Optimization of the energy transfer in a system combining photovoltaic source to ultracapacitors

The optimal energy transfer is investigated for a system combining a photovoltaic module, a bank of ultracapacitors and a resistive load. Each ultracapacitor element is modeled with an accurate multibranch circuit composed of resistors and nonlinear capacitors which permit to reproduce its non-ideal behavior. The charge/discharge of ultracapacitors fed with the photovoltaic module into the resistive load is numerically simulated for irradiance of 1000 W m−2 and cell temperature of 25 °C. The energy and the durations of the charge/discharge cycles are sought according to the low and high voltage thresholds of the controller switches. The cycle efficiency is found in the range [86.5%, 93.5%] and the best time ratio cycle is determined. Finally, the voltage thresholds of the controller switch which enable to transfer the maximal energy within an hour are deduced.