The back end of a cow provides the front end of the green-energy business that Kevin Maas is slowly expanding in Western Washington and Oregon. With missionary zeal, he and his brother Daryl build modest electricity-producing projects that help family-owned dairyfarms preserve their key role in the agricultural ecosystem.Their company, Farm Power, turns manure into electricity, fertilizer and bacteria-free animal bedding. The technology is fairly simple. What's hard about a manure digester is linking farmers, bankers, regulators, environmentalists and utilities.