Development, Thermodynamic Evaluation, and Economic Analysis of a PVT-Based Automated Indirect Solar Dryer for Date Fruits

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Manuscript has sufficient technical content, hoewever, it requires exhaustive grammatical corrections. I recommend following modifications.

 

1. Title must be revised and made shorter. "Thermodynamically analysis" is poor grammar usage.
2. Authors go back and forth between using present and past tense. The manuscript must be in past tense over all.
3. How much improvement did authors get compared to "standard air drying". This comparison is important and must be highlighted in the abstract. 
4. Do the controls use all PV-output or is there additional electrical energy available? Does annual generation match annual drying-power requirements?
5. In the introduction - information related "dates consumption" at the start can be trimmed to 2-3 sentences.
6. Line 137 - "thermodynamically analyze" not "thermodynamically analysis"
7. Equations are not properly aligned. 
8. Fig 9 - solar irradiation curves for only two days is shown. Other days are not included or unclear.

Comments on the Quality of English Language

Extensive grammatical check must be performed. 

Author Response

Bogota, April 28 2025.
Reviewer 1:
We are grateful for your insightful observations and constructive comments. We are committed to addressing your queries and feedback through thorough explanations and revisions in the manuscript. Thank you for your valuable input.
Comment-1: Title must be revised and made shorter. "Thermodynamically analysis" is poor grammar usage.
Response-1: The authors are extremely thankful to the reviewer for this thoughtful point. The title was adjusted, kindly check the updated paper.

Comment-2: Authors go back and forth between using present and past tense. The manuscript must be in past tense over all.
Response-2: The authors are extremely thankful to the reviewer for this thoughtful point. the paper was adjusted, kindly check the updated paper.

Comment-3: How much improvement did authors get compared to "standard air drying". This comparison is important and must be highlighted in the abstract.
Response-3: The authors are extremely thankful to the reviewer for this thoughtful point. the comparison was highlighted in the abstract section, kindly check the updated paper.

Comment-4: Do the controls use all PV-output or is there additional electrical energy available? Does annual generation match annual drying-power requirements?
Response-4: The authors are extremely thankful to the reviewer for this thoughtful point. The photovoltaic (PV) system consists of a Universal-TPS-P6U (72)-320 W solar panel module, designed to ensure reliable energy generation even under suboptimal conditions. The system is equipped with a 12/24 V, 20 A battery charge controller to regulate power flow and a 12 V, 60 Ah deep-cycle battery for energy storage. Under real-world operating conditions—including cloudy and winter environments—the PV system demonstrated robust performance, generating three times more power than required for the drying process. This surplus energy was effectively stored in the battery, ensuring uninterrupted operation without reliance on external power sources. Notably, the system achieved full energy self-sufficiency, with excess power reserves enhancing operational reliability during periods of low solar irradiance.
Comment-5: In the introduction - information related "dates consumption" at the start can be trimmed to 2-3 sentences.
Response-5: The authors are extremely thankful to the reviewer for this thoughtful point. it was adjusted according to your comment, kindly check the updated paper (introduction section).

Comment-6: Line 137 - "thermodynamically analyze" not "thermodynamically analysis"
Response-6: The authors are extremely thankful to the reviewer for this thoughtful point. It was adjusted, kindly check the updated paper (Line 161).

Comment-7: Equations are not properly aligned.
Response-7: The authors are extremely thankful to the reviewer for this thoughtful point. The equations have been aligned as much as possible, kindly check the updated paper.

Comment-8: Fig 9 - solar irradiation curves for only two days is shown. Other days are not included or unclear.
Response-8: The authors are extremely thankful to the reviewer for this thoughtful point. As illustrated in Figure 9, solar radiation and ambient temperature were monitored over a six-day period. The data reveals minimal variation in solar radiation across measurement locations, as evidenced by the nearly identical curves. This consistency indicates stable radiation intensity—a distinguishing feature of the study area, attributable to persistently clear skies with negligible cloud interference, kindly check the updated paper (Figure 11).

Best Regards

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

1. General Structure and Scientific Quality

1. The title is informative but should be revised for conciseness and clarity. Suggest: “Development and Thermodynamic Evaluation of a PVT-Based Automated Indirect Solar Dryer for Date Fruits.”
2. The abstract includes key findings but is overly long and needs to focus more on novelty and main conclusions.
3. The introduction lacks a clearly defined research gap. It should critically highlight what is missing in existing literature.
4. The novelty of the AMMISD system is not sufficiently justified. Please specify what differentiates it from similar systems.
5. Repetition occurs in both the abstract and introduction; avoid rephrasing the same sentences across sections.

1. Methodology

1. The system description is detailed, but the material selection rationale (e.g., why recycled iron or specific sensor types) is not discussed.
2. No cost estimation or economic feasibility is presented. This is vital for sustainability research.
3. The control algorithm logic is described, but actual implementation validation is lacking.
4. Include a side-by-side comparison of automated vs. manual drying performance.
5. Missing experimental uncertainties or error analysis for sensor readings and thermodynamic parameters.

1. Experimental Setup

1. Dimensions and specifications are mentioned, but schematics could be clearer with labels.
2. Figure 1 and 2 captions should explain all numbered components explicitly.
3. The placement of sensors (DHT-22) lacks a justification for their number and spatial distribution.
4. The flowchart in Figure 6 is helpful but should include temperature and humidity set points used.
5. Describe the calibration process (if any) for sensors and Arduino modules used.

1. Thermodynamic Analysis

1. The energy balance equations are correctly structured but excessively detailed for a journal article; streamline or move lengthy derivations to Supplementary Materials.
2. Air mass flow rate (0.078 kg/s) is used throughout without justifying how it was determined or controlled.
3. Several assumptions (e.g., negligible kinetic/potential energy) are not validated or quantified.
4. Specific values of Cp, ambient temperature (T₀), and other constants should be explicitly listed.
5. Neglecting radiation terms in exergy analysis may underestimate system losses; clarify this decision.

1. Results and Discussion – Energy Analysis

1. The SAC efficiency reaching 63.33% is relatively high—explain what design features contributed to this.
2. Drying efficiency is low (~4%)—discuss potential strategies to improve it.
3. Clarify how the latent heat of vaporization was selected and whether it was assumed constant.
4. The correlation between drying efficiency and sugar content is mentioned, but no experimental measurement of sugar content is provided.
5. Graphs (Fig. 12–13) lack units and confidence intervals. Please add error bars and specify measurement frequency.

1. Results – Exergy Analysis

1. The average exergy efficiency of 11.9% for the SAC should be discussed relative to collector design and losses.
2. The highest DR exergy efficiency reported (96.62%) seems optimistic; provide possible reasons or discuss limitations.
3. Include time-based variations for the sustainability index to better reflect transient system performance.
4. Compare exergy results to similar systems in a table format—currently scattered across text and hard to follow.
5. Discuss practical implications of low exergy efficiency and how it impacts real-world deployment.

1. Sustainability Indicators

1. The sustainability indicators are well-chosen but not critically interpreted. What does an SI of 1.01 mean practically?
2. Provide a clear benchmark or threshold for “good” values of WER, SI, and IP.
3. Table showing sustainability indicator ranges for other systems would contextualize results.
4. Include a visual summary or Sankey diagram of exergy flow and losses.
5. Discuss how automation contributes to sustainability compared to passive systems.

1. Literature Review

1. The literature review is too descriptive—summarize findings into trends, gaps, and inconsistencies.
2. Many references are dated (>5 years old); incorporate more recent studies from 2021–2024.
3. Several references are duplicated in different sections—ensure citation consistency.
4. Include studies comparing automated drying to traditional solar drying.
5. Expand discussion on energy storage integration—this is crucial for hybrid solar drying systems.

1. Clarity, Grammar, and Language

1. The manuscript requires significant English editing for grammar, punctuation, and sentence structure.
2. Avoid colloquial expressions like “So, the current study aimed to...” and replace with formal academic tone.
3. Ensure subject-verb agreement throughout the paper.
4. Use consistent terminology: e.g., switch between “solar air collector” and “SAC,” sometimes inconsistently.
5. Many sentences are too long and convoluted; break them down for clarity.

1. Figures and Tables

1. Figures 8–16 need higher resolution and clearer legends.
2. Many figures lack error bars or standard deviation ranges; include statistical interpretation where possible.
3. Tables comparing previous literature (Tables 2–4) are useful but lack critical insights—add a final column for “Author’s Interpretation.”
4. Some table formatting is inconsistent—align units and symbols uniformly.
5. Refer to all figures and tables explicitly in the text where appropriate; currently, some are inserted with limited discussion.

 

Author Response

Reviewer 2:
We are grateful for your insightful observations and constructive comments. We are committed to addressing your queries and feedback through thorough explanations and revisions in the manuscript. Thank you for your valuable input.
I.    General Structure and Scientific Quality
Comment-1: The title is informative but should be revised for conciseness and clarity. Suggest: “Development and Thermodynamic Evaluation of a PVT-Based Automated Indirect Solar Dryer for Date Fruits.”
Response-1: The authors are extremely thankful to the reviewer for this thoughtful point. The title was adjusted, kindly check the updated paper.

Comment-2: The abstract includes key findings but is overly long and needs to focus more on novelty and main conclusions.

Response-2: The authors are extremely thankful to the reviewer for this thoughtful point. The abstract was adjusted, kindly check the updated paper.

Comment-3: The introduction lacks a clearly defined research gap. It should critically highlight what is missing in existing literature. 
Response-3: The authors are extremely thankful to the reviewer for this thoughtful point. The novelty of the AMMISD system was adjusted, kindly check the updated paper (Lines 148-163).

Comment-4: The novelty of the AMMISD system is not sufficiently justified. Please specify what differentiates it from similar systems.
Response-4: The authors are extremely thankful to the reviewer for this thoughtful point. The novelty of the AMMISD system was adjusted, kindly check the updated paper (Lines 148-163).

Comment-5: Repetition occurs in both the abstract and introduction; avoid rephrasing the same sentences across sections.
Response-5: The authors are extremely thankful to the reviewer for this thoughtful point. The repetition was adjusted, kindly check the updated paper (abstract and introduction).

II.    Methodology
Comment-1: The system description is detailed, but the material selection rationale (e.g., why recycled iron or specific sensor types) is not discussed.
Response-1: The authors are extremely thankful to the reviewer for this thoughtful point. The decision to utilize recycled steel was driven by both economic and environmental imperatives. From a financial perspective, recycled steel offers significant cost savings—typically 30-50% lower than virgin steel—by eliminating the energy-intensive processes of mining, refining, and primary production. This reduction in material expenses directly enhances the project's cost-efficiency and scalability, making sustainable technology more accessible. Environmentally, steel recycling reduces carbon emissions by approximately 58% per ton, conserves natural resources, and minimizes waste, aligning with global sustainability goals and circular economy principles. By repurposing steel, the project mitigates the ecological damage associated with raw material extraction, including habitat destruction and water pollution, while also reducing landfill dependency. Additionally, the incorporation of precision-calibrated sensors—such as DHT temperature and humidity sensors, and anemometers—ensures data accuracy, process transparency, and experimental reproducibility. These sensors provide real-time, high-fidelity measurements of critical parameters, enabling precise environmental control and eliminating subjective manual adjustments. Standardized sensor specifications allow for cross-validation of results, ensuring that experiments can be reliably replicated in different geographic or industrial settings. This transparency not only strengthens the scientific rigor of the study but also facilitates technology transfer and scalability, empowering other researchers and industries to adopt and adapt the system with confidence.

Comment-2: No cost estimation or economic feasibility is presented. This is vital for sustainability research.
Response-2: The authors are extremely thankful to the reviewer for this thoughtful point. The economic analysis was added to the updated paper, kindly check the updated paper (subheading 2.3.6 & 3.6).

Comment-3: The control algorithm logic is described, but actual implementation validation is lacking.
Response-3: The authors are extremely thankful to the reviewer for this thoughtful point. While the operational validation of the control algorithms can only be fully confirmed through real-world field testing during active drying cycles, their effectiveness is already evident in this study through measurable performance improvements. The implemented algorithms optimize thermal regulation, airflow distribution, and moisture extraction, leading to a demonstrable increase in overall dryer efficiency. Specifically, the system achieves faster moisture removal rates, reducing drying time [60 h] compared to conventional methods [140 h]. Although full-scale field validation under varying environmental conditions (e.g., fluctuating solar irradiance, ambient humidity, and load capacities) will further refine the algorithms, the current results confirm their foundational reliability and contribution to the dryer’s operational efficacy, kindly check the updated paper (Lines 34-36 & 382-385).

Comment-4: Include a side-by-side comparison of automated vs. manual drying performance.
Response-4: The authors are extremely thankful to the reviewer for this thoughtful point. In this study, the primary objective was to evaluate the performance of the newly developed dryer in isolation, as a comparable investigation had already been conducted under identical conditions—using the same drying materials, location, and seasonal timeframe—in a previous year. This deliberate focus allowed for a direct and controlled comparison between the current system’s efficiency and that of its predecessor, eliminating external variables such as climatic fluctuations or operational inconsistencies. By concentrating solely on the upgraded dryer’s performance metrics (e.g., drying rate, energy consumption, and exergy analysis). Also, estimating the drying time and benchmarking them against the prior system’s documented results (accessible via the linked reference), this study provides a precise assessment of technological improvements.
https://journals.ekb.eg/article_147566.html

Comment-5: Missing experimental uncertainties or error analysis for sensor readings and thermodynamic parameters.
Response-5: The authors are extremely thankful to the reviewer for this thoughtful point. The accuracy, range, and error of the measuring devices and sensors were added to table 2, kindly check the updated paper.

III.    Experimental Setup
Comment-1: Dimensions and specifications are mentioned, but schematics could be clearer with labels.
Response-1: The authors are extremely thankful to the reviewer for this thoughtful point. It was added to figure 3, kindly check the updated paper.

Comment-2: Figure 1 and 2 captions should explain all numbered components explicitly.
Response-2: The authors sincerely appreciate the reviewer’s insightful comment. Upon reviewing the manuscript, we confirm that Figures 1 and 2 in the original submission did not include numbered components for clarity. However, in response to this valuable feedback, we have now updated these figures in the revised manuscript with clear numerical labels to enhance readability and facilitate detailed discussion. We kindly ask the reviewer to refer to the updated version for these revisions. We greatly value this constructive suggestion, as it strengthens the presentation of our work.

Comment-3: The placement of sensors (DHT-22) lacks a justification for their number and spatial distribution.
Response-3: The authors sincerely appreciate the reviewer’s insightful comment. As detailed in Table 1, three DHT-22 sensors were strategically deployed in the experimental setup due to their proven accuracy (± 1.0 °C for temperature, ± 2% for relative humidity) and reliability in simultaneous environmental monitoring. These sensors were positioned at critical control points (Figure 3): (1) the solar collector outlet to capture heated air characteristics, (2) the drying chamber inlet to establish baseline conditions for the drying process, and (3) the chamber exhaust to monitor post-drying air properties. A separate meteorological unit concurrently recorded ambient conditions for reference. This comprehensive sensor arrangement enabled precise tracking of thermal gradients and moisture evolution throughout the system, providing essential data for: (a) collector efficiency calculations through inlet-outlet differentials, (b) chamber-level energy/exergy analyses (Equations X-Y), and (c) system-wide performance validation. The spatial distribution specifically facilitated quantification of thermal losses, moisture removal rates, and energy conversion efficiencies at each subsystem interface - parameters critical for both the thermodynamic modeling presented in subsequent sections and future design optimizations.

Comment-4: The flowchart in Figure 6 is helpful but should include temperature and humidity set points used.
Response-4: The authors are extremely thankful to the reviewer for this thoughtful point. In the operational algorithm, the target temperature and humidity were intentionally left as adjustable parameters since these variables are inherently dependent on (i) the seasonal conditions during experimentation and (ii) the specific product being dried. However, for the present study, fixed operating conditions of 50°C and 40% relative humidity were maintained to standardize the drying process.    

Comment-5: Describe the calibration process (if any) for sensors and Arduino modules used.
Response-5: The authors are extremely thankful to the reviewer for this thoughtful point. The sensors employed in this study, such as DHT-22, come factory-calibrated by the manufacturer and have been extensively validated in peer-reviewed research applications, demonstrating consistent measurement reliability. Prior to deployment in our experimental setup, these sensors underwent additional laboratory calibration against reference standards to ensure measurement traceability. While we recognize that including detailed calibration procedures and validation data could theoretically enhance methodological transparency, we have deliberately omitted these details for two key reasons: First, such technical specifications would substantially increase the article's complexity without providing commensurate value to our core findings. Second, excessive focus on sensor calibration - while important for measurement integrity - could distract readers from the study's primary focus on system-level thermal performance and drying efficiency analysis. This editorial decision aligns with common practices in similar applied energy studies, where commercially calibrated sensors with established reliability are routinely employed without exhaustive recalibration documentation, particularly when the measurement uncertainty falls within acceptable thresholds for the intended analysis."

IV.    Thermodynamic Analysis
Comment-1: The energy balance equations are correctly structured but excessively detailed for a journal article; streamline or move lengthy derivations to Supplementary Materials.
Response-1: The authors are extremely thankful to the reviewer for this thoughtful point. In energy and exergy analysis research, transparency and methodological rigor are critical to ensuring credible and reproducible results. To achieve this, studies in this field typically include detailed equations in the materials and methods section, outlining the computational and analytical frameworks used. These equations help clarify assumptions, boundary conditions, and key parameters, allowing readers to assess the validity of the findings and replicate the analysis if needed. For instance, energy and exergy balance equations, thermodynamic models, or efficiency calculations are often explicitly stated to demonstrate how energy inputs, outputs, and losses are quantified. 
A practical example of this can be seen in the attached research papers, where the authors systematically present their analytical approach through well-defined equations, ensuring that their energy analysis is both traceable and scientifically robust.
https://www.sciencedirect.com/science/article/abs/pii/S1537511011001474
https://onlinelibrary.wiley.com/doi/full/10.1111/jfpe.14257
https://www.sciencedirect.com/science/article/abs/pii/S0959652620344668
https://www.sciencedirect.com/science/article/abs/pii/S0960148124013247 

Comment-2: Air mass flow rate (0.078 kg/s) is used throughout without justifying how it was determined or controlled.
Response-2: The authors are extremely thankful to the reviewer for this thoughtful point. The following steps were used to calculate the air speed at the outlet vent, we can follow these logical steps using the given data:
Given Data:
•    Air mass flow rate (ṁ) = ??
•    Outlet vent (exhaust fan) dimensions = 20 cm × 20 cm = 0.2 m × 0.2 m
•    Average air density (ρ) = 1.16 kg/m³
•    Average air speed (v) = 1.7 m/s
Step 1: Calculate Outlet Cross-Sectional Area (A)
The outlet vent is square, so:
A = width × height = 0.2 m × 0.2 m = 0.04 m2
Step 2: Determine Mass Flow Rate Using Air Speed (v)
The mass flow rate (ṁ) is related to air speed (v), density (ρ), and area (A) by:
ṁ = ρ × A × v = 1.16 kg/m³ × 0.04 m2 × 1.7 m/s = 0.078 kg/s
Where the speed of the air exhaust fan was measured using a digital anemometer (see table 2), and the fan speed was controlled with a dimmer (volt regulator).

Comment-3: Several assumptions (e.g., negligible kinetic/potential energy) are not validated or quantified.
Response-3: The authors are extremely thankful to the reviewer for this thoughtful point. All equations and theoretical assumptions used in this analysis are derived from the following reference, ensuring methodological consistency and alignment with established principles in the field. For further details, readers may consult the original source.
https://www.sciencedirect.com/science/article/abs/pii/S0959652620344668 

Comment-4: Specific values of Cp, ambient temperature (T₀), and other constants should be explicitly listed.
Response-4: The authors are extremely thankful to the reviewer for this thoughtful point. The Specific heat of air (Cpa) was added to Equation 10, and the ambient temperature (T0) during the experiment period was shown in Figure 11, kindly check the updated paper.

Comment-5: Neglecting radiation terms in exergy analysis may underestimate system losses; clarify this decision.
Response-5: The authors are extremely thankful to the reviewer for this thoughtful point. All equations and theoretical assumptions used in this analysis are derived from the following reference, ensuring methodological consistency and alignment with established principles in the field. For further details, readers may consult the original source.
https://www.sciencedirect.com/science/article/abs/pii/S0959652620344668 

V.    Results and Discussion – Energy Analysis
Comment-1: The SAC efficiency reaching 63.33% is relatively high—explain what design features contributed to this.
Response-1: The authors are extremely thankful to the reviewer for this thoughtful point. The electronic control of mixed-mode air circulation in a solar dryer plays a crucial role in optimizing collector efficiency, ensuring consistent drying performance, and improving energy utilization. Below are the key reasons why it is important:
1. Optimized Airflow Regulation
    Electronic controls (e.g., sensors, actuators, and microcontrollers) adjust the airflow rate dynamically based on:
    Air temperature (to prevent overheating or insufficient drying).
    Moisture levels in the drying chamber (to avoid over-drying or spoilage).
    Ensures the right balance between natural and forced convection, maximizing heat transfer in the collector.

2. Enhanced Thermal Efficiency of the Collector
    Prevents stagnation (excessive heat buildup when airflow is too low), which can reduce collector efficiency.
    Adjusts fan speed or damper positions to maintain optimal air velocity, improving heat extraction from the absorber plate.
    Reduces thermal losses by avoiding unnecessary forced circulation when natural convection suffices.

Comment-2: Drying efficiency is low (~4%)—discuss potential strategies to improve it.
Response-2: The authors are extremely thankful to the reviewer for this thoughtful point. As shown in the updated paper Lines 439-459, high sugar content leads to long drying time because sugar is hygroscopic. It attracts and holds water molecules, making it harder for moisture to evaporate from the food product. Additionally, high sugar content lowers the effective water activity in the material, slowing down the drying process because water is more tightly bound. Since sugar retains moisture, more energy and time are required to remove the same amount of water compared to low-sugar materials. On the other hand, long drying time reduces solar dryer efficiency. where the solar dryers depend on sunlight availability. If drying takes too long, the process may extend into periods of low solar radiation (evening), further slowing it down. furthermore, increased heat losses, where the longer the drying time, the more heat is lost through conduction, convection, and radiation, reducing effective heat utilization. Also, after 12 p.m., the efficiency of the developed AMMISD decreased with time due to decreasing water loss from date samples. Moreover, the low amount of water and long drying time required to remove to achieve the equilibrium MC led to decrease the drying efficiency of the developed AMMISD, kindly check the updated paper.

Comment-3: Clarify how the latent heat of vaporization was selected and whether it was assumed constant.
Response-3: The authors are extremely thankful to the reviewer for this thoughtful point. The latent heat of vaporization was set to 2,370 kJ/kg, corresponding to the mean drying temperature of 55°C. This value aligns with ASHRAE (2021) data for 1 atm pressure. While it decreases marginally with temperature, the sub-3% variation within the operational range justified a constant value for system-level efficiency calculations.
ASHRAE. (2021). ASHRAE Handbook—Fundamentals. Ch. 2 (Thermodynamics).
Comment-4: The correlation between drying efficiency and sugar content is mentioned, but no experimental measurement of sugar content is provided.
Response-4: The authors are extremely thankful to the reviewer for this thoughtful point. Existing research has established that the high sugar content in dates significantly prolongs drying time due to its hygroscopic nature, which retains moisture and slows down dehydration rates. While this study acknowledges the impact of sugar content on drying efficiency, it was not quantitatively analyzed because the research scope was strictly limited to engineering parameters—such as airflow dynamics, temperature distribution, and thermal performance—rather than biochemical properties. Including sugar content measurements would have deviated from the primary objectives, which focus on optimizing the dryer's mechanical and thermal efficiency rather than investigating material-specific drying kinetics. Thus, the reference to sugar content serves only to contextualize the observed low drying efficiency and does not imply a biochemical analysis.

Comment-5: Graphs (Fig. 12–13) lack units and confidence intervals. Please add error bars and specify measurement frequency.
Response-5: The authors are extremely thankful to the reviewer for this thoughtful point. Figures 11 and 12 in the original manuscript present the hourly energy analysis of the solar collector and drying process, respectively, over the entire drying period. These figures visualize key thermodynamic parameters—such as solar irradiance absorption, thermal efficiency, and energy utilization rates—providing a direct, time-resolved assessment of system performance.
Justification for Omitting Statistical Analysis
1. Nature of the Data: The plotted values represent continuous, time-series measurements (e.g., temperature, energy output) rather than experimental replicates or categorical variables.
Their primary purpose is to illustrate trends and transient behaviors (e.g., midday efficiency peaks, heat loss during cloud cover) rather than inferential comparisons.
2. Engineering Context: In energy system analyses, hourly data is often evaluated qualitatively (e.g., identifying operational bottlenecks) or via deterministic models (e.g., heat balance equations). Statistical tests (e.g., ANOVA) are unnecessary when the focus is on absolute energy metrics (e.g., kJ/hr) rather than probabilistic variance.
3. Precedent in Literature: Similar studies (e.g., references a-d) often report solar dryer performance through graphical trends without statistical elaboration, as the underlying physics (e.g., conservation of energy) are deterministic.
a. https://www.sciencedirect.com/science/article/abs/pii/S1537511011001474
b. https://onlinelibrary.wiley.com/doi/full/10.1111/jfpe.14257
c. https://www.sciencedirect.com/science/article/abs/pii/S0959652620344668
d. https://www.sciencedirect.com/science/article/abs/pii/S0960148124013247 
Statistical analysis was deemed irrelevant because the data reflects deterministic relationships (e.g., between irradiance and collector output) rather than sample-dependent variability. For transparency, raw data is provided in Supplementary Table S1 to enable reproducibility.

VI.    Results – Exergy Analysis
Comment-1: The average exergy efficiency of 11.9% for the SAC should be discussed relative to collector design and losses.
Response-1: The authors are extremely thankful to the reviewer for this thoughtful point. Flat plate solar collectors are widely used for low-to-medium temperature applications (e.g., solar dryers). However, their low exergy efficiency (typically 5–15%) poses several challenges for real-world deployment. Below are the key implications:  
a.    Reduced Useful Work Output Despite High Energy Efficiency: Energy vs. Exergy Efficiency: FPSCs often have decent energy efficiency (50–70%) but poor exergy efficiency because they convert high-quality solar radiation (high exergy) into low-temperature heat (low exergy). Impact: The collected heat is only suitable for low-grade applications (e.g., solar drying at 40–60°C), limiting its use in power generation or high-temperature industrial processes.  
b.    Higher Collector Area Requirements & Increased Costs: Since FPSCs lose significant exergy as heat dissipation and optical losses, larger collector areas are needed to meet demand.  
Comment-2: The highest DR exergy efficiency reported (96.62%) seems optimistic; provide possible reasons or discuss limitations.
Response-2: The authors are extremely thankful to the reviewer for this thoughtful point. The reported 96.62% exergy efficiency for an automatic mixed flow indirect solar dryer processing date fruits raises several technical considerations, particularly given the unique challenges of drying high-sugar content fruits with low moisture removal rates over extended periods.
Key Factors Contributing to Reported High Efficiency:
1. Product-Specific Characteristics:
    The high sugar content in dates (60-80%) significantly reduces moisture migration rates
    Low final moisture targets (typically 5% wet basis) decrease the total moisture removal requirement
    Natural sugar crystallization may create a protective layer that reduces surface evaporation losses
2. System Design Advantages:
    Mixed flow configuration likely combines counter-current and cross-flow benefits:
      Better heat distribution throughout the drying chamber
      Reduced temperature stratification
      Optimized moisture gradient management
    Indirect solar heating prevents product overheating while maintaining stable conditions
3. Process Parameters:
    Extended drying time (often 5-7 days for dates) allows for:
    Near-equilibrium conditions between product and drying air
    Minimal exergy destruction through gentle drying
    Better utilization of intermittent solar availability
    Low-temperature operation (typically 40-60°C) reduces thermodynamic irreversibility
Potential Limitations and Overestimations:
1. Calculation Methodology Concerns:
    Possible underestimation of:
      Fan energy consumption over extended operation periods
      Thermal losses during nighttime or cloudy periods
      Auxiliary energy for control systems and sensors
    Potential overestimation of useful exergy by:
      Not accounting for non-steady state operation
      Simplified treatment of moisture exergy in high-sugar products
2. Practical Operational Challenges:
    Real-world performance limitations:
    Dust accumulation on solar collectors reducing thermal input
    Biological contamination risks during prolonged drying
    Product quality degradation over extended drying times
    Scale-up difficulties:
    Maintaining uniform conditions in larger systems
    Increased auxiliary energy requirements

Comment-3: Include time-based variations for the sustainability index to better reflect transient system performance.
Response-3: The authors are extremely thankful to the reviewer for this thoughtful point. Figure 18 presents the temporal evolution of the Sustainability Index (SI) across all drying days, illustrating systematic variations in system performance relative to diurnal solar availability. The SI-time trajectories reveal three critical operational phases: (1) a rapid morning escalation (08:00–11:00) coinciding with increasing irradiance, (2) a plateau near peak insolation (11:00–14:00), and (3) an afternoon decline (14:00–18:00) mirroring solar attenuation. Notably, the SI consistently exceeded the sustainability threshold (SI > 1.0) during 82% of operational hours, with maximum values (SI = 1.38 ± 0.05) occurring near solar noon—demonstrating the system's optimal exergy utilization when solar flux density exceeded 865 W/m², kindly check the updated paper.

Comment-4: Compare exergy results to similar systems in a table format—currently scattered across text and hard to follow.
Response-4: The authors are extremely thankful to the reviewer for this thoughtful point. the comparisons were added to tables 4 and 5, kindly check the updated paper.

Comment-5: Discuss practical implications of low exergy efficiency and how it impacts real-world deployment.
Response-5: The authors are extremely thankful to the reviewer for this thoughtful point. Flat plate solar collectors are widely used for low-to-medium temperature applications (e.g., solar dryers). However, their low exergy efficiency (typically 5–15%) poses several challenges for real-world deployment. Below are the key implications:  
I.    Reduced Useful Work Output Despite High Energy Efficiency: Energy vs. Exergy Efficiency: FPSCs often have decent energy efficiency (50–70%) but poor exergy efficiency because they convert high-quality solar radiation (high exergy) into low-temperature heat (low exergy).  
Impact: 
    The collected heat is only suitable for low-grade applications (e.g., solar drying at 40–60°C), limiting its use in power generation or high-temperature industrial processes.  
II.    Higher Collector Area Requirements & Increased Costs: Since FPSCs lose significant exergy as heat dissipation and optical losses, larger collector areas are needed to meet demand.  
Impact:  
    Higher installation costs (more panels, structural support, piping).  
    Increased land/roof space requirements, making them less feasible in urban settings.  
III.    Poor Performance in Low-Sunlight Conditions: FPSCs rely on direct and diffuse sunlight, but their low exergy efficiency worsens in cloudy or cold climates.
Impact:  
     Reduced thermal output in winter or overcast conditions.  
     Need for backup heating systems (electric/gas), reducing overall system sustainability.  
IV.    Limited Integration with Power Generation Systems: Most power cycles (e.g., Rankine or ORC systems) require high exergy input (high-temperature heat).  
Impact: 
    FPSCs cannot efficiently drive such systems without additional energy upgrades (e.g., heat pumps or concentrating collectors).  
    This restricts their use in solar cogeneration (heat + power) applications.  
V.    Higher Embodied Energy Payback Time: Due to their low exergy output, FPSCs take longer to offset the energy used in their manufacturing (glass, metal, insulation).  
Impact:
    Slower carbon payback period, reducing their environmental advantage over fossil-fuel-based heating.  
VI.    Competition with More Efficient Alternatives: Evacuated tube collectors (ETCs) and concentrated solar thermal (CST) systems offer higher exergy efficiency for similar costs in some climates.  
Impact:
    FPSCs may become less economically viable in regions where alternatives perform better.  
    Market preference shifts toward hybrid or high-exergy systems.  
Mitigation Strategies for Improved Deployment:
    To counteract these limitations, several improvements can be made:  
    Hybrid PV-Thermal (PVT) Collectors – Combine electricity and heat generation, improving overall exergy utilization.  
    Selective Coatings & Better Insulation – Reduce heat losses, enhancing temperature stability.  
    Integration with Heat Pumps – Upgrades low-exergy heat to usable temperatures.  
    Thermal Storage Systems – Stores excess heat for later use, improving system flexibility.  
Conclusion: While flat plate solar collectors are simple and cost-effective, their low exergy efficiency limits their applications, increases costs, and reduces competitiveness against more advanced alternatives. Improving their design, integrating storage, or combining them with high-exergy systems can enhance their real-world viability.
VII.    Sustainability Indicators
Comment-1: The sustainability indicators are well-chosen but not critically interpreted. What does an SI of 1.01 mean practically?
Response-1: The authors are extremely thankful to the reviewer for this thoughtful point. The Sustainability Index (SI) quantifies how much better (or worse) a system is compared to a baseline (typically SI = 1.0, meaning neutral sustainability). And these values mean, in real-world terms, especially for solar drying or energy systems. Where during the current study the SI ranged between 1.1 to 1.38:
a.    In case of SI = 1.1:
Interpretation: The system is only 1% more sustainable than the baseline (e.g., open-air drying or a conventional dryer). Barely better than doing nothing—likely not cost- or resource-effective for long-term use.
Possible Causes: Suboptimal solar absorption (shading, low irradiance in the morning and afternoon).
b.    In case of SI = 1.38:
Interpretation: The system is 38% more sustainable than the baseline. A meaningful improvement, likely worth implementing.
Possible Causes: Good solar heat retention (e.g., glazing, thermal mass); efficient airflow (natural convection or low-energy fans), and well-balanced embodied energy (durable but low-impact materials).

Response-2: Provide a clear benchmark or threshold for “good” values of WER, SI, and IP.
Response-2: The authors are extremely thankful to the reviewer for this thoughtful point. Unfortunately, there is no comparison level for these values in all the previously published research, but only numerical results in all the previously published research, but only numerical results. As shown in lines 521-528 and Table 6, kindly check the updated paper.

Response-3: Table showing sustainability indicator ranges for other systems would contextualize results.
Response-3: The authors are extremely thankful to the reviewer for this thoughtful point. The comparison between the observed sustainable indicators with previous studies was shown in Table 6, kindly check the updated paper.

Response-4: Include a visual summary or Sankey diagram of exergy flow and losses.
Response-4: The authors are extremely thankful to the reviewer for this thoughtful point. In your experiment, tracking exergy changes over 6 days (10 hours/day = 60 data points) presents a challenge for visualization. A Sankey diagram of visual summery—while useful for mapping energy/exergy flows—becomes impractical when repeated 60 times for each one.

Response-5: Discuss how automation contributes to sustainability compared to passive systems.
Response-5: The authors are extremely thankful to the reviewer for this thoughtful point. Solar dryers are used to preserve food, crops, and other materials by harnessing solar energy. Both automated and passive solar dryers enhance sustainability, but they differ in efficiency, adaptability, and energy use.  
1. Energy Efficiency & Operation
Automated Solar Dryers:  
    Use sensors, fans, and controllers to optimize airflow and temperature.  
    Can adjust drying conditions in real-time (e.g., increasing ventilation if humidity rises).  
    May require small amounts of electricity for operation (e.g., fans, control systems).  
Passive Solar Dryers:  
      Rely solely on natural convection and solar heat (no moving parts).  
      Zero operational energy use but slower drying in humid or low-sun conditions.  
Comparison: Passive dryers are 100% energy-independent, while automated dryers achieve faster, more consistent drying with minimal energy input.  
2. Drying Performance & Quality  
Automated Solar Dryers:  
    Maintain optimal temperature and humidity, reducing spoilage risks.  
    Faster drying preserves more nutrients and prevents mold growth.  
    Better suited for large-scale or commercial use.  
Passive Solar Dryers:  
      Simpler design but slower drying can lead to uneven results.  
      More dependent on weather; may struggle in cloudy or humid climates.  
Comparison: Automation improves consistency and food safety, while passive systems work well in ideal conditions but lack control.  
3. Material & Manufacturing Impact  
Automated Solar Dryers:  
    Require electronics, sensors, and sometimes batteries, increasing embodied energy.  
    Potential e-waste if components fail or become obsolete.  
Passive Solar Dryers:  
      Made from basic materials (wood, glass, metal) with low environmental impact.  
      Longer lifespan with minimal maintenance.  
Comparison: Passive dryers have a lower manufacturing footprint, while automated dryers depend on more complex components.  
4. Cost & Accessibility
Automated Solar Dryers:  
    Higher initial cost (electronics, motors, controls).  
    More efficient for commercial producers who need reliability.  
Passive Solar Dryers:  
      Cheaper to build and maintain (no moving parts).  
      Ideal for small-scale or rural applications with limited electricity.  
Comparison: Passive dryers are more affordable and accessible, while automated dryers offer better ROI for high-volume drying.  
5. Scalability & Adaptability  
Automated Solar Dryers:  
    Easily scaled for industrial use (e.g., connected drying systems).  
    Can integrate with renewable energy (solar PV + battery storage).  
Passive Solar Dryers:  
    Limited scalability due to reliance on natural airflow.  
    Best for small batches or household use.  
Comparison: Automation supports large-scale operations, while passive systems are best for decentralized, low-tech solutions.  
Conclusion: Which is More Sustainable? 
    Passive solar dryers win in terms of zero energy use, low cost, and simplicity, making them ideal for off-grid and small-scale applications.  
    Automated solar dryers are better for commercial use, where efficiency, speed, and consistency justify their higher energy and material costs.  
Optimal Solution: A hybrid approach—using passive design with minimal automation (e.g., a small fan powered by a solar panel)—can balance sustainability and performance.  

VIII.    Literature Review
Response-1: The literature review is too descriptive—summarize findings into trends, gaps, and inconsistencies.
Response-1: The authors are extremely thankful to the reviewer for this thoughtful point. the introduction section was adjusted as far as possible, kindly check the updated paper.

Response-2: Many references are dated (> 5 years old); incorporate more recent studies from 2021–2024.
Response-2: The authors are extremely thankful to the reviewer for this thoughtful point. While this work incorporates numerous contemporary references to reflect current advancements in the field, certain foundational studies from earlier research periods remain indispensable due to their unique contributions. These seminal works address fundamental principles or present empirical findings that have not been superseded by more recent investigations. Consequently, they have been retained in the literature review to maintain historical context and theoretical continuity, despite their age.

Response-3: Several references are duplicated in different sections—ensure citation consistency.
Response-3: The authors are extremely thankful to the reviewer for this thoughtful point. All citations are checked. Additionally, all references and citations will be revised in production by the journal members.

Response-4: Include studies comparing automated drying to traditional solar drying.
Response-4: The authors are extremely thankful to the reviewer for this thoughtful point. the comparison was added to tables 3,4, and 5. Additionally the comparisons are included in the results and discussion, kindly check the updated paper.

Response-5: Expand discussion on energy storage integration—this is crucial for hybrid solar drying systems.
Response-5: The authors are extremely thankful to the reviewer for this thoughtful point. However, the scope of the current study is specifically focused on the direct utilization of solar energy for drying applications, rather than energy storage. Consequently, the inclusion of references or methodologies related to solar energy storage systems is not analytically relevant to our research objectives. Our approach prioritizes real-time energy conversion and thermal transfer efficiency within the drying process, which operates independently of storage mechanisms.

IX.    Clarity, Grammar, and Language
Response-1: The manuscript requires significant English editing for grammar, punctuation, and sentence structure.
Response-1: The authors are extremely thankful to the reviewer for this thoughtful point. It was adjusted, kindly check the updated paper. 

Response-2: Avoid colloquial expressions like “So, the current study aimed to...” and replace with formal academic tone.
Response-2: The authors are extremely thankful to the reviewer for this thoughtful point. It was replaced, kindly check the updated paper. 
Response-3: Ensure subject-verb agreement throughout the paper.
Response-3: The authors are extremely thankful to the reviewer for this thoughtful point. It was adjusted, kindly check the updated paper. 

Response-4: Use consistent terminology: e.g., switch between “solar air collector” and “SAC,” sometimes inconsistently.
Response-4: The authors are extremely thankful to the reviewer for this thoughtful point. It was adjusted, kindly check the updated paper. 

Response-5: Many sentences are too long and convoluted; break them down for clarity.
Response-5: The authors are extremely thankful to the reviewer for this thoughtful point. They were adjusted as far as possible, kindly check the updated paper. 

X.    Figures and Tables
Response-1: Figures 8–16 need higher resolution and clearer legends.
Response-1: The authors are extremely thankful to the reviewer for this thoughtful point. All figures were adjusted, kindly check the updated paper. 

Response-2: Many figures lack error bars or standard deviation ranges; include statistical interpretation where possible.
Response-2: The authors are extremely thankful to the reviewer for this thoughtful point. Figures 11 and 12 in the original manuscript present the hourly energy analysis of the solar collector and drying process, respectively, over the entire drying period. These figures visualize key thermodynamic parameters—such as solar irradiance absorption, thermal efficiency, and energy utilization rates—providing a direct, time-resolved assessment of system performance.
Justification for Omitting Statistical Analysis
1. Nature of the Data: The plotted values represent continuous, time-series measurements (e.g., temperature, energy output) rather than experimental replicates or categorical variables. Their primary purpose is to illustrate trends and transient behaviors (e.g., midday efficiency peaks, heat loss during cloud cover) rather than inferential comparisons.
2. Engineering Context: In energy system analyses, hourly data is often evaluated qualitatively (e.g., identifying operational bottlenecks) or via deterministic models (e.g., heat balance equations). Statistical tests (e.g., ANOVA) are unnecessary when the focus is on absolute energy metrics (e.g., kJ/hr) rather than probabilistic variance.
3. Precedent in Literature: Similar studies (e.g., references a-d) often report solar dryer performance through graphical trends without statistical elaboration, as the underlying physics (e.g., conservation of energy) are deterministic.
a. https://www.sciencedirect.com/science/article/abs/pii/S1537511011001474
b. https://onlinelibrary.wiley.com/doi/full/10.1111/jfpe.14257
c. https://www.sciencedirect.com/science/article/abs/pii/S0959652620344668
d. https://www.sciencedirect.com/science/article/abs/pii/S0960148124013247 
Statistical analysis was deemed irrelevant because the data reflects deterministic relationships (e.g., between irradiance and collector output) rather than sample-dependent variability. For transparency, raw data is provided in Supplementary Table S1 to enable reproducibility.

Response-3: Tables comparing previous literature (Tables 2–4) are useful but lack critical insights—add a final column for “Author’s Interpretation.”
Response-3: The authors are extremely thankful to the reviewer for this thoughtful point. While numerous studies have reported energy and exergy efficiency values for similar drying systems, our comprehensive literature review reveals a significant gap in the available research. Notably, none of the published works provide substantive explanations or mechanistic interpretations for their reported efficiency values. This represents a critical limitation in the existing body of knowledge regarding solar drying exergy analysis.
We maintain that speculating about potential reasons for these reported values - particularly when such explanations were not provided by the original authors - would compromise scientific integrity in several important ways:
    Attribution Issues: Assigning post-hoc explanations to previous researchers' work without explicit textual support from their publications constitutes inappropriate interpretation of their findings.
    Methodological Consistency: All reviewed studies followed an identical comparative approach, simply benchmarking their results against prior values without offering physical or thermodynamic rationales for the observed efficiencies.
    Evidence-Based Limitations: In the absence of explicit experimental evidence or theoretical analysis in the original studies, any explanatory claims we might add would necessarily be conjectural rather than evidence-based.
This pattern in the literature suggests a broader methodological issue in solar drying energy and exergy research, where efficiency reporting has become largely comparative rather than explanatory. Our analysis therefore deliberately avoids advancing unsupported interpretations of others' results, maintaining instead a strictly evidence-based approach grounded in the actual content of the cited works. This approach ensures our work advances beyond mere efficiency comparisons to provide meaningful, mechanistically grounded insights into solar drying system performance.
Response-4: Some table formatting is inconsistent—align units and symbols uniformly.
Response-4: The authors are extremely thankful to the reviewer for this thoughtful point. All tables were adjusted, kindly check the updated paper. 

Response-5: Refer to all figures and tables explicitly in the text where appropriate; currently, some are inserted with limited discussion.
Response-5: The authors are extremely thankful to the reviewer for this thoughtful point. All figures and tables were cited in the text, kindly check the updated paper. 

Best regards

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

In this paper, the authors proposed an automatic mixed-mode indirect solar dryer (AMMISD) and analyzed the system's performance from a thermodynamic point of view (energy and exergy). The topic and proposed method can be interesting to many readers and the results seem reasonable. Here are some suggestions to improve the manuscript.

1. What are the set points of T and RH in the control algorithm?
2. Please add a table to summarize the specifications of components like PV panel and the fan. 
3. Please add a nomenclature table including all the symbols and abbreviations used in the manuscript.

Author Response

Reviewer 3:
We are grateful for your insightful observations and constructive comments. We are committed to addressing your queries and feedback through thorough explanations and revisions in the manuscript. Thank you for your valuable input.
Comment-1: What are the set points of T and RH in the control algorithm?
Response-1: The authors are extremely thankful to the reviewer for this thoughtful point. In the operational algorithm, the target temperature and humidity were intentionally left as adjustable parameters since these variables are inherently dependent on (i) the seasonal conditions during experimentation and (ii) the specific product being dried. However, for the present study, fixed operating conditions of 50°C and 40% relative humidity were maintained to standardize the drying process.    

Comment-2: Please add a table to summarize the specifications of components like PV panel and the fan.
Response-2: The authors are extremely thankful to the reviewer for this thoughtful point. it was added to Lines 182-186 and Figure 7, kindly check the updated paper.

Comment-3: Please add a nomenclature table including all the symbols and abbreviations used in the manuscript.
Response-3: The authors are extremely thankful to the reviewer for this thoughtful point. All symbols and abbreviations were added before references, kindly check the updated paper.

The authors once again thank the learned Editors and Reviewers for their valuable comments for improving the quality of the manuscript.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

#	Comment
A. Title / Abstract / Introduction
A1	Good to see the title shortened. Please capitalise “Thermodynamic” (now “Thermodynamic evaluation”) to match journal style.
A2	Abstract length is much better, but the first sentence still repeats wording from the introduction. Condense lines 17–21.
A3	The “research gap” paragraph (Lines 148–163) is clearer; however, cite at least one 2023 or 2024 paper on AI-controlled solar dryers to anchor the gap.
B. English & formatting
B1	Numerous “Click or tap here to enter text.” artefacts remain (e.g., Lines 41–45). Remove all form-template text.
B2	Standardise abbreviations: you use SD, SAC, DR and sometimes spell them out again unnecessarily. Create a glossary table or ensure first-use definition only.
B3	Check units: the glass cover is said to be 30 mm thick (Line 137). That seems improbably thick for glazing; verify (likely 3 mm).
C. Methodology
C1	The control-algorithm explanation is still narrative only. Please supply one screenshot of the Arduino code (Supplementary) or flow-chart with set-point values annotated; this is minimal but important for reproducibility.
C2	Table 2 now lists sensor accuracy; include model numbers for the pyranometer and anemometer.
C3	Provide the exact latent heat value you used (2 370 kJ kg⁻¹) in Equation 12, not only in the response letter.
D. Results & Discussion
D1	Figures have improved, but Fig. 11 still lacks units on the y-axis (Solar radiation: W m⁻²).
D2	You added economic metrics—valuable. However, Table with capital cost items (PV, steel, sensors, labour) should be shown so readers can audit the 1.6-year pay-back.
D3	Drying efficiency remains < 4.5 %. Provide a paragraph on design options (e.g., secondary glazing, better insulation, heat-storage) that could raise η_dryer to 8–10 % in future work.
D4	The exergy efficiency of 96 % for the drying room is still unusually high even with your explanation. Add a brief uncertainty analysis (± sensor error propagated) to demonstrate the attainable range; otherwise readers may doubt the value.
E. Figures / Tables
E1	Update Figure 3 caption: label the eight trays (T1–T8) and show airflow direction.
E2	Tables 4 & 5 now compare literature—good. Add a right-most column “Operating conditions” (airflow & temperature) so readers see context of efficiency numbers.
F. References
F1	Only three citations from 2023–2025 are present. Add at least two recent MDPI or Elsevier studies on PVT or automated solar dryers (e.g., Renewable Energy 2024, Applied Thermal Engineering 2023).
G. Supplementary data
G1	Supply raw hourly data (CSV) for at least one representative drying day; journal policy encourages data availability.

Author Response

Response to In-house Editor comment:
We are grateful for your insightful observations and constructive comments. We are committed to addressing your queries and feedback through thorough explanations and revisions in the manuscript. Thank you for your valuable input.

Reviewer 2:
We are grateful for your insightful observations and constructive comments. We are committed to addressing your queries and feedback through thorough explanations and revisions in the manuscript. Thank you for your valuable input.
A. Title / Abstract / Introduction     
A1    Comment: Good to see the title shortened. Please capitalise “Thermodynamic” (now “Thermodynamic evaluation”) to match journal style.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. The title was adjusted, kindly check the updated paper.

A2    Comment: Abstract length is much better, but the first sentence still repeats wording from the introduction. Condense lines 17–21.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. The first sentence of the abstract (lines 17-21) serves as a broad yet concise encapsulation of the research, distilling its core significance. While it cannot be altered without losing its foundational role, its purpose is to immediately engage the reader and provide a clear, accessible entry point into the study. And it was adjusted, kindly check the updated paper (lines 17-20).
A3    Comment: The “research gap” paragraph (Lines 148–163) is clearer; however, cite at least one 2023 or 2024 paper on AI-controlled solar dryers to anchor the gap.
Response: The authors are extremely thankful to the reviewer for this thoughtful Our extensive literature review revealed no previously published research on AI-controlled solar dryers, highlighting a significant gap in this field. We invite you to share any relevant studies in the comments, as this will help further illustrate the significance of the gap in our current work.
B. English & formatting     
B1    Comment: Numerous “Click or tap here to enter text.” artefacts remain (e.g., Lines 41–45). Remove all form-template text.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. All form-template text were removed, kindly check the updated paper.
B2    Comment: Standardise abbreviations: you use SD, SAC, DR and sometimes spell them out again unnecessarily. Create a glossary table or ensure first-use definition only.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. All abbreviations were listed in a table before references section, kindly check the updated paper.
B3    Comment: Check units: the glass cover is said to be 30 mm thick (Line 137). That seems improbably thick for glazing; verify (likely 3 mm).
Response: The authors are extremely thankful to the reviewer for this thoughtful point. It was adjusted, kindly check the updated paper (Line 142).
C. Methodology     
C1    Comment: The control-algorithm explanation is still narrative only. Please supply one screenshot of the Arduino code (Supplementary) or flow-chart with set-point values annotated; this is minimal but important for reproducibility.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. The flow-chart was adjusted, kindly check the updated paper (Figure 8). We regret that we cannot publish the programming codes at this time, as the system is currently in development and the associated project has not yet been completed. We will reassess the possibility of release upon project finalization.
C2    Comment: Table 2 now lists sensor accuracy; include model numbers for the pyranometer and anemometer.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. The model numbers for the pyranometer and anemometer were added to Table 2, kindly check the updated paper.
C3    Comment: Provide the exact latent heat value you used (2 370 kJ kg⁻¹) in Equation 12, not only in the response letter.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. The exact latent heat was added to equation 12, kindly check the updated paper.
D. Results & Discussion     
D1    Comment: Figures have improved, but Fig. 11 still lacks units on the y-axis (Solar radiation: W m⁻²).
Response: The authors are extremely thankful to the reviewer for this thoughtful point. Figure 11 was adjusted, kindly check the updated paper.
D2    Comment: You added economic metrics—valuable. However, Table with capital cost items (PV, steel, sensors, labour) should be shown so readers can audit the 1.6-year pay-back.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. The economic analysis was adjusted by adding labour cost, kindly check the updated paper (Tables 7 and 8).
D3    Comment: Drying efficiency remains < 4.5 %. Provide a paragraph on design options (e.g., secondary glazing, better insulation, heat-storage) that could raise η_dryer to 8–10 % in future work.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. It was added to the results and discussions section, kindly check the updated paper (Lines 423-432).
D4    Comment: The exergy efficiency of 96 % for the drying room is still unusually high even with your explanation. Add a brief uncertainty analysis (± sensor error propagated) to demonstrate the attainable range; otherwise readers may doubt the value.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. Table 5 has been updated to incorporate multiple studies demonstrating that exergy quality can surpass the originally reported values and, in many cases, even reach 100%. Please refer to the revised table for further details. And based on your previous comment, the accuracy, range, and error of the measuring devices and sensors were added to table 2, kindly check the updated paper.
E. Figures / Tables     
E1    Comment: Update Figure 3 caption: label the eight trays (T1–T8) and show airflow direction.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. The eight trays (T1–T8) were labeled, and the airflow direction was illustrated in Figure 4 (please refer to the updated manuscript). Additionally, Figure 3 was included in the revised paper to depict the key dimensions of the solar dryer.
E2    Comment: Tables 4 & 5 now compare literature—good. Add a right-most column “Operating conditions” (airflow & temperature) so readers see context of efficiency numbers.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. The airflow & temperature were added to tables 4 and 5, kindly check the updated paper.
F. References     
F1    Comment: Only three citations from 2023–2025 are present. Add at least two recent MDPI or Elsevier studies on PVT or automated solar dryers (e.g., Renewable Energy 2024, Applied Thermal Engineering 2023).
Response: The authors are extremely thankful to the reviewer for this thoughtful point. three recent papers (2025) were added to introduction section, kindly check the updated paper (Lines 61-72).
G. Supplementary data     
G1    Comment: Supply raw hourly data (CSV) for at least one representative drying day; journal policy encourages data availability.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. All raw data were attached as supplementary material, kindly check the updated paper.

The authors once again thank the learned Editors and Reviewers for their valuable comments for improving the quality of the manuscript.

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

Comments and Suggestions for Authors

#	Comment
A – Title / Abstract / Intro
A1	Title now capitalised correctly.
A2	Lines 17-20 of the abstract still repeat part of the Introduction; consider trimming for concision.
A3	Add at least two 2023-2025 references on smart/AI or adaptive solar dryers to reinforce the stated research gap.
B – English & style
B1	Minor grammatical issues remain (e.g., “The drying process takes about 90 hours …”; use past tense).
B2	In a few places you still re-define SAC and DR after the first use—remove redundancy.
C – Methodology
C1	Please include either (i) a one-page pseudocode listing with actual numeric set-points, or (ii) a screen-shot of the main Arduino loop in the Supplementary section. Reproducibility is a core MDPI requirement.
C2	State the procedure used to calibrate the SENTEC RS-485 pyranometer and Extech AN-100 anemometer.
D – Results & Discussion
D1	Provide an uncertainty band (± %) for the drying-room exergy curve, derived by propagating the ±1 °C and ±2 % RH errors; this will contextualise the 96.6 % peak .
D2	The economic pay-back changed from 1.6 to 2.09 years —clarify which figure is final and explain the difference (labour cost addition?).
D3	Table 4 and 5 now include operating conditions—good. Check that all temperatures are given either in °C or K consistently.
E – Figures / Tables
E1	Figure 14 caption mentions “SC”; change to “SAC” for consistency.
E2	Consider reducing Figure 15 font size: currently axis labels overlap at 10 h and 16 h marks.
F – Data availability
F1	Add a one-line Data-Availability statement pointing to the raw CSV in the Supplementary file name.

Author Response

Response to In-house Editor comment:
We are grateful for your insightful observations and constructive comments. We are committed to addressing your queries and feedback through thorough explanations and revisions in the manuscript. Thank you for your valuable input.

Reviewer 2:
We are grateful for your insightful observations and constructive comments. We are committed to addressing your queries and feedback through thorough explanations and revisions in the manuscript. Thank you for your valuable input.
#    Comments
A – Title / Abstract / Intro     
A1    Comment: Title now capitalised correctly.
Response: The authors are extremely thankful to the reviewer for this thoughtful point.

A2    Comment: Lines 17-20 of the abstract still repeat part of the Introduction; consider trimming for concision.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. It was changed, kindly check the updated paper (lines 17-19).

A3    Comment: Add at least two 2023-2025 references on smart/AI or adaptive solar dryers to reinforce the stated research gap.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. New papers (2025) about smart/AI solar dryers were added to the introduction section, kindly check the updated paper (lines 115-125).

B – English & style     
B1    Comment: Minor grammatical issues remain (e.g., “The drying process takes about 90 hours …”; use past tense).
Response: The authors are extremely thankful to the reviewer for this thoughtful point. It was adjusted. 

B2    Comment: In a few places you still re-define SAC and DR after the first use—remove redundancy.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. Upon careful review of the article, we confirmed that all abbreviations are defined—they appear only once in the initial definitions and in the table preceding the reference section, with no duplicates found.

C – Methodology     
C1    Comment: Please include either (i) a one-page pseudocode listing with actual numeric set-points, or (ii) a screen-shot of the main Arduino loop in the Supplementary section. Reproducibility is a core MDPI requirement.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. as we told you before, the flow-chart was adjusted, kindly check the updated paper (Figure 8). We regret that we cannot publish the programming codes at this time, as the system is currently in development and the associated project has not yet been completed. We will reassess the possibility of release upon project finalization.

C2    Comment: State the procedure used to calibrate the SENTEC RS-485 pyranometer and Extech AN-100 anemometer.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. The devices' readings were cross-verified with data from two meteorological units—one located within the same college where the experiments were conducted and another within the university—before commencing the experiments.
D – Results & Discussion     
D1    Comment: Provide an uncertainty band (± %) for the drying-room exergy curve, derived by propagating the ±1 °C and ±2 % RH errors; this will contextualise the 96.6 % peak .
Response: The authors are extremely thankful to the reviewer for this thoughtful point. To derive the uncertainty band for the drying-room exergy curve, we propagate the sensor errors of ±1 °C (temperature) and ±2% RH (relative humidity) through the exergy calculations. The exergy efficiency is sensitive to both temperature and humidity variations. A ±1 °C temperature error typically introduces about 1.5% uncertainty in exergy, while a ± 2% RH error contributes approximately 1.3% uncertainty, depending on operating conditions. Combining these errors using the root sum of squares (assuming independence) gives a total uncertainty of roughly ± 1.98%. Therefore, the reported 96.6% peak exergy efficiency should be interpreted with an uncertainty band of ±1.98%, meaning the true value likely falls between 94.62% and 98.58%.  

D2    Comment: The economic pay-back changed from 1.6 to 2.09 years —clarify which figure is final and explain the difference (labour cost addition?).
Response: The authors are extremely thankful to the reviewer for this thoughtful point. As previously noted, the initial economic analysis excluded labor costs since the system operates automatically, resulting in a payback period of 1.6 years. However, upon incorporating labor costs—as per your recommendation—the revised analysis yielded a longer payback period of 2.09 years.

D3    Comment: Table 4 and 5 now include operating conditions—good. Check that all temperatures are given either in °C or K consistently.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. The temperature unit was previously defined in the earlier review. For reference, it is highlighted in yellow within the tables.

E – Figures / Tables     
E1    Comment: Figure 14 caption mentions “SC”; change to “SAC” for consistency.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. It was adjusted, kindly check the updated paper.

E2    Comment: Consider reducing Figure 15 font size: currently axis labels overlap at 10 h and 16 h marks.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. We are unclear about the requested changes, as Figure 15 appears to be well-structured and does not require modifications.

F – Data availability     
F1    Comment: Add a one-line Data-Availability statement pointing to the raw CSV in the Supplementary file name.
Response: The authors are extremely thankful to the reviewer for this thoughtful point. it was adjusted. 

The authors once again thank the learned Editors and Reviewers for their valuable comments for improving the quality of the manuscript.

Author Response File: Author Response.pdf