A method based on the efficiency energy coefficient (output/input) is proposed for the assessment of renewable energy sources implementation and for evaluation of their potential for CO2 emission reduction. Energy coefficients were evaluated for renewable energy sources (such as solar, wind and biomass) as well as for their conventional substitutes based on coal, oil and gas. Relative coefficients for CO2 emission reduction were calculated in cases where particular conventional energy technology is replaced by appropriate renewable energy technology. Taking into account renewable energy potential in Poland and the calculated relative coefficients, the results of this research indicate a possibility of reducing CO2 emissions in Poland by Ao 2030 by about 40 million tonnes per year, i.e. 9.9% of the total emissions in 1989. The biggest share in this substitution comes from the use of biomass (wood and straw) and solar energy (flat-plate collectors).