the coming years. In Europe and the US combined, over 160 GW of coal plants are scheduled to be retired by 2030. Decisions will need to be made very soon about what to do about these potentially stranded assets, how to address security of energy supply and how to maintain a stable and reliable energy system while accommodating the intermittency of renewables.

A long-duration energy storage technology that can be deployed in the near term will need to be part of the solution. E2S Power’s technology can indeed be used in the near term to provide urgently needed energy storage while repurposing retired thermal power plants, retaining jobs, and supporting clean power and carbon reduction.

E2S Power’s thermal energy storage solution, called TWEST (Travelling Wave Energy Storage), converts electricity from renewable sources into heat, stores it using advanced storage media, and returns the stored energy in the form of superheated steam to power existing steam turbine generators during peak periods. See Figures 2a and 2b.

TWEST is designed to integrate easily into existing power plants with three primary interfaces: electricity supply for charging the system; feedwater input; and steam supply into the existing steam cycle. The system is packaged in standard modules that can be stacked up to meet the storage requirements and plant footprint to adapt to a variety of power-plant sizes and configurations.

Building on experience gained from running a demonstration unit for a year, E2S Power built and tested a 250 kWh pilot with an optimised design. The pilot, once charged with electricity, is able to generate high-pressure steam at up to 540°C for a period of over four hours.

As part of the collaboration with E2S Power aimed at expanding in the Indian market, utility India Power Corporation will install the pilot in Kolkata, India. This will represent a showcase for key stakeholders in the region, including government representatives and power companies looking for a long-duration energy storage solution and a way to decarbonise existing assets.

India Power and E2S Power are already working with major power generators with a view to implementing utility-scale plants in the next few years.

Flexible, long-duration, implementable in the near-term As already suggested, the market needs a flexible, long-duration energy storage solution that can be implemented in the near term. For this reason, a key objective for the E2S Power engineering team when developing TWEST was to create a compact, modular system that would minimise integration complexity and cost. In addition, the system needed to be flexible and able to start charging and discharging within a few minutes.

With this in mind, E2S Power is utilising a high thermal conductivity and high energy density material with embedded steam generator piping. This has resulted in the development of a fast-responding compact system without the need for external heat exchangers or additional working fluids.

E2S Power plans to supply pre-assembled modules that can fit in a standard container, facilitating construction activities at the power plant site and reducing costs.

A very important feature of the TWEST system is the ability to maintain the temperature of the steam supplied within a narrow window for utility applications, typically ±5°C, during the entire duration of the discharge.

For this purpose, a proprietary solution was developed. See Figure 3.

The initial temperature control is achieved by splitting the whole storage volume into main storage modules heated to 700°C and temperature-control modules initially heated up to the target steam temperature, for instance, 540°C.

During discharge, the temperature-control modules absorb the extra heat from the flow when the steam is overheated and supplies the missing heat when the steam becomes colder than required.

In this way, the generated steam temperature remains constant at the required level. The outlet steam temperature can be further fine-tuned using a double-pipe heat exchanger at the system outlet for final control and quick dynamic response of the system. The inlet feedwater used for cooling is rerouted back to the storage inlet in order to avoid heat losses. Figure 4 shows actual test data from the pilot.

The fast responsiveness of the TWEST system, the ability to charge and discharge partially at different times, and use of the existing steam turbine synchronous generator will allow the storage plant to take full advantage of revenue opportunities already available in markets like the UK.

In addition to off peak/on peak electricity arbitrage revenues, expected to increase with additional renewable energy in the system, the system can take full advantage of capacity payments available to longer discharge storage systems, balancing mechanisms, inertia and other ancillary services.

By utilising existing power plant sites, TWEST will substantially reduce the time required for developing projects, including permitting, compared with greenfield projects, and will be able to take advantage of existing grid interconnection capacity.

This last aspect is becoming a key factor as long queues for securing interconnection capacity are becoming a big challenge for new renewable and storage projects in some of the major power markets, such as the UK and the US.

For a full scale utility storage project employing TWEST, an overall schedule of about 20-22 months is expected. This can be reduced further as E2S Power optimises its supply chain and key materials stock.

Due to its lower assembly cost, simpler integration and use of existing infrastructure, the total installed cost of TWEST is estimated to be about one fourth of that for a large-scale lithium-ion battery energy storage. The TWEST system also has superior energy density, with two to five times less space requirement than competing storage technologies.

Next steps

As a next step after the delivery of the 250 kWh pilot to India Power, E2S is in advanced discussions regarding a first phase 50 MWh utility scale project with key power generators in the US, UK/Europe and Asia.

Thanks to collaboration with key investors, E2S Power can offer funding and partnership possibilities with host power plant operators right from the early stages of commercialisation of its TWEST technology.

Figure 1. E2S Power 250 kWh pilot thermal energy storage unit
Figure 2. Schematic of the TWEST concept
Figure 2. Schematic of the TWEST concept
Figure 3. Temperature control functional diagram (TES = thermal energy storage module)
Figure 4. Steam outlet temperature in pilot testing was maintained within ±1.6°C during the entire discharge period

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