# 127

Dear Maja Mrkić-Bosančić, Srđan Vasković , Petar Gvero and Gojko Krunić

I read your paper

Optimal energy mix in relation to Multi Criteria Decision Making (MCDM), review and further research directions

My comments

1- In page 1 you say “Each geographical area has different energy sources, available natural resources, level of technology development, and energy systems for generation and distribution of energy to end users. Their sum results in determining the appropriate energy mix”

This is not exactly true, it is not a simple sum of sources but a sum of selected sources including percentages of uses, and as you say, it is not simple economic issues because it introduces in addition, health, environment, job generation, etc., plus a plan to shutdown fossil plants and at the same time to build new renewable ones. It is a very complex problem.

2- You put emphasis of territorial needs and availabilities. In my opinion, the electricity mix must be considered at country level, for it is probably seldom to find a region, unless it is very large, that have the different sources. That is PV can be excellent in a region of the country with intense sun radiation, but not in others. The same for wind energy, hydro, geothermal, etc.

Normally all large agglomerations are linked by the electrical grid, and so, energy produced in region A can be used in region F located at 2500 km from A

3- In page 5 “Special attention is given to methods for determining the weight of the criteria for MCDM optimization process and especially Entropy and AHP method”

Weights for criteria is a major issue and one of the biggest problems, because subjective weights from AHP are useless since they are not only invented values, but also because they cannot be used and evaluators of alternatives, while entropy weights can be used to evaluate alternatives.

In Table 1 you do not explain what is inclusion and exclusion criteria

4- In page 8 “The target function of the energy mix problem is the minimizing of total costs of electricity generation, meaning the costs of construction, operation and management, fuel, and CO2. The results showed that this optimization model could successfully generate an energy mix plan from 2012 to 2030”

I am afraid that I do not concur with this definition of energy mix problema. In my opinion the main objective is to satisfy the demand when the system is subject to a set of criteria, related to social, environment, economic, financial, etc. issues. You are here referring only to cost. Perhaps we can produce at a low cost but disregarding CO2 contamination, health problems and technical issues.

5- In page 8 you insist again in cost reduction not considering the main issues that is total decarbonization of energy production. Cost is in this context some sort of secondary aspect. In general, the world opinion is to have zero CO2 by 2050, of course at the minimum cost and satisfying demand

6- In page 8 “our scenarios were analyzed, and these are: basic scenario, CO2 reduction scenario, scenario of meeting the target of RES generation, international gas price scenario”

In my opinion there is only one scenario that must contemplate simultaneously all the criteria you mention

7- In page 9, Homer, as a computer model is excellent to test hundreds of options elaborated by experts. The problem is that these experts must progressively decrease the participation of fossil fuel sources for electricity generation, and I am not sure if Homer can handle it, albeit most probable yes, because at the end, it is some sort of supervised simulation. Really, I consider your suggestion as very important

8- In page 10 it is very interesting what you comment about energy and exergy, a subject that I have never seen before in articles. For me in particular, exergy has a primordial importance when the sites for PV farms are investigated, where the temperature of the cells in some areas may be higher than the air temperature and then paving the way to a great disequilibrium between cells surface and surrounding air, which without a doubt, affects the efficiency of the cell, measured by the temperature coefficient.

Similar analysis is important when investigating exergy in wind turbines due to wind speed, air density, a temperature and humidity.

9- Page 22 “Listed parameters are universal and can be applied to the mathematical description of the energy mix of any local community or region”

Where is the justification for this assertion? There are many aspects missing in that list like load factor, job generation, risks, environment, land use, new technologies, people acceptance replacement rate, etc.

I hope these few comments may be of help

Nolberto Munier