Using renewable energy to produce hydrogen will not be carbon...

Using renewable energy to produce hydrogen will not be carbon neutral until 100% of power generation is renewable. In the meantime, the power used to electrolyse water to produce hydrogen will simply be diverted from the grid and slow the retirement of fossil fuel generation.

Currently > 90% of hydrogen is produced using steam methane reformation (SMR), with CO2 as the byproduct (along with the CO2 produced generating the power used to drive the SMR process).

There may be a third option: there is another industrial process under development that catalyses LNG to produce hydrogen, but unlike SMR produces graphite rather than CO2 as the byproduct. The graphite is suitable for use in Lithium battery electrodes, so is a valuable product in its own right in addition to the hydrogen.

http://www.hazergroup.com.au/