Working capital is calculated by assuming that 1 period of working capital rotation is 1 month. Cost for the
building maintenance and the installation maintenance is set to 25,000.00 IDR per month respectively. Based on cow
manure price of 40.00 IDR per kg [11] (it is assumed that manure is bought from the farmers because the manure
have an economic value), the cost needed to provide manure monthly is 641,903.32 IDR. To provide the water for
biogas production the electricity supply cost is fixed as much as 50,000.00 IDR monthly. To operate the process, it is
employed 2 labors that work part time with the main job is feeding the digester daily and doing installation
repairement and maintenance. Due to their little job, the labor cost monthly is fixed as much as 200,000.00
IDR/labor. Working capital calculation for various farmers conditions are presented in Table 2.