# Influence of the Parameters of an Agricultural Biogas Plant on the Amount of Power Generated
###### Abstract
Many researchers indicate that to reduce greenhouse gas emissions significantly, one can either reduce animal production (and thus, with ever-increasing demand, reduce the supply of food) [33; 34] or, with the shortest possible storage period [35], process animal manure in agricultural biogas plants [36; 37; 38]. In addition, improper storage of manure increases emissions of CH\({}_{4}\), N\({}_{2}\)O, CO\({}_{2}\), and NH\({}_{3}\) into the atmosphere and contributes to a significant loss of the nutrients present in this manure [39; 40]. Such action brings ecological losses (excessive emissions, leaching) and financial losses (higher manure application rates per hectare are necessary) [41; 42]. Biogas plants are increasingly built next to sewage treatment plants [43]. While electricity generation may prove economically viable in large biogas plants, success is no longer evident in microgas plants. In such installations, the price of electricity and the need for capital to purchase and maintain an electrical generator significantly impact their profitability [44; 45]. In addition, the technical conditions for connecting such an energy source at the location must exist [46; 47]. An essential argument for constructing biogas plants is the reduction of unpleasant odours from the substrates used in the fermentation process [7; 29; 48]. Although these gains are difficult to quantify and often not included in economic assessments, the costs of odour reduction can be considered the price of continuing operations as residential areas encroach on land previously occupied by rural farms [7]. The costs associated with constructing biogas plants, calculated per cow, decrease with the increase in herd size. However, no correlation has been found between investment costs and the design of the digester or the presence or absence of electric generators [49]. The equipment must undergo regular maintenance and servicing to optimise the plant's efficiency and longevity [50]. This significantly impacts the operational costs of the biogas facility [30; 51]. Investing in biogas plants on dairy farms, in addition to the reduction of greenhouse gas emissions and the reduction of unpleasant odours, results in an increase in the income indicators of the farm in question [52]. The revenue from electricity production in a biogas plant is approximately EUR 20/MWh higher than the average electricity price in the second quarter of 2023 [53]. Selling the heat produced in the biogas plant or using it for a farm's needs would yield an additional profit of approximately EUR 35 per GJ [54]. It should be noted that the payback period for an agricultural biogas plant is just over six years [52] (finnacially favourable investments with a payback of 5-8 years are considered [55, 56, 57]). In the case of microbial biogas plants, where no investment in land is required, a payback period of even less than five years is achieved [52]. In comparison, an investment in a PV plant typically pays for itself within five to six years [58]. Biogas, resulting from the anaerobic digestion of agricultural waste, can be used for a variety of purposes (fuel, electricity, heat, cooling) [59]. Agricultural waste includes crop residues, animal manure [60], and other farm organic waste [61]. These substrates are readily available and easily harvested, making them popular for biogas production. In Europe, around 23 Mt of dry biomass is produced annually as straw residues from cereals, and in India and China, up to 368 Mt and 649 Mt of straw residues per year, respectively [62]. The composition of agricultural waste depends mainly on the type of crop or animal, which can affect both the quantity and quality of the biogas produced. Although manure is the most suitable substrate for reducing greenhouse gas emissions, it has a low energy value (due to its low organic matter content and high ammonium concentration) [63, 64]. For example, cattle slurry, biogas, and methane yield 25 Nm\({}^{3}\) and 14 Nm\({}^{3}\) per tonne of substrate, respectively [65].