The direct conversion of low-density electrical energy, from photocells, wind, or other "locally clean" sources to hydrogen for storage until the hydrogen is needed for fuel sounds pretty simple, but there are some drawbacks.

Gaseous hydrogen is incredibly difficult to store and extremely dangerous to handle.

There are several methods of storing hydrogen that various people tout as effective. A popular one has been to combine the hydrogen as a "metal hydride" in storage. Since there's no existing way to pump the metal hydrides through a pipe, this still requires handling gaseous hydrogen at least for fuelling and within the engine for combustion. This might be acceptable for a vehicle, but does nothing for the storage/transport problem.

A disadvantage of metal hydride storage especially in a vehicle is that the entire storage volume must be operated at high temperatures to release the hydrogen for burning. As a "personal opinion" either large high pressure inert gases or very high energy flywheels likely would be safer for any large-scale public use, especially for uses such as in vehicles.

The former Beech Aircraft company started a project to design a "hydrogen powered automobile" using metal hydride storage sometime ca. 1960, and the project was still running (after they became Raytheon Aircraft), without notable success, at least ca. 1998 if information overheard then was correct. A problem is that hydrogen is "very low octane" and tends to explode rather than burning smoothly, so small parts of the engine kept getting propelled into strange places, or mangled and bent inside the engine. (At least ca. 1970 - '74 when I had occasional "direct observation" contact with the project.)

The more "modern" idea for hydrogen burning engines seems to be "generating" the hydrogen directly from petroleum fuels. Lots of people are working on this concept, but few "hardware examples" have appeared outside laboratories. While this may result in lower emissions from the hydrogen burning device, there is at present no efficient way to directly produce more complex hydrogen-bearing molecules (hydrocarbons) from low density electricity, so it doesn't help the "store it as hydrogen" idea.

The "flying engine parts" that Beech/Raytheon encountered illustrates a difficulty of handling/transporting hydrogen as a gas. When compressed enough to provide useful expansion during burning, it has a tendency to detonate (engine knock). When compressed enough to be efficiently pushed through a pipe, it has a tendency to detonate, especially with very low amounts of oxygen intermixed, under any condition that can cause ignition.

Some years ago, ca 1950s(?), a few natural gas "pipeline explosions" occured that were quite spectacular. One or two destroyed more than 100 miles of pipe each.

Increasing the pressure of a gas increases the speed of sound in the gas. A detonation travels at approximately the speed of sound in the gas. A fracture under stress of the pipeline material cannot travel faster than the speed of sound in the material from which the pipe is made.

If the pipe is strong enough to contain the pressure at which burning of the gas transitions to detonation (produces a shock wave), any "ignition" will raise to pressure inside the pipe to the detonation point in the vicinity of the combustion/detonation front.

If the speed of sound in the gas (the speed at which the "explosion" travels) exceeds the speed of sound in the (usually metal) pipe, the shock wave stays ahead of the crack that would release the pressure enough to lower the burning condition below the "detonation transition pressure" so the explosion and the crack both travel to the end of the pipe, exiting potentially (it was suggested) where it blows your kitchen stove through your roof. Being a rather light gas, the speed of sound in moderately compressed hydrogen is "pretty fast."

Natural gas pipelines now have "interrupters" at frequent intervals, with valves that shut down all of the valves on the pipeline if pressure at any point on the line drops, and in some cases vent a few sections on both sides of where the drop was detected. Rupture points are built in that will allow the pipe to break and (hopefully) release the gas pressure locally before it rises high enough to allow the natural gas to produce a sonic shock. Working on natural gas pipelines is still considered a "hazardous occupation" even thought it's very much safer than any easily conceived hydrogen pipe.

There is no pressure at which gaseous hydrogen can be pumped efficiently through a long pipe that will not result in detonation if any ignition accident occurs, if even minute amounts of oxygen are available; and perfect exclusion of oxygen is extremely difficult.

John