# Voltage Problems on Farms with Agricultural Biogas Plants--A Case Study
## 4 Conclusions  
The authors' investigations revealed that the power supply voltage issues the owner reported were technical. Specifically, the problem with starting the second generator stemmed from an incorrect cable cross-sectional area used to supply the biogas plant. The inadequate cable size led to significant voltage drops, resulting in voltage levels at the connection point that significantly exceeded permissible limits. Replacing the power cable allowed both generators to operate continuously but did not fully resolve the voltage issues.  
The operation of the digester mixers caused the most substantial voltage fluctuations. When both mixers ran simultaneously, the power input to the electrical system dropped by an average of approximately 14.2 kW. Increasing the number of mixers while reducing their power ratings is recommended to address this. Additionally, operating the mixers in cycles--where only one mixer runs at a time--would help stabilise power consumption and reduce voltage fluctuations at the biogas plant's connection point. Lower-powered motors would also minimise inrush currents and reduce voltage variations during startup. The exact number and power rating of the mixers will depend on the size and design of each mixer.  
A well-sized agitator should be large enough to mix the fermentation mass thoroughly but small enough to be driven by a less powerful motor. Alternating between lower-powered mixers should mitigate voltage fluctuations caused by the activation and deactivation of individual devices. With appropriately selected mixing components, no significant changes in biogas production efficiency are expected. The authors are researching the optimal parameters for devices (agitator and motor) to maximise efficiency while minimising electricity consumption.  
Oversizing the generator capacity (relative to the connection capacity) would cover auto consumption and enable power close to the connection capacity to be fed into the grid. The costs of oversizing the generator, already at the design stage of the biogas plant, are not high compared to the costs incurred when replacing the already installed device. Instead of two generators with a capacity of 20 kW each, it is recommended to install units with a capacity of 22 kW, which follow the manufacturer's range of biogas generators. At the same time, it is necessary to simulate voltage changes caused by the operation of an agricultural biogas plant already at the design stage. It is also possible to post-measure the network parameters at the planned biogas plant connection point. These measurements allow well-known formulas to determine the maximum connectable power to meet the system's voltage requirements. It will enable the proper operation of not only the biogas plant itself but also other equipment installed on the farm. Their smooth functioning will be essential regarding sound management's organisational, financial, and environmental aspects.  
**Author Contributions:** Conceptualisation, A.B. and Z.S.; methodology, Z.S. and M.P.; software, A.M. ([PERSON]); validation, A.B., Z.S. and W.R.; formal analysis, W.R.; investigation, A.M. ([PERSON]); resources, A.M. ([PERSON]); data curation, Z.S. and A.M. ([PERSON]); writing--original draft preparation, Z.S. and M.P.; writing--review and editing, A.B. and W.R.; visualisation, A.M. ([PERSON]); supervision, Z.S. and A.M. ([PERSON]); project administration, W.R. and A.M. ([PERSON]); funding acquisition, M.P. and A.B. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
**Conflicts of Interest:** The authors declare no conflicts of interest.