Chemical Maximum-Power-Point Tracking System for Stabilized Liquid Solar-Fuel Production

Abstract

Electrochemical production of fuels from solar energy, commonly referred to as solar-fuel production, is a key technology for converting abundant yet intermittent solar energy into a stable energy source. Typically, this process employs an electrolyzer coupled with photovoltaic (PV) cells through an electronic maximum power point tracking (MPPT) system. Here, we propose a chemical MPPT system, integrated directly into the electrolyzer, to enable stand-alone and unmanned liquid solar-fuel production with stabilized concentration changes from sunrise to sunset. The working principle of the MPPT system is derived from the impedance and heat-transfer properties of the electrolyzer, which incorporates a solid-state electrolyte exhibiting ionic resistivity with a negative temperature coefficient. Application of the mathematical model to a real electrolyzer energized by a commercially-available monocrystalline-Si PV panel for producing pure aqueous formic-acid solution demonstrates a high utilization factor (75–99%) of PV energy and a 2% external solar-to-formic-acid (eSTF) energy efficiency for 0.1 kg of formic acid from pure water and carbon dioxide (CO₂) during daytime operation, all without the use of a conventional electronic MPPT system.