Hybrid greenhouse supplies electricity and saves water

Earth heat coupled and electricity generating Envelope greenhouse saves resources

Greenhouse inside © Sunvention GmbH
Read out

Whether tomatoes, beans or flowers - in greenhouses, plants thrive regardless of the seasons. But the price is high: In summer, the greenhouses heat up and have to be cooled consuming, in winter, however, the sunlight is usually not enough, so that is heated. This dilemma could now end a new type of greenhouse. Because the combined use of solar technology and geothermal heat storage no additional energy from the outside must be supplied and you save a lot of water at the same time.

In sunny Spain alone, more than 30, 000 hectares are cultivated with greenhouses, in Japan there are even more than 50, 000 hectares. After all, this corresponds to the area of ​​Hamburg. In order to keep the temperatures constant for the plants even in winter, between 300 and 500 kWh of thermal energy are usually required per square meter of surface and year. In summer, however, especially in the warm southern regions, the greenhouse must be actively cooled to prevent overheating. The evaporative cooling used for this purpose, however, consumes up to 20 times more water than the actual irrigation - water shortage is the result.

Geothermal and solar use in harmony

Now, German engineers have designed a novel greenhouse that bypasses these energy and water problems: it uses a sophisticated solar system to produce its own electricity and also transfers surplus electricity into the grid and excess heat energy into the ground. This eliminates the need for active water cooling and temperatures are within the so-called Envelope greenhouse between 20 to 25 ° C. A particular highlight is the storage heat in the subsurface of the plants in winter as a kind of "underfloor heating" available. Additional energy costs are eliminated or reduced to a minimum.

Fresnel lenses, focal line and solar cells © Sunvention GmbH

The hybrid use of solar energy and geothermal storage is carried out in three stages: First, the incident light is directed by so-called lightweight fresnel lenses on photovoltaic concentrator cells and converted into electricity. These special lenses are protected from wind and weather, just below the highly transparent greenhouse hull, the Envelope. As a special feature, the solar cells are actively cooled at the same time and thus generate a useful heat in the temperature range between 40 and 70 C. The diffused portion of the solar spectrum penetrates the Fresnel lenses without being focused and is the ideal illumination for the plants in the greenhouse.

Floor heating for plants

The waste heat from the cooling of the solar cells is dissipated at depths of up to 100 meters with the aid of geothermal probes. There, a limited soil volume heats up from under 10 C to about 40 C. In this way, it is possible to use the underground as a combined geothermal-solar long-term heat storage and the plants on gro fl chige Fu bodenheizungen in to supply heat of 20 C during the cold season. display

Solar energy is used optimally: of the roughly 900 W / m of incident energy, around 800 W are captured by the solar cells and removed from the greenhouse in the form of electricity and heat. The remaining 100 W are available to the plants in the form of light and heat energy sufficient for photosynthesis and to gen gend high temperatures for plant growth gew hrleisten.

"Earth heat" cools in the summer

Greenhouse with updraft chimney Sunvention GmbH

But that's not all. In summer, when needed, the Envelope greenhouse can also be cooled with the help of near-surface geothermal energy. Thanks to a special pipe system, the cool temperatures of deep soil layers of approx 12 C are tapped. This floor air conditioner comes out without electrical auxiliary power or fans. Because to generate the necessary air flow rate serves a Aufwindkamin, which generates the necessary air exchange rate in the greenhouse. As a small side effect, even water can be separated from the exhaust air and used again.

The Envelope greenhouse therefore allows the plant growth period to be extended to the year or year for heating or cooling without the use of fossil fuels. Another advantage is the targeted return of water from the exhaust air in a closed circuit. In particular, in semi-arid and arid areas, the greenhouse could therefore help to save important resources and contribute to the stabilization of livelihoods.

(Kleinw chter, J rgen (Sunvention GmbH), Horst R ter (HarbourDom GmbH), 16.02.2007 - AHE)