© University of Hof

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

Ener­gy stor­age is one of the key issues for a sus­tain­able ener­gy sup­ply. 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 to Tushar Shar­ma, research asso­ciate at the Insti­tute for Water and Ener­gy Man­age­ment at Hof Uni­ver­si­ty of Applied Sci­ences (iwe) and 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 store 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. This means that the process of ice pro­duc­tion in the tank by heat exchang­ers is known in detail. What is new, how­ev­er, 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 sur­plus solar PV ener­gy. This is of course an inter­est­ing approach for com­pa­nies to avoid ener­gy costs and to improve their own CO2 balance.
My research focus­es on max­i­miz­ing self-con­sump­tion of solar PV ener­gy to pro­duce ice in the ice bat­tery. This means that the con­trol sys­tem is opti­mized in such a way that the uti­liza­tion of the ice bat­tery is max­i­mized in order to meet the cool­ing require­ments of the indus­try under con­sid­er­a­tion. So far, we have applied the reg­u­la­to­ry strat­e­gy to 3 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 would you describe this tech­ni­cal­ly — 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 on the Münch­berg cam­pus, we have expe­ri­ence with var­i­ous types of heat exchang­ers, which dif­fer in their appear­ance. There are star-shaped, spi­ral-shaped, snake-shaped, flat plates and recent­ly also as cap­il­lary mats. We have also writ­ten 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, it was found that the cap­il­lary mat ice bat­tery has bet­ter per­for­mance in terms of ice mass frac­tion evo­lu­tion as well as the amount of latent heat exchanged on an ide­al oper­at­ing day. We have val­i­dat­ed the flat plate mod­el with the exper­i­ments and are cur­rent­ly con­duct­ing exper­i­ments with the cap­il­lary mat heat exchangers.

At the moment we can oper­ate the entire 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. This also allows us to sim­u­late a cool­ing load pro­file for any oper­a­tion. This gives us the abil­i­ty to test dif­fer­ent cool­ing load pro­files, dif­fer­ent solar PV data based on dif­fer­ent weath­er data, and adjust the con­trol strat­e­gy based on dif­fer­ent situations.

Mr. Genes, you have been on board with your com­pa­ny from the very begin­ning of the project. What prompt­ed you to do this and what do you expect from the project in con­crete terms?

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

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 stand in the ener­gy lab­o­ra­to­ry. On this test bench we are test­ing two dif­fer­ent types of ice bat­ter­ies based on flat plate and cap­il­lary mat heat exchang­ers. The Lab­View soft­ware allows us to imple­ment a hard­ware-in-loop sim­u­la­tion in which we can sim­u­late dif­fer­ent cool­ing load pro­files and test dif­fer­ent con­trol strate­gies. We do this by con­trol­ling the flow of the coolant through valves.
The sec­ond project is a coop­er­a­tion project with the Swiss SPF Insti­tute for Solar Tech­nol­o­gy in the OST Uni­ver­si­ty, Rap­per­swill in Switzer­land. In this project we val­i­date the TRNSYS mod­el with the exper­i­ments for an ice stor­age tank of VIESSMANN (Iso­cal), which is buried in the ground out­side the ener­gy lab­o­ra­to­ry. For a new set of exper­i­ments for this project, we installed new soil 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, full sys­tem val­i­da­tion is initiated.

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

The use of tech­nol­o­gy will cer­tain­ly always be in the man­u­fac­tur­ing sec­tor. In the pri­vate sec­tor, there could also be medi­um- and long-term inte­gra­tion into domes­tic sup­ply, e.g. for 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 become suit­able for mass use 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 on ener­gy and cost sav­ing analy­sis was also car­ried out for the tra­di­tion­al brew­ery “Meinel Bräu” in Hof. Based on the sim­u­la­tion results, the pay­back peri­od of the plant was esti­mat­ed to be about 5 years. After this pay­back peri­od, sig­nif­i­cant five-dig­it amounts 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 to be able to use it in real time with an indus­tri­al part­ner in the fore­see­able future. As soon as the project pro­pos­al has been elab­o­rat­ed, we will apply for project fund­ing in the Cen­tral Inno­va­tion Pro­gramme for SMEs (ZIM).

Thank you for the interview.