Edited sentence: Before the technical and economic challenges of implementing a "hydrogen economy" can be fully addressed, the fundamental problem of renewable energy production requires a solution.Even then, there are many problems to be solved before hydrogen can serve as a universal energy medium.It could take many decades to solve all of these problems, and even though the potentials are promising, hydrogen may never be the most economically feasible energy storage medium for all uses.These include difficulties with hydrogen production, transportation, storage, distribution and end use