Integration of Electrochemical Capacitors on Silicon Photovoltaic Modules for Rapid-Response Power Buffering

Photovoltaic (PV) power output can be variable and unpredictable due to the intermittence of sunlight. Based on real-field irradiance data, our model estimated that for a multicrystalline silicon module rated at 280 Wp, a minimum volumetric energy density of $\sim 0.62\ \mathrm{Wh}/\mathrm{cm}^{3}$ and a power density of 1.94 W/cm3 is required to limit the ramp rate to < 10%/min. Although current battery technology can achieve the required energy density, achieving high power density with long battery lifetime is challenging. In this paper, we propose a power buffering strategy in which electrochemical capacitors (ECs) are directly integrated into the module-level electronics where they can provide rapid and efficient buffering of PV power. We show that pseudocapacitive electrodes comprising micro-nanostructured TiOx, formed by anodizing a porous Ti microfoam, can achieve a maximum areal capacitance of 100 mF/cm2 (volumetric energy density of 0.65 mWh/cm3 when discharged at 1 mA/cm2). The measured areal capacitance was two orders of magnitude greater than previously reported values for anodic TiOx, electrodes. Although current storage is still insufficient to meet the requirements for module-level buffering, increased energy densities are expected through the use of TiOx, doping, refined anodization processes and incorporation of the electrode in an asymmetric device which can increase the voltage window of operation.