Compact Thermal Energy Storage Technologies: Status, Applications and Developments

you this kind introduction I am M van Aldin as said from the energy research centre of the Netherlands and this is the first time for me that I participate in such a webcast and it’s quite odd really because I cannot see any audience and I’m speaking and talking to my screen here but I hope that the things that I want to give to you the content is as a good receipt reception therefore from you and we have plenty of time for some feedback at the last 15 minutes of the presentation so let’s start with with this webinar on compact thermal energy storage just see you next slide yeah this next night just trying to get used to the navigation now this is the short content of the webinar the things that I wanted to present to you and have a discussion about the focus is on compact thermal energy storage systems so systems that in general are better in terms of density storage density than the traditional water based systems we’ll begin with an introduction to compact thermal energy storage and then have seen three bigger chunks an introduction to the different test technologies phase change materials sorption thermal storage and thermo chemical materials and I will finish with some comments on the international developments that are going on last years and in the near future the basis for working with energy storage is the fact that large part nearly 50% of at least energy consumption in the EU is means is used for heating purposes as you see to the right 49 percent is for eating while only 20 percent directly of the primary energy is for electricity generation purposes and 31 percent is for transportation services another aspect also of thermal energy storage is that there are a lot of application areas that are used that use thermal storage so you can say that in fact the thermal storage technology is an enabling technology it makes other technologies work better or makes it possible other technologies like solar thermal concentrated solar power biomass code in generation etc now the relevance of thermal energy storage is that as said it enables a larger share of renewables like with solar thermal it can be used for system optimization by for instance with heat pumps reducing the number of cycles on and off switches and for generation of heat for satisfaction of a higher peak demand so you can for instance work with a low power burner and supply the big demand with an additional heat storage device on the demand side heat storage can be used to manage the demand or either or else way manage the supply side in microcode generation so for all energy sources the buffering of thermal energy is desirable but for solar thermal and ambient heat and heat pumps it’s necessary even if we look to this development stages of different thermal energy storage technologies you can see that there are roughly four technology families for going from left to right the technology is from more mature to less mature and the the left side is the mature market its water it’s from very large

scale to the smaller scale and here with the pointer all the technologies from the right of the green line are the technologies that are not yet fully on the market the latent heat storage technology is still in a demonstration phase on an early market phase sorption storage is in the development phase while thermo chemical storage is still in a research phase we will come back to these technologies later on as said and you saw also in the previous slide the the three main principles for thermal energy storage are sensible heat the principle is that you use the heat capacity of substance for instance water but it could also be solid and the form of this energy storage devices are from reservoirs small or small or bigger aquifers underground water carrying layers or each storage in the ground or in the soil the second class of storage technologies is the storage in in a phase change so when melting a substance a lot of energy is used to melt or when evaporating a substance or even for crystallization water can be used as a PCM as a phase change material then at 0 degree centigrade you use the freezing or melting of water and the other PCMs are sub can be subdivided into organic or inorganic materials the third class is both sorption and chemical heat storage and sorption is in fact the the binding of vapour be its water vapor or another gas to to a substance to liquid or to a solid and chemical heat is in fact the using heat to split a substance into two components here’s a graph with the classification of thermal energy storage going from left to right sensible heat storage latent heat storage sorption and chemical you there are some numbers to characterize the thermal energy storage what is very important is that a temperature level is given for the storage because it’s more difficult to store heat at a higher temperature level it’s easier to store it at a lower temperature level the specific energy Danji density is very important how many kilojoules or mega joules can I store per amount of weight or per volume and the thermal power that I can extract from the heat storage or that I need to store it is also important then you can also discern between categories in with respect to time to market for instance is it in a research or test phase is it a demo or is it available for the market the periods over which you want to store the heat is important daily storage weekly storage or seasonal storage and building integration aspects are also important is it possible to integrate a storage into the building or is it not possible so you use an installation outside of a building why do we need compacted storage in some cases in the built environment but also in some industrial applications volume is not readily available so if you want to use or if you want to store a large amount of heat it could be that in practice the water storage would need too much volume in this example the volume of a storage for seasonal heat storage for a house is depicted if you use water 120 cubic metre will be needed while a latent heat storage would use say 60 cubic meter still too much too

big a volume for a single-family house but if you could use chemical heat storage with thermochemical material then perhaps a volume of six cubic metre is it’s enough to store the heat for a full season in this table below here you can see the typical storage densities of these classes going from 110 mega joules per cubic meter for sensible to 250 mega joules for latent typical and chemical could be between 500 and 3,000 mega joules per cubic meter now let’s go to the first class materials the technology of storing heat in the phase change the principle is that you use heat to melt a material or to evaporate a material for instance with water the phase change from ice to liquid water this is typically at very low temperature so if you need a higher temperature storage then you you should need other substances like phase change materials in paraffins storage densities are typical in the range from 250 to 350 kilojoules per liter of volume and the applications are that for lower temperatures you could can store cold and for higher temperatures you could use phase change materials for ovary protection for temperature control in comfort zones in a indoor climate and for cogeneration or for sorry concentrated solar power to optimize the system to enable the system to also generate electricity at night this is a typical behavior of a latent PCM phase change material on the horizontal axis you see the temperature when the temperature rises then on the vertical axis for a normal solid the the heat that is used is gradually increasing but for a PCM there’s a step at the melting point of the phase change material in which a large amount of heat is taken up by the phase change material in this example it’s a material it’s th 29 PCM and this material has a melting range around 29 degrees centigrade and this is the 29 degrees great middle of the Melting face of the curve here what you see that is that the heat uptake is very big in a very small temperature interval this means that as you can see from these pictures if you compare the heat taken up by water and the heat taken up by this th 29 it’s depending on the time if the temperature difference whether the water in the blue is taking up is needing more liters for the same amount of heat or the th 29 the smaller the temperature difference the bigger the difference is in volume that you need for water and volume that you need for T it’s 29 so for a smaller temperature difference the effect of using phase change material is much bigger this means that for applications with a low temperature difference using a phase change material is advantageous if you have very low temperatures you could use water as a phase change material at zero degree centigrade it has a high storage density 334 kilograms per kilo joules per kilogram order is cheap and it’s especially interesting when you have to combine a heating system with a cooling system within the same building then you can heat and heat with each bump and used a generated cold to be stored in water heat storage

device or cold storage device the advantage also is that if you have a mixture of water and ice you can treat it as a fluid up to 20 or 25 percentage of ice and then there are other advantages of using this ice storage this is an example of a big installation in which an industry uses big ice tanks to generate calls with overnights cheap electricity and use the calls for the daily production services in the factory another class for higher temperatures would be the organic phase change materials that would be paraffins or polymers major drawback of these materials are is the low heat conduction of the material so you need some geometry or some other means to improve the heat conductivity so let me see let me give some examples of the materials here the end the materials are on the market now and available in different forms from left to right here it’s a powder of silica material which is filled with paraffins then sort of clegg like material of grains that are impregnated also with paraffin and board material construction material made of say 65% paraffins if you want to have more paraffin per volume then this this new material is very interesting and this new material is more sort of sponge like construction in which the paraffin is soaked and these grains can be filled into a container and water can be used as a heat transfer fluid and in this case the heat transfer from from the phase change material to the fluid is very good because there’s a direct contact an example of a system using PCM for Latin teeth storage is this demonstration system in Perth Australia solar collectors preheat a floor in which PCM is integrated the PCM over day melts and then at nighttime the stored heat in the PCM comes free and heats up the room during the night and this way the floor more or less is used as a solar thermal boiler solar thermal storage device in Germany a lot of research and development was performed on so-called micro encapsulated phase change materials here is a electron microscope picture of these material you can see small bulbs small spheres of polymers that were filled with paraffins and in this way these small spheres are incorporated incorporated into a gypsum layer so then the other particles that you see here in the photograph are gypsum particles this is a commercial product now it’s developed by bus F a chemical company and they together with muck seeds and building company they had some demonstration projects in which they tested and demonstrated the the effect of gypsum board impregnated with this micro encapsulated paraffins the effect is that with lightweight constructions like an office made from wood timber structure you can achieve a reduction of the day temperatures in summer the black curves here are the maximum temperatures for the reference

office without the PCM boards while the other curves are the temperatures with the test office and you see that there is a reduction of some three to four degrees centigrade of the maximum temperature over day this means that the comfort temperatures are less extreme for the test office and in this way you can change you can save a lot of energy reducing the cooling the amount of buildings these are the products that are now on the market in Germany slaps with this PCM and then boards with the PCM micro encapsulated integrated into it for higher temperatures there are also in organic phase change materials available like this in these cans here these cans are used in transformer rooms or telecom installations to prevent overeating when there’s a peak switching of the electronic devices in such a room and this li means that the electronics are protected better – for overeating at higher temperatures the last years a big increase in development of storage for concentrated solar power has started at the moment several installations in Spain and the USA are being our either under construction or being started up and some of these installations have big storage installations to make them also make it also possible for the installations to generate electricity at nighttime when there’s no direct solar irradiation in practice for higher temperatures a mixture of potassium nitrate and sodium nitrate is used with a high melting temperature and in this case around 250 to 300 degrees centigrade and these installations are very big 30,000 or more cubic meter are needed to store the heat for this overnight production of electricity and especially for those installations it’s good to research the possibilities of having materials with higher melting temperatures because the higher the temperature of storage the better more dense the storage is you can store more say megajoules per cubic meter and the better also the performance of the generation of electricity is so there’s a lot of activity now going on into research for better performing high-temperature storage materials the next class of materials is sorption sorption heat storage it’s either either it’s a so-called physical sorption and it’s physical because in the process there’s no change of the structure of the substance so then there’s no chemical aspects in this change of material it’s it has all to do with the adhesion of one substance to another substance so there it’s the forces of molecular at ease it forces and it’s either adsorption to lit to a solid and then it’s surface surface effect on porous media and for instance silica gel or zeolites or materials that are used for this and its absorption if there’s a mixing effect so when you mix for instance water with ammonium or lithium chloride or lithium bromide and a lot of these sorption materials for each storage are also developed and used for sorption heat pumps so there’s a big interface a big overlap of research into materials for either purpose glass of Zee lights are very interesting for each storage especially at temperatures higher than say 150 degree centigrade Zee light have a very micro a good micro porous structure and in general the it’s a composition of aluminum oxide and silicon oxide and

there’s an amount of metal atoms connected into this composition and the size and number of atoms they determine in fact which sort of zeolite it is vapors and gases are absorbed in zeolite and it’s in a selective adsorption process that is dependent on the molecular size or on the size of the pores in the zeolite you can see three different crystal structures with a small and big or an intermediate porous size and there’s a very big number of zeolites that can be used for these purposes a typical example of the temperature dependence for zeolites and for another class of materials are is given here you see from on the horizontal axis from left to right and increasing temperature and in the experiments the zeolite was slowly heated up and then during the experiments the mass loss was measured and you see for normal Z lights like the green curve here it’s a sea light with lithium and sodium incorporated into this structure that the highest mass losses one is in the range between say 120 and 200 degrees centigrade this is a rather high temperature and therefore new classes of materials are being investigated like all posts these are aluminium phosphor oxides mixtures and they use slower temperatures lower temperatures than here I have to kill my telephone sorry then this means that the family of elbows is better for low temperature heat storage or for relatively low temperature heat storage then the zeolites to normalcy units a drawback with elbows is that they are very expensive so a lot of research is needed to find new methods to synthesize elbows in such quantities for such a price that they are being that they are also interesting for high volume applications like for seasonal storage or other high volume applications some examples of zeolite applications and these are forms of zeolites that can be acquired and can be bought from industry beats of zeolite 13x or pellets they can be used in bulk in big containers and then gases or gas vapor mixtures can be pumped through the zeolite to exchange heat and vapor with the material in practice there are some say research is going on to investigate the possibilities of the zeolite storage system for seasonal storage this is an example of a system that is being developed at the ITW in Stuttgart and it’s a so-called moana swap system you see on the Left picture a Z light brick its Zi light that has been cast into a brick with channel small channels and wet air can be led through these channels and discussed in then the sorption effect of the water vapor with zeolite a lot of these bricks are being stacked into a heat exchanger air heat exchanger and in summertime this these breaks are being dried and so heat is loaded by hot air that is generated through solar collectors on the air collectors and in winter when moist air is fed through the bricks the moist air is heated up by the zeolite and you have the heating system of heat that is stored from the summer it’s an experimental system now that is being tested on a one-to-one scale in the

laboratory another system that has been developed in the south of Germany and byun in Munich is this this storage system in with in which zeolite volume of 10 cubic meter is being used to store the heat at night I’m from a district heating system and a daytime the heat is used to heat up the ventilation air for a school it’s a system that has been realized and demonstrated and it’s still working now in Munich the last class that I want you to to learn more about is the chemical heat storage in fact it’s based on chemical reactions and the general principle of all chemical reactions is that you use two compounds that can react and these two compounds a and B if they react reaction heat is being released all reactions are reversible so if you use the reverse reaction then if you supply heat to the composite material a B then a reaction will take place that it will split in two say two components a and B again we’ve made a nice picture of this here the charging cyclists in which to come the composite plus heat produces to say components these can be stored separately and without any losses over a long time say from summer to winter or even longer and then winter a day we can be brought together and this discharge of heat will make eat available for heating or for her tap water or whatever so chemical heat storage in general is a very good method to store heat over a long time there’s however one big complication and that is that the better the heat is stored or the say the better the bonding chemical bonding energy is the higher temperatures you need for splitting this components so it’s easy to find chemical heat storage principles for high temperatures it’s less easy to find substances that react for low temperatures and this is to say the temperature range in which we are interested for solar thermal heat storage because we would like to use the solar thermal energy from collectors in the range of 100 to 150 degree centigrade has been a study here at ECM to find thermochemical materials that could serve as a high-density storage material for relatively low temperatures and one of these materials was taken as a good candidate material to be investigated further this is magnesium sulphate which has a say medium or intermediate turnover temperature reaction temperature temperature of 122 degree centigrade while it has a very big energy storage density in theory of 2.8 Giga joules per cubic meter so a high potential storage energy storage density with the relatively low temperature the solution is on a materials level and this means that very small quantities of this material are being investigated in an experimental apparatus the apparatus in is in fact nothing more than a mass scale in which we very accurately can determine the weight of this sample it’s only a few milligrams and what we do then is depicted here in this curve the temperature of the sample is gradually increased and then you see from the blue curve that there’s a reduction of the mass of the sample so when heating up the sample water that is originally in the magnesium sulphate structure is evaporating from the sample and therefore the sample mass decreases and you can see two ranges in which there is a big decrease this one small range at 50 degree centigrade and there’s one

bigger mass decrease at say 70 to 90 degree centigrade and these are exactly the temperature ranges that we are interested in and we see from other measurements that the potential energy storage range in in between 70 and 120 degree centigrade is something like 1.5 Giga joules per cubic meter of this material so in potential it’s a interesting material for seasonal storage of solar heat this is an electron microscope picture of a grain of magnesium sulphate and from this you can see the scale of this chemist sorption this is a grain but the reactions take place not even not in the slits that are visible here because these states are in the range of 1 micrometer but it’s even in the range of one thousandth of this one micrometer so the micro pores or the Nano pool also cracks in this the reaction takes place and from this you can also see that in practice the the ease with which the water vapor can penetrate through and say relatively big slits and cracks of the grains determines how fast the reaction will occur in the material going from the material to say a system setup this would be a schematic of such a system for seasonal storage of solar heat with magnesium sulphate on top we would have a solar array that in summer in the dehydration reaction will dry the material see to give dry magnesium sulfate and water vapor and then in winter the dry material plus water vapor will be put together in hydration reactor the heat will be released and will be available for space heating and domestic hot water and then the wet material will be so stored in a container see again there are also other examples of storage in Switzerland this system is being investigated it’s a storage system or based on sodium hydroxide and in principle it’s works the same but now with the liquid active material fire temperatures also systems have been investigated this system in Canberra Australia for higher temperatures here the temperature is four to five hundred degree centigrade and the reaction then is the splitting of ammonia into nitrous gas and hydrogen gas over a catalyst but it’s still in general the thermochemical material research is still in a very fundamental face what are the needs now to research and develop thermochemical materials we need material research process development and also system development and the aim would be then that in the end we would like to arrive at a heat storage system that has a density eight times better than the density of typical water-based system below are some requirements for the for the system and there are some international developments now going on let’s try to tackle all the challenges all the research challenges for for the thermochemical materials and for compact thermal energy storage there has been an IAEA task 32 of the solar heating and cooling program its advanced storage systems for solar and low energy houses the outcome of this task together with the outcome of other IEA activities was that more Materials Research is needed because materials that we use at the moment do not have the desired quality in terms of storage density and in terms of heat exchange we’ve had an project called preheat in which we tried to raise the awareness with politicians and decision makers of the necessity and importance of more research and the better basis

for thermal energy storage R&D there was the activity of the European solar thermal technology platform and strategic research agenda was set up and a lot of attention was paid to all the necessary R&D steps for storage both for low and for high temperature there are national R&D programs ongoing and starting we’d like to mention the programs in France and Germany that are now really also on a fundamental level trying to work on better new compact thermal energy storage materials and we have a new I a task that I can mention now to programs of the IEA the ESS program energy conservation through energy storage and the solar heating and cooling program started a new task task 42:24 on compact thermal energy storage and we actually have a quick kickoff meeting next month 11 to 13th of February in Germany in bottles and we would like to invite all interested organizations and individuals to join us with the big task that lies ahead of us the next four years and which we have this list of objectives and because we have little time and just skip this one you can also reread this on the the slides on the PDF file the domain thing said that need for are needed for compact thermal energy storage R&D is first political political awareness an international approach active national and in this industrial and participation and of course a lot of clever people attending and working on this subject these are the references please take your time reading the slides and I’m very curious for your questions there for your feedback thank you very much