Overall statement:

The study investigates the exergy and improvement potential of the hybrid photovoltaic thermal – thermoelectric system (PVT/TE) with air as the working fluid. A monocrystalline PV is used for the PV/T collector with a rating of 80 W and efficiency of 15%. While the thermoelectric module is characterized of having a voltage and current of 15.2 V and 6 A, respectively. Moreover, the analysis focuses on the exergy and exergy efficiency of the system under various mass flow rates. Moreover, the sustainability index (SI) and Improvement potential (IP) are both investigated for the presented system. Both theoretical and experimental investigations were carried out along with the error percentage.

A steady-state thermal analysis of a hybrid PVT/TE air collector is developed to predict air outlet and photovoltaic (PV) temperatures. The predicted results are in close agreement with the experimental study. The percentage error of air outlet and PV temperatures between theoretical and experimental value is 1.1% and 2.6% respectively. On the other hand, the simulated model is then used to study the performances of a hybrid PVT/TE air collector using exergy analysis for the mass flow rate ranging between 0.001 kg/s to 0.15 kg/s and a solar radiation of 600 W/m2. The effect of mass flow rate on exergy efficiency and an advance prospective are observed. The optimum exergy efficiency of PVT/TE obtained is relatively 0.38. In addition, IP is proposed in this study.

The strengths:

1) The introduction is well made; providing research background, problem statement a thorough literature review, which later in the following sections accumulate to Table 1. 2) The concept of exergy, the subject of the study, is well introduced and the steady-state thermal analysis is illustrated through equations and figures. 3) The review of previous works is well integrated into the study, allowing the authors to present the readers with valuable information and experiences from the literature, in addition to providing justifications for the analysis. 4) The results are discussed with respect to the objectives of the study and in light of other published studies, which were discussed in table 1, to provide the element of comparison, which is also provided in figure 11.

Weaknesses:

1. It is preferable to provide the irreversibility, or exergy destruction for the components individually, or for the system in total.
2. It is recommended to use the Root Mean Square Error in comparing the experiments with theoretical model; as it is a more accurate method.
3. It is not mentioned whether the TEC1-12706 modules were connected in series or parallel.

Conclusions and recommendations:

Overall, the paper presents an interesting step towards research in the area of PVT/TE systems and the use of exergy, IP, SI to assess the viability of these systems. The challenges surrounding air-based solar systems remains to be significant, from a commercial perspective. However, the advantages of such system could be viewed from an economic perspective in future studies, taken into account the operation and maintenance, and replacement costs of the thermoelectric module.

• This is a post-publication review. The adherence to journal guidelines is not considered as the paper has already been processed by the editorial team of the journal