The disclosed invention provides examples of preferred embodiments including systems for harvesting energy from variable output energy harvesting apparatus. The systems include energy harvesting apparatus for providing energy input to a switched mode power supply and a control loop for dynamically adjusting energy harvesting apparatus input to the switched mode power supply, whereby system output power is substantially optimized to the practical. Exemplary embodiments of the invention include systems for harvesting energy using solar cells in boost, buck, and buck-boost configurations.