Grid-Scale BESS for Ancillary Services Provision: SoC Restoration Strategies

Round 1

Reviewer 1 Report

The presented article "Grid Scale BESS for ancillary services provision: SoC restoration strategies" presents different approches for BESS use in the grid. Based on the basic droop control five different control variants mostly including SoC restoration are developed, presented and applied on data from the Italien electricity market in 2016. Even though no strategy proves considerable better than the others the article is still interesting as is clearly presents an interesting and open topic and includes all important aspects including also battery aging. 

The article is very well written in clear. Unfortunately, there was a problem with the references in the document. 

Moreover in the presentation of results a paragraph reminding the data used for modelling as well as the limitation of the the use of those data would be good. Additionally some information about the computer used for simulation and the simulation time for the different solution would be appreciated. 

Author Response

Dear Reviewer,

we warmly thank you for you thorough review, for the positive comments and for your valuable suggestions. Here below the response point-by-point including the cited text of the changes we made to comply.

Point 1: "Unfortunately, there was a problem with the references in the document. ".

We hope we fixed the issue. We are sorry for the inconvenience.

Point 2: "Moreover in the presentation of results a paragraph reminding the data used for modelling as well as the limitation of the the use of those data would be good."

Thank you for the comment. We improved the text by adding a paragraph both in the Methodology section and in the Results one. See here below or in the main text.

"The energy necessary to charge BESS for SoC restoration is valued at the yearly average purchase price in the Italian DAM, whereas the discharging energy at the yearly average positive imbalance price. NPP is valued at the average yearly marginal price in the Italian BM (to date, NPP for FCR is not defined in Italy, since FCR is mandatory). The selected parameters aim to be representative of the current situation and possible evolution in continental Europe."

"As previously introduced, simulations have been performed adopting network frequency data from CESA for year 2016 [27], with 1-second sampling rate and a resolution of 0.1 mHz. The economic data used come from the market prices on the DAM and on the BM for Italy and Germany (for what concerns FCR capacity remuneration). These choices have been operated for offering results that can be generalized to the whole CESA. The adoption of CESA’s frequency decrease the applicability of these results to systems with less inertia and with larger frequency deviations, such as UK [42]."

Point 3: "Additionally some information about the computer used for simulation and the simulation time for the different solution would be appreciated. "

We are glad to provide an answer to this comment, too. Indeed, we did not highlight the performances and limitations of the model in the previous version. We fixed this in the reviewed version. The model we use is an experimental, multiparameter model, able to represent the whole efficiency of the system. It is bound to the device on which it was validated. Therefore, it could include some peculiar behavior of it. The simulations were performed with an up-to-date, standard PC. We think that our model is low in computational effort. We provided these data in the Results section.

"The adopted workstation features an Intel® Core™ i7-10510U CPU @ 1.80GHz, 2304 Mhz, 4 Cores, 8 Logical Processors. The approximate elapsed time is 1.5 hours per simulated year."

We hope we cleared all the mentioned issues.

Best regards.

Reviewer 2 Report

This paper compared the provision of FCR with various SoC restoration strategies and indetified the crucial role of degrees of freedom. Overall, this topic is fine and a revision should be considered before acceptance. 

1. The specific reasons on the sinifiance of the ancillary services should be clearly clarified in the introduction part.
2. Is there any drawback for these chosen BESS models in thsi study? 
3. There are too many style errors in the main text, stating "Error! Reference source not found"! Please carefully check this.
4. Is there any experimental evidence to support this conclusion. It is better to give some evidence to make this more convincing. 

Author Response

Dear Reviewer,

we would like to warmly thank you for your comments and suggestions. We tried to implement what you highlighted in the main text. We provide here below point-by-point response and the quotes of the improvement done in the main text.

Point 1. "The specific reasons on the sinifiance of the ancillary services should be clearly clarified in the introduction part."

We thank you for the comment. We tried to modify the first paragraph to insert right at the beginning of the article a short sentence to clarify the main roles of the ancillary services in a power system. We propose here below the paragraph.

"Long-term renewable energy integrations studies show that the rise in renewables could call for increased levels of frequency control [1][2][3]. Frequency control is included in the ancillary services necessary to guarantee the quality of supply and stability in the power systems [4]. In particular, it assures the real time balance between electricity generation and demand."

Point 2. "Is there any drawback for these chosen BESS models in thsi study? "

We agree with you on the fact that we were not enough specific in the analysis of the pros and cons of our model. We introduced the following paragraph in the Results section to highlight the drawbacks of the model we developed and used in this study.

"The model adopted is an empirical multiparameter SoC evolution model. It is obtained via an experimental campaign on an industrial BESS. Therefore, if on one hand the model is accurate in representing the whole operational efficiency (also including the effect of PCS and of auxiliary systems) on the other hand this model is validated for that device only and it could feature its peculiar behaviors. Furthermore, the possibility of an outage of the plant during the year is neglected. "

Point 3. "There are too many style errors in the main text, stating "Error! Reference source not found"! Please carefully check this."

We are sorry for the inconvenience. We carefully checked the text and we hope we have solved the issue.

Point 4. "Is there any experimental evidence to support this conclusion. It is better to give some evidence to make this more convincing. "

Thank you for the comment. We tried to propose experimental evidences to support the conclusions at various level in the article.

At the model level, the numerical model is validated in the previous correlated studies by a experimental campaing including thorough verification and validation on an industrial Li-ion battery system.

At the service level, we listed the main projects or services already implementing the droop curves we are using and re-working in this article. These services are already present in some countries in EU. We focused on the description of these projects to highlight that we are focusing on real-world case studies and re-elaborating them to propose an effective comparison.

At the results level, a simulation campaign is detailed in the article. It is replicable by a Simulink user, since the model data are published and the data used are open and available online. Unfortunately, it was not possible for us to replicate the numerical simulations on a real system. Therefore, only the model evidences can be proposed to support the conclusions.

We hope to be clear and that the provided data and elaboration are convincingly supporting the conclusions.

We thank you for your attention and for the valuable contribution. We hope we provided all the information needed.

Best regards.