Energy and CO2 savings through ice batteries – powered by solar energy

Energy storage is one of the key issues for a sustainable energy supply in the future. Thousands of researchers around the world are currently working on this issue. An exciting project is also currently underway at the Münchberg campus of Hof University of Applied Sciences. Here, new types of ice batteries for cooling applications are being researched, which can help to sustainably reduce energy and CO2. They are powered by surplus solar energy.

We talked about this with Tushar Sharma, research associate at the Institute for Water and Energy Management at Hof University of Applied Sciences (iwe), and with Richard Genes, managing director of the cooperation partner Genes Kältetechnik GmbH from Hof.

-Mr. Sharma, please give a brief explanation: what exactly is an ice storage system and what do you want to find out and achieve with your research?

The technology itself has been on the market for decades and a lot of research has been done at a fundamental level. That is, the process of producing ice in a tank through heat exchangers is known down to the last detail. However, what is new is that with the concept of an ice battery, we want to market an affordable and energy-efficient alternative to the existing, electrochemical batteries that have been used to store excess solar PV energy. This is obviously an interesting approach for businesses to avoid energy costs and improve their own carbon footprint. My research focuses on maximizing self-consumption of solar PV energy to produce ice in the ice battery. This means optimizing the control system to maximize the utilization of the ice battery to meet the cooling needs of the industry under consideration. So far, we have applied the control strategy to three different cases, including a bakery and two breweries. The system was modeled in TRNSYS simulation software and the results showed significant energy and CO2 savings.

-How should you imagine this technically – after all, there is quite an extensive laboratory test stand in Münchberg?

An ice battery is basically just a water storage tank with heat exchangers immersed in it that can form ice by extracting the latent heat energy of the water. In our laboratory at the Münchberg campus, we have experience with different types of heat exchangers that differ in their appearance. There are star-shaped, spiral-shaped, serpentine-shaped, flat plates and, more recently, also capillary mats. We have also developed a detailed software model for flat plate and capillary mat heat exchangers based on the ice battery.
We are able to perform dynamic system simulations and compare the simulation results with the experiments performed in the laboratory test bench. Through dynamic system simulations performed in TRNSYS, we found out that the capillary mat ice battery has a better performance in terms of the evolution of the ice mass fraction as well as the amount of latent heat exchanged on an ideal operating day. We have validated the flat plate model with the validated experiments and are currently conducting experiments with the capillary mat heat exchangers. At the moment we can operate the whole test stand via remote control with the LabView-program. Through this LabView program we are able to monitor, measure and control various sensors and valves. In this way we can also simulate a cooling load profile for any operation. This gives us the possibility to test different cooling load profiles, different solar PV data based on different weather data and to adjust the control strategy based on different situations.

-Mr. Genes, you have been on board with your company from the beginning of the project. Why did you decide to get involved and what do you expect from the project in concrete terms?

I was impressed by the idea of putting solar energy that has been produced superfluously up to now to good use after all. This energy will be used to produce and store cold. This has great advantages, because more and more cold is needed, especially in the manufacturing industry. I think that if the project is pursued, there will be many people interested in the technology. The savings are convincing.

-Research is also always based on the principle of try & error: What kind of experiments are currently being carried out?

At the moment, two projects are running on the topic of ice storage: The first project is being carried out on the ice storage test rig in the energy lab. On this test stand we are testing two different types of ice batteries, based on flat plate and capillary mat heat exchangers. Through the LabView software we have the possibility to realize a hardware-in-loop simulation, in which we can simulate different cooling load profiles and test different control strategies. This is done by controlling the flow of the coolant through valves. The second project is a cooperative project with the Swiss SPF Institute for Solar Technology at OST University, Rapperswill in Switzerland. In this project, we validate the TRNSYS model with the experiments for an ice storage system of VIESSMANN (Isocal), which is buried in the ground outside the energy laboratory. For a new set of experiments for this project, we have installed new ground temperature and ice fraction sensors to get more accurate results. These should help us understand the dynamics of heat transfer between the soil surrounding the ice storage tank and the water/ice in the tank. Once the icing and melting properties of the Isocal model are validated with the TRNSYS model, a full system validation will be initiated.

-Are there any initial results you can report?

Yes, we conducted experiments last year with an ice battery based on a plate heat exchanger. The results were also published in the conference proceedings of RETCON 2021. From a simulation point of view, some models still need to be improved in order to reduce the deviations between the experimental and the simulation results.
Also in the second project, we already have some good results from the icing and melting tests carried out at the beginning of the year. Currently experiments are being conducted to learn more about the icing properties and the heat transfer process between the ground model and the ice storage model. We hope to have some satisfactory results soon so that we can publish them in renowned scientific journals.

-Where could the potential uses of the technology lie in the medium and long term, Mr. Genes, when you think about people’s everyday lives?

The use of the technology will certainly always be in the manufacturing sector. In the private sector, there could also be a medium- and long-term integration into domestic supply e.g. for the air conditioning of living spaces.

-The cost/benefit ratio is also always important for the feasibility of research. What is the situation in this area? Can the technology be used on a mass scale in the foreseeable future?

Both the economic and the energetic performance of the technology were theoretically determined through various case studies in the simulation software Polysun and TRNSYS. Recently, a case study was also conducted for the energy and cost savings analysis for the traditional brewery in Hof. Based on the simulation results, the payback time of the plant was estimated to be at about 5 years. After this payback period, about 34,000 euros can be saved annually in energy costs.

-What is the next step and when will the project be completed?

At the moment, we are planning a continuation project with a company that can develop a physical control system and implement our concept. We would like it to be used in the near future with an industrial partner in real time. As soon as the project proposal is elaborated, we will apply for project funding in the Central Innovation Innovation Program for SMEs (ZIM).

Thank you for the interview.

Wissenschaftliche Ansprechpartner:

Prof. Dr. Tobias Plessing
Hochschule Hof
Alfons-Goppel-Platz 1
95028 Hof

Fon: +49 (0) 9281 / 409 4720
E-Mail: tobias.plessing@hof-university.de

http://www.hof-university.de