In Punjab, thousands of family-size biogas plants are satisfactorily functioning for the last two decades with 5-10 cattle heads. PAU (Punjab Agricultural University) has designed biogas plants of various capacities to cover different sizes of dairies.
Links:
[1] http://admin.indiaenvironmentportal.org.in/feature-article/biogas-plants-essential-part-modern-dairy-farms
[2] http://admin.indiaenvironmentportal.org.in/category/author/sarbjit-singh-sooch
[3] http://admin.indiaenvironmentportal.org.in/category/journal/akshay-urja
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/dairy-development
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/energy
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/biogas
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/punjab