The FOTOPUR project aims to develop an innovative and effective solution to reduce pollutant emissions from slurry ponds on pig farms. This solution consists of using floating photovoltaic systems adapted to the pond so that, on the one hand, its surface is covered and ammonia emissions are prevented or reduced and, on the other hand, electrical energy is generated that can be used for self-consumption by the farm itself.
This makes it possible to comply with current legislation, which requires the pig sector to reduce ammonia emissions in order to be more environmentally friendly, while also generating added value. Installing photovoltaic modules on the pond makes use of an area that would otherwise be useless, and avoids having to use free land or the roofs of buildings, which are not always suitable for this purpose. The use of photovoltaics to meet the farm’s energy demand reduces the cost of the electricity bill and reduces diesel consumption. It is therefore a clean and cost-effective alternative.
While floating photovoltaic technology is already widely used in bodies of water (irrigation ponds, purification ponds, canals, reservoirs, etc.), its use in other liquid bodies and adverse environments, such as the saline environment of the sea, is still under study. An analysis carried out as part of the Aragonese project “Alternatives for the use and control of the potential of slurry ponds”, in which Intergia participated, showed that, in the ammoniacal environment of slurry ponds, some elements of the photovoltaic module mounting system and the wiring suffered oxidation and degradation.
The FOTOPUR project was created to solve these problems and take a step forward in defining a solution for covering slurry ponds with floating photovoltaic panels. To this end, two prototypes with different characteristics have been designed so that they can be compared to find the most suitable design. The first prototype was assembled in early November on a sow farm in the municipality of Calzada de Tera, in Zamora, and is now fully operational. This prototype was designed using a commercial system for floating photovoltaics on water, to which a series of adaptations were incorporated for safe use on the slurry pond. The prototype developed has effectively covered around 20% of the pond. The remaining free surface, as well as the gaps between the floats, will be covered with weighted hexagonal plastic elements, until 90% coverage is achieved. The installed photovoltaic system has 56 panels and a peak power of 33.04 kWp. The expected photovoltaic production is 50.04 MWh/year, which would mean savings of up to 22% on the farm’s electricity bill (which is connected to the grid).
The second prototype has just been installed on a feedlot in Tauste (Zaragoza) and has been designed specifically for this application.
Prototype designed specifically to cover slurry ponds: pig farm in Tauste
Characteristics
At the end of November, the second demonstration prototype of the FOTOPUR project was installed on a 6,000-head fattening pig farm in the municipality of Tauste, Zaragoza. The farm is disconnected from the electricity grid, and prior to installation it was powered by a diesel generator and a small photovoltaic system for the windows and feeders.
The slurry pond where the prototype is housed has a surface area of 1,100 square meters. To cover it, a system was designed to minimize the air-slurry contact surface between the floating elements and facilitate the support of the photovoltaic panels. In this case, the various floating systems for photovoltaics available on the market were rejected, and a floating dock system not designed for floating photovoltaics was chosen. The system selected was BulDock Modular Floating Pontoon Docks, manufactured in Europe. As these are cubic elements that are joined together to form a platform, the space between the floating elements is minimal.
The photovoltaic system is placed on top of the floating platform, including the support structure and panels. To do this, a specific structure had to be designed for this application. The structure consists of a matrix of horizontal and perpendicular anodized aluminum beams, anchored to the platform by bolts in the float connection screws. In this way, the structure is attached to the platform, giving it greater rigidity. Brackets are screwed onto the horizontal beams to raise the inclination of the panels to 15º. The 16 photovoltaic panels are supported on this structure, with a total power of 9.44 kWp. The panels are oriented slightly southeast. To prevent corrosion in the ammoniacal environment of the slurry, aluminum and stainless steel fasteners have been used.
Assembly of the support structure for the photovoltaic panels, based on a mesh of interlocking anodized aluminum beams, bolted to the floating platform.
Assembly of the support structure for the photovoltaic panels, with brackets screwed to the main mesh, to raise the panels to an angle of 15º from the horizontal.
In total, the floating platform measures 11.5 x 9.5 meters and has a solar cable evacuation corridor and perimeter safety railings. The platform is positioned in an area of the pond so that it is not affected by changes in the pond’s fill level, rising and falling with the slurry level without interacting with the slope. It is secured at four points to anchors located on the banks of the pond. When access to the platform is required (for maintenance tasks, for example), the ropes are simply pulled to bring the platform closer to an access ramp provided at the pond.
The floating platform effectively covers around 10% of the surface area of the slurry pond. The expected photovoltaic production is 15.2 MWh/year, which would cover up to 53% of the farm’s electricity demand through self-consumption, avoiding the use of expensive and polluting fossil fuels.
Detail of one of the moorings, attached to the floating platform.
Assembly
The system was assembled following a procedure designed by Intergia. First, the floating platform was assembled in its entirety on a piece of land adjacent to the pond, on which boulders had been placed beforehand to facilitate sliding when launching the platform. This process was carried out using an agricultural machine with a telescopic arm, which pushed the platform to the slurry pond, leaving it near the shore and next to the ramp to facilitate access. Once floating, the metal structure and photovoltaic panels were mounted on the platform. The connections were made and the cable evacuation walkway was installed to the room where the inverter is located, with the cable buried in a trench about 90 meters away.
Prototype assembly procedure: once the platform has been assembled on land, it is lowered into the pond using a telescopic arm.
View of the floating platform from behind. The corridor for easy access and the solar cable evacuation walkway can be seen. This image also shows the methane sensor located at the height of the platform, with a gas accumulation hood.
Measurements and analysis
vWith the prototype assembled, measurements of pollutant emissions from the slurry pond will be carried out to assess the coverage potential of the proposed solution. Photovoltaic production will also be monitored. Ammonia measurements will be taken in accordance with a standardized protocol, using a dynamic floating chamber. A total of 24 spot measurements will be taken in different areas of the pond at different times of the year. In addition, methane concentration is being monitored by two sensors with gas collection bells, located at two key points: above the floating platform and right at the edge. These sensors continuously collect data in real time. Finally, photovoltaic production and the self-consumption ratio will be analyzed using the data visualization platform of the installed photovoltaic inverter.
View of the complete prototype near the edge of the pond, before moving it away to avoid interference with the slope.
Analysis of the results of the various measurements taken on both prototypes (in Tauste and Zamora) will enable us to identify which of the two systems is more effective at reducing emissions from slurry ponds on pig farms. Finally, both solutions will be studied from an economic perspective, with a view to bringing the optimal solution to market.
FOTOPUR is a project funded by the European Union under the 2023 call for innovation projects of general interest by operational groups of the European Innovation Partnership for Agricultural Productivity and Sustainability (EIP-Agri), within the framework of the 2014–2020 National Rural Development Program of the Spanish Ministry of Agriculture, Fisheries and Food.
The FOTOPUR operational group consists of: Asociación de Defensa Sanitaria Porcino Nº1 de Tauste (ADS), Centro Gestor de Estiércoles de Tauste (TCGE), Cooperativa del Bajo Duero (COBADU), Universidad De Zaragoza (UNIZAR), Universidad Politécnica de Cartagena (UPCT) and INTERGIA.
