Resilience Under Heatwaves: Croatia’s Power System During the July 2024 Heatwave and the Role of Variable Renewable Energy by 2030

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article presents a study on the relationship between heat waves, energy consumption, and the share of renewable sources in Croatia's energy matrix in 2024. In addition, the work makes a projection for the year 2030, considering the prospects for growth in demand and the expansion of renewable generation in the country. The topic addressed by the manuscript is relevant given the impacts of climate change on energy systems and the energy transition goals on a global scale. However, there are limitations and points for improvement, which are suggested below:

1 – The manuscript presents a robust literature review on the insertion of renewable energy and the impacts of heat waves on energy consumption. However, at the end of the review in the introductory section, I recommend that you include a more concrete description of what the proposed study presents that is different from the other works cited.

2 – I recommend that you also include a description of the following chapters at the end of the introduction.

3 – It is necessary to include the description of each variable expressed in the equations (for example, equations 1 and 2). Do this procedure for all variables mentioned in the manuscript.

4 – In the cited excerpt, “When wind and solar PV generation is high (fVRE ³ 50%) and fossil fuel generation is 10 low (ffossil < 15%), electricity prices are low and can even drop below zero.”, the price below zero is mentioned. Explain what this means? I understand that there will be times when there will be energy exports. However, I believe there will always be some cost, and it will never be below zero. Given this, I ask that you make the necessary adjustments to the manuscript to justify this or correct it.

5 – The manuscript presents limitations regarding the cases carried out. An interesting test that could be carried out is to evaluate the system by removing plants with higher greenhouse gas emissions and proposing replacing them with other types of energy resources to compensate for this withdrawal.

6 – Although there is a minimum description of what is being proposed in the work, it is not enough to guarantee the manuscript's readability. I ask that you delve deeper into the contributions of the work to give greater robustness to the research developed, which currently presents itself in a shallow and limited manner to the situation in Croatia.  

Author Response

Please see the attached file.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

1. Line 20 & Section 3.4: The predicted 62% increase in fossil fuel generation during summer contradicts the paper’s general narrative of decarbonization. A deeper discussion is needed on the drivers and implications of this shift.
2. Lines 127–128: The generation of future solar PV profiles using the isotropic sky diffuse model should be supported by either literature validation or comparison to actual irradiance data from Croatia.
3. Line 134: Excluding self-consumption PV generation introduces a potential bias in the evaluation of renewable energy contribution. This methodological choice should be more transparently discussed.
4. Lines 153–159: The simplification of grid operations by excluding redispatch and curtailment might significantly affect the results under high VRE scenarios. A sensitivity or robustness check is strongly recommended.
5. Figure 4 & Line 217: The import share of 35% during peak hours is significant. Please clarify whether this is a singular occurrence, average value during the heatwave, or sustained pattern.
6. Lines 286–288: The sharp summer increase in fossil fuel generation is not sufficiently problematized. Please discuss this in light of Croatia's NECP targets and its impact on GHG emissions and energy security.
7. Lines 306–309: The assumption of a 1:1 wind-to-solar capacity ratio (1,500 MW each) requires better justification. Seasonal complementarity, diurnal profiles, and baseload matching should be taken into account.
8. Line 337 & Figure 8: The term "renewable oversupply" is central to the paper’s argument, yet it lacks a precise operational definition and hourly distribution. Please clarify the metric and its practical implications.
9. Lines 370–374: International examples of curtailment (Germany, Spain) are cited but not sufficiently contextualized for Croatia’s grid structure, market integration level, and flexibility assets.
10. Figures 9–10 & Lines 391–393: The visual correlation between generation mix and prices is informative but lacks statistical measures such as correlation coefficients or model fit indicators. Please consider adding.
11. Line 443: The statement that Croatia may become a net electricity exporter by 2030 should be rephrased more cautiously. Consider including scenarios where this outcome may not hold.
12. Lines 453–455: While the importance of energy storage is acknowledged, the paper does not estimate the storage capacity required to reduce curtailment or ensure evening supply. Please include indicative values or ranges.
13. Line 459: The mention of machine learning for future forecasting remains vague. Please propose at least one specific domain (e.g., demand prediction, solar irradiance forecasting) where this approach could be applied.
14. Section 3.5–3.6: The linkage between VRE curtailment, price volatility, and demand-side flexibility could be more clearly elaborated, perhaps through a conceptual figure or policy scenario.

Author Response

Please see the attached file.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I would like to thank the authors for their dedication in responding to all questions and addressing all recommended suggestions. I have no further questions.