# 214

Dear Maria Cristina Pinto, Maria Gaeta, Emere Arco, Piero Boccardo and Stefano Paolo Corgnati

I read your paper:

Mapping the suitability of North Africa for green hydrogen production: an application of a multi‑criteria spatial decision support system combining GIS and AHP for Tunisia

My comments:

1. In page 2 you mention using water electrolysis to ger hydrogen, which of course is correct, but you do not clarify what type of water you are referring to, i.e., fresh-water and its sources, that I guess are not abundant in Tunisia, or salt-water which is close in coastal areas to the inexhaustible source of the Mediterranean, as well say nothing is the predominant procedure to day or the difference in costs, unless there is pre-decision to use one or the other. You don’t explain the meaning of grey, blue and green hydrogen. The reader may not understand what you are talking about.

If your focus is on sustainability, remember that this concept involves the intersection of segments of Economics, Environment and Social. As you know, the typical Venn diagram defining sustainability, illustrates that segments or subareas of each of these three pillars share in an irregular common space, denoting strong interaction, between criteria (C∩D), or intersection, not summation (C∪D), as in MCDM methods.

You can consult AI about this. In simpler words: It is not valid to sum results from criteria; the result is achieved by considering all of them, at the same time

2-In page 2 you mention ‘externalities’ but do not explain which are they? Are you referring to the economics aspect of externalities, which of course there could be in this case? Which would they be?

3-In page 4 you say “, AHP is the most widely chosen—alone or in combination with other MCDM techniques—because (i) it is simple to understand and to be applied to complex problems; (ii) the procedure decom poses a large problem into smaller ones hierarchically”

Yes, AHP is by far the most widely chosen method, I agree, but I disagree with the two subsequent assertions because they are inexact. It cannot be applied to complex problems because the rigidity of a lineal structure, not apt for most scenarios that normally involves multiple relationships between criteria and criteria and alternatives.

Second, yes, you can decompose a problem into smaller ones, which is good for its understanding but useless fort solving, because a problem is a system that must be solved with all its characteristics at the same tire not separately. Why?

Because very often an alternative depends on other and the same for criteria. Remember that a result is probably greater that the sum of its parts and it is found in many fields and from ancient times

4- page 4 “Within this work, GIS techniques are combined with the application of fuzzy logic on AHP”

In my opinion, applying fuzzy to AHP derived weights is a waste of time, not due to fuzzy but because is absurd to ask a crisp value between two or three invented weights. Of course, fuzzy can find an average of crip, although not for the problem, but for the DM arbitrary values.Just think, what relation does it have with the GIS layers? None

5- I am far from being an expert in electrical generation, but calls my attention that no mention is made on two most fundamental aspects of PV, namely air temperature and humidity. In the coastal area in summer time the temperature is between 30 and 35 centigrade and in winter 18. This means that in summer the PV installation is subject to as a minimum to 30 degrees C, when the maximum acceptable is 25. This will produce a high reduction in energy output, that can reach in a 25%, and aggravated by high humidity of 70%, that can increase even more the loss.

Has this been considered taking into account the sharp increase in the generation cost?

These are my comments that I hope can help

Nolberto Munier