DUTCH R&D ADVICE ON ACTIVE SOLAR THERMAL ENERGY SYSTEMS

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1 DUTCH R&D ADVICE ON ACTIVE SOLAR THERMAL ENERGY SYSTEMS J. van Berkel and L. Bosselaar Dutch Solar Thermal Energy R&D advisory committee c/o Novem, P.O. Box 8242, 3503 RE Utrecht, The Netherlands Tel , fax , L.Bosselaar@novem.nl Abstract Whereas the steadily growing market for residential thermal solar energy systems in the Netherlands asks for a sustained input of research & development, a decline in interest at national universities and polytechnics is observed. To gain insight in how to stimulate academic participation and to develop a well-supported R&D-policy, participants in the Dutch long term agreement on solar water heaters decided to set up an advisory committee. A two-step procedure is followed: First a concept-advice was drawn-up by the advisory committee on the basis of interviews, a desktop study and a brainstorm session held with experts. Secondly, the concept-advice is presented and evaluated by a platform of 36 representatives from industry and research institutes (including universities). The R&D-advice exclusively concerns pre-competitive research (research which as yet does not affect competition between parties). Storage is identified as the most important subject, with an emphasis on more compact and efficient seasonal stores, followed by solar cooling; building integration and collector development (low weight and moderate concentrating). Development of fundamentally new solar conversion techniques (combined with storage development) is given priority for long term R&D, in addition 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 the future, the impact of the current R&D-advice on R&D-policy of universities and Research institutes will be monitored. In addition the R&D-advice will be updated with respect to national and international developments. 1. INTRODUCTION In the Netherlands, the market for residential thermal solar energy systems is growing steadily, both in volume (number of systems applied), as well as in diversity of systems applied (tap water systems, space heating and cooling systems). Participants in Dutch long term agreement on solar water heaters (government, industries, utilities and installers) realise that for further solar energy market development the scientific input of the universities and polytechnics is of crucial importance. Contrary to this trend, a decline in interest at national universities and polytechnics in solar thermal energy research is observed. Where e.g. 10 year ago, high quality solar thermal research was conducted on storage, and system control (e.g. at Eindhoven University), today solar thermal energy research is not selected anywhere as a major topic. Given these developments, the parties within the agreement decided to set up an advisory committee which was given the task to determine the current state of affairs with respect to national academic research on solar thermal energy and to identify research topics which are essential for further development. In 1999, eight members of the advisory committee are appointed on the basis of their experience and insight with respect to science, technology, manufacturing and marketing. The advisory committee is chaired by the Dutch organisation of energy and the environment (NOVEM). Operative goal of the committee is to give advice on the R&D-policy with respect to active solar thermal systems. The R&D-advice should be supported by all parties involved in research, and market implementation of solar thermal systems as to attain consensus on which developments should be supported. Ideally, the advice will be used as a guideline for financing of present research programs and as a means to attract new financial resources. 2. PROCEDURE 2.1 Long term procedure In general, three steps can be discerned in the formation and 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 institutes, manufacturers and related institutes (e.g. involved in normalisation & testing). For a broad support, it is of vital importance that the platform parties represent most of the organisations involved in solar thermal R&D and business. All platform parties are invited to give their opinion, add research subjects and set priority to all subjects. The platform reaction is taken into consideration by the advisory committee, which finally draws-up the final version of the R&D-advice. The advice is drawn-up for a period of three years, it will be updated annually, according to changing circumstances and insights. The Dutch government (NOVEM) will use the R&D-advice to set priorities in the long term research programs on active solar thermal energy research. The

2 advisory committee will stimulate other research fund organisations to comply with the priorities as specified by the R&D-advice. 2.2 Start-up procedure As the first R&D advice ('99 version) could not be based on a previous version, a slightly different procedure was followed. Given the goals identified, the committee started with two basic questions : What is the current state of affairs with respect to national academic research on solar thermal energy and what should be done for further development? Both questions are approached rather pragmatically. Insiders were asked to give their opinion, in addition to desktop research on public domain information (report and internet web-pages). A two-step procedure was followed in formation of the '99 R&D-advice, see figure 1. I nt er vi e w s A ca de m ic s D e sk t o p r e se ar c h Bra in st o r m ex p er t s Figure 1 Ad v i so r y c om m i t t e p re - ad vi c e N at ion al Pl at f or m First year's procedure flow chart ' 99 R& D-ad vi c e First, the advisory committee formulated a conceptadvice, based on the opinions of university and market insiders. Secondly, the concept-advice was presented to the platform of representatives of Dutch universities, research institutes manufacturers and related institutes. For the '99 version of the R&D-advice, the platform meeting was attended by 36 persons, representing 30 organisations. 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 to name the current research subjects and to give their opinion on which subject should be given attention in the future. During a desk-top study, reports of University research groups, research evaluation committees, mono- and interdisciplinary research schools and strategic research development committees, in addition to internet homepages, were scanned for current and future research subjects. Five market insiders (from industry and applied research institutes) were asked in a plenary session, to propose subjects which deserve considerable attention in the future. The inventory showed that currently solar thermal energy related research is conducted mainly at the Technical Universities of Delft and Eindhoven and at the Universities of Twente and Groningen. The most active research topics are thermal/pv hybrid collectors, ambient air and solar heat roof collectors in Eindhoven; predictive control, indoor climate control, absorption cooling in Delft; control, energy storage in building foundation poles in Twente and storage in Phase Change Materials (PCM's) in Groningen. All subjects suggested for future research were evaluated by the advisory committee to form the concept-advice to be evaluated by the platform parties. In addition to evaluation of the concept-advice, the platform parties were invited to add research subjects which were incorporated in the evaluation procedure. During the evaluation procedure, it showed that the platform's advice did not differ considerably from the committee's concept-advice. All topics suggested and selected for incorporation into the R&D-advice should meet two main criteria : A research subject should, after some time, contribute significantly to further application of solar active thermal energy systems. Pre-competitiveness. To attain an impartial selection procedure of subjects, they may not interfere with the near term competition between e.g. manufacturers. At the same time, only subjects which will become competitive at some time deserve financial support. All subjects are categorised into the term at which they are expected to become competitive : within 3 years time, between 3 to years time and after years time. One basic democratic principle was adopted for ranking the research subjects within a category : Each member (of the advisory committee for formation of the concept-advice and of the platform for evaluation thereof) was given 10 points to distribute over the subjects within a category. In addition 10 points were given to rank the priority of the category. The priorities given to a subject were summed-up and normalised to an overall maximum of 10. The same procedure was followed to attain the ranking of the categories. Finally, the priority given to a subjects was multiplied by the priority given to the corresponding category. All subjects awarded with less than 1 point (normalised) were eliminated from the advice DUTCH R&D-ADVICE The R&D-advice drawn-up after consultation of the platform parties is given in table 1. In addition to the subjects, the argumentation for selecting the subject from the concept-advice is given in one-liner.

3 Table 1 Research topics incorporated in the '99 Dutch R&D advice on Solar Thermal systems. Rank 10 marks the highest priority. The argumentation is given in Italic. Competitive within 3 years Storage : more compact (than in water) e.g. PCM's, chemical, underground heat storage. Due to limited space available in Dutch residents Solar cooling (range kw). Focus on cooling media, system technology Solar system-building integration, dynamical effects. Due to more severe indoor climate demands and energy consumption. Lightweight collector. Easier to install. Competitive in 3 to years Storage : long term efficient, e.g. PCM's, chemical, underground heat storage. For time in-dependent matching of supply and demand. Combined thermal/pv collectors. Functional integration, effective usage of material, space and solar energy supply. Solar cooling (range < 30 kw). Especially with respect to cooling media. Solar system-building integration, dynamical effects. In combination with civil engineering research. Low concentrating collectors for higher temperatures at high latitudes. Especially for Space heating systems. Competitive after years Storage : more compact and long term efficient. Fundamental research on new technologies. New solar-thermal conversion techniques e.g. : Thermo-chemical Photo-electro-chemical Photo-boilogical Fundamental research on new technologies. New materials, e.g.. sustainable plastic insulation. Focussed on solar thermal applications, Life Cycle analysis. Rank 10 It shows that some subjects receive priority in more than one category. This holds especially for storage, which is the main subject identified for future development of solar thermal energy systems. In the sequel the research topics will be elaborated SELECTED RESEARCH TOPICS 4.1 Storage Storage is considered a key component of a future sustainable energy system. Due to the seasonal phase-lag of supply and demand, this holds especially for solar thermal systems. Two aspects are relevant. Store volume. Especially in Dutch residential buildings, limited space is available for storage of thermal energy. This is true for diurnal hot water storage but especially for seasonal storage for space heating. Storage in a sensible form in water is attractive because of low cost and non toxicity. On the other hand, the storage density of 4.2 kjkg -1 K -1 makes that considerable volumes are required (typically 150 litre for hot water storage and m 3 for seasonal storage). Several options are now being studied, e.g. storage in a sensible form outside the building (underground thermal energy storage (UTES); as latent heat in Phase Change Materials; using the principle of sorption/desorption (thermochemical storage) or storage in a biofuel. Long term efficiency. In addition to reduction of the store volume, stores must become more long term efficient in order to bridge the seasonal gap between supply and demand. This aspect is especially important for relative small individual systems which experience large losses through store envelope relative to store capacity. In order to reduce storage heat loss several ways are open : Increase the store dimensions (collective systems), improve the store insulation (super vacuum insulation) and/or reduce the temperature difference between storage and ambient conditions (storage as latent heat or thermo-chemical storage). On short term attention could be focussed on development of phase change stores (synthetic media or water) and vacuum insulation. On longer terms relatively new storage techniques like thermochemical storage should be developed further. Figure 2 Storage of solar heat in a 90 m 3 tank at Van Melle, Breda. For insight into the current status of storage techniques, a world-wide inventory has been made on advanced solar thermal storage techniques. Results of the research will be presented separately.

4 4.2 Solar cooling Due to increasing indoor climate demands (comfort) on the one hand and increasing internal heat load on the other hand, the need for utility and residential cooling also increases. As the cooling load is more or less in phase with the supply of solar energy, solar cooling seems a sensible choice. Figure 3 Solar Desiccant Cooling at the headquarters of energy utility company EZK. Just visible behind the foreground collector array is the air conditioning unit (photo: Novem/H. Pattist) The spectrum of solar cooling techniques range from sorption/desorption in liquids an solids (Desiccative Evaporative Cooling) to Photovoltaic driven compression cooling. In addition this research topic comprises the operation of solar cooling systems for heating purposes outside the cooling season. 4.3 Solar system-building integration Cost effective application of solar energy in residential and utility buildings can be stimulated by means of integration of system components into building components. One supply-side example is integration of the solar collector in a roof-element. A demand side example is integration of a low temperature heating system with pre-fab floors, ceilings and walls. also process integration (building construction and system installation) could provide overall savings. 4.4 Solar collector development Two aspects are discerned with respect to solar collector development. On short term, attention should be focussed on a light weight collectors which are easier to install, e.g. by application of lightweight materials (plastics) for insulation and top cover. Figure 5 Production of flat-plate collectors at ZEN, Veldhoven. On longer term, attention should be given to the development collectors for higher temperatures at moderate climates (Western Europe), e.g. by means of medium concentration, and reduction of collector heat losses (better insulation). With respect to both aspects (light weight and higher temperatures) the aspect of durability is of prime importance. 4.5 Combined thermal/pv collectors Higher collector effectivities (yield per kg material) and a higher efficiencies (yield per m2) could be attained when thermal collectors are physically integrated (into a single envelope) with a PV-panel. As a result of the increased effectiveness and efficiency the price/performance ratio could reduce. In addition, less space is required for coproduction of heat and power, which also offers advantages from aesthetic point of view. Figure 4 Urban Villa in Amstelveen. Passive and active solar. The system dynamics and response to changing conditions deserved further attention, in addition to the behaviour of inhabitants. Apart from the functional integration Figure 6 Outdoor collector testing at Eindhoven University. From left to right : thermal collector, thermal/pv hybrid collector and PV-panel.

5 Though some combined systems have been build, a considerable amount of research remains to be done. 4.6 New solar energy conversion techniques Closely related to new storage techniques is the further development of solar energy conversion techniques. For long term research solar energy conversion techniques should be considered in direct combination with energy storage. The entire solar energy conversion system should be considered in an integral manner : from electromagnetic radiation (light) as the energy input, to the thermal energy output. In between many energy conversion and storage steps can be worth wile considering. Examples are fixation of solar energy in biofules, development of co-production of heat and power e.g. by means of a solar driven Organic Rankine Cycle. Figure Fundamentally new conversion techniques for our oldest source of energy? All possible conversion and storage routes from input to output should be evaluated by means of a thermodynamic Second Law approach (exergy, reduction of entropy production). 4. New materials, amongst others durable, stagnation resistant plastics Application of plastics has been mentioned already in the 4.4 : solar collector development as a means to reduce the weight of a collector or to improve the collector temperature. Here application is focussed on insulation materials for tubes and stores. Especially attention should be given to aspects like the life cycle effects of extreme conditions (high temperatures, high humidity and high thermal radiation). 5. NON-SELECTED RESEARCH TOPICS In addition to the topics which made it to the R&D-advice, many other topics were suggested. As the topics received not enough priority (normalised less than 1), they were removed from the overall list. For an overall view the topics are specified in table 2, again with an argumentation given in a one-liner. Table 2 Topics not selected for the '99 R&D-advice. The argumentation for not selecting the topic is given in Italic. Uncovered collectors, especially suited for low temperature applications. Already taken up by industry. Manufacturing technology : thin, spectral selective absorber 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 technological sense. 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 system dynamics. Distribution of solar irradiation. Optics, e.g. lenses in concentrating collectors. Incorporated in selected topic on concentrating collectors. Building regulations. Partly covered by selected topic on installation aspects. Material research durability and weight. Incorporated in selected topic on material science. Alternative solar conversion technologies, specifically photon-transport of energy from collector to storage, fuel cell/solar system integration. Incorporated in selected topic on new conversion technologies. Figure 8 Systems tests under realistic conditions at TNO, Delft. 6. FOLLOW-UP The R&D-advice is intended as a tool for organisation (selection of priority and financing) of future research. To avoid redundant research, it is important to know which research topics identified in the R&D advice already gains considerable attention elsewhere. To identify and

6 avoid the redundancy, an inventory is made of international current (and future) research on active solar thermal energy. Of prime interests is also whether or not the R&D-advice has indeed effect on the R&D-policy of parties involved in solar development and business (manufacturers, government, research institutes). To determine the "R&D-effect", the status of the research effort will be assessed prior and one year after the presentation of the R&D-advice (September ). Both the findings of the international inventory as well as the R&D-effect monitoring will be used to adjust the next version R&D-advice, which is foreseen in CONCLUSIONS A well supported national R&D-policy on active solar thermal systems is of direct importance as the steadily growing market for these systems asks for a sustained input of research & development. Thirty parties involved in research and development of active solar thermal energy systems in the Netherlands have set priorities to future solar thermal research topics. On the basis of these priorities, an R&D-advice has been formulated. This advice is intended to be used as a guideline for organisation of future research and its financing. More compact and long term efficient storage has been identified as the prime research topic, followed by solar cooling, building integration, lightweight collector development and thermal/pv hybrid systems. In the near future the effect of the R&D-advice will be determined by comparing the research effort status before and after presentation of the R&D-advice. As to avoid redundancy with foreign research activities, an inventory will be drawn-up. Results of the R&D-effect monitoring and the international research inventory will be incorporated into the next version of the Dutch R&D-advice. REFERENCES Bosselaar L. and J. van Berkel, (1999) R&D Advice on Active Solar Thermal Energy Systems, R&D advisory committee on active solar thermal energy, c.o. Dutch organisation for energy and the environment (NOVEM), report DV , September 1999.