Up to 15% of electricity savings with dimmable lighting on direct current

In this study calculations were made to determine what energy-saving can be realized with dimmable assimilation lighting and what the effects are on the growth of plants. The switch to lighting on DC voltage brings an added property that the light can be dimmed. The calculations were made for the crops bouvardia, anthurium and phalaenopsis. The calculations take into account the dynamics of the light utilization efficiency of photosynthesis and the possibilities to regulate natural daylight with screen installations. Different dimming strategies are compared with the current way of lighting. Usually this is an on-off arrangement, but also possibilities for the lighting to be switching on and off in a stepped arrangement are included in the calculations. Economic calculations show that savings through dimming amount to 5 to 7% of annual electricity costs.

Switching off the lighting above the young crop in winter costs more than 70% of the assimilate production. This will lead to a slow growth of the Leaf Area Index (LAI), as a result of which the use of light will remain poor for even longer times. The potential for saving is therefore small, unless the regrowth for a large part takes place on the basis of reserves in the plant. By reducing the lighting, the heat demand increases by approximately 2.7 MJ for every kWh of electricity saved. However, there is electricity to be saved after the harvest and before there is growth of young leaves.

Energy can be saved by screening less than usual and to compensate for the extra daylight by dynamically dimming the assimilation lighting. In the heavily screened cultivation of anthurium in the winter, electricity consumption can be reduced by 10 to 15% in that way.

Electrical energy can be saved with a dimmable installation by slowly increasing the intensity in the morning. This results in a 10% saving during the cold cultivation finish. There is hardly any difference between a stepped arrangement with 4 light steps and a stepless dimmable installation. During the propagation (at Pikoplant) there is less lighting required and the morning savings are nil. Saving in the afternoon is more difficult and depends, among other things, on the time in the night when the light is switched on.