Why is the comparison between hydrogen and battery technologies not so simple?
Before comparing hydrogen and battery technologies, let us first talk about energy integration and electrolyzer efficiency.
Have you ever had the feeling that once you start talking about a topic, you begin seeing related things everywhere? Something similar is happening to us. We are currently running several projects where we are designing heat recovery systems for the electrolytic process. Both for electrolyzers and fuel cells, and they all came at once, which is interesting.
Beyond trivialities, something we felt was important to emphasize, and the reason we created this post, is that by recovering heat, efficiency improves. Why? You might be wondering. Because we harness more energy than we invest in breaking the water molecule; simply put, this energy is found in the form of heat.
Put simply, the inefficiencies of the electrolytic process generate heat, and before releasing it into the environment, we pass it through a heat exchanger and transfer it to another process.
To give you an idea, a rough example: if an electrolyzer of about 1,000 kW (1 MW) has an efficiency of 60%, this roughly means it generates heat losses of around 40%, therefore, 400 kW. This heat is low-grade, meaning it doesn’t have much temperature (though a caveat: this only happens in low-temperature electrolysis – if you’re unfamiliar with this terminology, feel free to ask us). However, it is useful heat for processes that require heating water starting from room temperature, such as domestic hot water, swimming pools, and many more. However, it’s obvious that if you don’t have “another process,” this efficiency improvement cannot be achieved.
When this heat is reused, it clearly represents an improvement in energy efficiency since heat no longer has to be supplied from another process. Continuing with the previous example, for every 100 kW of heat recovery, efficiency improves by 10% (yes, a full ten percent). It is estimated that, at the start of the electrolyzer’s useful life, about 200 kW can be recovered. Therefore, an electrolyzer with a heat recovery system (“heat recovery” in English) increases the electrolyzer’s efficiency by 20%. So, in this example, we have an electrolyzer with an efficiency of 80%. You can see the equation with and without heat recovery in the image.
At this point, you might be asking, “Okay, what does this have to do with batteries?” Well, simply put, batteries do not allow for this type of process integration. Batteries move electrons, and we always talk in electrical terms. In hydrogen technologies, the process is more of a combo between ‘electrons and molecules’, so temperature, pressure, and flow play as important a role as voltage, current, or frequency.
Another tangible value, seen through healthcare systems and their budgets for combating respiratory diseases, is the air purification capability of fuel cells. This is something we’ve been advocating since our inception. A fuel cell system leaves the air 99.9% cleaner than how it entered. Another point that makes it not so easy to compare batteries with hydrogen technologies.
Questions? Opinions? Follow us on LinkedIn and let’s share ideas in the comments. If you found this post interesting, we have many more on the blog “Lean Hydrogen”
Author: Eugenio Trillo León, General Director of Lean Hydrogen. Industrial Engineer designing hydrogen installations and machines since 2013. See his bio here.
Publication date: 09/13/2023
