so the goal is to transport renewable energy from the point of production (e.g. coastline for offshore wind) to the point of consumption (e.g. big factory 300 miles from the coast).
what is the cost of doing this? when comparing different technologies. i.e. you can just build a cable and transport the electricity through that, or you convert the energy into hydrogen at the point of production, then pipe that hydrogen gas through a pipeline to the point of consumption. many big consumers can naturally consume hydrogen instead of electric power anyways, for example large steel mills. they require power for heating and reduction, but in both cases, both power sources can be used (for reduction, electrolysis vs. chemical reduction).
it's well-known that the LCOE (levelized cost of electricity) for solar and wind is around 6 ct/kWh (citation needed, i'm citing from memory). so what is the cost of transporting that electric power over 300 miles? according to the diagram, it's 4 ct/kWh over 1000 miles, so probably 1.33 ct/kWh over 300 miles using wires. so it makes a small part of the cost.
meanwhile if you use hydrogen, you have around a 70% conversion+storage efficiency (electric power -> hydrogen, plus storing it in an underground cavern) (source: this paper and german wikipedia about hydrogen storage). so to produce 1 kWh hydrogen, you need 1.4 kWh electricity at the cost of 1.4 * 6 ct/kWh = 8.4 ct/kWh. transmitting it over the pipeline, meanwhile, costs almost nothing, as seen in the diagram.
so in summary, producing+storing+transmitting hydrogen is slightly more expensive than just producing+transmitting electric power, but that already includes the storage cost. for electric power, you need additional batteries which i'm too lazy to write about now. just to give you an idea.
I really like this post, it gets down to nitty gritty brass tacks and brings some data.
That's usually the thing that gets me grumpy about such conversations, people don't bother discussing the realities of actually doing the thing, they just trade feel good articles about how everything is fine.
One thing about the paper is, the cost of high voltage DC lines is likely assuming you're on land. Bringing the energy in from sea could be even more expensive, since you need much more expensive equipment, the environment is brutal, repairs involve sending people and material into that environment, and I have a feeling but I don't know, I think that the movement of the offshore wind turbines could be mechanically stressful on cables that are relatively safe up in the air only dealing with wind (and they still can cut right through insulators swinging in the wind and vibrating at 60hz)