High Efficiency Solar Thermal Power Using Allam Cycle

Summary

Need

The cost of solar power can be reduced by combining high-concentration solar energy with highly efficient power cycles to generate electricity.

In a concentrating solar thermal power (CSP) plant, the cost of the solar field (comprised of mirrors arranged around a tower), is currently a large part of the plant’s capital cost. The more efficient the conversion of sunlight to energy, the less mirror area is required, and thus the lower the cost of the electricity produced.

For the past decade, CSIRO has been researching the use of solar concentration to provide the high temperatures needed for high efficiency power cycles. The best outcome is achieved when highly concentrated solar energy is combined with the highest efficiency power cycle.

Two key challenges must be addressed for this approach to be successful: identification of materials and receivers that can convert high-concentration solar energy into a hot fluid, and integration of this solar-heated fluid with advanced power turbines.

Project innovation

The High Efficiency Solar Thermal Power Using Allam Cycle project builds on CSIRO’s existing solar work in high temperature and high pressure power cycles, including supercritical CO2. It involves partnering with industry and research organisations to develop the components, materials and processes necessary to progress this technology to a commercial-scale system.

The supercritical CO2 power cycle is one of the most promising technologies for CSP to produce electricity, with storage, at costs comparable with fossil fuel, but without emissions. It offers efficiencies substantially greater than the steam turbines used today, by making use of the unique properties of CO2 at very high pressures and temperatures. The CO2 is a working fluid within the turbine and as such is continuously circulated, not released.

This project will advance a particular version of the supercritical CO2 turbine technology the Allam cycle that is one of the highest efficiency power cycles under development for the fossil power industry today. It will investigate the most cost-effective means of producing a solar-heated fluid and integrating it into the turbine cycle, with storage so it can produce electricity at any time.

The concentrated solar energy generates a hot fluid in the receiver on top of the tower. A liquid metal will be used as the heat transfer fluid in the receiver to ensure very high levels of heat transfer at temperatures of the order of 700 degrees Celsius. Liquid metals offer the highest heat transfer performance and thus smaller, more efficient receivers with lower heat losses. This heat is then transferred either to storage or directly to powering the supercritical CO2 turbine.

The project brings together some of the most experienced industry and research organisations in the field and provides a very strong team to tackle the identified challenges:

• Toshiba (one of the largest suppliers of electricity turbines for the global power industry) and 8Rivers (the technology innovation and commercialisation firm that invented the Allam cycle) are leading the development of the world’s most advanced commercial-scale supercritical CO2 power cycle, the Allam Cycle, through their work on a 50 megawatt (thermal) natural gas-fuelled demonstration plant.
• Abengoa Solar, the largest developer of commercial CSP plants in the world, has a proven history of developing new technologies and bringing them to market and recognises that the next generation of technology requires breakthoughs in higher concentration receivers in order to further drive cost reductions in renewable energy.
• NREL is one of the global leaders of research into high efficiency CSP technology, while CAS brings insights into material interactions at high temperatures.
• CSIRO has achieved world firsts in the development and demonstration of solar supercritical steam, liquid metal thermal storage, high temperature pressurised air and the heliostat (mirror) controls necessary for such high temperature operations.

Benefit

The project strives to develop the lowest cost dispatchable solar thermal electricity available to the industry.

The unique combination of industry and research depth and experience in this team provides a strong focus toward this goal by development of a very advanced product with near-term commercial application.