BÜRSTADT, OPERATED BY EBF (BÜRSTADT, GERMANY)
David Volk (EBF), Pierre Raulier (ULg)
Time-lapse of the construction
The RTG will be located in Bürstadt, between Frankfurt and Heidelberg (Germany), on the roof of the packaging hall of a farm owned by the company. The packaging hall is a building from the late 1950’s, and right now it is heated by fossil fuels. EBF will install a solar greenhouse of approximately 160 m² surface area. The greenhouse will have a low heating demand, produce electrical energy, and will serve as a solar collector for the packaging hall. It will altogether generate a net positive energy balance.
EBF has been specialised in industrial and horticultural energy management for more than 20 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 will be implemented within the regular operation of the whole site. It will serve as a unique selling point for the farm and show how RTGs can increase the farming capacity without increasing the farmed land area.
Business – value creation
The RTG project and the whole farm will serve 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 will supply markets, restaurants, and customers with fresh vegetables directly on the farm all year round.
The main sale argument is that locally produced vegetables can be offered off-season while still maintaining good quality products. Therefore, the farm will most probably generate the highest revenues when traditional market supply only comes from imported products.
However, it remains to be demonstrated that customers will choose locally produced food over imported products. Heavily industrialised food production can still supply cheap vegetables, so the food produced on the farm will have to be of a better quality to justify a higher price.
Since production on the farm will not be industrialised, it will also be more flexible. In combination with its year-round operation, the farm will be able to precisely adjust its mode of operation to match customers’ needs.
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 consists of wooden beams that are strong enough for the current roof covering but cannot bear more than the current corrugated Eternit® roof, which is itself partly damaged and not fully sealed anymore.
The current roof and the whole beam structure will have to be removed to install the new rooftop. After the roof is removed, a concrete ring beam on top the walls will be installed. Then, wooden roof beams will be added, and the bearing structure will be 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 5 - 15 kN/m² depending on the location. This made it possible to have greater loads in the greenhouse like a water tank or thermal storage walls.
The greenhouse will consist of a light-gauge steel frame connected directly to the wooden roof beams. The platform and the connection to the steel frame will be coated with a special waterproofing material that will prevent water damage to the bearing structure.
The outer shell of the greenhouse will be heavily insulated on its side walls, back walls and on parts of its roof. The arched south side will be 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 is planned to be able to get access to the greenhouse from all sides and to collect rainwater which will be reintroduced in the water circuit of the farm after UV filtration to prevent contamination from birds.
The main goal of the solar greenhouse is to reduce the energy demand of food production while being operated all year-round. This will be done by creating a heavily insulated outer shell that will reduce heat losses. Additionally, different systemic devices will be set up to help save produced energy, and each device will have more than one use.
An important problem for greenhouses in summer is overheating. The solar greenhouse will use PV systems installed inside the greenhouse to generate shadowing while generating electricity. If there is no need for shadowing, the PV system will get rotated out and the reflective bottom side of the panels will help get the light to the plants. Additionally, ventilation flaps will be installed on the bottom south side and at the highest point in the greenhouse. These strategically installed openings will generate a natural flow through the greenhouse that will cool it down with fresh air without requiring forced ventilation and thus no energy demand.
Due to the insulated and opaque side walls, the total incoming sunlight will be reduced in comparison to other greenhouse types. Therefore, internal heat storage and management becomes more important. This will be managed partly by insulation that will reduce radiative heat losses, and by the heat storage wall consisting of compressed earth bricks that take in the heat of the day and radiate it back into the greenhouse at night. On the other hand, the wall will cool down at night in summer, supported by the ventilation system, and keep the greenhouse cool for a longer time the next day. Additionally, a thermal blanket will be used to save energy and prevent direct sunlight in the intense summer heat.
As all the extra devices for the greenhouse will be installed in the host building, they will not take up any space inside the greenhouse, and the available growing space will be all the greater.
One of the key aspects of an RTG is accessibility. The height of the building is one of the key constraints for viable operation. For the EBF RTG, a conveyor belt is planned which helps getting the growing systems up and the vegetables down.
Production will be based on growing media-based hydroponics. A special kind of Dutch growing buckets will used, with a comparatively large amount of material. The growing media will be composed of a classical planting soil enriched with Tera Preta. It will be reused several times inside the greenhouse with additional enrichment, and then as replacement soil for outdoor growing.
A selected variety of chilies will be grown first. 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. The building bearing the RTG was a packaging hall of the historical farm; it will keep the same function.
As nature proceeds by finding a balance between all living things, natural pest and disease control using insects and natural remedies is planned.