Farms are more than just  cute animals and crops and fields. They also are major consumers of energy, which can be expensive. Realizing this, the National Sustainable Agriculture Information Center put together a web page to help farmers calculate and cut down on costs. The site features energy calculators for many variables including animal housing, tillage, and nitrogen. It also has calculators for biomass as well as renewable energy.
http://attra.ncat.org/attra-pub/farmenergycalc.html