Computation and assessment of solar electrolyzer field performance: comparing coupling strategies

Abstract

Carbon-free solar fuel generation through use of photovoltaic-driven electrolyzers (PV-ECs) and photoelectrochemical cells (PECs) has recently grown to be a subject of much interest. Advancements have been provided through improved catalytic activity, high-performance tandem PV and extensive materials exploration, development and characterization. The generally accepted figure of merit is solar-to-fuel efficiency (SFE), measured with the device at standard testing conditions (STC) at ‘1 sun’ i.e., 1000 W m⁻² insolation, clear sky spectrum, and 25 °C operating temperature. However, this does not offer a comprehensive measure of system performance as actual field operating conditions are rarely close to those used for testing. A thorough understanding of PV-EC field performance under realistic operating conditions can assist in holistic device design and scalability. Here, a model is developed to compute their real-life performance using hourly variation in solar irradiance and air temperature over a one-year period. It is then applied to two systems: a previously reported bench-scale high-efficiency CO₂ PV-EC and a MW-scale solar H₂O electrolysis system conceptually designed employing commercial solar panels and water electrolyzers. While the use of DC power optimizer devices was shown to increase annual gas yield by up to 5% for an optimally-matched directly-coupled system, the benefit is shown to be much higher for even slightly mismatched systems.