Hybrid Solar Spectral-Splitting Photovoltaic-Thermal Hydrogen Production Systems

Abstract

Utilizing solar energy to produce green hydrogen is sustainable, but achieving high efficiencies remains challenging. In this study, a hybrid solar spectral-splitting photovoltaic-thermal hydrogen (SSPVTH) system is developed. Leveraging emerging membrane-less electrolyzers, this system simultaneously employs photovoltaics and solar thermal energy to maximize solar-to-hydrogen (STH) production efficiency. The SSPVTH system based on gallium arsenide solar cells achieves an STH efficiency of 21.1%, representing a 31.1% relative improvement over a conventional PV-electrolyzer that relies solely on photovoltaic electricity for water electrolysis. When equipped with perovskite photovoltaics, the system attains an STH efficiency of up to 19.0%. Additionally, with the integration of direct current power converters, the system maintains relatively stable performance across varying solar irradiance levels. Overall, this study provides a new design with the potential for achieving high-efficiency hydrogen production through hybrid solar technologies.

Keywords: concentrated photovoltaics; energy conversion; membrane‐less electrolyzer; photovoltaic‐thermal system; solar hydrogen; spectral splitting.

Figure 1

Schematic illustration of the spectral‐splitting photovoltaic‐thermal hydrogen (SSPVTH) production system. a) Concept of SSPVTH system integrated the parabolic reflector, spectral‐splitting filter, photovoltaics (PV), solar evacuated tube absorber (ETA), and membrane‐less electrolyzer stack. The SSPVTH system employs concentration and spectral splitting to generate high‐temperature heat from irradiance at wavelengths that cannot be utilized by PV cells. This high‐temperature heat is then used to heat the electrolyte in the electrolyzer, thereby enhancing the system's hydrogen production efficiency. b) Spectral‐splitting process for PV and ETA. The spectral‐splitting filter divides the solar spectrum into two parts. One part is directed to PV modules to generate electricity and the PV waste heat is used for domestic hot water, while the remaining portion, which cannot be utilized by PV, is directed to the ETA to generate heat. c) The electrical series / parallel connection of membrane‐less electrolyzer cells inside the stack. d) Working principle of the membrane‐less electrolyzer cell. The electrolyzer uses fluidic forces, rather than solid barriers, to separate the gas products of electrolysis.

Figure 2

Light and thermal management in the SSPVTH system with the GaAs PV. a) The relationship between air mass 1.5 direct (AM 1.5D) solar spectrum, the spectral response of GaAs PV, and the cut‐off edge (λ _cut) of the spectral‐splitting filter. b) Comparison of simulated current density‐voltage (jV) curves of the PV with reported experimental data. The simulation results show that the efficiency of GaAs PV is 29.5%, which agrees well with the efficiency reported in the literature, which is 29.1%. c) The impact of λ _cut on the I‐V curve of GaAs PV. The I‐V curve no longer changes after λ _cut exceeding 900 nm. d) The effect of electrolyte temperature on the I‐V curve of the electrolyzer. As the temperature increases, the voltage required at the same current density (same hydrogen production rate) decreases, indicating an increase in efficiency.

Figure 3

Performance of the SSPVTH system with the GaAs PV. a) Current‐voltage curves of PV and electrolyzer under optimal conditions. Under this condition, the temperature of the PV is 56.4 °C, and the temperature of the electrolyzer is 179.6 °C. b) The efficiencies of PV, electrolyzer (EC), STH, and STH & hot water (STH&HW) in the system under optimal conditions. The STH efficiency achieves 21.1%. The reduction in STH efficiency (Δη _mis) due to the mismatch between the I‐V curves of the PV and the electrolyzer is only 0.9%. The decrease in PV efficiency (Δη _PV) resulting from overheating, compared to the standard temperature of 25 °C, is only 2.6%. Conversely, the improvement in electrolyzer efficiency (Δη _EC) due to heating the electrolyte is 47.1%. c) Effect of HTF flow rate in PV modules on PV temperature and system performance. d) Effect of HTF flow rate in ETA on electrolyzer temperature and system performance. Due to thermal decoupling, the flow rates in the PV and ETA can be controlled independently, allowing for adjustments to the temperatures of the PV and electrolyzer. e) Diagram of a conventional photovoltaic‐hydrogen (PVH) system and the SSPVTH system. f) Comparison of PVH and SSPVTH Performance. Both systems use record‐efficiency GaAs PV.

Figure 4

Results of SSPVTH system with perovskite PV. a) The relationship between Air Mass 1.5 direct, the spectral response of perovskite PV, and the λ _cut of the spectral‐splitting filter. b) Comparison of simulated performance curves of perovskite PV modules with reported experimental data. The simulation results show that the efficiency of perovskite PV is 25.2%, while the efficiency reported in the literature is 25.6%. c) I‐V curves of PV and electrolyzer under optimal conditions. The temperature of the PV is 58.9 °C, and the temperature of the electrolyzer is 185.8 °C. d) The efficiencies of PV, electrolyzer (EC), STH, and STH & hot water (STH&HW) in the system under optimal conditions. The STH efficiency achieves 19.0%. The reduction in STH efficiency (Δη _mis) due to the mismatch between the I‐V curves of the PV and the electrolyzer is only 0.1%. The decrease in PV efficiency (Δη _PV) resulting from overheating, compared to the standard temperature of 25 °C, is 5.8%. Conversely, the improvement in electrolyzer efficiency (Δη _EC) due to heating the electrolyte is 48.9%.

Figure 5

Performance of GaAs‐based SSPVTH system under different solar irradiances. a) PV and electrolyzer temperatures under different solar irradiances. Solar irradiance significantly impacts the temperature of the electrolyzer, which in turn affects its efficiency. b) Diagram of changing the operation point from the blue dot to the blue star through a DC‐DC converter. c) Comparison of STH efficiency with and without a DC‐DC converter at various solar irradiances. The DC‐DC converter can maintain the STH efficiency in a stable state. When irradiance is reduced to 450 W m^{− 2}, the STH efficiency remains at 17.6%, a significant improvement compared to the 6.5% efficiency without the DC‐DC converter. However, due to the efficiency loss of the DC‐DC converter (5%), when irradiance exceeds ≈800 W m^{− 2}, the losses incurred by the converter surpass those experienced without it. d) Efficiency changes of the PV and electrolyzer (EC) compared to the standard conditions at various solar irradiances.

Figure 6

Performance of SSPVTH systems under different solar concentration ratios. a) Effect of concentration ratio on GaAs PV and electrolyzer performance. The electrolyzer temperature surpasses 200 °C when the concentration ratio exceeds 20×. b) Current‐voltage characteristics of the GaAs PV and electrolyzer at the optimal concentration (20×). c) Efficiencies of the GaAs PV, electrolyzer, STH, and solar‐to‐hydrogen & hot water (STH&HW) at the optimal concentration (20×). A maximum STH efficiency of 21.9% is achieved under this configuration. d) Effect of concentration ratio on perovskite PV and electrolyzer performance. The electrolyzer temperature surpasses 200 °C when the concentration ratio exceeds 19×. e) Current‐voltage characteristics of the perovskite PV and electrolyzer at the optimal concentration (19×). f) Efficiencies of the perovskite PV, electrolyzer, STH, and STH&HW at the optimal concentration (19×). Due to the higher temperature coefficient of perovskite PV, its efficiency decreases as the concentration ratio reaches 19×. However, the rising electrolyzer temperature enhances its efficiency, leading to a slight increase in the overall STH efficiency to 19.3%.

Figure 7

Impact of optical and thermal adjustments on system performance. a) Effect of optical losses in the spectral‐splitting filter on GaAs‐based SSPVTH system performance. b) Effect of optical losses in the spectral‐splitting filter on perovskite‐based SSPVTH system performance. c) Effect of PV cooling channel outlet temperature on GaAs‐based SSPVTH system performance. d) Effect of PV cooling channel outlet temperature on perovskite‐based SSPVTH system performance. e) Effect of thermal insulation thickness on electrolyzer performance and STH efficiency in the GaAs‐based SSPVTH system. f) Current‐voltage curves of the GaAs PV and electrolyzer for thermal insulation thicknesses of 0 and 24 mm, with a DC‐DC converter used to match the PV and electrolyzer.