It sounds crazy to first convert electricity into hydrogen, with the respective efficient loss, and then convert it Bach into electricity, again with a sizable efficiency loss. At least 50% of the energy are wasted. How can this still make sense in a green paradigm?
Indeed the reconversion of hydrogen into electricity results in a significant overall system loss. Nevertheless, hydrogen is still the most efficient long term storage of renewable electricity. And with renewable supply (from photovoltaics) being high in summer and energy demand being high in winter there is a fundamental need for seasonal energy storage. What is most important is the availability of energy when it is needed and the related costs. The (lack of) efficiency may be deplorable but it is secondary. And as long as the original energy is carbon free, there is also no negative impact on climate emissions. On the contrary : if extra fossil energy production in winter can be avoided by stored renewables, there is a positive impact on the climate.
The basic issue here is the significant lack of renewable electricity when trying to replace all fossil forms of electricity. So the issue is, how to best use „additional“ renewable electricity to maximize the climate impact. And if it is looked upon at national level, there are many countries in the EU which will never be able to produce sufficient renewable energy to replace all fossil based energy. But there are countries who today already have an excess of renewables and have to shunt (=throw away) renewable electricity at peak times. This is called curtailment and Spain alone had curtailments of 9 TWh in 2018. So there is not only a „time of day“ issue when talking about converting to renewable energy supply but there is also a „season in the year“ issue and a „geographic location“ issue. In summary : The issue of „additionality“ is a real one in the context of maximizing the utilization of renewable electricity to fight climate change. But it cannot be solved by a simple no to all non-electrical uses. The issue behind the emotional discussion is the legal uncertainty created by the „additionality“ requirement in the Renewable Energy Directive of the EU. This legal uncertainty blocks the evolution of alternative sources of supply, in particular green hydrogen. That is why it should be resolved and clarified as soon as possible.