Skip to main content



FRIENDSHIP is a project funded by the European Union’s Horizon 2020 research and innovation programme coordinated by Commissariat à l’Énergie Atomique et aux Énergies Alternatives from Grenoble, France.
FRIENDSHIP plans to bring together research centres, industrial designers, technologies & heat suppliers into the same consortium in order to unite skills towards the boost and control of the heat supply temperature according to processes needs. It will evaluate to what extent high share of solar heat heating and cooling will allow to reduce the dependence of industrial processes on carbon energies and associated polluting emissions, and to quantify economic gains related to the use of solar energy in a context of a changing fossil fuel market and changing climatic constraints. More...


Project partners:

Coordinator: National Institute of Chemistry (NIC), Slovenia


 - Chemcolor Sevnica d.o.o., Slovenia

 - Inaventa Solar, Norway

 - FOSS University of Cyprus (UCY), Cyprus

Period: 1. June 2017 - 30. September 2020

Funding: M-ERA.NET Call 2016: Financial support by the Ministry of Education, Science and Sport (Slovenia), Research Promotion Foundation Cyprus (Cyprus), Research Council of Norway



Architects and designers have long requested energy-producing, architecturally appealing and cost-efficient building modules. The aim is to substantially reduce energy use and CO2 emissions in the building sector and the potential serious consequences of climate change.

Inaventa Solar has developed a new solar collector technology, which is based on high-performance polymers (HPP) and designed as a building envelop system. Using available solar collector coatings on the market, we were faced with three challenges: i) existing, multifunctional coatings were made of solvent-borne resins, causing high volatile organic solvent emissions in the production process, ii) coatings were only offered as non-selective black paints without performance enhancing properties, and iii) dust and dirt remained over time on the surface resulting in decreased efficiency.

These challenges were addressed in Wabaselcoat (WAter BAsed SELective COATings for intelligent façade collectors), a R&D project within the M-ERA.NET program, an EU funded network which has been established to support and increase the coordination of European research programs and related funding in materials science and engineering. Partners in the project are National Institute of Chemistry-Ljubljana (NIC), Chemcolor, FOSS and Inaventa Solar.

Solar collector facade (Inaventa Solar, Oslo) with black, red and blue TISS paint coatings (simulation adapted for Chr. Roacker, EPFL)



The main objective of WABASELCOAT was to overcome these challenges and develop new, multi-functional, spectrally selective paint coatings using nanotechnology for improving the performance and the visual aesthetics of building-integrated, polymeric solar collectors. The coating should also be cost-efficient, waterborne and environmental-friendly, hence applicable for up-scaling in a solar collector production line. Concretely the project aimed to develop waterborne, thickness-insensitive, spectrally selective (TISS) paints for polymeric absorber surfaces with the following characteristics:

  • solar absorptance higher than 93% for black coatings and solar absorptance higher than 90% for coloured coatings under normal operation;
  • thermal emittance lower than 35% in the operating temperature range from -5°C to +80°C;
  • Durability reflected by a lifetime requested by building industry (at least 25 years);
  • Can stand dry stagnation with temperatures up to 150°C;
  • Meet or exceed safety standards and low costs: i.e. anti-soiling, anti-frost, flame retardant paint, cost competitive coatings for final application;
  • Another aim was securing IPR protection of the invention in WABASELCOAT.


The work in WABASELCOAT was organised in 5 WORK PACKAGES

WP0 Project management and reporting

WP1 Identify needs and system definition

WP2 Development of additives

WP3 Formulation of water-borne paints and scale up

WP4 Industrial scalability

WP5 Prototype fabrication, testing and system evaluation


Reducing collector heat losses - enhancing sustainability

The performance of a solar collector can be improved by reducing the heat losses in the thermal range of the electromagnetic spectrum. Hence, absorber coatings should have lowest thermal emittance. In this project, we analysed the structure and thermal emissivity of various waterborne binders. In order to keep industrial scaling realistic within the project period we focused on commercial binders. The study included commercially available binders, 13 single-component binders and one binary component. The binders were analysed spectroscopically (UV-VIS reflection measurements; IR spectroscopy) and on different substrates (PPS absorber samples, Al and silicon wafers). Among 32 binders, one polyurethane-based resin was chosen as the right candidate towards a waterborne and more sustainable solar collector coating.

Various flakes, suitable for waterborne and solvent-based coatings, were investigated. It turned out that the size of the scales and their surface area played a key role for the increased reflection in the infrared range of the electromagnetic spectrum, which was evident from SEM images. We found that flakes from the Aquamet program are suitable for waterborne systems and had the lowest thermal emittance (eT = 0.16).

Blue and black metallized flakes (left) and SEM (scanning electron microscope) image of Aquamet CP-BG 3200/60 flakes (right)


High solar absorptance for black and coloured solar collector TISS coatings

We have incorporated various Multi-Walled Carbon Nano Tubes (MWCNTs) and 2D carbon nanomaterials (platelets graphene and graphene nano-ribbons) in the Thickness Insensitive Spectrally Selective (TISS) absorber paints to improve the solar absorption and for corrosion protection of the metallic pigments. In the selection of MWCNT, price and market availability were main criteria.

We found that as received MWCNT needed to be shortened (by cryo-milling or Ultra-Turrax) and their surface properties modified. This led to good distribution of the tubes in the binder and enhanced the solar absorptance to targeted 93% (black) and 90% (coloured coatings) under optimized lab conditions. Efforts were focused on pigment concentration, milling procedure, pigment modification, pot-life, rheology tuning and spray application. All those factors are reflected in the optical properties of the coatings.

With the new waterborne TISS coatings we succeeded to improve the solar energy transformation efficiency; further the visual attractiveness by making blue and red hues available replacing black without major efficiency losses.

Multi-walled carbon nano tubes: Synthesis of functionalized (NR1-NR3) GNRs


Durability againts UV radiation, thermal and mechanical loads

The durability of the prepared paint formulations was studied with PPS solar absorber samples as substrate.  The free surface energy of individual binders was measured before and after curing in order to optimize the spreading of the coating on polymer substrates, which is very important for good adhesion of coatings. For the pre-treatment of the absorber substrate best adhesion was obtained with sandblasting, which allowed for lower free surface energy, greater roughness, resulting in better coating flow, better adhesion and cohesion of the coating. For industrial use, this process would be environmentally friendly and inexpensive although less feasible in online production.

On-going, accelerated service-life testing of the TISS paints applied on absorber substrate samples did not reveal mechanical or optical failures. These durability tests included direct exposure to UV radiation, dry heat, humidity, temperature cycling, wind and soiling. Furthermore, samples were exposed to evaluated temperatures in order to test the thermal stability of the coating. Besides, samples were exposed to the accelerated standard testing procedure and UV load. We study the influence of the thinner on paint stability. Final formulations were found to be UV, thermally and mechanically stable and are appropriate for preparation of TISS paints. Coloured TISS paints were prepared in blue and red colour hues. All samples disclose spectrally selective properties.

Coloured TISS paints were prepared in black, blue and red colour hues on PPS absorber samples (left)


Sustains operating conditions in solar collectors and stagnation temperature

The paint coatings developed in WABASELCOAT are able to sustain the extreme conditions in a solar collector: The highest load occurs during solar collector stagnation and system standstill, when no cooling is present (approx. 140 C above ambient temperature). For exposure to realistic, maximum thermal load, a full-sized, TISS-paint coated absorber was integrated in a solar collector frame and exposed to dry-hot Mediterranean climate at the test facility of FOSS University of Cyprus. First stagnation tests in WABASELCOAT revealed satisfying results after the inspection of exposure to one summer season.

Coloured TISS paints were applied on full-size PPS absorbers (left) and exposed to dry-hot Mediterranean climate at the test facility of FOSS University of Cyprus (right)


Anti-soiling, flame-retardant and low costs with nanotechnology

Soiling of surfaces coated with spectrally selective paints can be a critical issue for glazed and unglazed solar collectors. It decreases "solar-to-thermal conversion" and consequently lowers the collector and overall system efficiency. For anti-soiling surfaces we needed to fulfil two parameters: i) low surface energy and ii) roughness of the surface. Optimal combination of both parameters will result in hydrophobic, anti-soiling or easy to clean surfaces.

Part of the efforts in the project was dedicated to the development of a hydrophobic and anti-soiling properties of the solar absorber coating. Various, POSS molecules (Polyhedral oligomeric silesquioxanes) were synthesized as additives for the TISS paint coatings to improve the anti-soiling properties of the coated surface. The synthesis can be done at room temperature and is scalable and easy applicable to industrial production. It was new having developed this property for environmentally friendly, waterborne coatings.

Moreover, we worked on the synthesis of flame-retardant additives for polymeric binders. Flame retardant additives provide greater safety in the use of waterborne coatings. With the synthesis and incorporation of fluoro-isooctyl amino based POSS molecules, we achieved high sliding angles for water (>130°) and hexadecane (>90°). The work on fireproof additives resulted in improved paint coatings characterized by flame retardants for high-performance, multifunctional paints. Furthermore, synthesised amphiphilic POSS molecules can be used also as additives for improving the efficiency of Dye synthesized solar cells.

Various homo and heteroleptic POSS molecules sythesized as additives for Thickness Insensitive Spectrally Selective paint caoating on PSS substrate


See more: Hydrophobism and Spectrally selective paint coatings


Protection of European technology

NIC has submitted a Slovenian patent application with the title "Water-based sickness insensitive spectrally selective paint coatings" during 2020, which protects their invention in WABASELCOAT.

Dr. Jerman was leading WABASELCOAT (left). Guided tour through the laboratories of the National Institute of Chemistry, Ljubljana in May 2018 during our 1st project meeting: Prof. Georges Makrides, Mohor Mihelčič, dr. Pavli Pori, dr. Marija Čolović, dr. Ivan Jerman (right)


Further reading

J.Vasiljević, M.Čolović, I.Jerman et al. In situ prepared polyamide 6/DOPO-derivative nanocomposite for melt-spinning of flame-retardant textile filaments. Polymer Degradation and Stability, Vol. 166, 2019, Pages 50-59.

L.Noč, F.Ruiz-Zepeda, F.Merzel, I.Jerman, High-temperature “ion baseball” for enhancing concentrated solar power efficiency. Solar Energy Materials and Solar Cells, Vol. 200, 2019, 109974.

M.Čolović, J.Volavšek, E.Stathatos, N.Čelan Korošin, M.Šobak, I.Jerman, Amphiphilic POSS-based ionic liquid electrolyte additives as a boost for dye-sensitized solar cell performance. Solar Energy, Vol. 183, 2019, 619-631.

E.Šest, G.Dražič, B.Genorio, I.Jerman, Graphene nanoplatelets as an anticorrosion additive for solar absorber coatings, Solar Energy Materials and Solar Cells, Vol. 176, 2018, 19-29.

Jelena Vasiljević, M.Čolović, N.Čelan Korošin, M.Šobak, Ž.Štirn,I.Jerman, Effect of Different Flame-Retardant Bridged DOPO Derivatives on Properties of in Situ Produced Fiber-Forming Polyamide 6Polymers 2020, 12(3), 657.

Method for the preparation of a polyamide 6 copolymer and filaments, flame retardant polyamide 6 copolymer and copolymer filaments. Patent, issued Jan 2, 2020, WO 2020/002403 A1, Inventors: Colovic Marijan, Demšar Andrej, Jerman Ivan, Simoncic Barbara, Vasiljevic Jelena, Šehic Alisa;

color contrast
text size
highlighting content
zoom in