The assessment of the return on investment in the evaluated consolidated simulation cases reveals that every chosen type of farm business could increase profitability with an investment in a biogas plant and reduce the risk factor compared to a singular agricultural business. Even the 75-kW biogas plants, which are not or not very profitable when operated singularly, slightly increase the average profitability in singular dairy farms by 0.3 % (investment in 2005) and 2.1 % (investment in 2009). On the other hand, this means accepting considerably deteriorated values for the equity ratio and the dynamic gearing ratio, which are still acceptable in a sectoral comparison, though. The additional investment in photovoltaic systems improves the situation with regard to profitability and risk in singular dairy farm businesses with a 75-kW biogas plant only. Investment in a 250-kW biogas plant is a profit-increasing source of income for every type of farm business and brings about an increased return on investment while also improving the risk indicators. Due to their financial structures, the effect is more pronounced in smaller low-profit individual businesses than in larger legal bodies. From the singular point of view, photovoltaics is worthwhile for all types of farm business, which is again particularly true for the individual businesses. From a consolidated point of view, the effect of PV investments on the economic condition of the entire farm business is negligible, particularly for the legal bodies, due to their larger financial dimensions.