A renewable energy storage system for storing renewable energy, comprising: electrical power generating means for converting the renewable energy into an electrical power; hydrogen producing and energy storing means for producing hydrogen, using the electrical power obtained by the electrical power generating means and/or the electrical power stored by the energy storing means, and for storing electrical power; hydrogenating means for adding the hydrogen produced by the hydrogen producing and energy storing means to unsaturated hydrocarbon; saturated hydrocarbon storing means for storing saturated hydrocarbon produced by adding the hydrogen to the unsaturated hydrocarbon; unsaturated hydrocarbon storing means for storing the unsaturated hydrocarbon; output voltage detecting means for detecting an output voltage value of the electrical power generating means; charge voltage detecting means for detecting a charge voltage value of the hydrogen producing and energy storing means; electrical current detecting means for detecting an electrical current amount supplied to the hydrogen producing and energy storing means; characherized by processing means for estimating an amount of hydrogen produced by the hydrogen producing and energy storing means on the basis of the detected output voltage value, the detected charge voltage value, and the detected electrical current amount; and unsaturated hydrocarbon supply amount control means for controlling an amount of the unsaturated hydro-carbon that is stored in the unsaturated hydrocarbon storing means and is to be supplied to the hydrogenating means on the basis of the amount of hydrogen estimated by the processing means. electrical power generating means for converting the renewable energy into an electrical power; hydrogen producing and energy storing means for producing hydrogen, using the electrical power obtained by the electrical power generating means and/or the electrical power stored by the energy storing means, and for storing electrical power; hydrogenating means for adding the hydrogen produced by the hydrogen producing and energy storing means to unsaturated hydrocarbon; saturated hydrocarbon storing means for storing saturated hydrocarbon produced by adding the hydrogen to the unsaturated hydrocarbon; unsaturated hydrocarbon storing means for storing the unsaturated hydrocarbon; output voltage detecting means for detecting an output voltage value of the electrical power generating means; charge voltage detecting means for detecting a charge voltage value of the hydrogen producing and energy storing means; electrical current detecting means for detecting an electrical current amount supplied to the hydrogen producing and energy storing means; characherized by processing means for estimating an amount of hydrogen produced by the hydrogen producing and energy storing means on the basis of the detected output voltage value, the detected charge voltage value, and the detected electrical current amount; and unsaturated hydrocarbon supply amount control means for controlling an amount of the unsaturated hydro-carbon that is stored in the unsaturated hydrocarbon storing means and is to be supplied to the hydrogenating means on the basis of the amount of hydrogen estimated by the processing means.