Not really. For long term storage, the cost of a unit of energy storage capacity becomes more important than the round trip efficiency. This is all the more the case when the cost of the input energy declines.
For seasonal storage, hydrogen is vastly better than batteries, even with a RTE of 40%. That's because the cost of an underground hydrogen storage cavern can be as little as $1 per kWh of storage capacity.
Efficiency of the discharge part, yes. But that's a less than factor of 2 effect that can't overcome the two orders of magnitude superiority over batteries in cost per unit of storage capacity.
Compared to batteries maybe, but that’s not the only alternative, and isn’t even the main alternative for long term storage.
Hydro being the simplest long term alternative.
Even if we stay with batteries, they’re price is continuing to trend down. That two order of magnitude you quote is only going to get smaller. What can’t be overcome is again the thermodynamic limit.
I don't see how is that relevant. When for example PV energy is abundant and cheap enough to power green hydrogen manufacture, then it's a game of scale, not thermodynamical efficiency.
We should be so lucky as to have so much excess energy to throw away freely of green hydrogen.
But that future is nowhere in sight.
For starters we currently have 90 million tones of H2 that is made from fossil fuels. We should focus on making that green before we consider NEW use cases for it.
As for what to do with the excess energy:
1. Store it in hydro
2. Make water.
#2 is real informative. To make 1 kg of H2 you need ~9kg of pure water (let’s call it 10 for simplicity) and 50-65kWh of electricity. To make those 10 kg of water by desalinating seawater you need 0.035 kWh.
So instead of creating 1 kg of hydrogen, we could create 13,800-18,000 kg of pure water.
Given all the water problems we’re having, that might be a smarter use of that energy.
Every time the spot price goes to 0 or less we are throwing energy away. This is already happening. Every time we could be instead generating hydrogen, or desalinating water, whatever we are not doing right now. But with the ensuing enormouos rise in PV and wind this will get much much worse. Eventually something will use that energy. Why not generate supply for the time when sun is not shining? I don't really care if it's hydrogen, ammonia (easier to store) or pumped hydro (probably best, but not enough capacity possible) or something else.
Also not every country has access to sea and while here in EU the energy markets are interconnected, it's not perfect. And some countries have enough water, no need to desalinate.
The difference is that energy prices don’t go below 0 for solar. They go below zero for coal, gas, and nuclear since you can’t shut the plants down on a whim. But you can with solar. You aren’t throwing energy away by turn off panels or stopping turbines, the wind blows and the sun shines for free, whether or not we capture it. The concept that energy price can go negative only comes into the picture because of things like gas, coal, and nuclear where we have to active produce heat to turn into electricity.
As for ammonia being easy to store. Yes, but only compared to hydrogen. But now you have a highly toxic gas. And, creating ammonia from hydrogen is another extremely energy intensive process.
> But you can with solar. You aren’t throwing energy away by turn off panels or stopping turbines, the wind blows and the sun shines for free, whether or not we capture it.
We are throwing away the electricity that would be created if we could use it at the time. So, in the name of optimal utilization of resources, we should be using it.
> But now you have a highly toxic gas.
Working with which we do have decades of experiences.