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Improving efficiency, controlling cost and reducing the temperature of solar cells are great challenges for linear concentrated photovoltaic/thermal systems (LCPV/T). In this work, we report a new design with a linear Fresnel lens as the primary optical element and an additional multi-functioned solar collector tube as the secondary optical element. With such design, the low-cost solar collector tube acts multiple roles simultaneously, i.e., lens, spectral beam-splitting filter and heat collector. It was demonstrated that the addition of such multi-functional solar collector tube in LCPV/T system can significantly increase the irradiation uniformity and decrease the average temperature of photovoltaic (PV) module under the same thermal condition, which results in the improved electricity output performance of PV module. Under the solar irradiance and ambient temperature for a typical daytime, the average electrical, thermal and total energy efficiencies of the proposed system are 11.39%, 64.72% and 76.11%, respectively. Our work should be of guidance for the design of LCPV/T system with high efficiency, long-life and low cost. [Display omitted] [ABSTRACT FROM AUTHOR]

• Novel CPV/T system with liquid spherical lens as secondary optical element. • Secondary optical element and spectral beam splitting filter are merged into one. • Irradiation unavailable to solar cell is used for heating electrolyte. • A solar-to-hydrogen efficiency of 22.7% is achievable in experiments. How to efficiently convert solar radiation into energy sources for easy storage and consumption is an urgent issue. Although concentrated photovoltaics can achieve high efficiency, it places higher demands on the optical system and heat management. Herein, a new design is presented where a liquid spherical lens acts as a secondary optical element of the concentrating solar system, refracting the light beam while participating in spectral beam splitting. The radiation energy unavailable for solar cells is harvested by the liquid spherical lens through spectral beam splitting which serves to raise the temperature of the electrolyte. Compared with the conventional concentrated photovoltaic coupled electrolytic hydrogen production system, the addition of a liquid spherical lens improves the solar cell heat dissipation while increasing the operating temperature of the electrolyzer, achieving higher solar-to-hydrogen efficiency. The system with this design obtains a solar-to-electricity efficiency of 31.7% as verified by indoor experiments. The solar-to-hydrogen efficiency of the system achieved an average value of 22.1% and a benchmark maximum value of 22.7% during 7 h of continuous operation. The solar-to-hydrogen efficiency is improved by at least 10% compared to the design that separates the secondary optics from the spectral beam-splitting filter. Compared with existing systems employing commercial CPV modules, the efficiency is improved by at least 6% benefiting from the rational distribution of the spectrum by the liquid spherical lens. [ABSTRACT FROM AUTHOR]