Before considering energy sources, the building needs to be sealed for maximum efficiency. At little to no cost, most buildings of a certain age can be upgraded to burn fewer watts. The point of an energy audit is to decrease the number of watts needs to use the building.
Lighting is a major consumer of watts. Heating is another area of concern followed by windows, doors and ducts. An energy audit covers every system in the building.
One congregation put a measuring meter on their commercial refrigerator and learned that a significant portion of their electric bill was used for a box that was designed to be opened 100 to 150 times a day and maintain a steady cold temperature. Even on their busiest feast day, they do not open their refrigerators that often (unless you count the kids sneaking into the kitchen). By swapping out the commercial model for two high efficiency home models, they cut their bill by fifteen percent (15%).