Advancing performance assessment of a spectral beam splitting hybrid PV/T system with water-based SiO₂ nanofluid

Abstract

Spectral beam split is attracting more attention thanks to the efficient use of whole spectrum solar energy and the cogenerative supply for electricity and heat. Nanofluids can selectively absorb and deliver specific solar spectra, making various nanofluids ideal for potential use in hybrid photovoltaic/thermal (PV/T) systems for solar spectrum separation. Clarifying the effects of design parameters is extremely beneficial for optimal frequency divider design and system performance enhancement. The water-based SiO₂ nanofluid with excellent thermal and absorption properties was proposed as the spectral beam splitter in the present study, to improve the efficiency of a hybrid PV/T system. Moreover, a dual optical path method was applied to get its spectral transimissivity and analyze the impact of its concentration and optical path on its optical properties. Furthermore, a PV and photothermal model of the presented system was built to investigate the system performance. The result indicates that the transimissivity of the nanofluids to solar radiation gradually decreases with increasing SiO₂ nanofluid concentration and optical path. The higher nanofluid concentration leads to a lower electrical conversion efficiency, a higher thermal conversion efficiency, and an overall system efficiency. Considering the overall efficiency and economic cost, the optimal SiO₂ nanofluid concentration is 0.10 wt.% (wt.%, mass fraction). Increasing the optical path (from 0 to 30 mm) results in a 60.43% reduction in electrical conversion efficiency and a 50.84% increase in overall system efficiency. However, the overall system efficiency rises sharply as the optical path increases in the 0–10 mm range, and then slowly at the optical path of 10–30 mm. Additionally, the overall system efficiency increases first and then drops upon increasing the focusing ratio. The maximum efficiency is 51.93% at the focusing ratio of 3.

Graphical abstract

Keywords

full-spectrum solar energy / photovoltaic/thermal (PV/T) system / water-based nanofluid / system efficiency

1 Introduction

With the ever-increasing concern of protecting the environment as well as controlling carbon emissions, the utilization of renewable energies and improving energy efficiency are being increasingly essential and catching more attention. The most plentiful and easily accessible solar resource stands out among all renewable energy sources [1]. Thus, developing effective technology for utilizing solar energy is an approach to alleviating energy scarcity and environmental pollution issues.

Among the approaches of solar energy conversion and utilization, obtaining heat and generating electricity from solar energy are two essential applications [2]. The former can harvest solar energy as heat, while the latter harvests solar energy as electric power [3]. Additionally, the former is simpler and more affordable than the latter. However, the high irreversible loss in the solar-to-heat conversion process limits the application of the former [4]. The photovoltaic (PV) power generation technology converts incident sunlight to high-grade electrical power directly by PV effect [5]. However, the energy of the photons used to produce electricity must be higher than the band gap of the PV material [6]. The remaining photons are transmitted and eventually transferred into hazardous heat in the PV cell base [7]. In addition, other losses including fill factor loss, electron kinetic loss, etc, are converted to harmful heat. These energy losses result in a sharp increase in the temperature of PV cells. With every 1 °C rise in the working temperature of PV cells, the output power and the converting efficiency of PV cells are reduced by 0.65% and 0.08%, respectively [8].

For high energy conversion efficiency at a low cost and to enhance the overall efficiency of the system, a hybrid photovoltaic/thermal (PV/T) system was proposed to cogenerate electricity and thermal energy [9]. Conventional PV/T hybrid systems are cooled behind the PV panels with a heat transfer fluid (HTF), but the maximum output temperature of the system is limited by the operating temperature of the PV cells, where the HTF can only reach temperatures of 310–320 K [10]. Yu et al. [11] innovatively fabricated a vacuum PV/T collector using a glass cover layer to keep the upper and lower spaces of the absorber under vacuum, minimizing the heat loss coefficient factor by 16.08%. Margoum et al. [12] evaluated the effect of nanofluid volume fraction and mass flow rate on the thermoelectric performance of a PV/T system and showed that the nanofluid mixing was optimal when the Ag/water volume fraction was 2.0% and the mass flow rate was 3.0 × 10—3 kg/s. The spectral beam splitting (SBS) technology divides the incoming sunlight into several wavelength bands using optical components, which can significantly enhance the collection temperature and system efficiency. PV cells can convert energetic photons in the spectral response range into electricity, while the thermal receiver absorbs the rest of the photons to produce high-grade heat energy [13].

In general, there are three approaches to SBS hybrid PV/T systems using whole spectrum solar energy: semitransparent nanofluids, optical nanofilm, and translucent PV cells with photonic management [6]. Nanofluids commonly serve as splitters in the SBS hybrid PV/T system due to their excellent thermal and flexible optical characteristics [14]. Nanofluid-based SBS hybrid PV/T system places the nanofluid above PV cells. The nanofluids absorb the solar radiation appropriate for the heat-producing part (mainly infrared solar radiation) while the rest is photovoltaically converted by PV cells [15]. If appropriate nanofluids are used in the above system, it is possible to entirely transmit sunlight in the effective bands of PV cells while still achieving a heat output at a temperature of 375–475 K [16,17].

Rosa-Clot et al. [18,19] proposed a water-based SBS hybrid PV/T system named thermal electric solar panel integration (TESPI). The experimental results demonstrated that the system proposed possesses a good stability. The addition of the water layer reduced the power yield of the PV cells but doubled the overall system energy conversion efficiency. Yazdanifard et al. [20] proposed a concentrated PV/T (CPV/T) system with a hybrid phase-change material (PCM)-nanofluid spectral separator. Placing PCMs and nanofluids above the PV cells can reduce the operating temperature of the PV by up to 30% and increase the outlet temperature by 54%. Hamada et al. [21] researched PV/T solar collectors using phase-change nanoparticle capsules as spectral filters. The results demonstrate that nano-ePCM26 is the most effective HTF in terms of optical filtering and thermal regulation. In recent years, many researchers have attempted to enhance the performance of PV/T systems by utilizing metal oxide-based nanofluids. Cui & Zhu [22] tested the spectral transimissivity for different concentrations of water-based MgO nanofluids and then analyzed the performance of the system under various conditions. The analysis indicated the spectral transimissivity of nanofluid was reduced by 44% with the mass fraction increasing from 0.02 to 0.1 wt.%, and the electrical efficiency of utilizing nanofluid for the SBS hybrid PV/T system was decreased below the single PV cell system, but its energy conversion efficiency was higher overall. The overall system efficiency with a 2 mm thick liquid layer exceeds 60%. Liu et al. [23] prepared five kinds of water-based nanofluids using carbon, CuO, SiO₂, Al₂O₃, and graphite nanoparticles. The photothermal conversion performance and overall system efficiency were estimated and compared. The results indicated that the water-based SiO₂ nanofluid exhibited the optimal PV/T system performance, with a 60.1% higher equivalent generation than the PV system alone.

One of the most creative applications of nanofluids in solar energy devices is in PV/T systems. Yu et al. [24] pointed out that integrating PV/T systems into buildings as building-integrated PV/T (BIPV/T) systems has a higher overall efficiency and significantly reduces building energy consumption. The application of PCM in PV/T systems can regulate and store thermal energy. Alsaqoor et al. [25] indicated that PV/T-PCM systems can notably reduce solar cell temperature and improve electrical efficiency. The novel curved solar balcony of the PV/T system not only meets the architectural requirements and collects electricity but also provides hot water for users. The integration of the CPV/T technology with the heat pump membrane distillation (HPMD) system using nanofluid filtration is a clean and reliable technology for co-generation of electricity and fresh water. In the system designed by Ding & Han [26], the thermal energy absorbed by the nanofluid is used to heat seawater, and the PV cells provide electricity for the compressor in the heat pump system. The application of new technologies in PV systems has made significant contributions to the safe and reliable operation of grid-connected PV systems. Bellagarda et al. [27] trained two autoencoder neural network (ANN) models, 1 dimensional convolutional neural network (1D-CNN) and long short-term memory (LSTM), using limited but realistic actual power generated by a real PV system. Migration techniques were then used to tune the optimized models. The results clearly showed that the best prediction performance was achieved by the LSTM model. Seghiour et al. [28] proposed a deep learning-based fault detection and diagnosis method for PV systems using an ANN. The autoencoder was trained using deep learning techniques to enhance and improve fault detection in PV systems. Sharma & Suhag [29] introduced and implemented a novel control scheme based on the feedback linearization theory for grid-connected PV systems using LCL filters. This design not only significantly improved the occurrence of grid voltage collapse but also reduced the severity of system faults.

Most of the existing studies have directly used different types and concentrations of nanofluids for SBS hybrid PV/T systems, focusing on the effect of adding nanofluids as frequency dividers on the system efficiency. However, there is still insufficient research on the effect of design parameters of nanofluids and experimental setups on the optical-thermal and PV conversion efficiency of the system, especially for water-based SiO₂ nanoparticle fluids with significant potential applications. Therefore, this paper extensively investigates the influence of design parameters such as nanofluid concentration, optical path, and focusing ratio on system performance. It uses water-based SiO₂ nanofluid as a beam splitter for SBS hybrid PV/T systems, and investigates the effect of design parameters on system performance enhancement through actual transimissivity measurements and established PV and photothermal models. The findings of this study are of significant importance for selecting appropriate frequency division liquid and optimizing splitter design in SBS PV/T hybrid systems.

2 Material selection and system principle

In the process of preparing nanofluids, organic solvents and deionized water (DI) are usually used as base liquids. The organic solvents are usually denser and more viscous. Therefore, they have better stability in the process of preparing nanofluids. However, their low thermal conductivity and high toxicity are the disadvantages [6]. In contrast, DI is inexpensive. It mainly absorbs radiation at infrared wavelengths of 1100–3000 nm [30] and has a good transimissivity at the spectrum of the response band of solar cells [31,32]. In addition, the SiO₂ nanoparticles show good heat absorption properties [23]. Therefore, DI and SiO₂ nanofluid were selected as frequency divider fluids in this paper. Tab.1 presents the primary parameters of the experimental materials.

A two-step method was employed to prepare the nanofluids, with the preparation and dispersion processes conducted separately. The main procedure involved dispersing the prepared nanoparticles into the base liquid to form a preliminary stable suspension through magnetic stirring, while using a combination of dispersants and ultrasonic oscillation to enhance the stability of the nanofluids. The two-step method is simple to operate and enables the production of nanofluids with different concentrations, making it more suitable for practical applications.

To obtain realistic optical properties of the nanofluid, this paper used solar radiation with a standard air mass of 1.5 (AM1.5) to calculate the transimissivity of the SiO₂ nanofluid in the whole band and specific bands. From Fig.1, it is observed that the effective electricity generation band (700–1100 nm) occupies about 33.22% of the full band for the monocrystalline silicon (Si) solar cells, and the other spectral energy regions (300–700 nm, 1100–2500 nm) are suitable for thermal energy utilization [28].

The nanofluid-based SBS hybrid PV/T system is schematically presented in Fig.2. Clearly, the present system mainly comprises two separate modules, a solar thermal module and an optoelectronic module. The solar thermal module is used as a fluid-based SBS filter, where sunlight is concentrated using the lens. Then, the nanofluid absorbs incident sunlight selectively lower below the bandwidth energy of PV cells and gains high-grade heating energy. The optoelectronic unit absorbs the rest of the sunlight spectrum and generates electricity. In this system, nanofluids serve as spectral dividers and heat collectors at the same time, enabling effective use of the whole spectrum and reducing the energy loss in the heat transfer process. Thus, the nanofluid-based SBS hybrid PV/T system exceeds the temperature limits of the traditional system, allowing for the cogeneration of both electricity and high-grade heating energy.

3 Method

3.1 Dual optical path method

The dual optical path method of testing was used to get the true spectral transimissivity of the nanofluids presented in this paper. Based on the Lambert−Beer law, at λ wavelength, the spectral transimissivity of the fluid is deduced as [15]

(1)\tau (\lambda )=\exp [-\alpha (\lambda )\cdot x],

where α and x are absorption coefficients of nanofluids and fluid thickness.

During the measurement, due to the reflective and absorptive effects of the experimental material itself, the relationship between the measured transimissivity T and true liquid spectral transimissivity τ could be derived as [33]

(2)T=(1-R_{\mathrm{a}\mathrm{i}\mathrm{r},\mathrm{c}\mathrm{u}\mathrm{v}}{)}^2(1-R_{\mathrm{f}\mathrm{l}\mathrm{u},\mathrm{c}\mathrm{u}\mathrm{v}}{)}^2\mathrm{e}\mathrm{x}\mathrm{p}(-2{\alpha }_{\mathrm{c}}\cdot d)\cdot \tau ,

where R_air,cuv and R_flu,cuv express the reflectance at the intersection of air−cuvette and fluid−cuvette interface, respectively, α_c is the absorption coefficient of the colorimetric dish, and d denotes the colorimetric dish thickness, mm.

Nanofluids absorption coefficient α(λ) in the corresponding wavelength can be expressed as

(3)\alpha (\lambda )=- \frac{1}{x_2-x_1}\cdot \ln \frac{T_2(\lambda )}{T_1(\lambda )},

where x₁ and x₂ are two different optical paths, respectively; T₁(λ) and T₂(λ) are the corresponding spectral transimissivity measurements for optical paths x₁ and x₂, respectively.

3.2 Numerical model

3.2.1 Working principle of PV cells

PV cells transform solar radiation into electricity directly based on the PV effect of semiconductors. The principle of the PV effect is shown in Fig.3. Under solar irradiation, free charges are created within a specific semiconductor, and the directional movement and accumulation of free charges result in an electric potential difference. Then a photogenerated current flows through the load to generate electricity.

3.2.2 Mathematical model of PV cells

Considering the resistance characteristics inherent in the PV module itself, the PV cell is considered as an ideal current source. Fig.4 shows the schematic of the equivalent circuit. The model includes a parallel diode and two resistors. Through the mathematical relationship between PV voltage and current, and in combination with the corresponding variables, the output properties of PV cells could be obtained.

Following Kirchhoff’s current law, the output current of PV cells is calculated as

(4)I=I_{\mathrm{p}\mathrm{h}}-I_{\mathrm{d}}- I_{\mathrm{s}\mathrm{h}},

where I_ph means the photogenerated current, I_d is the dark current running through the diode (without light), and I_sh represents the parallel branch current.

The photogenerated current is defined as [34]

(5)I_{\text{ph}}=\left[I_{\text{sc}}+r_{\text{i}}\cdot \left(T_{\mathrm{p}\mathrm{v}}-298\right)\right]\cdot \frac{G}{1000},

where I_sc refers to a short-circuit current; r_i denotes the relative temperature coefficient of PV cells with the ambient temperature of 25 °C, and the solar radiation intensity of 1 000 W/m² is assumed to be 0.0032; and T_pv and G represent the working temperature and the solar radiation intensity over PV cells.

The dark current flowing through the diode can be defined as

(6)I_{\mathrm{d}}=I_0\cdot \left[\exp \left(\frac{q\cdot \left(V+I\cdot R_{\mathrm{s}}\right)}{n\cdot K\cdot N_{\mathrm{s}}\cdot T_{\mathrm{p}\mathrm{v}}}\right)-1\right],

where q denotes the electronic charge, which is taken as 1.6029×10⁻¹⁹ C; V and R_s response to the output voltage of PV cells and series resistance, respectively; n means the ideal factor of the diode, which is taken as 0.79; K denotes the Boltzmann constant, which is generally taken as 1.38×10⁻²³ J/K; N_s expresses the quantity of cells in series; and I₀ is the diode saturation current, which is defined by

(7)I_0=I_{\mathrm{s}}\cdot {\left(\frac{T_{\mathrm{p}\mathrm{v}}}{T_{\mathrm{n}}}\right)}^3\cdot \exp \left[\frac{q\cdot E_{\mathrm{g}0}\cdot \left(1/T_{\mathrm{n}}-1/T_{\mathrm{p}\mathrm{v}}\right)}{n\cdot K}\right],

where T_n is the standard temperature and is assumed to be 298 K; E_g0 is the bandwidth gap energy of the semiconductor, which is considered to be 1.1 eV; and I_rs refers to the reverse saturation current, expressed as

(8)I_{\mathrm{r}\mathrm{s}}= {\displaystyle \frac{I_{\mathrm{s}\mathrm{c}}}{\exp \left({\displaystyle \frac{q\cdot V_{\mathrm{o}\mathrm{c}}}{n\cdot N_{\mathrm{s}}\cdot K\cdot T_{\mathrm{p}\mathrm{v}}}}\right)-1}},

where V_oc indicates the open-circuit voltage.

The current passing through the shunt resistance is calculated as

(9)I_{\mathrm{s}\mathrm{h}}= \frac{V+I-R_{\mathrm{s}}}{R_{\mathrm{s}\mathrm{h}}},

where R_sh is shunt resistance, Ω.

3.2.3 Simulation model of PV cells

To investigate the impact of multiple design parameters on the performance of the hybrid PV/T system, a PV cell model was built based on the mathematical model in Section 3.2.2. The PV cell model and its internal detailed structure can be seen in Fig.5.

The working parameters for the model of PV cells are listed in Tab.2.

3.2.4 Photothermal model and performance evaluation index

According to the absorption spectra of the nanofluid, the thermal output power for each nanofluid can be calculated as [35]

(10)P_{\text{th}}={\eta }_{\text{collector}}{\int }_{300}^{2500}G\left(\lambda \right)\cdot {\alpha }_{\text{fl}}\left(\lambda \right)\mathrm{d} \lambda ,

where η_collector is the thermal collection efficiency of nanofluids frequency divider, G(λ) is the solar radiation corresponding to a wavelength of λ, α_fl(λ) represents the nanofluid absorption rate. The thermal conversion efficiency of the system is expressed as [36]

(11){\eta }_{\text{th}} =\frac{P_{\text{th}}}{{{\displaystyle \int }}_{{\lambda }_{\mathrm{l}}}^{{\lambda }_{\mathrm{h}}}G\left(\lambda \right)\mathrm{d}\lambda },

where λ_l and λ_h are the starting and ending wavelengths of solar radiation. The output power of the PV cells is figured as [37]

(12)P_{\text{el}}=I_{\text{sc}} \cdot V_{\text{oc}}\cdot \mathrm{F}\mathrm{F},

where FF is the filling coefficient of PV cells, defined as the real maximum power to the theoretical power ratio, which is usually obtained by [38],

(13)\mathrm{F}\mathrm{F}={\displaystyle \frac{V_{\mathrm{m}}}{V_{\text{oc}}}}\left(1-{\displaystyle \frac{\mathrm{e}\mathrm{x}\mathrm{p}\left({\displaystyle \frac{q{V}_{\mathrm{m}}}{K{T}_{\text{pv}}}}\right)-1}{\mathrm{e}\mathrm{x}\mathrm{p}\left({\displaystyle \frac{q{V}_{\text{oc}}}{K{T}_{\text{pv}}}}\right)-1}}\right),

where V_m denotes the maximum output power voltage on the I–V curve of PV cells. V_m can be expressed as [38]

(14)V_{\mathrm{m}}=k\times V_{\mathrm{o}\mathrm{c}},

where k represents the experience parameter of PV cells, which is generally taken in the range of 0.7–0.8 [36].

The electrical conversion efficiency of the system proposed is derived as [38]

(15){\eta }_{\text{el}} =\frac{P_{\text{el}}}{A_{\text{pv}}\cdot {{\displaystyle \int }}_{{\lambda }_{\mathrm{l}}}^{{\lambda }_{\mathrm{h}}}G\left(\lambda \right)\mathrm{d}\lambda }={\eta }_{\text{ref}}\left[1-\delta \left(T_{\text{pv}}-T_{\text{ref}}\right)\right],

where η_ref refers to the photoelectric transformation efficiency of PV cells at the referent temperature T_ref, δ is the temperature coefficient of the power generation efficiency of PV cells, A_pv is the effective area of the PV cells, and T_ref is the referent temperature, which is generally considered to be 298 K.

Taking into account the energy level difference between electrical and thermal energy, the overall efficiency of a system can be expressed as [37]

(16){\eta }_{\mathrm{t}\mathrm{o}\mathrm{t}}={\eta }_{\mathrm{t}\mathrm{h}}+\frac{{\eta }_{\mathrm{e}\mathrm{l}}}{{\eta }_{\mathrm{p}}},

where η_p shows the electricity generation efficiency of the conventional power plant, generally taken as 38%.

4 Results and discussion

4.1 Model verification

4.1.1 PV cell model validation

To assess the reliability of the PV cell model proposed, the model was applied to simulate the output current and voltage of the PV/T system using Ag nanofluid as the HTF. The simulated results were then compared with the experimental data published in Zhang et al. [31]. As Fig.6 shows, the simulated results of both the I–V and P–V curves correspond well with experimental results, and the maximum relative errors of short-circuit current and power are only 2.64% and 10.72%, respectively. The comparison validated the viability and reliability of the PV cell model of the system proposed in this paper.

4.1.2 Model validation of SBS hybrid PV/T system

The SBS hybrid PV/T system model was utilized to further validate the accuracy of the model proposed, by simulating the electrical and thermal conversion efficiencies of water-based Ag/CoSO₄ nanofluids and propylene glycol-based Ag/CoSO₄ nanofluids at concentrations of 5.3, 31.8, and 84.7 mg/L. The simulated results were compared with Chen’s [39] experimental results under the same condition. Tab.3 compares the experimental and simulation results of the model proposed. The largest relative errors in electrical and thermal conversion efficiency between the experimental and simulated results are 7.71% and 10.15%, respectively. Moreover, the experimental and simulated results of the electrical and thermal conversion efficiency follow the same trend as the concentration of nanofluid increases. While the simulated values deviate from the experimental values, the relative errors between the two are small, indicating that the model proposed has a certain degree of reliability and accuracy.

4.2 Spectral transimissivity analysis of water-based SiO₂ nanofluid

4.2.1 Impact of concentration on optical characteristics of nanofluids

To further investigate the impact of SiO₂ nanofluid concentration on the optical characteristics of water-based SiO₂ nanofluid, the optical path was set to 5, 10, 15, 20, 25, and 30 mm, and the concentration to 0.01, 0.05, 0.10, and 0.50 wt.%, sequentially. A comparison and analysis of the spectral transimissivity of DI and various concentrations of water-based SiO₂ nanofluid were performed.

Fig.7(a) gives the impact of SiO₂ nanofluid concentration on the spectral transimissivity of water-based SiO₂ nanofluid at a 5 mm optical path. It can be observed from Fig.7(a) that the DI and water-based SiO₂ nanofluid with a 0.01 wt.% have higher transimissivity for solar radiation at wavelengths of 300–900 nm, which are 99.29% and 93.59%, respectively. As the SiO₂ concentration rises to 0.50 wt.%, the spectral tran-simissivity of the presented nanofluid in the 300–900 nm range sharply reduces by 10.00%, 34.90%, and 62.90%, respectively. The spectral transimissivity of DI in the wavelength of 900–1100 nm decreases at first and then increases, and the minimum spectral transimissivity is at the wavelength of about 980 nm. Similar trends in transimissivity are observed for various concentrations of water-based SiO₂ nanofluid. The average spectral transimissivity of DI and SiO₂ nanofluid at 0.01 and 0.05 wt.% and at wavelengths of 900–1100 nm is 89.23%, 85.81%, and 83.96%, respectively. As the SiO₂ concentration continues to rise to 0.10 and 0.50 wt.%, its average transimissivity shows a clear trend of decline. The transimissivity of DI and SiO₂ nanofluid at the wavelengths of above 1100 nm diminishes, and drops to a low point at about 1400 nm, after which the transimissivity of nanofluids is almost zero. The SiO₂ nanofluid at 0.50 wt.% has the lowest spectral transimissivity of 5.13% at wavelengths above 1100 nm while the SiO₂ nanofluid at 0.01 wt.% has the highest spectral transimissivity of 11.77%.

Fig.7(b) illustrates the influence of SiO₂ nanofluid concentration on the spectral transimissivity of water-based SiO₂ nanofluid at a optical path of 10 mm. The average spectral transimissivity of DI at the wavelength of 300–1200 nm is 88.38%. Compared with Han et al. [40], Hale & Querry [41], Smith & Baker [42], and Kent & Palmer [43], the deviations are 0.07%, 0.63%, 0.31%, and 0.31%, respectively. The small deviation proves that the experimental results are accurate and reliable. It is shown that the SiO₂ concentration has an impact on the optical characteristics of water-based SiO₂ nanofluid. A higher SiO₂ concentration leads to a lower spectral transimissivity of water-based SiO₂ nanofluid. However, water-based SiO₂ nanofluid at different concentrations show a low transimissivity to infrared solar radiation at wavelengths larger than 1400 nm. The main reason for this is that the base fluid DI has a strong absorption of infrared solar radiation [32].

Furthermore, the influence of concentration on the spectral transimissivity of water-based SiO₂ nanofluid is analyzed at different optical paths of 15, 20, 25, and 30 mm, as depicted in Fig.7(c)–7(f). It is evident that with an increase in the optical length, the transimissivity variation of the nanofluid for different spectral bands of solar radiation remains consistent with that at a 5 mm optical path. The transimissivity of infrared solar radiation at wavelengths greater than 1400 nm is consistently low. However, the difference is that as the optical path grows, the spectral transimissivity gradually decreases. Particularly, when the optical path exceeds 20 mm, the water-based SiO₂ nanofluid at a concentration of 0.50 wt.% exhibits almost 0 transimissivity for the entire spectrum (300–2500 nm) of solar radiation. This indicates that the nanofluid layer absorbs the entire spectrum of solar radiation.

4.2.2 Impact of optical path on optical characteristics of nanofluids

Fig.8 exhibits the influence of optical path over the spectral transimissivity of the DI. It can be seen in Fig.8 that as the optical path is in the 5–30 mm range, DI has a high transimissivity at 300–700 nm, and the average transimissivity is higher than 98.51%. The optical path of DI significantly affects the spectral transimissivity at wavelengths of 700–1400 nm. The average transimissivitye of the DI is 74.08% at an optical path of 5 mm. As the optical path increases from 5 to 10, 15, 20, 25, and 30 mm, the average transimissivity of the DI decreases by 11.3%, 18.31%, 23.17%, 26.8%, and 29.66%, respectively. When the wavelength is greater than 1400 nm, the optical path has the minimum influence on the spectral transimissivity of DI However, at a 5 mm optical path, the DI has a maximum value of spectral transimissivity in the wavelength range of 1560–1780 nm. The maximum spectral transimissivity is 5.70% at the wavelength of 1680 nm. When the optical path exceeds 10 mm, the spectral transimissivity of DI for wavelengths above 1400 nm is almost zero.

The influence of the optical path on the spectral transimissivity of water-based SiO₂ nanofluid is depicted in Fig.9(a)–9(d) at concentrations of 0.01, 0.05, 0.10, and 0.50 wt.%. It is evident that as the optical path increases, the transimissivity gradually declines. For example, in Fig.9(a), the water-based SiO₂ nanofluid with a concentration of 0.01 wt.% exhibits a high transimissivity for solar radiation in the wavelength range of 300–900 nm. At an optical path of 5 mm, the average spectral transimissivity is 93.59%. As the optical path increases to 10, 15, 20, 25, and 30 mm, the average transimissivity gradually decreases to 87.63%, 82.08%, 76.92%, 72.10%, and 67.62%, respectively. Although there is a certain reduction in transimissivity for solar radiation within this wavelength range, the water-based SiO₂ nanofluid with a concentration of 0.01 wt.% still maintains a relatively high-level of transimissivity. Regarding the wavelength range of 900–1400 nm, the transimissivity of nanofluid shows a “decrease–increase–decrease–increase–decrease” trend. The transimissivity shows a pronounced minima at the wavelengths of 980 and 1200 nm, a significant maxima at the wavelengths of 1080 and 1260 nm, followed by a subsequent decrease at a wavelength of 1400 nm. For solar radiation with wavelengths greater than 1400 nm, the spectral transimissivity of water-based SiO₂ nanofluid is similar to that of DI. The reason for this is that SiO₂ nanoparticles only exhibit a certain level of absorption and scattering for short-wavelength solar radiation, and their light absorption capability is lower than that of the base fluid (DI) under long-wavelength solar radiation. Therefore, the transimissivity for long-wavelength solar radiation is mainly determined by the properties of the DI itself.

The above findings show that the optical path has an influence on the optical characteristics of water-based SiO₂ nanofluid. The spectral transimissivity of the nanofluid declines gradually with the addition of the optical path. When the SiO₂ nanofluid concentration is 0.50 wt.% and the optical path exceeds 20 mm, the spectral transimissivity of the full-wavelength range is almost 0.

4.3 Parameter effect on performance of SBS hybrid PV/T system

4.3.1 Effect of concentration on system efficiency

The particle concentration of the nanofluid directly impacts its optical characteristics, which is an essential parameter in the optimization of PV/T receiver performance. The influence of various concentrations of water-based SiO₂ nanofluid on the system efficiency is investigated and evaluated in this paper. The analysis was based on Section 4.2, the optical path was set to 10 mm, and the focusing ratio was 1. Additionally, the heat collection efficiency was initially set to 0.67 based on Chen [44] and Sultana et al. [45].

Fig.10(a) displays the impact of SiO₂ concentration on the power generation performance of the system proposed. From Fig.10(a), an increase in SiO₂ concentration causes a remarkable reduction in the short-circuit current. While the largest short-circuit current without the frequency divider is 128.43 mA, the corresponding short-circuit current of PV cells with DI as the frequency division liquid is 107.09 mA. As the concentration of water-based SiO₂ nanofluid rises from 0.01 to 0.50 wt.%, the short-circuit current decreases from 97.57 to 11.50 mA, decreasing by 88.21%. The result can be explained by the fact that PV cells have a short-circuit current in proportion to the intensity of solar radiation reaching its surface. The greater the concentration of the frequency divider liquid is, the stronger its extinction effect on solar radiation is. Thus, fewer photons can reach the surface of PV cells. Additionally, the SiO₂ concentration has very little effect on the corresponding open-circuit voltage. It is caused by the large internal resistance of PV cells.

The impact of SiO₂ concentration on the system efficiency is observed in Fig.10(b). The PV system without the frequency divider only produces electric energy. The system electrical conversion efficiency is 15.01%, and the corresponding overall system efficiency is 39.50%. Compared to the case without a frequency divider, the electrical conversion efficiency of the water-based SBS hybrid PV/T system is reduced by 2.57%, and the thermal conversion efficiency and the overall system efficiency are improved by 12.95% and 6.18%. In the absence of PV conversion, exposing a solar cell directly to abundant solar radiation will result in excess energy being converted into heat within the cell. The efficiency of PV modules is largely dependent on the operating temperature, and as the temperature increases, the efficiency of PV/T systems decreases [46]. Increasing the temperature of the PV cell also leads to a higher thermal stress and hotspots, thereby shortening the working lifespan of the PV cell [47]. However, the addition of a splitter allows for the utilization of divided solar radiation, leading to an overall improvement in system efficiency. As the SiO₂ concentration rises, the electrical conversion efficiency of the system proposed gradually decreases, with the thermal conversion efficiency and the overall efficiency showing an upward trend. As the results show, the system proposed based on the water-based SiO₂ nanofluid with a 0.50 wt.% shows a maximal overall system efficiency of 64.59%, corresponding to an electrical conversion efficiency of 1.23% and a thermal conversion efficiency of 61.36%.

It is known that a higher SiO₂ nanofluid concentration leads to a higher overall efficiency. To further clarify the relationship between nanofluids concentration and the overall system efficiency, setting 0.01 wt.% as a unit concentration, the efficiency improvement of the whole system per unit concentration was shown in Fig.11. Compared with the water-based SiO₂ nanofluid with 0.01 wt.%, the overall efficiency of the SiO₂ nanofluid with 0.05, 0.10 and 0.50 wt.% increases by 0.71%, 1.09%, and 0.33% per unit of concentration, respectively. However, higher nanofluid concentrations increase the demand for nanoparticles, and the market price of commercial solar nanofluids can be as high as 2796.16 $/L, thus increasing input costs [48]. Several countries have introduced market incentives for solar PV, including feed-in tariffs, renewable energy quotas, installation subsidies, net metering, and tax incentives [49]. From the overall analysis of the economic viability of the PV/T system based on nanofluid, it can be observed that the shortest payback period with a 75% government subsidy is about 2.5 years, and the longest payback period without any government subsidy is about 8 years [50]. The above results show that the optimal SiO₂ nanofluid concentration is 0.10 wt.% in the water-based SiO₂ nanofluid hybrid PV/T system, considering the overall efficiency and economic effectiveness of the trade-off system.

The frequency divider surface is transparent glass which is directly in contact with the surrounding environment. It has a greater heat loss than an ordinary collector. Therefore, the efficiency of the system proposed is further analyzed, assuming a heat collection efficiency of 0.4. Fig.12 shows the system overall efficiency variation with different SiO₂ nanofluid concentrations. A higher nanofluid concentration leads to a lower electrical conversion efficiency and a higher thermal conversion efficiency. The corresponding overall efficiency tends to rise first and then decline. For this system, the electrical conversion efficiency is consistent with a collector efficiency of 0.67. When the frequency liquid is DI, it has an overall efficiency of 40.46%, compared with the heat collection efficiency of 0.67, which decreases by 5.22%. At a concentration of 0.05 wt.% of water-based SiO₂ nanofluid, the overall system efficiency reaches a maximum of 41.25%, which is 1.75% higher than that of the system without frequency divider and 0.79% higher than the DI hybrid PV/T system.

4.3.2 Effect of optical path on system efficiency

The optical path is an essential parameter to affect the radiation transmission of the HTF. The larger the optical path, the thicker the nanofluid layer, and the more solar radiation it absorbs. Fig.13 presents the impact of optical path on the efficiency of DI and 0.05 wt.% SiO₂ hybrid PV/T system. According to the discussion in Section 4.2, the focusing ratio was set to 1 and the heat collection efficiency was 0.67 [44].

Fig.13(a) and 13(c) display the impact of optical path on the electrical properties of the DI and 0.05 wt.% SiO₂ hybrid PV/T system. Owing to the optics loss from the lens itself, the short-circuit current of PV cells is 128.43 mA without the frequency divider, the system electrical conversion efficiency is 15.01%, and the corresponding overall system efficiency is 39.50%. It is found that a larger optical path causes a lower short-circuit current and open-circuit voltage. This result can be accounted for by the fact that a greater optical path leads to a lower fluid transimissivity, and the effective solar radiation arriving at the PV cells is reduced. The short-circuit current of PV cells decreases as the effective solar radiation diminishes. The reason for the small open-circuit voltage drop is that the temperature is the primary element affecting the open-circuit voltage, whereas the quantity of solar radiation arriving at PV cells does not affect the open-circuit voltage. When the optical path increases from 5 to 30 mm, the short-circuit current of the DI PV/T system decreases from 110.66 to 97.33 mA, decreasing by 12.05%. The corresponding short-circuit current sharply declines from 98.82 to 49.21 mA, decreasing by 50.21%. This can be explained by the fact that the presence of SiO₂ nanoparticles in DI effectively enhances the absorbing and scattering of solar radiation by the fluid. Thus, less solar radiation arrives at the PV cell, which affects the photoelectric conversion of this system.

Fig.13(b) and Fig.13(d) manifests the impact of optical path on the system efficiency of the DI and 0.05 wt.% SiO₂ PV/T system. As can be observed in Fig.13(b) and Fig.13(d), as the optical path grows, the electrical conversion efficiency of the system drops by 60.43%, while the overall system efficiency increases by 50.84%. Moreover, the overall system efficiency grows faster at an optical path of 0–10 mm than that of 10–30 mm. For DI, the overall system efficiency is 45.68% at the optical path of 10 mm, which is 3.11% higher than that of 5 mm, while the overall system efficiency at the optical path of 30 mm is only 0.51% higher than that of 25 mm. Likewise, when the frequency divider is the 0.05 wt.% SiO₂ nanofluid, the overall efficiency at the 10 mm optical path shows an increase of 8.34% compared to that at 5 mm, while the overall system efficiency improves by only 2.31% when the optical path is raised to 30 from 25 mm. For this reason, the thermal conversion efficiency of the system rises as the optical path grows. However, as the thickness of the frequency fluid rises to a certain level, the photothermal conversion gradually reaches saturation, making the overall system efficiency smooth. These results conform with those of Al-Shohani et al. [51], who conducted a study on the variation of PV conversion efficiency of a splitter at different water layer thicknesses. The results of Al-Shohani et al. [51], also indicate that when the thickness of the water layer ranges from 1 to 5 cm, it can help reduce the temperature of the PV cells by 14%–30.2%. In addition, a larger optical path (a larger thickness of frequency divider fluid) means that the amount of frequency divider fluid required by the system is greater, increasing the input cost of the system. Therefore, it is crucial to consider the overall efficiency and input cost of the receiver when selecting the optical path.

4.3.3 Effect of focusing ratio on system efficiency

Focusing ratio represents the dimensionless number of the ratio of the concentrated radiation energy density per unit area to its incident energy density. Focusing devices (such as through focusing, tower focusing, and Fresnel focusing) are often used to focus the incident sunlight exponentially on the surface of the frequency divider in the solar energy utilization technology. An appropriate focusing ratio can improve the system efficiency to the greatest extent possible. To understand the impact of focusing ratio on the hybrid PV/T system based on nanofluids, DI and SiO₂ nanofluid with 0.05 wt.% were used as the frequency divider, and the optical path was set at 10 mm.

Fig.14 displays the impact of focusing ratios on the efficiency of the DI and 0.05 wt.% SiO₂ PV/T system. It can be noted in Fig.14(a) that the electrical conversion efficiency of the system with no frequency divider ranges from 14.47% to 15.11%, and the overall system efficiency is between 38.08% and 9.77%. Fig.14(b) shows that when the frequency divider is DI, the electrical conversion efficiency of the DI PV/T system varies between 11.98% and 12.59%, and the maximum overall system efficiency is 46.07% at a focusing ratio of 3, which is 6.3% higher than that the case in which there is no frequency divider. Fig.14(c) shows that when the SiO₂ nanofluid is 0.05 wt.%, the maximum electrical conversion efficiency of the PV/T system is 9.95%, and the overall system efficiency is up to 51.93%. Taking the focusing ratio of 3 as an example, the electrical conversion efficiency of the system proposed decreases by 5.16% compared with that without the frequency divider, but the overall efficiency increases by 12.16%. The reason for this is that adding water-based SiO₂ nanofluid can absorb more solar radiation and thus improve the system thermal conversion, resulting in a reduction of the system electrical conversion efficiency as less radiation reaches the surface of PV cells. This is because SiO₂ nanoparticles can absorb solar radiation outside the “spectral response” band of PV cells, which promotes the effective use of solar energy and improves the overall system efficiency.

In summary, the overall system efficiency and electrical conversion efficiency of the PV/T system first rise and then decline with the increasing focusing ratio. The highest overall system efficiency and electrical conversion efficiency are 51.93% and 12.59% when the focusing ratio is 3. The impact of the focusing ratio on system performance using water-based Ag/CoSO₄ nanoparticle fluid as a frequency divider is consistent with the findings in Chen [39], mainly because of the electrical properties of PV cells. The increasing focusing ratio results in a higher solar radiation intensity on the surface of PV cells. Then, the working temperature rises sharply. However, the upsurge of cell temperature negatively affects the electricity output and efficiency [15]. The surface of PV cells receives less solar radiation at a low focusing ratio. The “electron” absorbed by the “electrons” is not sufficient to turn all of the electrons into “photoelectrons,” which can limit the efficiency of electrical conversion to some extent. The results show that the optimal focusing ratio is 3 in this study.

5 Conclusions

A dual optical path method was used to gain the spectral transimissivity of water-based SiO₂ nanofluid in this paper. Then, the impacts of SiO₂ nanofluid concentration and optical path of water-based SiO₂ nanofluid on the optical performance were investigated on the basis of the Lambert−Beer law. The numerical simulation model of the SBS hybrid PV/T system was built to evaluate the influence of the SiO₂ nanofluid concentration, optical path, and focusing ratio on the efficiency of the presented system. The following are the main conclusions obtained from the aforesaid discussion:

1) With the increasing concentration of SiO₂ nanofluid and optical path, its spectral transimissivity progressively decreases. When the concentration is 0.50 wt.% and the optical path exceeds 20 mm, its transimissivity to full-band solar radiation is almost 0.

2) In the nanofluid-based SBS hybrid PV/T system, a higher concentration leads to a lower electrical conversion efficiency and a higher thermal conversion efficiency. The overall system efficiency at a heat collection efficiency of 0.67 increases with increasing concentration of SiO₂ nanofluid and has a maximum value of 64.59% at 0.05 wt.%. Compared with the water-based SiO₂ nanofluid with 0.01 wt.%, the overall efficiency of the SiO₂ nanofluid with 0.05 and 0.50 wt.% increases by 0.71% and 0.33% per unit of concentration, respectively. However, the optimal SiO₂ nanofluid concentration with an overall efficiency improvement of 1.09% per unit of concentration is 0.10 wt.%, considering the overall efficiency and economic cost.

3) Increasing the optical path (from 0 to 30 mm) results in a 60.43% reduction in the electrical conversion efficiency as well as a 50.84% improvement in the overall system efficiency. The effect of increased overall system efficiency decreases with a higher optical path. This means that it does not benefit the overall system efficiency a great deal to increase the optical path from 10 to 30 mm. The overall system efficiency rises faster only at the optical path of 0–10 mm.

4) The overall system efficiency tends to increase first and then drop with increasing focusing ratios. The maximum overall system efficiency is 51.93% when the focusing ratio is 3, and the frequency divider fluid is 0.05 wt.% SiO₂.

The research on nanofluid-based SBS hybrid PV/T systems is a challenging and extensive endeavor. Based on the current results of simulation studies, it is possible to prepare and select binary or ternary nanofluids with optimal spectral response for PV cells to enhance solar energy utilization efficiency in SBS hybrid PV/T systems. Additionally, it is necessary to establish an outdoor PV/T system experimental platform taking into account external factors such as geographical location, ambient temperature, and climatic conditions. This will facilitate long-term stability and continuous operation characteristic studies.

References

[1] Li G, Li M, Taylor R. . Solar energy utilisation: Current status and roll-out potential. Applied Thermal Engineering, 2022, 209: 118285

[2] Liu D Y, Lei C X, Wu K. . A multidirectionally thermoconductive phase change material enables high and durable electricity via real-environment solar–thermal–electric conversion. ACS Nano, 2020, 14(11): 15738–15747

[3] Tang Z D, Gao Y, Cheng P. . Metal-organic framework derived magnetic phase change nanocage for fast-charging solar–thermal energy conversion. Nano Energy, 2022, 99: 107383

[4] LiW. Photovoltaic–photothermal–thermo–chemical comple-mentary solar energy utilization theory, method and system. Dissertation for the Doctoral Degree. Beijing: University of Chinese Academy of Sciences, 2018 (in Chinese)

[5] Kumar V S, Kumar R, Barthwal M, et al. A review on futuristic aspects of hybrid photovoltaic thermal systems (PV/T) in solar energy utilization: Engineering and technological approaches. Sustainable Energy Technologies and Assessments, 2022, 53(Part A): 102463

[6] Qi Y, Liu Z Y, Shi Y. . Size optimization of nanoparticle and stability analysis of nanofluids for spectral beam splitting hybrid PV/T system. Materials Research Bulletin, 2023, 162: 112184

[7] Bellos E, Tzivanidis C. Investigation of a nanofluid-based concentrating thermal photovoltaic with a parabolic reflector. Energy Conversion and Management, 2019, 180: 171–182

[8] Zhou B, Pei J, Nasir D M. . A review on solar pavement and photovoltaic/thermal (PV/T) system. Transportation Research Part D, Transport and Environment, 2021, 93: 102753

[9] Christiansen J, Vester-Petersen J, Roesgaard S. . Strongly enhanced upconversion in trivalent erbium ions by tailored gold nanostructures: Toward high-efficient silicon-based photovoltaics. Solar Energy Materials and Solar Cells, 2020, 208: 110406

[10] Lebbi M, Touafek K, Benchatti A. . Energy performance improvement of a new hybrid PV/T Bi-fluid system using active cooling and self-cleaning: Experimental study. Applied Thermal Engineering, 2021, 182: 116033

[11] Yu Q, Chan S, Chen K. . Numerical and experimental study of a novel vacuum photovoltaic/thermal (PV/T) collector for efficient solar energy harvesting. Applied Thermal Engineering, 2024, 236: 121580

[12] Margoum S, El Fouas C, Hajji B. . Modelling and performances assessment of a nanofluids-based PV/T hybrid collector. Energy Sources. Part A, Recovery, Utilization, and Environmental Effects, 2023, 45(1): 3070–3086

[13] Maka A O M, O’Donovan T S. A review of thermal load and performance characterisation of a high concentrating photovoltaic (HCPV) solar receiver assembly. Solar Energy, 2020, 206: 35–51

[14] Bayrak F, Oztop H F, Selimefendigil F. Experimental study for the application of different cooling techniques in photovoltaic (PV) panels. Energy Conversion and Management, 2020, 212: 112789

[15] Chauhan A, Tyagi V V, Anand S. Futuristic approach for thermal management in solar PV/thermal systems with possible applications. Energy Conversion and Management, 2018, 163: 314–354

[16] Deymi-Dashtebayaz M, Rezapour M. The effect of using nanofluid flow into a porous channel in the CPVT under transient solar heat flux based on energy and exergy analysis. Journal of Thermal Analysis and Calorimetry, 2021, 145(2): 507–521

[17] Yang M, Cao B Y. Numerical study on flow and heat transfer of a hybrid microchannel cooling scheme using manifold arrangement and secondary channels. Applied Thermal Engineering, 2019, 159: 113896

[18] Rosa-Clot M, Rosa-Clot P, Tina G M. . Submerged photovoltaic solar panel: SP2. Renewable Energy, 2010, 35(8): 1862–1865

[19] Rosa-Clot M, Rosa-Clot P, Tina G M. . Experimental photovoltaic–thermal power plants based on TESPI panel. Solar Energy, 2016, 133: 305–314

[20] Yazdanifard F, Ameri M, Taylor R A. Numerical modeling of a concentrated photovoltaic/thermal system which utilizes a PCM and nanofluid spectral splitting. Energy Conversion and Management, 2020, 215: 112927

[21] Hamada A T, Sharaf O Z, Orhan M F. Photovoltaic/thermal (PV/T) solar collectors employing phase-change nano-capsules as spectral filters: Coupled, decoupled, and partially-coupled configurations. Applied Thermal Engineering, 2024, 236(Part D): 121841

[22] CuiYZhuQ Z. Study of photovoltaic thermal systems with MgO-water nanofluids flowing over silicon solar cells. In: Proceedings of the 2012 Asia-Pacific Power and Energy Engineering Conference. Shanghai: IEEE, 2012

[23] Liu Y, Dong S, Liu Y. . Experimental investigation on optimal nanofluid-based PV/T system. Journal of Photonics for Energy, 2019, 9(2): 1

[24] Yu G, Yang H, Yan Z. . A review of designs and performance of façade-based building integrated photovoltaic-thermal (BIPVT) systems. Applied Thermal Engineering, 2021, 182: 116081

[25] Alsaqoor S, Alqatamin A, Alahmer A. . The impact of phase change material on photovoltaic thermal (PVT) systems: A numerical study. International Journal of Thermofluids, 2023, 18: 100365

[26] Ding F, Han X. Performance enhancement of a nanofluid filtered solar membrane distillation system using heat pump for electricity/water cogeneration. Renewable Energy, 2023, 210: 79–94

[27] BellagardaAGrassi DAlibertiA, . Effectiveness of neural networks and transfer learning to forecast photovoltaic power production. Applied Soft Computing,2023,149(Part A): 110988

[28] Seghiour A, Abbas H A, Chouder A. . Deep learning method based on autoencoder neural network applied to faults detection and diagnosis of photovoltaic system. Simulation Modelling Practice and Theory, 2023, 123: 102704

[29] Sharma R, Suhag S. Feedback linearization based control for weak grid connected PV system under normal and abnormal conditions. Frontiers in Energy, 2020, 14(2): 400–409

[30] Menbari A, Alemrajabi A A, Ghayeb Y. Experimental investigation of stability and extinction coefficient of Al₂O₃ –CuO binary nanoparticles dispersed in ethylene glycol–water mixture for low-temperature direct absorption solar collectors. Energy Conversion and Management, 2016, 108: 501–510

[31] Zhang C, Shen C, Zhang Y. . Optimization of the electricity/heat production of a PV/T system based on spectral splitting with Ag nanofluid. Renewable Energy, 2021, 180: 30–39

[32] Zhou Y P, Li M J, Hu Y H. . Design and experimental investigation of a novel full solar spectrum utilization system. Applied Energy, 2020, 260: 114258

[33] Han X, Wang Q, Zheng J. Determination and evaluation of the optical properties of dielectric liquids for concentrating photovoltaic immersion cooling applications. Solar Energy, 2016, 133: 476–484

[34] RenJ. Research on the control strategy of PV microgrid hybrid energy storage. Dissertation for the Doctoral Degree. Changsha: North Central University, 2021 (in Chinese)

[35] Hjerrild N E, Mesgari S, Crisostomo F. . Hybrid PV/T enhancement using selectively absorbing Ag–SiO₂/carbon nanofluids. Solar Energy Materials and Solar Cells, 2016, 147: 281–287

[36] Han X, Chen X, Wang Q. . Investigation of CoSO₄-based Ag nanofluids as spectral beam splitters for hybrid PV/T applications. Solar Energy, 2019, 177: 387–394

[37] Meraje W C, Huang C C, Barman J. . Design and experimental study of a Fresnel lens-based concentrated photovoltaic thermal system integrated with nanofluid spectral splitter. Energy Conversion and Management, 2022, 258: 115455

[38] Li W, Abd El-Samie M M, Zhao S. . Division methods and selection principles for the ideal optical window of spectral beam splitting photovoltaic/thermal systems. Energy Conversion and Management, 2021, 247: 114736

[39] ChenX B. Performance study of photovoltaic/thermal system based on Ag/CoSO₄ nanofluid spectral filtration. Dissertation for the Doctoral Degree. Zhenjiang: Jiangsu University, 2019 (in Chinese)

[40] HanX YXue D SGuoY J, . Analysis of the spectrally selective liquid optical properties of a concentrated frequency division PV/T system. Journal of Engineering Thermophy, 2017, 38(11): 2313−2319 (in Chinese)

[41] Hale G M, Querry M R. Optical constants of water in the 200 nm to 200 m wavelength region. Applied Optics, 1973, 12(3): 555–563

[42] Smith R C, Baker K S. Optical properties of the clearest natural waters (200–800 nm). Applied Optics, 1981, 20(2): 177–184

[43] Kent F, Palmer D W. Optical properties of water in the near infrared. Journal of the Optical Society of America, 1974, 64: 1107–1110

[44] ChenX B. Performance study of photovoltaic photothermal system based on Ag/CoSO₄ nanofluid spectral splitting. Dissertation for the Doctoral Degree. Zhenjiang: Jiangsu University, 2019 (in Chinese)

[45] SultanaT M GTaylorRRosengarten G. Performance of a linear Fresnel rooftop mounted concentrating solar collector. In: Proceedings of the 50th Australian Solar Energy Society Conference. Melbourne Australia, 2012

[46] Karthikeyan V, Sirisamphanwong C, Sukchai S. . Reducing PV module temperature with radiation based PV module incorporating composite phase change material. Journal of Energy Storage, 2020, 29: 101346

[47] Al-Shohani W A M, Al-Dadah R, Mahmoud S. Reducing the thermal load of a photovoltaic module through an optical water filter. Applied Thermal Engineering, 2016, 109: 475–486

[48] Balakin B V, Struchalin P G. Eco-friendly and low-cost nanofluid for direct absorption solar collectors. Materials Letters, 2023, 330: 133323

[49] Huo M, Zhang X, He J. Causality relationship between the photovoltaic market and its manufacturing in China, Germany, the US, and Japan. Frontiers in Energy, 2011, 5(1): 43–48

[50] Ahmed S, Ahshan K H N, Mondal M N A. . Application of metal oxides-based nanofluids in PV/T systems: A review. Frontiers in Energy, 2022, 16(3): 397–428

[51] Al-Shohani W A M, Sabouri A, Al-Dadah R. . Experimental investigation of an optical water filter for photovoltaic/thermal conversion module. Energy Conversion and Management, 2016, 111: 431–442

RIGHTS & PERMISSIONS

Higher Education Press 2024