Returning here to the topic of electrification of heat. This is one that we keep coming back to, both because industrial heat is such a massive (and hitherto neglected) part of the emissions pie, and also because cost declines in renewable energy production paired with challenges with grid connections and transmission open up opportunities for these off-grid electrification applications. Antora Energy is using electricity to heat a medium (graphite, in their case) in a similar fashion to Rondo or Electrified Thermal, but can use that heat either for heat end uses or turn it back into electricity (like Malta). The company raised $50mm earlier this year from Breakthrough Energy Ventures and Lowercarbon amongst others. I tuned into Emily Kirsch’s conversation with CEO Andrew Ponec on Watt it Takes podcast as a jumping off point.
Most previous technologies for thermal storage (e.g. concentrated solar) have been at (comparatively) low temperatures of around 500-600 degrees. Additionally, they generally use convection as the medium of transfer using gases or liquid salts, which requires complex industrial plant with many moving parts and high maintenance costs. [Recall from secondary school science, the three methods of heat transfer - conduction - heat moving through a solid body or two touching, convection - the current of hot stuff through a liquid or gas, and radiation - through electromagnetic waves, not needing a medium to pass through, and how we get heat from the sun.]
Similar to Rondo’s technology (covered in more detail here), Antora’s technology creates heat by running electricity through a resistor (graphite), which is heated to up to 2000 degrees C and the energy is captured via radiation rather than convection. Radiation is transmitted via photons and can be turned back into electricity via thermal photovoltaic (TVP) cells that work like solar PV, but for heat rather than light.
Antora have innovated on the TVP technology to make it especially tuned to a specific wavelength of radiation, with a reflector that bounces photons travelling at other wavelengths back into the system to prevent energy loss.
More on Antora’s tech can be seen via their patent. It was filed two years ago, so one might expect some evolution since. For instance, it doesn’t talk at all about using the heat directly, so it isn’t fully clear to me how the heat transfer works when heat is the end-product, but would assume it’s convection and not with use of TVP, and would look more like Rondo in that case.
The high temperature is critical for this to work because radiative heat energy increases to the fourth power with temperature. In other words, for every doubling of temperature, the energy increases 16-fold! (Described by the Stefan-Boltzmann Law, in case of interest.)
The company expects one shipping container-sized module to be able to store 50MWh thermal or 20MWh electricity, and systems can be stacked modularly. If realised, that is pretty impressive when compared to a Tesla mega pack of similar size which has just 3MWh of electricity storage.
Acceptance into ARPA-E’s DAYS program for long duration storage was a key development for Antora and served to fill exactly the role that government should fill - bridging the early gap between science and engineering where the technical risks are still too high for private investors. [For more on how the DoE is supporting the scale up of climate tech, I’d recommend checking out CTVC’s excellent Founder’s Guide to the DoE.]
Antora took a very purposeful approach to developing their technology to use abundant materials and established supply chains and also mapped the go-to-market in advance of doing multiple engineering prototyping. Their business model is geared towards ‘as-a-service’, delivering heat or electricity through Heat Purchase Agreements or PPAs.