Category Archives: EUROSUN 2008

Solar thermal collection, storage and distribution system for greenhouses

L. H. Godinho1*, M. P.F. Gra^a 1,2

1) Prirev, Lda, Zona Industrial de Vagos, Lt.61, 3840-385 Vagos — Portugal
2) Physics Department, I3N — Institute of Nanostructures, Nanomodelling and Nanofabrication,
Aveiro University, Campus Universitario de Santiago, 3810-193 Aveiro, Portugal
* Corresponding Author, lhalgodinho@gmail. com

Abstract

The main purpose of a greenhouse is to create and maintain a controlled artificial environment that will favour the crop production with the maximum profit. Late increase on fuel prices, together with colder than normal seasons, make heating costs a significant burden on greenhouse operations. Therefore, the use of renewed energy systems, namely solar thermal systems, to control the inner environment of agricultural greenhouses becomes an economical and technological topic of unquestionable interest. This publication is related with the analytical analysis of the possibility of using a solar thermal system to control the climate environment of a greenhouse. Preliminary calculations show that, in certain climate conditions, a solar greenhouse can collect sufficient solar energy to feed, at least, another standard thermally optimised greenhouse of the same size. The implementation of this project, which is based on Portuguese Utility Model n°10218 — “Thermal Solar System for Collection, Storage and Distribution of Heat at Low Temperature”, considers the construction of a prototype and, later, of a larger industrial greenhouse, to verify the technological and economical viability of the patented idea.

Keywords: greenhouse, energy, solar, agriculture,

1. Introduction

Since the beginning of the XX century the world has been suffering from rising exploitation of its natural resources, with the resulting consequences in pollution and degradation. Oil, for example, considered a traditional energy source, have been extracted in such huge amounts that oil-wells already started to be depleted less than 100 years after the beginning of its effective use.

The “Lisbon strategy”, set in March 2000 by the European leaders, assumed the commitment of the UE to become, up to 2010, an economy based on the most dynamic and competitive knowledge of the world, capable to guarantee a sustainable economic growth, with more and better jobs, bigger social cohesion and respect for the environment. One of the main goals will be the ambient sustainability, that is, to develop and to spread out the echo-innovations and to build the leadership in the echo-industry; to adopt policies to generate long term improvements supported in increased productivity through echo-efficiency. Economic growth will be supported by the echo-innovations leading to a decrease in pollution and to a more efficient management of the resources. Many examples of these echo-efficient innovations already exist in several areas, agriculture and energy included.

The conversion of traditional agriculture, which is strongly climate dependent and characterized by extremely hard work conditions, in a more technical agriculture in controlled environment, will have an enormous impact in the reduction of the risk and in the increase of productivity and quality of the cultures, providing more appealing work conditions.

Basically, greenhouses are solar collectors with poor heat storage capacity. From local weather conditions in the last years we know that in late autumn, winter and beginning of spring, night temperatures can be quite low for long periods. Temperature represents a critical factor to the survival and growth of the plants. In fact, keeping the greenhouse at the most suitable temperature for the development of a given plant will significantly improve its productivity and quality.

Also in summer we can have in greenhouses a phenomena called “inversion” whenever the inside temperature drops dramatically at dawn when the sun rises, due to the evaporation of water condensed during the night.

Traditional Portuguese greenhouse consists of a galvanized iron pipe structure, covered with single layer of polyethylene (PE) film. This type of greenhouse implies enormous heat losses with consequent high fuel consumption. As a result, an increasing number of farmers have just switched off the heating and given up some greenhouse cultures in the last years due to the rise in energy costs.

The main objectives of this project are the thermal efficiency analysis of the greenhouse (type of covering, heating system, thermal curtains, etc.) and how much of its heating by traditional energy sources can be replaced by solar energy. The economic viability of its construction, the use of low cost (and yet efficient) polymeric solar thermal collectors together with simple water heat storage tanks — made from expanded polystyrene (EPS) blocks with an inner bag of reinforced polyvinyl chloride (PVC) film — and the way to transport and release the thermal energy inside the greenhouse, will also be studied.

During the cold night periods, water from the storage tanks will flow through small polymeric tubes inside the greenhouse and will heat the ground (if buried), or the bottom of the vases (if covering the growing tables).

At the energy level, the phases of this project are:

• pre-study of thermal properties in the design phase of the project;

• design of energy monitoring systems;

• data analysis and presentation of results.

Intended results are:

• substantially improved production conditions (quantity and quality);

• increased effectiveness of the heating using thermal efficient greenhouses;

• lower fuel consumption and, consequently, less air pollution;

• promotion of specialized agriculture, more competitive and with better work conditions.

In this paper we describe the analytical analysis that supports this solar thermal system project.

Chemical stability of microencapsulated alkaline nitrates in a graphite matrix

Two peaks appeared on DSC solidification curve of a Composite 3 (Fig.1), as a simple signal of inhomogeneous composite or chemical products generated during crystallization process. The re­crystallization of the Composite 3 was made with DSC at a cooling/heating rate of 0.50C/min and temperature range from 150-2200C. Comparable FTIR spectral study was performed on Composite 3 for examination of the possible chemical degradation or chemical interaction (Fig.2).

Fig.2. FTIR spectra of the (Na/K)NO3eutectics/graphite GFG (curve 1), compared to the (Na/K)NO3eutectics/graphite composite NG (curve 2), and to the (Na /K)NO3 Eutectics (curve 3).

Relative intensities of the absorption peaks were almost the same for the two samples of salt/eutectics graphite composites Fig.2, (1), (2), but lower as compared to the single NaNO3/KNO3 eutectics (3). Evaluations of the spectra provided with an evidence of a maximum characteristic absorption band at 1379 cm-1, displayed for vibrations of the nitro functional group of NaNO3 and KNO3 compounds. Products of chemical degradation or chemical reaction were not identified from anion frequencies recorded for all samples.

Simulation results

The main findings from the simulation are as follows:

The heat exchanger effectiveness increases with

• Smaller sand grain size

• Air inflow velocity

• Heat exchanger dimensions (height and width)

With the air and sand inflow temperatures of 800 °C and 200 °C, the obtainable average sand and air output temperatures are in the range TSand= 720-740 °C, TAir= 250-270 °C and heat exchanger effectiveness in the range sHX = 85-90 %.

Further results are

• For sand grain sizes < 3 mm and heat exchanger dimension of 50 cm height and 5 cm width (as given in the heat exchanger set-up described below) a smaller grain size has limited effect on the heat transfer

Dynamic behaviour: short-term sand blockage with blocking period below 20 s are uncritical with respect of air outflow temperatures increase due to the sand bed heat capacity

• To minimize pressure drop and to increase specific heat flux per volume (dimension of 1 MW/m3) a sand grain size dSand =1-3 mm is favourable

A Proposed Index for Characterizing the Charging of Thermal Energy Stores

In the methods listed above, effectiveness is principally equated in terms of the total exergy content of an experimental TES, with comparison to an ideal and/or mixed system. Although this is useful when assessing the overall performance of a complete simulation, the indices are not particularly suited to highlight not only the effect of thermal mixing within a TES, but more importantly, clearly indicate at which point turbulent mixing effects become negligible, if at all. They also offer a varying degree of applicability for different TES simulations. Panthalookaran’s method, for instance, does not seem to apply easily to variable temperature inflow conditions. [7]

stored

(t)

V£CR (t) _

if Ver (t) > 0

(4)

(5)

£

stored

(t 2) -£

stored

(ti)

12 ti

stored, real

stored, strat

(t)

(t)

■ 100%

Подпись: if VER (t) > 0

In support of the existing indices, a new characterization index has been derived and is proposed in eq. (4). The index, deemed the Exergy Charge Response (nCR), examines the rate at which the exergy stored within a real TES increases, and compares it to that of an ideal tank. The index is derived principally from eq. (3) above, which describes the exergy stored within a TES at a given time.

The applicability of the Exergy Charge Response is limited by the understanding that, given sufficient energy input with high inlet temperatures, a fully-stratified and a fully-mixed tank will eventually reach similar exergy levels:

да да со

J£stored, strat(t) £stored, real (t) stored, mix (t) if! iS Estored (t) > 0 (6)

0 0 0

It is therefore possible that at some point towards the end of a simulation with high energy availability, n^CR must become greater than 100%. This will only occur, however, when the energy response efficiency of the tank, tfER, begins to decrease from 100%. Therefore, so long as (nER > 0), hcR will be affected primarily by internal mixing, particularly at the early stages of charging.

The particular advantage of the Exergy Charge Response applied to TES simulations is the ability to effectively monitor the transient relationship between the thermocline and the fluid motion within the TES itself. It is clear that when п^ск ~ 1, the inlet plume is not thermally mixing the TES, and oppositely so when ncR ~ 1.

. Charging of Ice Store

Measurements have shown a maximum storage capacity of approximately 30 kWh for operation with external melting. Otherwise, a maximum storage capacity of 45 kWh is possible. In this case no liquid phase is left in the ice store. At a charging temperature of -10°C, the ice storage can be loaded with System A at a rate of 4 kW, on average (Figure 4). System B provides an average charging rate of 2.5 kW. Fluctuations at the beginning of the charging are caused by adjustment of the thermostat. Figure 5 compares the charging times of both systems at -12 and -10°C.

900

840

780

720

660

600

540

480

420

360

-12 -10 Charging Temperature / [°C]

Figure 5: Charging System A at different flow temperatures

Figure 5 compares the charging times of System A and B at two different charging temperatures.

As expected from the different charging rate System A charges the ice store faster than System B. Charging the ice store at -10°C with System A takes 421 minutes and with System B 657 minutes. Table 1 offers an overview about all results for charging.

Table 1: Experimental results for charging

System A

System B

Area of Heat Exchanger

[m2]

5,5

3,9

Charging

Temperature

[°C]

— 12

— 10

— 8

— 6

— 4

— 2

— 12

— 10

Maximum Capacity

[kWh]

30,5

29,6

29,5

30,22

30,5

23,9

30,3

30,06

Charging Period

[min]

366

421

507

675

960

1200

565

657

Average Charging Rate

[kW]

5,01

4,22

3,50

2,68

1,91

1,20

3,23

2,75

LMTD

[W/K]

565

562

563

570

573

611

310

309

Average Mass Flow

[kg/s]

0,295

0,267

Increase of Volume

[l]

19,99

19,45

19,69

19,96

19,57

12,08

19,94

19,88

Mass of Ice

[kg]

226,9

220,1

223,2

226,1

221,8

139,9

226,1

225,3

Average Starting Temperature in Store

[°C]

17,92

17,15

17,66

17,57

17,64

17,79

17,83

17,8

General features

The ANZEH is a two storey, wood-frame, detached building, with 210 m2 of inhabitable area. The insulation values selected for the building envelope are higher than conventional Canadian homes: walls with 5.6 RSI (U = 0.18 W/m2K), ceiling with 12 RSI (U = 0.08 W/m2K) and floor insulation of 4.6 RSI (U = 0.22 W/m2K). This house relies heavily on passive solar design to satisfy its

[7] The hygroscopy increases in the order: dry, slightly hygroscope, hygroscope, strongly hygroscope.

[8] O = Oxidizing agent, Xn = Harmful, N = Dangerous for the environment, T = Toxic

[9] No data available, dry to hygroscope

[10] Introduction

Extension of the testing facility by a 500 l storage and variable flow pumps

Now this testing facility has been extended by variable flow pumps and a 500 l storage tank without any built-in components such as stratification device or heat exchanger as shown in Figure 1.

1st International Congress on Heating, Cooling, and Buildings — 7th to 10th October, Lisbon — Portugal /

Fig. 1: System scheme of the testing facility

All temperatures and volume flow rates are measured in all four circuits so all energy fluxes can be evaluated. Additionally the pressure difference at the slurry side of the hot side heat exchanger is recorded so it can be compared to water. The temperatures in different heights of the storage are also measured, so the charge state and the degree of stratification can be ascertained. The sensors are labelled TS_xx_yy with xx representing the height from the bottom and yy the distance from the centre of the storage in centimetres.

The sensors and measuring equipment have the following accuracies:

— All temperature sensors are Pt100 class A with dT = ± (0,15 °C + 0,2% • T) or better (if manually calibrated)

— The pressure sensors have a dp = -0,1% due to pressure at 2bar and a thermal dp of — 0,25% at 0 °C and 1% at 75 °C

— The volume flow rate is measured by a magnetic flow meters with dV = ± (1 mm/s + 0,3% • V)

— The measuring equipment has deviations of ± 0,06 °C for Temperatures, ± 1mbar for pressures and ± (0.0003 • V + 0,5 l/h) for volume flow rates

For the measurement of thermal powers the maximum inaccuracy adds up to ±3,1% at 2000l/h.

The properties of the components are as follows:

— Nominal chiller capacity 0.5.. .20 kW

— Heater power 0.5.20 kW

— Volume flow rate of pumps 50.2000 l/h

The testing facility is designed for operation between -10 °C and 80 °C. This wide range of temperatures and the good variability of the components offer the possibility to reproduce a large variety of system configurations and operating conditions. The control program can automatically perform different series of measurements as to be seen in the subsequent example. Furthermore the program can read load data files and adjust the heating and cooling power accordingly. Thus the effect

of PCS can be evaluated under reality-like conditions. This function can also be used to verify control strategies developed in simulations.

Experimental Evaluation

In a previous study, a modular thermal storage was studied under constant-temperature charge

conditions [3]. These results, although uncharacteristic of the normal operation of a typical solar system, illustrate the level of stratification possible in multi-tank configurations. To conduct this evaluation, an experimental rig was constructed and instrumented, allowing the time/temperature

3

I

2

3

Q.

c

1

I

0

5 10 15

Time (hour)

(a) Case A (b) Case B (c) Case C

Fig. 3. Radiation profiles used in experimental sequence.

history within the storage to be recorded, Fig. 2 [4]. To record vertical temperature profiles, an array of thermocouples was inserted into each storage tank at 0.15 m intervals. During testing, a computer based data acquisition (DA) system was used to record and display storage and heat exchanger temperatures in real time. For the current study, this apparatus was modified to allow the simulated solar input power to be adjusted according to prescribed charge sequences, Fig. 3.

3.0 Experimental Results

Constant Temperature Charge Sequences. A previous study [3] investigated the response of both series and parallel connected multi-tank storages to constant temperature charge sequences. For reference and comparison, typical results for the series connected case are shown in Figs.4 and 5 for a supply temperature of 46oC and a collector-loop flowrate of 1.5 L/min. (0.024 kg/s). The rate of heat transfer measured across each of the heat exchangers is shown in Fig. 6. Results indicated that sequential stratification was achieved during the constant temperature charge sequences [3] i. e., during charging, the first storage would initially charge, followed by the downstream storages in sequence. Under these test conditions, there was minimal carry-over of heat from the high temperature storage to the lower temperature, downstream storages. Constant charge temperatures, however, are not typical of the normal operation of a solar system where the thermal input typically rises in the morning and falls in the afternoon. These falling collector fluid temperatures may result in destratification.

Variable Input Power Charge Sequences. In an effort to measure the unit’s thermal performance and temperature profiles under specified charge conditions, laboratory tests were conducted on the series-connected prototype [5]. For this study, a series of multiple-day radiation profiles were simulated. Using a computer controller, an electric heater was adjusted to provide the desired power output at any time throughout the day. The shape of the radiation profiles was chosen to represent the power output of a fixed solar array oriented directly at zero azimuth. As an approximation of these profiles, a sine function was applied to the output control signal as shown in Fig. 3. In particular, three test sequences were studied, Figs. 3(a), 3(b) and 3(c), corresponding to three hypothetical test cases, i. e., Cases A, B and C, respectively. Case A consisted of two consecutive clear, sunny days; Case B consisted of one clear, sunny day followed by one overcast day and Case C consisted of one overcast day followed by one clear, sunny day. The clear days provided a maximum input to the storage of 3000 W, while an overcast day peaked at 1500 W. Sunrise to sunset consisted of 10 hours in both cases. In order to reduce testing time, nighttime periods were removed from the test sequence as shown below. Typical results for the above charge sequences are shown in Figs. 7 to 15 for a collector-loop flowrate of 1.5 L/min. (0.024 kg/s).

The net heater input power and corresponding charge temperatures for each of the test sequences are shown in Figs. 7, 10 and 13, for Cases A, B, and C, respectively. As expected, for all cases, the temperature of the fluid feeding the first heat exchanger (i. e., the charge temperature) is seen to follow the input power profile, rising in the morning and falling in the afternoon. For Case A, the charge temperature on the second day is higher than that of the first day and the net power input is slightly lower. This is due to the fact that on Day 2, the tanks are at a higher temperature than on Day 1, thus requiring the charge loop to reach a higher temperature to facilitate further charging of the storage. This effect is even more evident in Fig. 10 where the charge temperature on the second day is considerably higher than would be expected at lower input powers.

The temperature profiles recorded in each of the storage tanks are shown in Figs. 8, 11 and 14 for the corresponding charge sequences. Referring to these figures, it is immediately evident that, although the temperature profiles resemble the previously recorded constant temperature charge case, Fig. 5, subtle differences exist. For example, in Fig. 8, the temperature profiles of the first day closely resemble those of Fig. 5 during the morning period; however, at hour six of the test, the temperatures at the top of the tank converge in Tank 1 due to falling charge temperature occurring at that time. As shown in Fig. 9, this sequence of events is consistent with the decrease in heat transfer rate across the heat exchanger at Tank 1, which goes to zero by hour eight.

4000

3500

3000

2500

2000

1500

1000

500

0

Net Heater Power Input (W)

Подпись: Net Heater Power Input (W)

Time (hour)

Fig. 7. Case A: Net heater input power and charge temperature for 2-day high input power test.

 

Fig. 4. Net heater input power and charge

temperature for constant temperature test.

 

Heat Transfer Rate (W)

Подпись:

Time (hour)

Fig. 5. Temperature profile of storage tanks

during charging for constant temperature test.

Подпись:

Fig. 6. Individual charge rates across each heat exchanger for constant temperature test.

Подпись:

each heat exchanger for 2-day high input power test.

Time (hour)

Fig. 8. Case A: Temperature profile of storage

tanks during charging for 2-day high input power test.

Time (hour)

Fig. 11. Case B: Temperature profile of storage tanks during charging for 2-day high/low input power test.

Fig. 12. Case B: Individual charge rates across each heat exchanger for 2-day high/low input power test.

Подпись:

Fig. 10. Case B: Net heater input power and

charge temperature for 2-day high/low input power test.

Time (hour)

Fig. 13. Case C: Net heater input power and

charge temperature for 2-day low/high input power test.

4000 3500 ■ 3000 j 2500 ■ 2000 j 1500 ‘ 1000 ; 500 0

Net Heater Power Input (W)

Подпись: Net Heater Power Input (W)

Time (hour)

Fig. 14. Case C: Temperature profile of storage

tanks during charging for 2-day low/high input power test.

Time (hour)

Fig. 15. Case C: Individual charge rates across each heat exchanger for 2-day low/high input power test.

Also evident in Fig. 9 is that due to limited heat exchanger capacity, a portion of the total energy transferred to the storage is transferred across the heat exchangers of Tanks 2 and 3. The heat transferred to Tank 2 is seen to increase during the day as the charge level in Tank 1 increases, finally reaching a maximum at hour eight, as the charge temperature drops below the temperature of Tank 1. Later in the day, as the charge temperature drops even further, Tank 3 takes up the charge. Although the top section of the Tank 1 in Fig. 8 is seen to remain at a fairly uniform temperature between hours eight and thirteen (corresponding to the period when the natural convection flowrate goes to zero), it is evident that the temperatures within the storage tank are slowly reducing due to standby heat losses or reverse thermosyphoning. Careful examination of Fig. 9 for the corresponding period shows that the heat transfer rate across the first heat exchanger is slightly negative indicating that some heat is being removed from Tank 1 and transferred to the downstream heat exchangers. While undesirable, the magnitude of this effect appears to be small. As well, in a typical solar heating system, the differential temperature controller would have normally shut off the circulation pump at this time.

With the onset of Day 2, the charge temperature increases and heat is initially transferred to Tank 3 which is at the lowest temperature. As the charge temperature rises throughout the day, Tanks 2 and 1 accept further charging. At the midpoint of the second day, the charge temperature is high enough that the majority of the heat input goes to Tank 1. The net result of this sequence of events is that the storage system is observed to be directing the energy input to the tank with the closest temperature distribution. In this way, sequential stratification is passively maintained. This process, however, is not perfect, as there is a small degree of carry-over from the high temperature storage to the downstream storage tanks.

The capability of the storage system to direct energy to the storage tank at the appropriate temperature is further illustrated in Figs. 11 and 14 for the Case B and C charge sequences. In particular, referring to the temperature profiles for Tank 1, it may be observed that none of the heat input from Day 2 is directed to Tank 1 for Case B whereas the majority of the heat input is directed to Tank 1 for Case C. This results because the charge temperatures are too low to successfully charge Tank 1 for Case B and above the tank temperature in Case C. As well, the rate of heat transfer measured across each of the heat exchangers is shown in Figs. 9, 12 and 15, and illustrates the sequential charging of the storage unit, i. e., Tank 1 initially charges, followed by Tanks 2 and

2. Lastly, Figs. 16 to 19 show the temperature profiles and charge rates of a series and parallel connected multi-tank system as measured for a charge flow of 4.5 L/min (0.072 kg/s). The similarity of the temperature and energy rates is evident.

Innovative design

The innovation with the High-Combi system, examined in this paper, is the achievement of high solar fractions in combination with relatively small SST. The original design of the system under investigation includes the solar heating and cooling plant and the SST coupled with ground heat exchangers (GHE) to minimize heat losses from the storage tank. The main system components of the installation are the solar thermal collectors (180 m[26] [27], selective flat plate), the heating/cooling elements (a combination of floor heating and fan coils2), the absorption cooling machine (35 kWc), the SST (200 m3) and the GHE. The simulated total building area is equal to 700m2 having space heating and cooling energy demands of about 40 and 45 kWh/m2 respectively.

A schematic of the High-Combi plant’s operation is illustrated in Figure 1. This configuration corresponds to one of the five pilot plants (the one to be constructed in Greece) in the framework of the High-Combi project.

The cooling machine is driven by the solar thermal energy (Qh or Qs) at a high temperature (i. e., 70- 90°C) from the SST3, and provides useful cooling by extracting heat (Qc) from the building. To keep the absorption process going, the latent heat from the absorber and the heat from the condensation of the desorbed refrigerant in the condenser, is rejected to the ground heat exchangers, positioned in the earth, around and concentric to the hot water storage tank. In this way, the earth surrounding the tank

will be heated, thus reducing the tank’s thermal losses. Currently, the ground heat exchangers (GHE) are not included in the simulated plant’s configuration and the heat rejection is accomplished through a cooling tower. The use of GHE will be investigated at a follow-up stage.

Figure 1. HIGH-COMBI schematic plant layout

The plant’s operation can be described as follows: during summer, whenever an excess of solar energy is available, this excess heat is delivered directly into the water storage tank. The water in the tank may be heated up to almost 100°C in the summer. The combination of a good conventional thermal insulation and an additional low cost thermal insulation (composed of low cost materials, for example, empty plastic bottles and chipped tires[28]) will reduce the heat losses from the SST, extending its use into the winter months and potentially cover a substantial amount of the heating loads (reaching even 100%). During winter, part of the heating load will be covered directly by the solar heat gains.

At a first glance, it seems contradictory to make a small SST, compared to the conventional ones that are of the order of at least some thousand cubic meters. Thermal losses from the heat storage are proportional to its envelope surface to volume ratio; this ratio increases as the volume becomes smaller. Thus, a smaller SST is expected to have higher thermal losses that need to be accounted for. On the other hand, the construction of a “small” sized SST is attractive since it will permit solar heating and cooling applications at a different scale.

Simulations made in this paper, show that there are still advantages against what might initially be regarded as unfavourable scale application. The use of a relatively low-temperature heat distribution system will allow using the stored heat at a wider range of supply temperatures. This will result to a higher amount of usable energy accumulated in the SST for the same storage volume, and to lower overall heat losses as the mean storage temperatures are reduced.

An overview of the simulation methods and results is presented in the following section.

Objective and scope

The objective of this international collaboration is to develop advanced materials for compact storage systems. The systems will store thermal energy for renewable heating and cooling or for energy conservation.

The objective can be subdivided into six primary goals:

• to identify, develop, and test advanced materials for compact storage,

• to design and develop new materials or composites,

• to develop measuring and testing procedures to characterise these new materials reliably and reproducibly,

• to perform pre-standardisation work for advanced thermal energy storages,

• to develop and demonstrate novel compact thermal energy storage systems employing the advanced materials, and

• to disseminate the gained knowledge.

Because seasonal storage of solar heat is the main application for thermal energy storage, this field will have the focus of this task. However, other applications are also very important, including applications in both renewable energy and energy conservation technologies. Because of this, and because materials research is not and can not be limited to one application only, this task will not focus on only one application area. Other applications in renewable energy and energy conservation-such as solar cooling, micro-cogeneration, biomass, or heat pumps-will also be taken into account.

In terms of classes of materials, this task will be focused around three main classes:

• phase change materials, including micro — and macro-encapsulation and slurries,

• thermochemical materials, including sorption, and

• composite materials and nanostructures.

The latter category includes for instance the combination between zeolites and silicagels, and materials where the molecular and crystalline structure are engineered in detail. Production technologies, the ability to produce advanced materials on a large scale at reasonable costs, is an important aspect in all of these classes.

Main activities

The task will be organised around the following main activities:

• material engineering: analysis and engineering of advanced materials, synthesis of new materials and composites, and materials characterisation and testing;

• numerical modelling: numerical modelling of materials, including molecular interactions, mass and heat transport phenomena, and bulk behaviour;

• components and systems: development, numerical modelling, and testing of (prototypes of) thermal storage components and systems that use the materials developed in the other activities.

Collaboration

The main challenge for this task is to bring together material experts and application experts (particularly solar applications, given the primary scope of the task). The active participation of both groups of experts is essential for this task. However, these groups are traditionally organised in different Implementing Agreements. ECES, Energy Conservation through Energy Storage, has a strong tradition in material research, while SHC, Solar Heating and Cooling, has a strong tradition in solar applications.

Because of the particular nature of this task, a collaboration between these two Implementing Agreements is essential. Hence, this task will take the form of a Joint Task between these Implementing Agreements.

Progress

On October 5, 2007, a first expert meeting was held in Zurich, Switzerland, followed by a Task Defintion Workshop in Petten, The Netherlands, on April 10-11, 2008. Both meetings were very well attended, not only by researchers, but also by representatives of European industries, both large and small. Based on these meetings, the outline of the new task’s objective, scope, and main activities were defined. In a subsequent expert meeting in Bad Tolz, Germany, on June 4-6, 2008, the topics of the task were discussed in more detail.

One of the conclusions of these meetings wass that the main value in this task is to actively combine the knowledge of experts from materials science as well as from solar/renewable heating and energy conservation. Hence, a strong co-operation with other IEA Implementing Agreements is essential to the success of the task, as already mentioned above. Another noteworthy conclusion of the meeting was the strong interest of industry in this task: the industry representatives at the meeting all agreed on the importance of the development of new storage materials.

In their respective ExCo meetings in May and June 2008, the new task was officially approved by both the SHC and ECES Executive Committees. The task will be designated as Task 42 in SHC, and as Annex 24 in ECES. Both ExCos were very positive on the scope and topic of this task. Wim van Helden of ECN, the Netherlands, and Andreas Hauer of ZAE Bayern, Germany, were appointed as Operating Agents.

The official starting date for this four-year task is January 1, 2009. Although four years is relatively long compared to other tasks in either SHC or ECES, this is warranted by the fundamental nature of the work in this task. Because the work on advanced storage materials is still in a very fundamental stage, the trajectory towards applications is still relatively long. It takes several years to identify, characterise and optimise the right materials or composites, and again to develop the reactors, proof-of-principles, and prototypes of the advanced storages made of these materials.

Join the task

Experts from industries and research organisations worldwide, that are active in this field, are cordially invited to join this new task. If you are interested, please contact the authors of this paper or your national ECES or SHC ExCo member.

More information on this task can be found on the temporary task website at www. ecn. nl/ieamaterials.