Conclusions
As presented in this study, CHP from biogas based on manure is not profitable under current market conditions in Sweden. However, key parameters and their effect on the economic outcome have been identified and evaluated. These results could be used by market operators and policy makers in order to stimulate production and utilization of biogas from manure.
The economic conditions for farm-scale production of biogas and CHP are markedly influenced by the scale of production. Thus, it may be advantageous for farmers to cooperate and invest in larger biogas plants in order to increase the production of biogas and electricity. However, it is not clear whether a large, centralized biogas plant, collecting manure from numerous farms, is the better choice compared to a large, farm-scale plant utilizing manure from a few neighboring farms.
Comparing different technologies for CHP, the compression ignition engine is in most cases the best choice from an economic point-of-view. However, each biogas installation is unique, and the comparison of different installations should be performed based on the specific local conditions regarding individual investments.
Regarding the utilization of heat, it is clear that the level of income, reflected by the potential price, and level of utilization, has a significant impact on the economic outcome. Most farm-scale plants have limited possibilities to utilize heat. One way to improve the economic result could be by implementing a biogas process operated under thermophilic conditions, which has a higher demand for process heat than a mesophilic process. This in turn will increase the amount of manure treated and thereby biogas production, without increasing the investment, leading to a higher profitability compared with the mesophilic process. However, the calculations for a process operated under thermophilic conditions presented in this study do not include the increased risk of process disturbances and their potential impact on the overall economy. Thus, the economic feasibility of the thermophilic process should be further analyzed under practical conditions.
When producing biogas, digestate is produced as well and the economic value of the digestate given in literature varies. Based on these values, the inclusion of digestate in the economic calculations will have a minor impact on the profitability. However, further studies should analyze digestate qualities and their economic value further since the value may increase in the future.
As for the policy instruments implemented today, it is clear that current investment subsidies are not sufficient to reach profitability if the biogas production is based on manure only. The suggested production subsidy for biogas from manure would, however, improve economic conditions significantly and make farm-based CHP profitable in many cases. Thus, the implementation of various economic policy instruments is still crucial in making manure-based biogas for CHP production profitable and thereby enabling a market expansion.