Alternatives in the use and control of the potential of slurry ponds

Program: Call for subsidies to support collaborative actions by actors in the agricultural sector, 2020.

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

Start date: 2020                    Finish date: 2023

Total budget: 150,000.00€

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

Beneficiary members of the collaboration group:

  • Tauste Centro Gestor de Estiércoles S.L. (TAUSTE CGE)
  • Agrupación de Defensa Sanitaria de Porcino Nº 1 de Tauste (ADS TAUSTE)
  • Intergia Energía Sostenible S.L. (INTERGIA)
cartel-acciones-cooperacion-2020

Project updates

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

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

  • Photovoltaic production
  • Degradation of materials
  • Interaction between the covering components of the basin
  • Ammonia emissions, comparing the covered basin with the uncovered area
  • The economic profitability of the complete system.

resultados-proy-purines

Results

Photovoltaic production

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.

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

The production profile is the usual one for any photovoltaic plant.

slurry-production-graphic

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.

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. The rest of the materials – rivets and washers – were in good condition.

The conclusions 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 staples, have remained rust-free.

  • Dirt on the panels: the panels need to be cleaned from time to time, either with water at low pressure or with soapy water by climbing onto the platform.

  • Dirt on the floats and components: it has been found that dirt from the slurry remains embedded in the plastic of the float and the connecting parts (long and short joints, screws 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.

slurry-oxide1 slurry-dirty-module slurry-oxide2

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 in the floats. And, in any case, there are some gaps between the floats that are too narrow for the parts to pass through, leaving them partially exposed.

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.

Reduction of ammonia emissions

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

It was found that there was a significant reduction in ammonia emissions in the area covered with 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 limited way.

Economic profitability

Complete 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, or 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, in the form of self-consumption 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 assembly of the demonstration prototype of the project was carried out on the slurry pond of the Mampel Ansó pig farm, in the municipality of Tauste.

This is a 20.7 kWp photovoltaic system, with 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.

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terminada1

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 de Tauste, held at its headquarters in this town. These conferences act as a meeting point for the transmission of knowledge between the different agents involved in the sector and pig farming professionals. More than 40 professionals from the pig sector attended these information days.

presentation_INTERGIA

cooperation_group

group

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

The experiment was carried out in a private pool in Tauste (Zaragoza). Two panel support floats and two perimeter corridor floats were assembled. The hexagons were poured into the water, which were repositioned between the free spaces between the floats and joined together, so that the sheet of water was almost completely covered.

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.

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The article “Proyecto de investigación para definir alternativas en el aprovechamiento y control del potencial de las balsas de purines” has been published in issue 187 of the journal Anaporc, published by the National Association of Scientific Pig Farming.

Anaporc 187