The main environmental impact of livestock activity comes from greenhouse gas emissions such as methane (CH₄) and nitrous oxide (N₂O), as well as pollutants like ammonia (NH₃). These gases are largely emitted during the manure and slurry storage phase on farms, particularly pig farms. Under current Spanish legislation, in accordance with European regulations on reducing pollutant and greenhouse gas emissions, pig farms are required to partially or completely cover slurry ponds to prevent ammonia emissions.
In response, the FOTOPUR research project aims to provide the pig sector with an innovative and effective solution to reduce its pollutant emissions: floating photovoltaics adapted to cover slurry ponds. The system involves covering the slurry-air interface with floating structures that support photovoltaic modules. This not only reduces the rate of ammonia emissions into the atmosphere but also enables the use of the pond’s surface for photovoltaic energy generation, which can supply the farm’s electrical consumption.
More and more agricultural holdings are investing in renewable energy, based on both environmental and economic criteria. In rural areas, the most efficient option is usually to install a photovoltaic self-consumption system either on free land or on a building roof. This reduces electricity costs and provides energy autonomy for farms located far from the national grid. Floating photovoltaic technology is already a competitive alternative today. This type of installation offers advantages such as eliminating the need for free land or suitable roof space and benefiting from the additional cooling effect provided by the liquid surface.
While floating photovoltaics are already widely used on bodies of water such as irrigation ponds or lakes, their use on other liquid surfaces is still under study. An analysis carried out within the Aragonese project “Alternatives in the utilization and control of the potential of slurry ponds”, in which Intergia participated, showed that in the ammoniacal environment of slurry ponds, some components of the photovoltaic module support system and cabling suffered from oxidation and degradation.
Within the FOTOPUR project, we have developed and implemented two floating photovoltaic systems adapted to slurry ponds in a testing phase. These systems are specifically designed to maximize the percentage of slurry-air interface coverage—thus reducing emissions—and to withstand the ammoniacal environment. The main difference between them lies in the fact that one uses commercial floating photovoltaic components, while the other has been custom-designed for this specific application.
Each system will be installed and tested on two pig farms with different characteristics in terms of stored slurry and energy needs: a sow farm in Zamora and a fattening farm in Tauste.
Prototype using commercial components: sow farm in Zamora
Characteristics
At the beginning of November, the first demonstration prototype was installed at a 1,400-sow farm located in Calzada de Tera (Zamora). The farm already had a photovoltaic system connected to the electrical grid to meet its energy demand. The new photovoltaic system forming part of the prototype integrates with the existing one, increasing the total capacity and the farm’s self-consumption percentage.
The slurry pond where the prototype is installed has a surface area of about 880 m². It is covered with the Lamaru commercial floating photovoltaic system by the Spanish company Landatu Solar, typically used in water ponds, adapted here for slurry ponds to ensure maximum possible surface coverage. To prevent corrosion in ammoniacal environments, all steel parts were replaced with aluminum and stainless-steel components.
The photovoltaic system comprises 56 panels with a peak power of 33.04 kWp, oriented southwest along the pond’s longitudinal direction, with a 15° tilt.
The floating platform measures 13.5 × 25 meters and includes an access walkway made from the same floating elements. For safety, both the perimeter of the platform and the walkway include stainless-steel railings. The structure is designed to adapt to the changing slurry level—rising or lowering with the pond’s fill level. The platform doesn’t collide with the slope, the walkway bends due to the flexibility between floats, and the moorings adjust accordingly.
To complete the system and assess compatibility, hexagonal plastic elements with ballast will be used to fill the gaps between floats and cover the remaining free surface of the pond.
With the floating platform, around 20% of the pond is directly covered, which—combined with the coverage from the hexagonal elements—will achieve over 90% total surface coverage. The expected photovoltaic production is 50.04 MWh/year, representing up to 22% savings on the farm’s electricity bill.
Access walkway to the floating platform. Perimeter safety railings and moorings can be seen.
View of the floating platform from behind. Note the tilt of the photovoltaic panels and the flexibility of the access walkway when the slurry level is low. The gaps between the floats beneath the panels will be covered with hexagonal plastic elements.
Assembly
The system was assembled following the same methodology used for conventional floating photovoltaic installations on water: floats and panels were assembled row by row along the pond’s edge, then gradually pushed into the slurry pond. Before launching each row, the electrical connections between photovoltaic panels were made. A plastic sheet was used between the floats and the shore to reduce friction and facilitate sliding. Once launched, the DC cables were routed along the access walkway to the inverter room, about 80 meters away, and buried in a trench.
Five rows of panels mounted on the floating platform are lowered into the slurry pond.
Measurements and analysis
With the prototype now assembled, measurements are being taken to analyze the reduction in ammonia emissions achieved through coverage, and the photovoltaic production used for the farm’s self-consumption. In addition, methane concentration beneath the photovoltaic panels is being monitored using a real-time methane sensor.
Ammonia measurements are being carried out following a standardized protocol, using a floating dynamic chamber. A total of 24 measurements will be taken at different points of the pond and at different times of the year.
Finally, photovoltaic production and the self-consumption ratio will be analyzed through the inverter’s data visualization platform.
Methane sensor and gas concentration hood, placed under a photovoltaic panel, in the gap between floats.
Photovoltaic inverter and main protection panel. This is the part of the electrical installation that transforms the direct current generated by the photovoltaic panels into alternating current suitable for consumption on the farm.
In the coming weeks, the second demonstration prototype will be installed on a fattening pig farm in Tauste (Zaragoza), using a custom-designed system. The analysis of the measurement results will help identify which of the two systems is more effective in reducing emissions from pig slurry ponds. Lastly, both solutions will also be evaluated from an economic perspective, with the goal of 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: ADS Porcino Nº1 de Tauste (ADS), Tauste Centro Gestor de Estiércoles (TCGE), Bajo Duero Cooperative (COBADU), University of Zaragoza (UNIZAR), Polytechnic University of Cartagena (UPCT) and INTERGIA.
