Renewable Biomass Fairness Act - Amends the Internal Revenue Code to: (1) extend through 2018 the tax credit for production of electricity from closed and open-loop biomass facilities; (2) eliminate the reduction in the rate of such credit for electricity produced from open-loop biomass; (3) extend to 10 years the credit period for open-loop biomass facilities; and (4) amend the definition of "cellulosic biofuel" for purposes of the tax credit for alcohol used as fuel to exclude any fuel if more than 4% of such fuel is any combination of water and sediment or if the ash content of such fuel is more than 1%.