They make small diesel generators as well. A friends brother custom builds diesel or propane generators, I could contact him for specifics on what one is more economical to run for a given size. What size generator are you needing?

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).