DUTCH R&D ADVICE ON ACTIVE SOLAR THERMAL ENERGY SYSTEMS

J. van Berkel and L. BosselaarDutch Solar Thermal Energy R&D advisory committee

c/o Novem, P.O. Box 8242, 3503 RE Utrecht , The NetherlandsTel. +31 30 2393495, fax. +31 30 2316491, email : L.Bosselaar@novem.nl

Abstract – Whereas the steadily growing market for residential thermal solar energy systems in theNetherlands asks for a sustained input of research & development, a decline in interest at nationaluniversities and polytechnics is observed. To gain insight in how to stimulate academic participation andto develop a well-supported R&D-policy, participants in the Dutch long term agreement on solar waterheaters decided to set up an advisory committee. A two-step procedure is followed: First a concept-advicewas drawn-up by the advisory committee on the basis of interviews, a desktop study and a brainstormsession held with experts. Secondly, the concept-advice is presented and evaluated by a platform of36 representatives from industry and research institutes (including universities).The R&D-advice exclusively concerns pre-competitive research (research which as yet does not affectcompetition between parties). Storage is identified as the most important subject, with an emphasis onmore compact and efficient seasonal stores, followed by solar cooling; building integration and collectordevelopment (low weight and moderate concentrating). Development of fundamentally new solarconversion techniques (combined with storage development) is given priority for long term R&D, inaddition to development of new materials (e.g. durable plastic insulation).This advice is used as a guideline by the Dutch government and other research financing parties. In thefuture, the impact of the current R&D-advice on R&D-policy of universities and Research institutes willbe monitored. In addition the R&D-advice will be updated with respect to national and internationaldevelopments.

1. INTRODUCTION

In the Netherlands, the market for residential thermalsolar energy systems is growing steadily, both in volume(number of systems applied), as well as in diversity ofsystems applied (tap water systems, space heating andcooling systems). Participants in Dutch long termagreement on solar water heaters (government, industries,utilities and installers) realise that for further solar energymarket development the scientific input of theuniversities and polytechnics is of crucial importance.Contrary to this trend, a decline in interest at nationaluniversities and polytechnics in solar thermal energyresearch is observed. Where e.g. 10 year ago, high qualitysolar thermal research was conducted on storage, andsystem control (e.g. at Eindhoven University), today solarthermal energy research is not selected anywhere as amajor topic.Given these developments, the parties within theagreement decided to set up an advisory committee whichwas given the task to determine the current state of affairswith respect to national academic research on solarthermal energy and to identify research topics which areessential for further development. In 1999, eight membersof the advisory committee are appointed on the basis oftheir experience and insight with respect to science,technology, manufacturing and marketing. The advisorycommittee is chaired by the Dutch organisation of energyand the environment (NOVEM).Operative goal of the committee is to give advice on theR&D-policy with respect to active solar thermal systems.

The R&D-advice should be supported by all partiesinvolved in research, and market implementation of solarthermal systems as to attain consensus on which devel-opments should be supported. Ideally, the advice will beused as a guideline for financing of present research pro-grams and as a means to attract new financial resources.

2. PROCEDURE

2.1 Long term procedureIn general, three steps can be discerned in the formationand actualisation of the R&D-advice :• The advisory committee proposes an R&D-concept

advice on the basis of a preceding advice.• The concept advice is presented to a platform of

representatives of Dutch universities, research insti-tutes, manufacturers and related institutes (e.g.involved in normalisation & testing). For a broad sup-port, it is of vital importance that the platform partiesrepresent most of the organisations involved in solarthermal R&D and business. All platform parties areinvited to give their opinion, add research subjectsand set priority to all subjects. The platform reactionis taken into consideration by the advisory committee,which finally draws-up the final version of theR&D-advice. The advice is drawn-up for a period ofthree years, it will be updated annually, according tochanging circumstances and insights.

• The Dutch government (NOVEM) will use theR&D-advice to set priorities in the long term researchprograms on active solar thermal energy research. The

advisory committee will stimulate other research fundorganisations to comply with the priorities as speci-fied by the R&D-advice.

2.2 Start-up procedureAs the first R&D advice ('99 version) could not be basedon a previous version, a slightly different procedure wasfollowed.Given the goals identified, the committee started with twobasic questions : What is the current state of affairs withrespect to national academic research on solar thermalenergy and what should be done for further development?Both questions are approached rather pragmatically.Insiders were asked to give their opinion, in addition todesktop research on public domain information (reportand internet web-pages).A two-step procedure was followed in formation of the'99 R&D-advice, see figure 1.

I n t e r vi e w sA ca d e m ic s

D e sk t o pr e se a r c h

Bra in st o r me x p e r t s

Ad v i so r yc o m m i t t e

N at io n alPl a t f o r m

' 99R& D-a d vi c e

p re -ad vi c e

Figure 1 First year's procedure flow chart

First, the advisory committee formulated a concept-advice, based on the opinions of university and marketinsiders. Secondly, the concept-advice was presented tothe platform of representatives of Dutch universities,research institutes manufacturers and related institutes.For the '99 version of the R&D-advice, the platformmeeting was attended by 36 persons, representing 30organisations.During the initial step (formation of the concept-advice),the information sources cover :• Five academic insiders with considerable university

experience (mostly -former- research group leaders)were interviewed individually. They were asked toname the current research subjects and to give theiropinion on which subject should be given attentionin the future.

• During a desk-top study, reports of Universityresearch groups, research evaluation committees,mono- and interdisciplinary research schools andstrategic research development committees, inaddition to internet homepages, were scanned forcurrent and future research subjects.

• Five market insiders (from industry and appliedresearch institutes) were asked in a plenary session,to propose subjects which deserve considerableattention in the future.

The inventory showed that currently solar thermal energyrelated research is conducted mainly at the TechnicalUniversities of Delft and Eindhoven and at the Universi-

ties of Twente and Groningen. The most active researchtopics are thermal/PV hybrid collectors, ambient air andsolar heat roof collectors in Eindhoven; predictive con-trol, indoor climate control, absorption cooling in Delft;control, energy storage in building foundation poles inTwente and storage in Phase Change Materials (PCM's)in Groningen.

All subjects suggested for future research were evaluatedby the advisory committee to form the concept-advice tobe evaluated by the platform parties.In addition to evaluation of the concept-advice, the plat-form parties were invited to add research subjects whichwere incorporated in the evaluation procedure. During theevaluation procedure, it showed that the platform's advicedid not differ considerably from the committee's con-cept-advice.All topics suggested and selected for incorporation intothe R&D-advice should meet two main criteria :• A research subject should, after some time, contribute

significantly to further application of solar activethermal energy systems.

• Pre-competitiveness. To attain an impartial selectionprocedure of subjects, they may not interfere with thenear term competition between e.g. manufacturers. Atthe same time, only subjects which will become com-petitive at some time deserve financial support. Allsubjects are categorised into the term at which theyare expected to become competitive : within 3 yearstime, between 3 to 7 years time and after 7 years time.

One basic democratic principle was adopted for rankingthe research subjects within a category : Each member (ofthe advisory committee for formation of the con-cept-advice and of the platform for evaluation thereof)was given 10 points to distribute over the subjects withina category. In addition 10 points were given to rank thepriority of the category. The priorities given to a subjectwere summed-up and normalised to an overall maximumof 10. The same procedure was followed to attain theranking of the categories. Finally, the priority given to asubjects was multiplied by the priority given to the corre-sponding category. All subjects awarded with less than 1point (normalised) were eliminated from the advice.

3. 1999 DUTCH R&D-ADVICE

The R&D-advice drawn-up after consultation of the plat-form parties is given in table 1. In addition to the sub-jects, the argumentation for selecting the subject from theconcept-advice is given in one-liner.

Table 1 Research topics incorporated in the '99Dutch R&D advice on Solar Thermalsystems. Rank 10 marks the highest priority.The argumentation is given in Italic.

Competitive within 3 years RankStorage : more compact (than in water) e.g.PCM's, chemical, underground heat storage.Due to limited space available in Dutchresidents

10

Solar cooling (range 30-100 kW).Focus on cooling media, system technology

7

Solar system-building integration, dynamicaleffects.Due to more severe indoor climate demandsand energy consumption.

7

Lightweight collector.Easier to install.

5

Competitive in 3 to 7 yearsStorage : long term efficient, e.g. PCM's,chemical, underground heat storage.For time in-dependent matching of supplyand demand.

7

Combined thermal/PV collectors.Functional integration, effective usage ofmaterial, space and solar energy supply.

6

Solar cooling (range < 30 kW).Especially with respect to cooling media.

5

Solar system-building integration, dynamicaleffects.In combination with civil engineeringresearch.

4

Low concentrating collectors for highertemperatures at high latitudes.Especially for Space heating systems.

3

Competitive after 7 yearsStorage : more compact and long term effi-cient.Fundamental research on new technologies.

8

New solar-thermal conversion techniquese.g. :• Thermo-chemical• Photo-electro-chemical• Photo-boilogicalFundamental research on new technologies.

7

New materials, e.g. . sustainable plasticinsulation.Focussed on solar thermal applications, LifeCycle analysis.

3

It shows that some subjects receive priority in more thanone category. This holds especially for storage, which isthe main subject identified for future development ofsolar thermal energy systems. In the sequel the researchtopics will be elaborated.

4. SELECTED RESEARCH TOPICS

4.1 StorageStorage is considered a key component of a future sus-tainable energy system. Due to the seasonal phase-lag ofsupply and demand, this holds especially for solar ther-mal systems. Two aspects are relevant.• Store volume. Especially in Dutch residential

buildings, limited space is available for storage ofthermal energy. This is true for diurnal hot waterstorage but especially for seasonal storage for spaceheating. Storage in a sensible form in water isattractive because of low cost and non toxicity. Onthe other hand, the storage density of 4.2 kJkg-1K-1

makes that considerable volumes are required (typi-cally 150 litre for hot water storage and30-40 m3 for seasonal storage). Several options arenow being studied, e.g. storage in a sensible formoutside the building (underground thermal energystorage (UTES); as latent heat in Phase ChangeMaterials; using the principle of sorption/desorption(thermochemical storage) or storage in a biofuel.

• Long term efficiency. In addition to reduction of thestore volume, stores must become more long termefficient in order to bridge the seasonal gap betweensupply and demand. This aspect is especiallyimportant for relative small individual systemswhich experience large losses through store enve-lope relative to store capacity. In order to reducestorage heat loss several ways are open : Increasethe store dimensions (collective systems) , improvethe store insulation (super vacuum insulation)and/or reduce the temperature difference betweenstorage and ambient conditions (storage as latentheat or thermo-chemical storage).

On short term attention could be focussed on develop-ment of phase change stores (synthetic media or water)and vacuum insulation. On longer terms relatively newstorage techniques like thermochemical storage should bedeveloped further.

Figure 2 Storage of solar heat in a 90 m3 tank at VanMelle, Breda.

For insight into the current status of storage techniques, aworld-wide inventory has been made on advanced solarthermal storage techniques. Results of the research willbe presented separately.

4.2 Solar coolingDue to increasing indoor climate demands (comfort) onthe one hand and increasing internal heat load on theother hand, the need for utility and residential coolingalso increases. As the cooling load is more or less inphase with the supply of solar energy, solar coolingseems a sensible choice.

Figure 3 Solar Desiccant Cooling at the headquartersof energy utility company EZK. Just visiblebehind the foreground collector array is theair conditioning unit (photo: Novem/H. Pattist)

The spectrum of solar cooling techniques range fromsorption/desorption in liquids an solids (DesiccativeEvaporative Cooling) to Photovoltaic driven compressioncooling. In addition this research topic comprises theoperation of solar cooling systems for heating purposesoutside the cooling season.

4.3 Solar system-building integrationCost effective application of solar energy in residentialand utility buildings can be stimulated by means of inte-gration of system components into building components.One supply-side example is integration of the solar col-lector in a roof-element. A demand side example is inte-gration of a low temperature heating system with pre-fabfloors, ceilings and walls.

Figure 4 Urban Villa in Amstelveen. Passive and activesolar.

The system dynamics and response to changing condi-tions deserved further attention, in addition to the behav-iour of inhabitants. Apart from the functional integration

also process integration (building construction and sys-tem installation) could provide overall savings.

4.4 Solar collector developmentTwo aspects are discerned with respect to solar collectordevelopment. On short term, attention should be focussedon a light weight collectors which are easier to install,e.g. by application of lightweight materials (plastics) forinsulation and top cover.

Figure 5 Production of flat-plate collectors at ZEN,Veldhoven.

On longer term, attention should be given to the devel-opment collectors for higher temperatures at moderateclimates (Western Europe), e.g. by means of mediumconcentration, and reduction of collector heat losses(better insulation). With respect to both aspects (lightweight and higher temperatures) the aspect of durabilityis of prime importance.

4.5 Combined thermal/PV collectorsHigher collector effectivities (yield per kg material) and ahigher efficiencies (yield per m2) could be attained whenthermal collectors are physically integrated (into a singleenvelope) with a PV-panel. As a result of the increasedeffectiveness and efficiency the price/performance ratiocould reduce. In addition, less space is required for co-production of heat and power, which also offers advan-tages from aesthetic point of view.

Figure 6 Outdoor collector testing at Eindhoven Uni-versity. From left to right : thermal collector,thermal/PV hybrid collector and PV-panel.

Though some combined systems have been build, a con-siderable amount of research remains to be done.

4.6 New solar energy conversion techniquesClosely related to new storage techniques is the furtherdevelopment of solar energy conversion techniques.For long term research solar energy conversion tech-niques should be considered in direct combination withenergy storage. The entire solar energy conversionsystem should be considered in an integral manner : fromelectromagnetic radiation (light) as the energy input, tothe thermal energy output. In between many energyconversion and storage steps can be worth wileconsidering. Examples are fixation of solar energy in bio-fules, development of co-production of heat and powere.g. by means of a solar driven Organic Rankine Cycle.

Figure 7 Fundamentally new conversion techniques forour oldest source of energy?

All possible conversion and storage routes from input tooutput should be evaluated by means of a thermodynamicSecond Law approach (exergy, reduction of entropyproduction).

4.7 New materials, amongst others durable, stagnationresistant plasticsApplication of plastics has been mentioned already in the4.4 : solar collector development as a means to reduce theweight of a collector or to improve the collector tem-perature. Here application is focussed on insulation mate-rials for tubes and stores.

Figure 8 Systems tests under realistic conditions atTNO, Delft.

Especially attention should be given to aspects like thelife cycle effects of extreme conditions (high tempera-tures, high humidity and high thermal radiation).

5. NON-SELECTED RESEARCH TOPICS

In addition to the topics which made it to theR&D-advice, many other topics were suggested. As thetopics received not enough priority (normalised lessthan 1), they were removed from the overall list. For anoverall view the topics are specified in table 2, again withan argumentation given in a one-liner.

Table 2 Topics not selected for the '99 R&D-advice.The argumentation for not selecting the topicis given in Italic.

Uncovered collectors, especially suited for low tem-perature applications.Already taken up by industry.Manufacturing technology : thin, spectral selectiveabsorber plate, sputtering of spectral selective coatings.Keep-up with strong developments in Germany.Development of solar thermal systems for greenhouses.Greenhouses do not need additional heating.• Definition of future sustainable energy society.• Residents behaviour, social aspects.Important, but not a research topic in technologicalsense.• Integration of heating system and solar storage .• Lowering costs of current systems.• Inherently freeze protected active solar system.• Light access to residential and utility buildings.Incorporated in selected topic on integration and sys-tem dynamics.• Distribution of solar irradiation.• Optics, e.g. lenses in concentrating collectors.Incorporated in selected topic on concentrating col-lectors.Building regulations.Partly covered by selected topic on installationaspects.Material research durability and weight.Incorporated in selected topic on material science.Alternative solar conversion technologies, specificallyphoton-transport of energy from collector to storage,fuel cell/solar system integration.Incorporated in selected topic on new conversion tech-nologies.

6. FOLLOW-UP

The R&D-advice is intended as a tool for organisation(selection of priority and financing) of future research. Toavoid redundant research, it is important to know whichresearch topics identified in the R&D advice alreadygains considerable attention elsewhere. To identify and

avoid the redundancy, an inventory is made of interna-tional current (and future) research on active solar ther-mal energy.Of prime interests is also whether or not the R&D-advicehas indeed effect on the R&D-policy of parties involvedin solar development and business (manufacturers,government, research institutes). To determine the"R&D-effect", the status of the research effort will beassessed prior and one year after the presentation of theR&D-advice (September 1999-2000).Both the findings of the international inventory as well asthe R&D-effect monitoring will be used to adjust the nextversion R&D-advice, which is foreseen in 2002.

7. CONCLUSIONS

• A well supported national R&D-policy on active solarthermal systems is of direct importance as the steadilygrowing market for these systems asks for a sustainedinput of research & development.

• Thirty parties involved in research and developmentof active solar thermal energy systems in theNetherlands have set priorities to future solar thermalresearch topics. On the basis of these priorities, an

R&D-advice has been formulated. This advice isintended to be used as a guideline for organisation offuture research and its financing.

• More compact and long term efficient storage hasbeen identified as the prime research topic, followedby solar cooling, building integration, lightweightcollector development and thermal/PV hybridsystems.

• In the near future the effect of the R&D-advice will bedetermined by comparing the research effort statusbefore and after presentation of the R&D-advice. Asto avoid redundancy with foreign research activities,an inventory will be drawn-up. Results of theR&D-effect monitoring and the international researchinventory will be incorporated into the next version ofthe Dutch R&D-advice.

REFERENCES

Bosselaar L. and J. van Berkel, (1999) R&D Advice onActive Solar Thermal Energy Systems, R&D advisorycommittee on active solar thermal energy, c.o. Dutchorganisation for energy and the environment (NOVEM),report DV-1.1.151 99.09, September 1999.