FEATURE

Dr. Asegun Henry who eventually became professor at MIT. They both started to work on Thermoelectric and Photovoltaic Energy Conversion as lab mates back in 20062007. Currently, Dr. Henry has taken a leave of absence from his professor position at MIT and has set up a startup called Thermal Battery to commercialize the very technology discussed in the research.

Why long-term storage through thermal batteries

While the world is filled with different types of batteries, these batteries are either too expensive or lack long-term storage capabilities at affordable prices.

According to the research, Lithium-ion batteries for example have been the state-of-the-art technology for short-term storage but cost between $80 to $100 / kWh making them unaffordable for time horizons above a few hours not to mention the multi-day storage required to completely decarbonize the grid.

Studies suggest that achieving cost-efficient multi-day storage requires a capital cost reduction to $3–30 kWh compared to the $80 cost for lithium batteries. Resolving this issue could enable more rapid decarbonization of the power system, resulting in a 25% reduction in global GHG emissions.

Dr. Chiesa explains, “We believe that our study of hightemperature thermo storage can scale up in an economically viable way given the need for storage of 12 hours or more when the sun is not shining or period when the wind is not blowing. Today with electrochemical batteries we can theoretically get up to 8 or 10 hours but it is unrealistically costly.”

Dr. Chiesa adds that while electrochemical batteries are very good commercially for shorter time periods that can cover rapid fluctuation during the day, they are not the solution to deliver stored electricity while the sun is not shining.

This is why the thermal energy storage concept published in the recent research has shown promising potential to achieve sufficiently low capital cost in the multiday storage regime. TES stores the electricity as heat rather than electrochemically and then converts it back to electricity when needed.

How does Thermal Energy Grid Storage work?

The Thermal Energy Grid Storage (TEGS) concept stores electricity as sensible heat in graphite storage blocks and uses Thermo-Photovoltaic (TPV) to convert heat back to electricity on demand. Storing energy as heat at very high temperature has a much higher round-trip efficiency than heat at low temperature. It is still not as efficient as storing electricity in electrochemical batteries, but the heavily reduced investment cost can justify the energy penalties.

He states, “So for example, if you take 1 kilowatt of electricity from the grid you can transform it into heat with 100 percent efficiency, however, you cannot transform back that heat into the same amount of electricity, it loses a lot and this is because of thermodynamics. The higher the temperature is, the higher the possible efficiency in getting it back to electricity. In the study we store the heat at 2400 C degree temperatures thus our round trip efficiency is demonstrated at 41 percent but we are convinced we can bring it up to 50%.”

Chiesa conveyed that currently at the solar testing lab platform at Khalifa University in Masdar, two companies have been commercially testing their heat storage into cement technologies which can store 500-600 degree temperature but have a round trip efficiency of just above 20 percent.

So while electrochemical batteries have the highest round trip efficiency, there are two issues with them, you cannot take out all the energy from the battery without affecting the lifetime of the battery, and it is super expensive.

So according to Chiesa, giving up some efficiency for something much cheaper is the most logical solution. The technology tested by Chiesa and the team achieved a projected cost below $20 Kwh1 at Gigawatt scales.

Another unique property of TEGS (Thermal Energy Grid

Storage) is that given that heat is stored in chains of graphite blocks and then converted to electricity using TPV (a special photovoltaic cells optimized for the spectrum radiated at the operating temperature) the TEGS can charge (i.e., store heat) at a much higher capacity than that required for discharging.

The benefit of such a mechanism is that a large amount of energy can be charged in a short amount of time when generation surpluses exist and discharged over a longer period to cover the electricity load in periods where demand exceeds supply. The TEGS system also has advantages in terms of durability, safety, and replaceability which make this technology a promising option to adopt into a decarbonized electricity grid.

Future of Thermal Battery Study

One of the most important aspects of this study was that it was not modeled as a greenfield case study abstract in nature but was represented on an existing grid, a brownfield model to analyze how adding a PV storage system can contribute to decarbonizing the grid. This way to look at the problem is very important for transmission and distribution system operators.

The two brownfield grids were in New England and Texas. Dr. Chiesa stated, “It is very important to integrate this technology into an existing brownfield system fixed in time. We will continue to model this over a longer time span and study the dynamic of the possible capacity expansion of these electricity grids and the adoption of variable renewable energy when low cost energy storage becomes available.”

Dr. Chiesa believes that the UAE is one of the best proponents of solar energy, but this solar energy cannot meet the needs for 24 hours a day, and here is where Thermal Battery technology can take the surplus electricity from the sun and store it. He affirms, “We need storage or we will never be able to have fully renewable energypowered grids.”

Dr. Chiesa is waiting for permission to connect the 500 KW PV plant at the Masdar Institute Solar Platform and create a microgrid that will allow testing the integration of thermal storage energy solutions in the UAE. He is eager to test the integration of energy storage through Virtual Power Lines to manage grid congestion efficiently.

Finally, even the technology itself has a lower carbon footprint than those of electrochemical batteries. Electrochemical batteries’ carbon footprint stems from the material used and how they are mined. The TEGS hightemperature thermal battery storage has a much lower carbon footprint because of the material used and the difference in the way it is mined.

Currently, Prof Asegun Henry, who holds the Guinness World Record, has launched a startup Thermal Battery, and is looking for investors. The startup is currently working on scaling up the technology, with a 1 MWh pilot and commercial demonstrations in the future. It would be good to test it at the Masdar Institute Solar Platform.

Title of Published Paper:

Power Availability of PV plus Thermal Batteries in real-world Electric Power Grids

Published in: Applied Energy

Journal Metrics:

The impact factor: APPLIED ENERGY is 11.446.

The APPLIED ENERGY is a reputed research journal.

It is published by Elsevier BV.

The journal is indexed in UGC CARE, Scopus, SCIE.

The (SJR) SCImago Journal Rank is 2.907.