Account for inflation and increases in utility costs over the next few years to obtain a realistic cost-benefit analysis, as ROI and payback are highly dependent on utility charges for conventional energy. Look up the costs of electricity in your state an

Account for inflation and increases in utility costs over the next few years to obtain a realistic cost-benefit analysis, as ROI and payback are highly dependent on utility charges for conventional energy. Look up the costs of electricity in your state and projected price for the calculations. Also obtain the actual inflation rate current at the time of the ROI analysis. Retail residential electricity prices increased an estimated 8% during the first quarter of 2009 compared to the first quarter of 2008 according to a June 2009 report by the U.S. Energy Information Administration. (See Resources.)