Fig. 34: Used kWh of seedlings of tomatoes (a) and of tomatoes in continuous production (b) under different light sources

4.4 Economics

4.4.1 Used energy

The number of lighting hours is contributing to high annual costs and needs therefore special consideration to consider decreasing lighting costs per kg “yield”. The total hours of lighting and the used kWh’s during the growth period of seedlings and at the continuing growing period after transplanting were measured with dataloggers.

Young plant production of tomatoes resulted in the HPS chamber in a daily usage of 118 kWh, while the LED chamber had with 100 kWh 15% less energy use (Fig. 34a). This means that the costs for growing seedlings with HPS lights are higher, due to 18% higher energy costs. Regarding the continuous production used the treatments “HPS, Hybrid+LED” and “LED, Hybrid+LED” (181 kWh/day) less energy than “HPS, Hybrid” and “LED, Hybrid” (237 kWh/day) (Fig. 34b). The used energy was about 21% lower at treatments with LED interlighting. The light treatment in young plant production did not influence total used energy (Tab. 7).

b

Fig. 34: Used kWh of seedlings of tomatoes (a) and of tomatoes in continuous production (b) under different light sources.

4.4.2 Energy use efficiency

When tomatoes were lightened with “Hybrid+LED” were kWh’s transferred better into yield than with “Hybrid” (Fig. 35). This difference amounted 15-20%. Also, with HPS lights in young plant production was the utilization of kWh’s better transferred into yield compared to LEDs in young plant produciton. This difference amounted 6-12%. However, differences between the treatments were not statistically different.