There's something wrong with energy storage. It is WAY easier than it should be in general, and even straight stupid and wrong in some specific places

1) Power out of compressed gases
It just should not be possible because it is stupid. Sure, IRL you can take some pressurized air or nitrogen into bottle, and then release it into a fan and get energy from it, but effectiveness of such a storage will be crawling in around some FRACTIONS of percent no matter how pressurized air was and how advanced is your fan. But in game we can make very simple c.nitrogen storage with around 47% effiency. This is just WRONG
The biggest problem of green power IRL is namely energy storage. And if it would be possible to build something as simple as c.nitrogen storage that we have in game, we would do so everywhere around the globe, be it even 10% effective. But no such a battery exists. And will not exist. Ever.
The only real storage solution is burnable fuel of some kind, which we thankfully have, but...

2) Hydrogen power storage is WAY too effective
If you lyze some water and then burn it, you will get around 90% of your energy back, even counting all the water cleaning procedures. It isn't exactly wrong from gameplay perspective (lover effectiveness will just mean that we build K times more wind/solar generators), but it just FEELS wrong when you think about it.

3) Hydrocarbons
And even something as stupid as burning synthesized methane has around 54% effectiveness. We would be happy to have something like that in real economy. We could then forget about fossil fuels entirely. But no. Not possible.
Synthesizing of hydrocarbons should cost from 20 to 50 times more energy than how, or more precisely air separation. To get something out of air, you should cool it to condensation point of one gas, then to cond. point of other gas and so on. It is VERY long, complicated and expensive process. One cycle should take many in-game hours, if not days. And the same goes for alkenes synthesis (separate a mixture of resulting gases or use it as is), volcanic gases fractioning and all the similar processes. Any separation of gases or liquids should not be as easy as it is now.

3) Thermal tanks in current incarnation are way too simple
You place some solar collectors, a "stirling engine" and a thermal tank, repeat this blueprint 100 times and forget about power for the rest of the game. It feels like it should not be like that. The complexity of such a system is incomparable to hydrogen storage
"Thermal tank" as one building should not exist. In reality, thermal energy storage systems are very large and complex. And interesting. Would seem reasonable to get rid of "thermal tanks" in favor of something as complex as hydrogen power storage

4) Solar panels and accumulators should be either more expensive, prone to maintain, ineffective, difficult to produce or all of that together.
Because they are overpowered and preferable over anything else. I do not how to solve this problem other than some maintenance implementation, which would allow them to have "cons.", not only "pros."

1) What is your source for that? You're pretty wrong about that. These facilities have already been built in real life and are becoming more common and better as renewable energy becomes more important. They can have efficiency more like 85%, not "fractions of a percent". Our utility scale energy storage technology in real life is underdeveloped, because renewable energy didn't used to be as good as it is now, coal was cheap and people didn't care enough about the downsides to invest in alternatives until recently. You don't need CAES (compressed air energy storage) for coal plants, so the technology is immature, but moving along.

2) This is a simple and viable potential method for energy storage when alternatives are constrained. In real life this can achieve efficiencies of around 50-60%, which is less than in the game. But it wouldn't be a good game mechanic to have more gritty realism there. Players coming from vanilla (or any other mod really) already have a hard enough time adjusting to energy storage in Nullius. If the efficiency losses were much more punitive than they already are then people wouldn't bother with energy storage, which isn't good gameplay. Sometimes when there is a choice between realism and gameplay, you have to remember that this is a video game, not a simulation. Accumulators are the vanilla alternative, and they're 100% efficient and never deteriorate, which is a bit nicer than real life too, because at the end of the day this is a game.

3) It's way worse than the alternatives, so nobody uses this for energy storage. That's enough. In real life nobody does this for energy storage, and in Nullius nobody does this on any large scale. It's only really used for vehicle fuel, since we don't have fossil fuels to use instead. The end result is basically the same that this isn't viable, so the amount that it's not viable by is not that important. If the chemistry was impossibly expensive that wouldn't be fun. Nullius is already slow. You're mean to be played by an android who is infinitely patient and can slowly build up these chemicals over decades, but in real life you're a human and that wouldn't be fun to simulate in real time.

3b) Yet nobody uses thermal tanks. There are plenty of gameplay limitations that make them pretty niche. People in real life absolutely do store the thermal energy from compressed solar thermal energy collectors in heat tanks, using mediums like molten eutectic salt to store a lot of heat (same as the ingredients for thermal tank). Yes, there is complexity to it, which is why these molten salt tanks are expensive and complicated to build in Nullius.

4) They're significantly more expensive than any of the other power generation methods in Nullius. They're just simpler and more vanilla-like, so easier to understand without having to learn anything. Their construction costs are already very expensive for the power you get, so they don't need to be even more so.