Description

The effect of diffuse light has been proven in research. Diffuse glass has been extensively developed by manufacturers and there are various products for sale for growers. However, the choice of the right glass type remains difficult for a grower due to numerous uncertainties including the integral effect of light transmission and the diffusion of various glass types in a practice greenhouse and the effect of the glass on his crop during the season. Especially the additional yields associated with diffuse glass appear to be an uncertain factor for growers. As a result, we see that more (large) growers tend to choose the "certain/'the known", namely glass with a (very) low diffusion or even clear glass, sometimes equipped with 2xAR to go for maximum light. In practice, there is also the idea/feeling that the use of diffuse glass increases energy consumption.

The aim of this project is to obtain and understand practical data of different crops and glass types. This is to gain insight into:

The added value of diffuse glass on production depends on the diffusion.

Whether there are indications that energy consumption under diffuse glass is higher

Whether there is an increased head temperature in the summer months

To this end, the project is divided into five work packages:

Work Package 1: Inventory. Visit and interview participating companies. After this inventory, a group of 20 companies that actually participate should remain. The final data collection is also set up in consultation with the entrepreneur. Climate data will usually be part of this, in addition to any additional measurements in the greenhouse and of the glass.

Work Package 2: Set up data collection. It concerns measuring climate data and the amount of light in the greenhouse at the various companies, of a number of companies measuring the diffusion and light transmittance of the glass. For a clear comparison between the diffuse and the "same" (the reference) greenhouse with clear glass, greenhouse calculations will be used (where necessary) to separate effects of the glass type from effects of light transmission (greenhouse arrangement, etc.).

Work package 3: Determination of crop performance. In this work package the crop performance is determined on the basis of cultivation and crop registration data and a comparison of a simulated reference greenhouse is made as good as possible since there will be differences in variety and plant data. Using the results from wp2, the amount of light on the farm in the greenhouse departments to be monitored is determined and monitored and related to the crop performance. Finally, a rule of thumb is drawn up for production effect in relation to diffusion.

Work package 4: Energy performance. Calculate the energy consumption and relate it to the glass type to determine whether diffuse glass requires more energy or not. Relating the energy consumption to that of the (simulated) reference greenhouse. Analyze any differences in energy consumption due to season, climate conditions or any other factors.

Work Package 5: Communication and Reporting. In addition to 'regular communication', a broad diffuse light afternoon is organized.

Tomato, cucumber, bell pepper, chrysanthemum, alstroemeria and – provided there are enough growers involved – rose and strawberry are also included.

Results

Diffuse glass can potentially contribute to the goal of profitable sustainable greenhouse horticulture, due to the improved growing conditions (production and quality) without energy consequences. In practice, diffuse glass has found its way, but doubts arose. The main cause is that in practice (unlike experiments) the components light and diffusivity are inextricably linked. That was the reason for doing this research, in particular to unravel light transmission and diffusivity in practice.

For this project, data from five companies were used that have both a greenhouse with diffuse deck and a greenhouse with clear deck, with the washed cucumber, tomato and cherry tomato. Climate data, light level at crop height and yield data were analysed around the two questions 1.' Does diffuse glass in practice result in a higher yield?' and 2.' Does the energy consumption under diffuse glass differ from the energy consumption under clear glass?' to answer. To correct for other factors (such as planting date), the 'radiation use efficiency' has been determined for all crops, i.e. how many kilograms are harvested per unit of available solar radiation. On average, the RUE in the diffuse greenhouses was 8% higher in all crops (including exposed greenhouses). After correction for all other factors, there is clearly no difference in energy consumption between a diffuse and a clear greenhouse. Therefore, the energy efficiency in diffuse greenhouses is higher than in clear greenhouses.