Elkas (the electricity supplying greenhouse) shows how to convert solar energy into electricity. In designing energy generating greenhouses the emphasis still lies in systems that supply low-grade forms of energy (i.e. warmth). The electricity generating greenhouse is aimed at catching the radiation that is not being used for crop growth and converting it in high grade power.
The inteligent solution for this greenhouse is an integrated filter for rejecting near infrared radiation (NIR) and a solar energy delivery system. Cooled greenhouses are an important issue to cope with the combination of high global radiation and high outdoor temperatures. As a first measure, the spectral selective cover material, which prevents the entrance of NIR radiation, is investigated.
The special spectral selective properties of these materials have to block up to 50% of the solar energy outside the greenhouse, which will reduce the needed cooling capacity.
The second measure is the integration of a solar energy system. When the NIR reflecting coating is designed as a parabolic or circular shaped reflector integrated in the greenhouse, the reflected solar energy of a PV cell in the focus point delivers electric energy. With a ray tracing computer program the geometry of the reflector was optimally designed with respect to the maximum power level. The PV or TPV cells mounted in the focal point require cooling due to the high heat load of the concentrated radiation (concentration factor of 40-120).
Or to say it simple PAR light (growth light) enters the greenhouse and the NIR light is reflected via the special foil to produce electricity. The foil to produce the electricity contains a few hundreds very thin layers, during tests the cheap silicium cells where found the most efficient solar cells. Because the sun is moving during the day and during the season the solar pannels are moveable and will move with the sun.
So far the results are promising and there was decided to built a research greenhouse which has been finished construction by the end of June 2008. This is the first electricity producing greenhouse in the world but so far it’s a small greenhouse of only 10m2 by 10m2. According to researcher Piet Sonneveld the concept has a lot of potential and it will be economically profitable within the next 5 years. In potential the ELKAS only needs 10% of a conventional Greenhouse. The electricity production of the ELKAS should be around 0.4 MW / Ha. Because the smart foil is keeping the excessive heating outside the climate inside the greenhouse for the plants is much better.
Policy of the Dutch governments is aimed at sustainable glasshouse horticulture in terms of economy, environment and labour conditions. In the Covenant Glasshouse Horticulture and Environment, government and glasshouse industry have set ambitious goals for energy, crop protection and fertilization for glasshouse industry in 2010.
The goals for energy saving are linked to the Kyoto protocol on the reduction of CO2 emission by setting a maximum for the glasshouse industry CO2 emission to 6.5 Mton at the actual area of 10.500 ha, which will be increased to 7.1 Mton if the area increases to 11.500 ha.
The ambition is that greenhouse systems built from 2020 on will compensate equally energy consumption by energy production. Assimilation lighting has proven to be a powerful tool to increase production and quality, especially in winter.
Partners in development of ELKAS
- Wageningen UR
- Plant Research International B.V. WUR
- Bosman kassenbouw
- EOS regulation center/Novem (financing)
- Dutch ministry of Agriculture (financing)
- Product Board of Horticulture (financing)
- Stichting Energy Leverende kas (financing)