On Sun, 21 Oct 2012 14:18:18 +0100, Martin Brown wrote:

The really expensive bit is splitting water into hydrogen and oxygen.
Plants mastered that a very long time ago - we are still unable to.

We are working on it though, there is a crowd sourced project out there
somewhere trying to develop an "artifical leaf". There are some
prototypes that do work but not very well, yet.

--
Cheers
Dave.