# Voltage Problems on Farms with Agricultural Biogas Plants--A Case Study
###### Abstract  
Constructing agricultural microbial gasification plants near livestock farms is essential for technical, economic, and environmental reasons. Utilising substrates from these farms allows for producing electricity, heat, and environmentally friendly manure. However, biogas plants often face technical challenges. This study evaluates the power quality of an agricultural biogas plant on a dairy farm. It was found that the plant was connected via a cable with an insufficient conductor cross-section, leading to significant voltage overshoots exceeding 14.6%, which prevented the activation of the second generator. Both generators could operate after replacing the feed-in cable, but considerable fluctuations in the feed-in voltage persisted. Further measurements indicated the need for changes in the digester design. Specifically, replacing the current two mixers with more lower-powered mixers operating alternately was proposed. Sharing these solutions more broadly can help prevent similar issues in future microbial gas plant constructions and optimise electricity production. p 20  
fuels [7]. Biogas produced in biogas plants mainly contains methane (CH\({}_{4}\)) and carbon dioxide (CO\({}_{2}\)) [8]. It also contains smaller proportions of water, nitrogen, hydrogen sulfide, ammonia, oxygen, siloxanes, and other particles [9]. The composition of biogas depends primarily on the substrates used and the technology employed [10]. When building a biogas plant, the location plays a key role, which mainly depends on the availability of input materials (type of farm), the availability of the electricity grid, and the distance from urbanised areas (due to the potential impact of the biogas plant on noise and odours) [11; 12; 13]. From the point of view of sustainable agricultural development, the most important are micro biogas plants, built directly on farms and fed with waste (e.g., slurry) generated on the farm. These measures allow for efficient and rational use of resources at an optimal cost level. A farm with a micro biogas plant is seen as modern and environmentally friendly. The profitability of agricultural biogas plants located at cattle farms depends mainly on the price of electricity and on having the capital to purchase and maintain an electrical generator [14; 15]. In addition, suitable technical conditions for connecting such an energy source at the location are necessary [16]. As herd size increases, there is a noticeable decrease in the cost of building a biogas plant per cow [17]. When calculating the profitability of an investment in an agricultural biogas plant, the equipment's maintenance and servicing costs should also be considered [18; 19]. Various numerical methods, such as AHP [20], Vikor [21], and the numerical taxonomy method [22], can be used to assess the profitability of the investment. The payback period for the construction of an agricultural microbial gas plant is 6-7 years [23] (investments with a payback of up to 8 years are considered financially beneficial [24; 25]). In comparison, the payback for a P.V. plant is within 5-6 years [26]. Agricultural biogas plants enable the generation of electricity heat and cooling and have several other advantages, among which are:  
* the possibility of using biogas as a fuel for internal combustion engines [27];
* an increase in regional/national energy security through the development of distributed energy [28];
* a reduction in the cost of disposing of organic waste [29];
* mitigation of adverse climate change [30];
* use of local energy resources [31];
* production of wholesome manure [32]. Despite the apparent increase in biogas production, there is often a lack of relevant knowledge and technology in agriculture [33]. Therefore, an essential action is to broker information from agriculture to the technology industry, covering all legal, environmental, administrative, organisational, and logistical aspects, to implement as many biogas plant projects as possible successfully [34].