In a system which generates a variable amount of electric power based on fluctuations in the amount of power received from a source, a method for controlling an amount of power delivered by a power source to a power line, comprising: providing a power subsystem comprising the source and an energy storage unit; operating the energy storage unit (i) to receive and contain portions of energy generated by the system to limit power provided directly to the power line by the source and (ii) to provide portions of energy stored therein to the power line to supplement power directly output from the source to the power line; defining maximum and minimum limits in a range of change in the power delivered to the power line by the power subsystem; during each in a sequence of time periods, defining an amount of power to be delivered by each of the source and the energy storage unit to the power line based on (i) a determined amount of power available for delivery directly to the power line from the power source, (ii) a determined level of energy in the storage unit available for delivery to the power line, and (iii) the limits in the range of change in the power to be delivered by the power subsystem to the power line, wherein power available for output to the power line from the power source during a first period in the sequence of time periods is compared with the power received by the line during a second time period occurring prior to the first period, when the power available during the first period exceeds the amount of power received by the line during the second and prior time period: the power output directly from the source to the power line is permitted to increase during the first period to a level which does not exceed the defined maximum limit in the range of change in the power, and other power available from the source during the first period is applied to the storage unit, wherein the sequence of time periods comprises a plurality of equal time periods, wherein the second time period is the period in the sequence which immediately precedes the first time period, wherein the storage unit comprises a battery, wherein the actual output during the first time period is the product of a factor times the difference between available power for output from the source to the power line during the first time period and the amount of power output from the source to the power line in the second time period, and wherein under at least some circumstances, the factor is a function of: E s − E s min E s max − E s min where: E s, amount of energy stored in the battery, E s Max, the maximum permitted storage level in the battery, and E s Min, the minimum permitted storage level in the battery. providing a power subsystem comprising the source and an energy storage unit; operating the energy storage unit (i) to receive and contain portions of energy generated by the system to limit power provided directly to the power line by the source and (ii) to provide portions of energy stored therein to the power line to supplement power directly output from the source to the power line; defining maximum and minimum limits in a range of change in the power delivered to the power line by the power subsystem; during each in a sequence of time periods, defining an amount of power to be delivered by each of the source and the energy storage unit to the power line based on (i) a determined amount of power available for delivery directly to the power line from the power source, (ii) a determined level of energy in the storage unit available for delivery to the power line, and (iii) the limits in the range of change in the power to be delivered by the power subsystem to the power line, wherein power available for output to the power line from the power source during a first period in the sequence of time periods is compared with the power received by the line during a second time period occurring prior to the first period, when the power available during the first period exceeds the amount of power received by the line during the second and prior time period: the power output directly from the source to the power line is permitted to increase during the first period to a level which does not exceed the defined maximum limit in the range of change in the power, and other power available from the source during the first period is applied to the storage unit, the power output directly from the source to the power line is permitted to increase during the first period to a level which does not exceed the defined maximum limit in the range of change in the power, and other power available from the source during the first period is applied to the storage unit, wherein the sequence of time periods comprises a plurality of equal time periods, wherein the second time period is the period in the sequence which immediately precedes the first time period, wherein the storage unit comprises a battery, wherein the actual output during the first time period is the product of a factor times the difference between available power for output from the source to the power line during the first time period and the amount of power output from the source to the power line in the second time period, and wherein under at least some circumstances, the factor is a function of: E s − E s min E s max − E s min where: E s, amount of energy stored in the battery, E s Max, the maximum permitted storage level in the battery, and E s Min, the minimum permitted storage level in the battery. E s, amount of energy stored in the battery, E s Max, the maximum permitted storage level in the battery, and E s Min, the minimum permitted storage level in the battery.