247Solar Develops Solar Thermal Power System with Integrated Fossil Fuel Backup

Image: Ars Technica · Source

US startup 247Solar is building a concentrated solar power plant in India that uses heated air and ceramic pellets for storage, allowing it to run on solar heat or fossil fuels via the same turbine hardware, offering flexible, round-the-clock power generation.

Concentrated solar power (CSP) plants, once seen as a promising technology for renewable energy generation, typically convert sunlight into heat using mirrors that focus rays onto a receiver tower. This heat drives traditional steam turbines to generate electricity, with some designs incorporating thermal storage to enable power production after sunset. However, the rise of inexpensive photovoltaic (PV) solar panels has significantly undercut CSP’s economic competitiveness, causing construction of new CSP facilities to stall globally.

In a recent development, US-based startup 247Solar is reviving interest in CSP by proposing a hybrid approach that integrates fossil fuel backup into the solar thermal system itself, sharing most of the generation hardware. Their first project, a small 1-megawatt plant in India, combines concentrated solar thermal with photovoltaic panels for daytime power and uses a unique receiver system that heats ambient air to around 970° Celsius.

Unlike traditional molten salt thermal storage, 247Solar stores heat in ceramic pellets, which can supply stored energy for between nine to twenty hours post-sunset, depending on usage. This heat is transferred via a heat exchanger that replaces the combustor in a conventional turbine setup, allowing the turbine to produce electricity using either stored solar heat or combustion of various fuels during periods of low solar availability.

This design makes the system "its own backup," eliminating the necessity to invest in separate natural gas plants or large battery systems for nighttime power, as stated by 247Solar's Mark von Keszycki. The air heated via combustion or solar means feeds the turbine system identically, providing operational flexibility and cost savings, with fuel-burn capability adding less than 10% to total system cost.

The company’s initial installation with paired 200 kW generators will validate engineering and performance, with plans underway for a modular 3 MW facility featuring multiple receivers and shared storage. While grid economics currently offer limited incentives for continuous renewable power, 247Solar sees promising applications in off-grid settings such as remote mining sites, where fossil fuel logistics are costly and emission reductions are increasingly mandated.

If this approach proves financially viable, it could redefine CSP’s role within clean energy portfolios by providing stable, on-demand renewable energy supplemented seamlessly by fossil fuels within the same infrastructure. However, broader market structures and incentives will be crucial to realizing its potential impact on the energy transition.