BÜRSTADT, OPERATED BY EBF (BÜRSTADT, GERMANY)
David Volk (EBF)
The RTG is in Bürstadt, between Frankfurt and Heidelberg (Germany), on the roof of the packaging hall on a farm owned by ebf. The packaging hall is a building from the late 1950’s, and right now it is heated by fossil fuels. In several iterations the heat supply on the whole site is going to be replaced by renewable heating in the next years. The solar greenhouse has a 160 m² growing area and is designed to have a low heating demand, produce electrical energy, and serves as a solar collector for the support building. Altogether, it achieves a net positive energy balance over the course of one year of operation.
EBF has been specialised in industrial and horticultural energy management for more than 25 years now and is implementing new technologies and systemic solutions in the horticulture business to help transform the food production sector and make it more sustainable and truly future proof.
The RTG is implemented within the regular operation of the whole site. It serves as a unique selling point for the farm and shows how RTGs can increase the farming capacity without increasing the land use.
Business – value creation
The RTG project and the whole farm serves as a showcase of the EBF approach for an economically competitive horticulture business. Due to the low energy demand of the solar greenhouse and the flexible year-round operation, the farm can supply markets, restaurants, and customers with fresh vegetables directly on the farm all year round.
The greenhouse growing space as well as the rest of the farm are being rented out to a chili pepper specialist who uses the site for organically grown products and ships them directly from there.
This gives ebf the possibility to examine the energy flows and function of a fully operational solar greenhouse responsibly handled by an expert in horticulture.
The packaging hall is built in a traditional way, with heavy walls and strong foundations. It is structurally stable, even after more than 50 years of existence. The roof itself consisted of wooden beams that were strong enough for the previous roof covering but could not bear more than the corrugated Eternit® roof, which itself was partly damaged and not fully sealed anymore.
The old roof and the whole beam structure were removed to install the new rooftop platform. After the removal of the roof, a concrete ring beam was placed on top the walls. Then, wooden roof beams were added, and the bearing structure was finished with a platform made of OSB boards. Since substantial changes in the roof structure had to be made, it was possible to generate a bearing capacity of the platform of 2.5 kN/m² depending on the location. At the backside of the greenhouse, due to the range of the beams the potential load is substantially higher.
The greenhouse consists of a light-gauge steel frame connected directly to the wooden roof beams. The platform and the connection to the steel frame are coated with a special waterproofing material that will prevent water damage to the bearing structure.
The outer shell of the greenhouse is a heavily insulated hempcrete wall on both sides and the back. Parts of its roof are insulated as well, with light weight hemp straw. The arched south side is covered with a highly transparent double layered ETFE coating. For cold nights, a thermal blanket will be rolled down from the greenhouse top to reduce thermal radiation losses.
A walkway around the greenhouse was established to be able to get access to the greenhouse from all sides and to collect rainwater.
The main goal of the solar greenhouse is to reduce the energy demand of food production while being operated all year-round. This is done by creating a heavily insulated outer shell that will reduce heat losses. An important problem for greenhouses in summer is overheating. The solar greenhouse will use PV systems installed inside directly under the film to generate shadowing while generating electricity. If there is no need for shadowing, the PV system will get rotated out. Additionally, ventilation flaps are installed on the bottom south side and at the highest point in the greenhouse. These strategically installed openings generate a natural flow through the greenhouse that cool it down with fresh air without requiring forced ventilation and thus no energy demand. This is possible due to the high transparency of the ETFE film. Since the PV panels are not exposed to atmospheric influences, they can be light weight and thin. Due to the insulated and opaque side walls, the total incoming sunlight is reduced in comparison to other greenhouse types. Therefore, internal heat management becomes more important. This is mainly managed by insulation that will reduce radiative heat losses and a thermal blanket which will be used to save energy and prevent direct sunlight in the intense summer heat.
As all the housing services and other devices for the greenhouse will be installed in the support building, they don’t take up any space inside the greenhouse, increasing the available growing space. Production is realized with substrate-based hydroponics. Therefore, Dutch buckets with a comparatively large volume are used. The growing media will be composed of a classical planting soil enriched with Tera Preta. It will be reused several times over a few growing periods with additional enrichment in the greenhouse, and then as replacement soil for outdoor growing to reduce the maintenance workload. First, a selected variety of chilies are grown. Since the RTG is part of a larger operation, it will be used in a flexible way, within the boundaries of normal operation. Harvesting and packaging will therefore be directly done by the farm workers without any restriction. One of the most important fields of application is the utilization of this rooftop greenhouse for seedling cultivation. The low energy demand helps with starting earlier in the year and therefore having the possibility to enter the market with fresh products early. Since seedling cultivation does not need much space, the seedlings of the whole site can be produced in the rooftop greenhouse.
Vidéos - EBF Rooftop Greenhouse Construction