Thermal Storage Research Webinar Plus Q & A – What Did You Want to Know?

In the first of our series of research webinars, we focused on our thermal storage work. Led by Dr Jon Elvins, our Thermal Storage Research Lead and Sara Walsh, Technology Transfer Fellow, the webinar gave an overview of our route from lab scale to building demonstrators and our progress upscaling our heat storage material. Watch it to find out more…

But what else did you want to know? Here are the questions asked by webinar attendees, answered by Jon.

1. Where is the best opportunity for an efficiency / performance gain in the future – materials development / process engineering / optimised integration?

To be honest, in all areas that you mention. However, my personal belief is that we will see the greatest optimisation by reducing the matrix component and increasing salt. This is the focus of a lot of research at the moment.

2. How hot can the hot air stream be?

We currently have plans to test up to 600oC. The operational limit would be in the late 700oC’s, based on the melting point of CaCl2. Other salt / matrix combinations will have different operational limits. We have focused on CaCl2 because its activation temperatures are compatible with solar thermal devices. There are other salts and materials that operate best at much different temperatures and so selecting the correct active material for the use case is important too.

3. Once the material is charged with heat – how long does the stored heat last? And how many cycles before it needs recharging?

As long as the material remains sealed and moisture excluded the energy will remain there indefinitely as it’s stored chemical energy. We operate a cycle of charge / discharge. Currently we have data from 20+ cycles, although we are working on more.

4. What’s the a) material & b) system volumetric energy density? Is there degradation of the material over the course of the cycle?

These vary depending upon configuration and conditions.
a)The theoretical material Energy Density (ED) for our operation window is 1.85 GJ/m3 (~520 kWh/m3) and the measured system density (currently) is 300 + kWh/m3.
b)Yes, there is degradation due to the deliquescence and redistribution of the salt. We are working on ways to limit / prevent this.

5. How long could the Salt in Matrix (SIM) withstand? Is it necessary to change the SIM after some years?

Currently we have data from 20+ cycles, although we are working on more. Possibly yes, for the generation 1 commercial systems, although we are working on ways to reduce / prevent degradation. The stability within the matrix and redistribution of the salt is likely to be a factor in lifetime. Chemically the reactions are perfectly reversible and so no degradation should occur, but physical changes do occur and will impact on the lifetime.

6. What is the end to end energy efficiency?

We are in the early stages of the charge cycle work, the MESH and IDRIC projects will inform more on this. However in the early studies the ECharge: EDischarge ratio is ~4:1.

7. What’s the maximum temperature lift?

We have seen up to 60oC uplift from the current setup, the salt in solution has been recorded at 80oC+. Other salts and matrices will vary.

8. What Technology Ready Level (TRL) is this at? What do you see as the route to commercialisation?

We are just designing a second full scale demo so TRL 5. I envisage a scaled demonstration project at multiple sites (with different building types) with close engagement from Innovation Knowledge Centre (IKC) partners and sponsors.

9. Have you considered data mining to tap into the large sensors data you have?

Yes – the analysis of the data is key and this is always changing – especially when looking at the charge temperatures from renewable energy and prediction of the control of the system.

10. Are there other salt candidates that can take higher temperatures?

There are many other salts, to achieve consistent T increases it may be better to go to different chemical reactions, not using moist air, but different working pairs such as BaCl2 -ammonia.

11. So in a domestic situation you would fit some kind of ‘salt’ radiator system and just need to add water when heat was needed? (forever??)

Not that simple unfortunately as the salt would dissolve into solution. In principle, a closed reactor with a heat exchanger will work for domestic situation – assuming you get the desired output temperature.

12. There’s lots of discussion of efficiency. What is the definition of efficiency in this context?

We are talking about the efficiency of energy storage and energy discharge into the delivery medium.

13. I guess the idea is to use ambient / outside air in the final product. Is the idea of using compressed air / vaporized water for standardization?

Yes, or with an ultrasonic humidifier if required. Yes, we need a consistent set of input conditions to complete scientific studies / analysis.

14. How does it differ from TU Eindhoven’s heat battery?

It’s a similar principle operating in a different way. The TU battery operates in a closed loop system, whereas we are investigating open loop. Both systems have pros / cons and provide a different end solution.

15. For a house that needs 10MWh heat per year, what volume would the SIM be for this heat demand?

A lot! In the current form it’s ~ 33 m3. We have research programmes looking to elevate the ED to reduce this. We also have a slightly different model that is part of the MESH / IDRIC projects. In this model (looking at capturing waste heat from industry) fresh ‘cassettes’ of SIM would be delivered to the end user and inserted into the system, whilst the spent ‘cassettes’ are removed for recharge. The project investigates the technological, economic and environmental pros & cons of this solution.

If you have any further questions, please get in touch, we’d love to hear from you.

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