How does Fourth Power’s thermal battery work?

Without energy storage, renewable energy has to be used when it is generated, making it difficult to cease our reliance on fossil fuels while maintaining a 24/7 energy supply. Often, renewable energy goes unused because generation and demand are not equally matched, so utilities will pay producers to curtail their renewable resources and take them off the grid. Other times, there is too little production, and utilities rely on fossil fuel peaker plants to meet demand.

Our groundbreaking thermal battery stores excess renewable energy as heat in a fully enclosed system roughly the size of half of a football field. Liquid tin is pumped through a closed-loop graphite plumbing system to transport the energy throughout the battery.

Fourth Power uses thermophotovoltaic (TPV) cells to turn the light emitted by the glowing white hot plumbing system into electricity for the grid. This is similar to traditional solar generation but uses light from very hot — up to 2400°C — graphite rather than light from the sun to produce electricity. At almost half the sun’s temperature, we are essentially storing the sun in a box.

The battery is sealed in a warehouse of argon gas to maximize system lifetime and ensure safety.

What are the advantages of Fourth Power’s thermal battery?

Our utility-scale thermal battery — able to store renewable energy when it is generated and dispatch it as needed — is the key to utilizing renewable energy for all of our needs, making it as agile as fossil fuels and ultimately paving the way to a fully decarbonized electrical grid.

Lowest Cost:

The cost of storing energy is less than $25/kWh.

  • Fourth Power is able to output electricity at the lowest cost because our groundbreaking high temperatures result in a very high energy density.
  • Our technology is more than ten times cheaper than lithium-ion batteries ($25/kWh-e vs. $330/kWh-e) because we use less expensive materials and can offer lower overall system costs.
  • Our system is greater than 95% carbon, which is the tenth most abundant solid element on Earth, making it cheap and accessible. There is no concern over mining limitations with our thermal storage.

Full Scalability:

We can grow with the grid.

  • By adding graphite blocks to increase storage duration, we provide a modular, scalable solution that can meet today’s short-duration (5-hour) needs and the long-duration energy storage (500 hour) needs of tomorrow.
  • In the future, batteries must be able to store and discharge renewable energy anywhere with different durations, and most of the market will require durations between 10 to 500 hours.
  • However, today’s needs differ, and Fourth Power can uniquely meet these requirements and remain cost-effective.

Absolute Flexibility:

Grid operators have complete control over how and when the storage energy is used.

  • Our technology provides flexible discharging within seconds of notice to turn renewables into a stable power source for grid operator planning.
  • The system is highly flexible and configurable for specific applications because the charging rate, discharging rate and amount of energy stored are independent.

Maximum Power Density:

We reach the highest temperature (up to 2400°C) and highest efficiency TPV (41% and working up to 50%).

  • The higher the temperature of a thermal battery, the higher the power density. Our groundbreaking achievements allow us to transfer 10 to 100 times more heat than any other company with the same size equipment and store electricity at a lower cost.

Enhanced Safety:

Our system is engineered for safety.

  • There is no risk of thermal runaway because our system is chemically inert.
  • There is no risk of explosion because our system is not pressurized and immediately vents any increased pressure.
  • The battery is kept in a stationary facility filled with argon gas to prevent oxidation. Thick layers of insulation and cooling panels would minimize oxygen’s entry into the system in the event it was compromised.
  • The liquid tin is completely shielded and contained in our plumbing system. If it were to leak, it would freeze in the insulation or as soon as it touches the concrete floor of the enclosure.

Fourth Power’s technology has been extensively peer-reviewed and is financially backed by BEV and DCVC, two of the most prominent climate tech VCs.

R&D Breakthroughs

High Temperature Pumping

Fourth Power’s technology is based on the ability to pump liquid metal at extreme temperatures using all graphite mechanical pumps. This advancement was pioneered by Fourth Power’s founder Dr. Asegun Henry, who holds the Guinness World Record.

High Efficiency Thermophotovoltaics (TPV)

Fourth Power achieved its second breakthrough when its TPV technology surpassed an unprecedented efficiency of 41%. Fourth Power’s technology leverages advances in TPV cells initially designed and fabricated at the National Renewable Energy Lab (NREL) and tested at MIT.

Emitter Deposition Prevention

Fourth Power’s technology is based on patented strategies that inhibit material buildup on TPV cells to prevent degradation.