This paper presents shortening the payback period of greenhouse gas reduction benefits from photovoltaic rooftop system. The objective was to evaluate the amount and returns of carbon credits. Economic analysis, and comparison of economic analysis with and without consideration of carbon credits from a 149.80 kWp, and 25.68 kWp photovoltaic rooftop system. This study evaluated the amount of electrical energy produced by a photovoltaic rooftop system estimated from the PVsyst program of the factory in Pathum Thani Province, Thailand. The economic indices that the researcher analyzed include the payback period, net present value (NPV), benefit cost ratio (B/C ratio), internal rate of return (IRR). It is divided into four cases studies: Case 1 is the base case, and Cases 2, 3, and 4 are considered carbon credits for 7, 14, and 25 years, respectively. The economic indices analyzed in Case 1 include financial internal rate of return (FIRR), payback period, financial net present value (FNPV), and B/C ratio. The economic indices analyzed in Cases 2, 3, and 4 are the economic internal rate of return (EIRR), economic net present value (ENPV), B/C ratio, payback periods, respectively. This paper outlines a new economic calculation approach that considers carbon credits produced by photovoltaic rooftop system to reach break-even points more quickly, and the application of carbon credits in conjunction with renewable energy.