Tulips are forced from December to April. During the summer the greenhouse is empty. Tulip farmer Sam Ruijter thought up a method to transform the tulip hydroponic forcing system into a solar heat collector in order to store the heat in water tanks. Through a heat exchanger the heat could be used for drying bulbs, for heating the bulb stores, and possibly for heating the greenhouse in the winter. WUR monitored this system to see if the use of a heat pump could be avoided. The temperature of the solar heat collector was fitted to the global radiation, the outdoor temperature and to the waterflow from 15 September to 22 October 2018. With data from the Dutch Meteorological Institute (KNMI) the total harvested heat could be estimated. Results showed that if water storage capacity is sufficient (> 2800 m3 per collector of 300 m2), enough ≥ 35oC water could be harvested to cover the energy needs for drying and storing the bulbs without a heat pump. Heat harvested at 23 – 35oC could be stored in an aquifer and cover the energy needs of tulip forcing in the winter for ± 70%. This latter however, requires a heat pump.
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