Evaluation of photovoltaics power systems with energy buffer to improve energy efficiency using a time series simulation model

We proposed a novel power converter system with lithium-ion capacitors (LiCs) or lithium-ion batteries (LiBs) as the energy buffer for photovoltaics (PVs). This system can improve converter efficiency in partial load and increase total power output by charging the energy buffer without a power converter when solar irradiance is low, such as in the morning/evening or on cloudy/rainy days. However, calculation is necessary to accurately evaluate the benefits, such as conversion efficiency and total output energy under various weather conditions throughout the year. Then, we developed a time series simulation model for evaluation of PVs with energy buffer to improve energy efficiency. The simulation model reflected the characteristics of the components of the power converter systems with energy buffer, such as PVs, LiCs, or LiBs, a power conditioning subsystem (PCS), and switches. In addition, the model was reflected in the system control algorithm and PCS operation. We calculated available electric energy throughout the year using weather time series data based on solar irradiance in Japan. When using LiCs, we found that PCS electric energy output increased by 117.4 kWh (5.0%), and the average efficiency of PCS increased by 3.3%.