Task 39 - Polymeric Materials for
Solar Thermal Applications
Newsletter No 10 - Nov.
2011
Task 39 Newsletter
This newsletter summarises the topics at the
Task 39 Meeting in Aveiro Portugal on September 19-21, 2011
hosted by Luis Godinho, PRIREV, and Pedro Graca, Aveiro
Technical University, Portugal.
September 19-21,
2011 Recent IEA-SHC Task 39 Meeting in Aveiro,
Portugal The 12th Task 39 experts meeting took place at
the University of Aveiro, Portugal from September 19-21, 2011.
The meeting was hosted by Luis Godinho, Prirev, and Pedro
Graca, University of Aveiro. 23 experts participated in the
meeting, among them new industry participants from DuPont
Performance Polymers, Brasil. A factory visit of Bosch
Termotecnologia S.A., Aveiro was arranged.
February 13-14,
2012 Kunststoffe: Einsatz in Solarthermie und
Photovoltaik Lösungswege – Anwendungen –
Marktpotential, Regensburg, Germany; fachliche Leitung: PCCL,
Austria; http://www.otti.de/
May 15-16,
2012 13th IEA-SHC Task 39 Experts meeting,
Berlin, Germany The next Task 39 Experts meeting will
be organised by Beate Röder, Humboldt University of Berlin,
Germany.
May 15,
2012 Task 39 Industry Workshop, Berlin,
Germany A public industry workshop will be arranged in
connection with the 13th Task 39 Experts meeting in
Berlin.
July 9-11, 2012
SHC 2012 - International Conference on Solar
Heating and Cooling for Buildings and Industry, San Francisco,
USA; more information: http://www.shc2012.org/cms/
Task 39 Meeting in Aveiro, September 19-21,
2011, Aveiro Technical University, Portugal.
Accessing weathering stability by Raman Microscopy
High performance and engineering
polymers like PPS and PPE-PS have been investigated at
Fraunhofer ISE regarding their weathering stability and
therefore their applicability for polymeric solar thermal
collectors. Accelerated aging tests were carried out and a
systematic variation of the climatic parameters heat, UV
radiation and humidity is supposed so simulate real-life
conditions as accurate yet quick as possibly. Additionally,
outdoor exposure tests were carried out in Freiburg, Germany
and Gran Canaria, Spain. The polymeric plates were, inter
alia, characterized by the means of Raman microscopy with the
objective of a quantification of the degradation. Due to a
carbon black pigmentation of the plates, fluorescence is
already present for the non-aged samples. Raman spectra show
an increasing fluorescence at the beginning of the aging,
especially under presence of UV radiation during aging. At
later stages of the degradation process, different aging
mechanisms are apparently proceeding simultaneously, leading
to an overall decrease in fluorescence intensity. Furthermore,
the homogenity of the aging process was investigated via Raman
image scans.
Fig. 1 Progress of fluorescence intensity in
Raman Spectra during accelerated aging of PPS samples (top).
Outdoor exposure of different polymeric plates in Freiburg
(bottom).
Optical and thermal properties of polypropylene absorber
materials
Polyolefin materials are of high relevance for absorbers of
solar thermal collectors with integrated overheating
protection. The main objective of WP-04 of the collaborative
research project SolPol-2 (http://www.solpol.at/) is to develop novel
black polyolefin grades for solar absorber applications. In
this work the effect of various black pigments (carbon black
(CB) and carbon nanotubes (CNT)) on optical and thermal
properties of PP-RCT (Polypropylene-Random Copolymer with
special crystalline structure (ß-phase) for elevated
temperature applications) is investigated. To meet the
requirements of high absorptance in the solar wavelength range
(> 90%) and a high amount of β-crystallinity for enhanced
mechanical properties at a service temperature of 90°C for at
least 10 years, the supplied materials are characterized in an
unaged state by UV-Vis-NIR spectroscopy and differential
scanning calorimetry (DSC). The investigations revealed
that pigmentation with CB and CNT is a suitable measure to
fulfill high absorptance requirements. Integral absorptance
values of all black-pigmented PP-RCT compounds are ranging
from 95 to 96% (Fig. 2). Regarding the thermal behaviour and
the derived morphological parameters, the ß-phase content in
all black-pigmented PP-RCT specimens is ranging from 61 to 76
%. Specimens with carbon black grade CB1 and the master batch
MB2 (in both, the carbon black primary particle size was 20
nm) exhibited best ratio of ß-crystallinity. For the CNT
filled grade the lowest amount of ß-phase was obtained.
M. Kurzböck, G.M. Wallner, R.W. Lang,
Johannes Kepler University, Linz; Markus.Kurzboeck@jku.at;
K. Klimke, Borealis AG, Linz; K. Rametsteiner, KE KELIT
Kunststoffwerk GmbH, Linz, Austria;
Fig. 2 Normal-hemispherical reflectance
spectra of various black pigmented PP-RCT compounds in the
solar wavelength range (incl. AM 1.5).
Thermotropic glazing for overheating protection
applications: Effect of the morphology on the light-shielding
performance
Various prototype layers of thermotropic systems with fixed
domains (TSFD) for overheating protection applications
(reducing transmittance upon reaching a certain threshold
temperature) were manufactured by applying a systematic
material formulation approach. TSFD consist of a thermotropic
additive that is finely dispersed in either a thermoset or
thermoplastic matrix. Material modelling revealed, that
highest back scattering efficiency of TSFD in the opaque state
is obtained with spherical additive domains exhibiting a
diameter between 200 and 400 nm. In the cold state the
formulated TSFD exhibit a solar hemispheric transmittance
between 39 and 85%. Above the switching threshold, the
transmittance changed by -32 to +34% to values ranging between
53 and 88%. Morphological analysis of the inner material
structure revealed partially unfavourable geometrical domain
properties. The best performing materials exhibited either
plate-like domain structure with length and width ranging from
6 to 85µm and from 0.2 to 7 µm, respectively or spherical
domains with diameters between 0.6 and 5 µm. Furthermore a
distinct correlation between the thermotropic properties of
the TSFD and the coefficients of thermal expansion (CTE) of
material constituents was determined. Current research work is
focusing on the optimization of the material structure and the
scattering domain size by optimization of processing
conditions and surface functionalization.
The organisers of the 12th Task 39 Experts meeting in
Aveiro arranged a guided factory visit of Bosch
Termotecnologia's solar thermal collector production facility
in Cacia – Aveiro. Representatives from Bosch Termotecnologia
S.A. participated also in the Experts meeting.
Technical guidance during the factory visit:
Mateus Tiago, Project Leader for Solar Thermal Systems Tiago.Mateus@pt.bosch.com
DuPont Latin America - Division of Performance Polymers -
participated in the Task 39 meeting in Aveiro.
Founded in 1802, DuPont puts science to work by creating
sustainable solutions essential to a better, safer, healthier
life for people everywhere. Operating in approximately 90
countries, DuPont offers a wide range of innovative products
and services for markets including agriculture, nutrition,
electronics, communications, safety and protection, home and
construction, transportation and apparel. The company believes
that by collaborating with customers, governments, NGOs, and
thought leaders we can help find solutions to such global
challenges as providing enough healthy food for people
everywhere, decreasing dependence on fossil fuels, and
protecting life and the environment.
Polymeric collectors are less resistant to the combination
of high temperature and high pressure than conventional, metal
collectors. Necessarily this influences the design of the
hydraulic scheme connected to glazed polymeric collectors. One
example is shown in Fig. 4 (top). The collector modules are
inter-connected in parallel and to a solar loop with
unpressurized heat store, which has a free volume at the top
for pressure stabilisation. The system design (drain-back)
prevents damages by freezing and boiling of the heat carrier
in the solar loop. In each collector module, a built-in flow
resistance provides equal circulation of the heat carrier.
The performance of such a system was studied in the
project Bjørnveien 119 in Oslo (Fig. 4, bottom), a solar
combisystem with 77 m² collector area on the south oriented
facade and a 8000 litres heat store. The system supports the
heating in 8 apartments (total heated floor area: 1200 m²).
The supply of auxiliary energy (electricity) from
January-August was compared in 2010 without the solar system
and 2011 with the solar system in operation. The amount of
bought electricity was lowered from 74000 kWh to
51000 kWh, an improvement close to 30%.
Fig. 4 Top: Hydraulic scheme of solar heating
system, unpressurised and adopted to polymeric collectors;
bottom: Solar collector system with polymeric collectors,
Bjørnveien 119, Oslo;
Environmental costs may vary considerably between
different heating systems
Environmental performance characteristics based upon LCA
and Ecoinvent data for a set of different heating systems show
that there are many differences. In the comparison made the
location and yearly amount of heat utilized by the systems are
assumed the same which mean that only the design and the size
of the different systems vary. In the table below and in Fig.
5 the results are shown for the following systems: (a) solar
heating system with 15 m2 of a polymeric solar
collector (Aventa), (b) solar heating system with
12.5 m2 of a flat plate collector (Ecoinvent
reference system where a copper absorber is used in the
collector), (c) solar system with 8 m2 of an
evacuated tube collector (Ecoinvent reference system), and (d)
natural gas system.
It can be concluded from the data in the table that the
environmental costs appear relatively small in comparison with
other life cycle cost contributions associated with the use of
the different systems. However, it is quite clear that the
environmental costs of all the solar heating systems are very
small when compared with a system where burning of a fossil
fuel is used as heat source. How the total costs or life cycle
costs of the different systems vary will be analysed in the
next phase of work to be performed in IEA SHCP Task 39.
Bo Carlsson, Linnaeus University, Sweden, bo.carlsson@lnu.se Helena Persson, Linnaeus University, Sweden, helena.persson@lnu.se Michaela Meir, University of Oslo, Norway,
m.g.meir@fys.uio.no
Fig. 5 Comparison of CO2 emission (IPCC GWP
(100 a)) for different equivalent heating systems situated in
Oslo (under operation for 25 years and producing totally 0.11
TWH);
Accelerated aging testing of polymeric materials for solar
thermal applications
The long-term thermal stability (LTTS) of polymers is a
major criterion for their applicability in solar thermal
systems. For example, heat storage applications require a
maximum service temperature of about 95°C. High-temperature
aging is common to evaluate LTTS, however it is time-consuming
and limited in acceleration on common test specimen with
application relevant thickness. Hence, a main goal of the
basic research project SolPol-1 (http://www.solpol.at/) is to develop
accelerated aging methods for polymeric materials in solar
thermal applications. Current work focuses on the evaluation
of a testing approach based on micro-sized specimens with a
thickness of 200 µm, which is a factor 10 below the nominal
component thickness for polyolefin liner materials for heat
storage tanks. To prepare micro-sized specimen manual and
automated procedures and equipment were implemented allowing
for planing of specimen with a thickness down to 50 µm. By
mechanical testing the high reproducibility in specimen
preparation and thus, the high quality of the micro-sized
specimen was confirmed. From selected polyolefin formulations
for heat storage applications 200 µm thick specimen were
prepared from extruded sheets. To check potential acceleration
factors for hot air exposure micro- and macro-sized specimen
were exposed to air at elevated temperature of 135°C.
Regarding the aging behaviour (s. Fig. 6) a similar ranking of
the investigated polyolefin materials was obtained for micro-
and macro-sized specimen. However, potential differences in
the aging mechanisms have to be elucidated.
What needs to be done to ensure that the high potential of
plastics in the field of low-temperature solar-thermal energy
supply can be used to obtain marketable products? This
question is dealt with in the upcoming project
Solar COllectors made
Of Polymers (SCOOP). The aim
of the project is to select and develop suitable polymer
grades and collector designs for flat plate collectors for
building integration as well as thermo-siphon systems. The
work packages include a comprehensive assessment of the
market, costs and scale effects, the selection and
optimization of polymeric materials for injection moulding and
extrusion as well as a continuous qualification of new
materials, absorbers and components. The development and
installation of demonstration systems round off the work done
and is assessed in the final work package, where a comparison
with energy yields of conventional systems is undertaken. At
the end of the project, the most effective materials,
technical designs and system concepts for the application of
polymers in solar thermal systems shall be defined.
Partners within SCOOP are Fraunhofer ISE
(coordination), AEE INTEC, HSR Hochschule fuer Technik
Rapperswil, University of Oslo, Humboldt-University of Berlin
and Johannes Kepler University of Linz as research
institutions and the industrial partners GREENoneTEC, HTCO,
PPI, APC, DS Smith Kaysersberg and Aventa. The project is
funded by the European Commission within the Seventh Framework
Programme (FP7). It is launched in November 2011 and runs for
3.5 years.
Paint is the most versatile decorating product on the
market. The number of choices is innumerable: colours, degrees
of gloss, patterns, textures and special effects. When the
spectrally selective paint was used only for roof absorber,
only a handful of people were thinking on coloured selective
paint, but now when the absorbers are reality: As façade
elements the colour becomes a very important parameter. The
distinctive properties of Thickness Sensitive Spectrally
Selective (TSSS) and Thickness Insensitive Spectrally
Selective (TISS) were outlined and the use of the latter paint
coatings as cool paints was proposed and demonstrated. The
material aspects of the coloured cool TISS paint coatings are
reviewed, focusing on cool pigments, metallic and metallised
flake pigments and polymeric resin binders used for the
production of solar paint coatings with the help of dispersant
molecules in order to achieve uniform distribution of the
finely ground pigment particles in the polymeric resin binder.
Intentionally, we have focused on organo (silicon) i.e. silane
dispersants because they have proven to be effective
dispersants for various nano-particle systems (also spheres)
and also commercial pigments.
I. Jerman, M. Mihelčič, B. Orel, NIC –
National Institute of Chemistry, Slovenia, boris.orel@ki.si R.
Kunič, FRAGMAT TIM, d.d., Spodnja Rečica 77, SI-3270 Laško,
Slovenia
Fig. 7 Proposal for solar façade absorbers,
variation of green TISS paint on polymeric substrate.
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