## 3 Results
### Regional Potential Modeling  
GIS modeling maps data items in terms of geographic coordinates (latitude, longitude) to calculate the regional potential of biogas (degradable substrates in their original condition) [53]. These data are known or can be calculated. The results are used mainly to calculate regional biomass or biogas potential, but they can also be the basis for sustainability studies or regional energy systems according to regional infrastructure. This technique is, for example, used for the planning of wind parks [54; 55]. Investigating the biogas potential as a result of the AD of manure, Reference [16] used GIS-dependent information about the capacity and locations of dairy farms located in a northwestern region of Portugal (Entre-Douro-e-Minho Province). This region consists of 10 counties with 294 parishes and 1705 dairy farms with more than 100,000 animals. The electrical energy potential was calculated as the linear relationship between one cubic meter of biogas and the number of animals needed to produce the relevant amount of manure. Including biogas plant costs for investment, maintenance and costs for transportation of manure, a multi-objective mixed integer linear programming was performed to identify locations of biogas plants with minimal investment, operation and maintenance or transportation costs. In a similar way, the sectoral biogas potential from livestock manure (cattle, pigs, sheep/goats, poultry) was evaluated in [56] with a GIS approach for a region in Greece. Accordingly, the year-dependent manure production per animal (since 1970) and biogas potential of the manure led to a sectoral energy potential. A time dependent biogas potential made of agricultural residues and municipal biowaste with a seasonal variation approach was examined in [57]. Taking account of residue-to-product ratios, sustainable removal rates, and specific methane yields of agricultural wastes while including a seasonal residue generation, this approach led to a linear relationship between feedstock and its methane yield and was calculated for a land cover of Croatia. Up to 40% less storage capacity is required for the seasonal approach compared to a conventional annual approach. A more detailed regional model of biogas potential to obtain an optimization of GHG emissions for the Finnish province of North-Savo was presented in [58]. GHG emissions were calculated as a sum of emissions of the CHP plant and feedstock transportation. The calculation of CHP emissions is based on specific methane yields of the feedstock and the associated CO2 emissions of methane combustion. Consequently, data for regionally available feedstock (mamure, grass silage and municipal waste) was collected to calculate a regional methane potential based on feedstock production (per animal or mass of waste). Taking the total solid ratio and the methane yield into account, the regional feedstock production led to a regional methane potential. An optimization algorithm calculated and minimized the GHG emission due to different sizes and efficiencies of CHP units and hydraulic retention times. A regional gas grid was contemplated in order to examine the biogas availability in the area near the gas pipeline. Based on feedstock-specific (municipal waste, sludge, manure, silage, and crop residues) biomass, a rural methane yield was calculated due to its volatile solid ratios and methane yields to optimize biogas plant placing in a rural area of southern Finland (Turku, Salo and Kymenlaakso) [59]. Forty-nine biogas plants were identified with a total energy potential of 2.8 TWh. The production capacity of the biogas plants could be raised from an average of 3.7 to 13.4 MW by increasing the transportation distance of feedstock from 10 to 40 km, while over 50% of feedstock potential lies inside a 10 km radius around the biogas plant locations. In summary, regional modeling in the field of biogas production focuses on GIS-based studies of substrate availabilities.