You cannot compare it in general, but in a particular case you can very well compute it so you can determine whether you have spent well your energy, or you have wasted it because using it otherwise would have produced more hydrogen.
Even if you might not be able to compute the efficiency before the process is actually completed, it would be foolish to start it without at least some rough estimate, to see if there are chances for this to be worthwhile.
I agree with the previous poster that the article should have included some estimate of the efficiency they hope to obtain, otherwise it is impossible to say whether this is newsworthy in a positive way (it could be newsworthy in a negative way, if they had wasted resources for a negligible outcome).
Even if you might not be able to compute the efficiency before the process is actually completed, it would be foolish to start it without at least some rough estimate, to see if there are chances for this to be worthwhile.
I agree with the previous poster that the article should have included some estimate of the efficiency they hope to obtain, otherwise it is impossible to say whether this is newsworthy in a positive way (it could be newsworthy in a negative way, if they had wasted resources for a negligible outcome).