When purchasing a small photovoltaic system for the single-family house, the question often arises whether and to what extent professional system monitoring via data loggers makes sense. For small systems under 5 kWp, system monitoring can also be carried out manually, as the purchase of a data logger with 300 € to 1,000 € surcharge is hardly worthwhile here. Loss of yield caused by such small plants is manageable and manual or weekly reading of the meter reading is usually sufficient here. For systems between 5-10 kWp, automatic monitoring is already quite useful and for systems larger than 10 kWp, an automatic data logger is recommended.