A method for controlling an operating condition of an electric power grid, the electric power grid having an intermittent power supply coupled thereto, the method comprising: using an energy variability controller, controlling variability of a delivered power output of the intermittent power supply to the electric power grid by: monitoring an actual environmental value for a location proximate the intermittent power supply, an available power output of the intermittent power supply being dependent on the actual environmental value; when the actual environmental value is increasing and hence the available power output is increasing, increasing the delivered power output according to a predetermined rate of increase; monitoring a forecast environmental value for the location; when the forecast environmental value is decreasing, decreasing the delivered power output according to a predetermined rate of decrease; and, limiting the delivered power output to below a predetermined threshold.