Alternatives in the use and control of slurry pond potential


The general objective of the project is to develop an innovative solution for covering slurry ponds to reduce the emission of harmful gases, such as ammonia, and to make it easier for farms and management centres to adapt and comply with the emission parameters set by recent national and European regulations. In addition, the aim is to use these ponds to produce electricity from renewable sources without having to allocate additional land, by means of floating elements incorporating photovoltaic panels.

Reference: GCP-2020-0008-01

Duration: 03/2020 - 10/2023

Programme: Call for subsidies to support collaborative actions by agents in the agricultural sector, 2020

Financing body: Department of Agriculture, Livestock and Environment of the Government of Aragon

Total budget: 150,000€

Co-financing: 80% EU, 20% Government of Aragon

Project completed

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INTERGIA presented the results of the project at the IV Conference on Innovation in the pig sector, organised by Inneara and A.D.S. Porcino Nº1 of Tauste, held at its headquarters in Tauste. These conferences act as a meeting point and knowledge transfer between the different agents involved in the sector and pig farming professionals. More than 40 professionals from the pig sector attended these information days.


The demonstration prototype has been in test operation for almost ten months, during which time measurements have been taken and evaluated:

  • Photovoltaic production

  • Degradation of materials

  • The interaction between the pond cover components

  • Ammonia emissions, comparing those of the covered pond with the uncovered area

  • The economic profitability of the entire system.


1) Photovoltaic producción

Bi-weekly data provided by the inverter platform (direct consumption data, grid consumption, grid feed-in) has been taken from the start-up of the prototype at the end of November 2022 until dismantling at the end of August 2023. However, in order to make the data comparable with each other, only the full months are presented: December 2022 to July 2023.

In total, 34.6% of the farm's consumption has been covered directly.

The production profile is typical of any photovoltaic plant.

During its operation, the demonstration prototype produced a total of 23,371.25 kWh, of which 83.5% was used to directly cover the farm's demand, while the remaining 16.5% was injected into the grid. These surpluses, if the farm were to use self-consumption with compensation, could produce additional savings on its electricity bill.

2) Degradation of materials

In order to check the degradation of the materials, visual inspections were carried out, including taking samples of components after dismantling the prototype. Corrosion was found to have occurred in the material of the terminals of the grounding hoses and in the screws with which they are attached to the panel clamps. All other materials - rivets and washers - were in good condition.

The conclusions drawn are as follows:

  • Rust: the bolts, nuts and connectors of the grounding hoses between panels have rusted. On the other hand, the bolts used to connect the panels to the floats, by means of clamps, have remained rust-free.

  • Dirt on the panels: need to clean the panels from time to time. A low pressure water jet or cleaning with soapy water by climbing onto the platform would be sufficient.

  • Dirt on the floats and components: Dirt from the slurry has been found to remain embedded in the plastic of the float and the connecting parts (long and short joints, bolts and nuts). In addition, due to the shape of these floats, bugs accumulate in the "bathtub" below the panels, although, in principle, they have not been found to affect the materials or the operation of the installation in any negative way.

3) Interaction between components

The interaction between the floats and the hexagonal plastic elements is visually assessed: for an adequate number of plastic elements, it is found that they are placed in a honeycomb arrangement around the PV system without problems. However, they do not quite manage to squeeze through the holes between the floats. And in any case, there are still some gaps between the floats that are too narrow for the parts to pass through, leaving them partially uncovered.

A problem for the correct interaction between the two types of elements is the crusts that form on the semi-liquid slurry, which stick to the walls of the floats and the hexagons. This makes it difficult for them to enter the gaps between floats. It is therefore recommended that the hexagons are thrown into the pond after the slurry has been churned. It is concluded that it is not worthwhile to hand-pour the hexagons one by one into each float gap because of the time cost involved.

4) Reduction of ammonia emissions

Measurements were taken both in the area covered by the photovoltaic system and on the free surface of the basin (which was subsequently covered with plastic hexagonal elements). The frequency of the measurements was 15 days.

It has been found that there is a significant reduction in ammonia emissions in the area covered by the photovoltaic plant compared to the uncovered pond area. There is more than a 40% reduction in NH3 emissions in the covered area compared to the uncovered area, which would be sufficient for an existing farm to comply with emission reduction regulations.

However, some limitations are noted with regard to the measurement method used: during the project, difficulties were encountered with the ammonia sensors, as the sensor used did not initially measure with sufficient sensitivity; furthermore, measurements should be taken over a longer period of time (during a warm period, summer, and a cold period, winter) in order to be able to adequately assess the reduction in emissions. Therefore, these results give rise to the possibility of continuing with the study in the future, extending it to other types of situations and taking a more precise measurement protocol, having access to a larger budget, in order to verify the reduction of emissions in a more precised way.

5) Economic profitability

Total cost of the installation: 30,577€.

Expected annual production: 29,576 kWh/year

Percentage of direct consumption: 34.6%. The rest of the production that is not self-consumed at the moment is fed into the grid. This means that, of the total photovoltaic production, 10,233 kWh are used directly to cover the farm's consumption in a year. The remaining 19,343 kWh are fed back into the grid.

Assuming an average cost of 18 cents per kWh, the percentage of direct self-consumption saves around €1,842, which represents 14% of the electricity bill. Furthermore, assuming an average value of 6 cents per kWh injected into the grid, with the compensation of surpluses it is possible to save around €3,482 on the bill.

In total, the photovoltaic system, under the self-consumption mode with surplus compensation, represents a total saving of 41% on the electricity bill.

Taking these savings into account, the initial investment would pay for itself in about 6 years.

During the month of November, the demonstration prototype of the project was installed on the slurry pond of the Mampel Ansó pig farm in the municipality of Tauste. It is a 20.7 kWp photovoltaic system, with an inverter power of 20 kW. It has 46 photovoltaic panels placed on support floats.

The system will be capable of producing a theoretical annual PV generation of up to 34,378 kWh.

INTERGIA presented the project and the actions developed so far in the III Conference on Innovation in the pig sector, organised by Inneara (Esmedagro) and A.D.S. Porcino Nº1 of Tauste, held at its headquarters in Tauste. These conferences act as a meeting point and knowledge transfer between the different agents involved in the sector and pig farming professionals. More than 40 professionals from the pig sector attended these information days.

The first experiment of the project has been carried out, aimed at evaluating the buoyancy of the elements of the raft covering system and their interaction with each other: photovoltaic panel support floats, perimeter corridor floats and hexagonal elements to cover the free spaces between floats.

El experimento se llevó a cabo en una piscina particular en Tauste (Zaragoza). Se montaron dos flotadores de soporte de panel y dos flotadores de pasillo perimetral. Se vertieron al agua los hexágonos, que se fueron recolocando por entre los espacios libres entre flotadores juntándose entre sí, de manera que la lámina de agua queda cubierta casi en su totalidad.

As conclusions of the experiment, it was found that the buoyancy of the elements will allow the photovoltaic panels to be at a surface of the liquid film such that the risk of slurry splashing, due to the movement caused by the incorporation or churning of slurry in the pond, is minimised. In addition, it was found that the free space between floats is easily covered by the hexagonal elements.

Publication of the article "Proyecto de investigación para definir alternativas en el aprovechamiento y control del potencial de las balsas de purines", in the number 187 of the magazine Anaporc, published by the Asociación Nacional de Porcinocultura Científica.

Read the article here.