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Durable, easy- clean coating for greenhouse horticulture

In greenhouse horticulture, light is the most important factor for plant growth. In practice, the light transmittance of the glass diminishes over time, due to dirt accumulation, among other things. TNO is developing an innovative coating that prevents contamination, is long-lasting and has no negative impact on transmittance. Consequently, plant growth - and thus the yield of the greenhouse - remain high without the need for frequent cleaning.

Horticultural glass (the greenhouse) must allow maximum light transmittance, as light is the most important factor in plant growth. In practice, two factors appear to reduce transmittance. The first is contamination of the glass, and the second is the reduced effectiveness of the anti-reflection coating that may be present on the glass. The goal of this project is to develop a demonstrator coating that keeps both factors at bay. In other words: reduction of the fouling rate of the glass and significant slowing of the degradation of the anti-reflective coating. At the same time, the coating to be developed must not have any negative impact on the light transmittance and must be long-lasting. The coating can be applied, and restored if necessary, to existing greenhouses, with a simple process which does not require any specialist knowledge. The coating will be tested at the end of the project in a real-world greenhouse horticulture situation (TNO field lab at Demokwekerij Westland).

Planning

The project consists of the following phases:

  • Establishing the requirements
  • Collecting samples of various types of glass (including standard and diffuse glass, as well as anti-reflective glass)
  • Laboratory testing to determine the best coating composition
  • Evaluation of the coatings for their effect on light transmittance, contact angle with water before and during durability tests in an environmental chamber at 85 °C and 85% relative humidity and, finally, the process of condensation formation
  • Application of the best performing coating to glass at the TNO field lab (Demokwekerij Westland)
  • Acquisition of necessary measuring instruments and installation in the TNO field lab
  • Conduct of the practical test
  • Continuous measurement and maintenance
  • Processing of measurement results, evaluation and drawing conclusions
  • Drafting recommendations for follow up (and distribution)

Important considerations

Important considerations for the study:

  • Measurements in real-world greenhouse horticulture operations show an increase in light transmittance of around 5% after the annual cleaning of the greenhouse roof (inside and outside). No data on the loss of light transmittance in greenhouses is found in the open literature. Several open publications of multi-year studies into contamination of glass in urban areas are available, however, with reported losses in light transmittance due to contamination that vary widely from a few per cent to peaks of 20% or more.
  • The rule of thumb in greenhouse horticulture is: 1% less light means 1% less production which is 1% less turnover.

Dr. Aike Wypkema

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