To compare apples-to-apples - for approximating the optimal use of solar
energy, whether it is solar-photovoltaic, or solar photoelectrochemical
(hydrogen output) or both - here are some ballpark numbers which
incorporate the new water splitting research of Yan, as reported in Nature.
For the idealist, the end result is looking brighter that ever before,
so to speak. We could be on the verge of solving the future energy
dilemma in a way that pleases almost everyone except the owners of the
power grid.
For solar-photovoltaics, 100 sq meters of cells/mirrors could capture
approximately 100 kW of spectral irradiance of which 15% is in the UV
range. Higher elevation is better for UV. Commercial solar panels can
convert about 18% of this in the form of DC electricity, with losses to
convert to AC. The OU water splitter, however, is 114% efficient so even
though only 15% of the radiation is UV, the net output could be very
close to the same percentage as photovoltaic.
But of course, the better option is to combine the two and have both
hydrogen and electricity as the outputs. Thus, an optimized home roof
of the future can supply both the electrical power, heating and the
transportation fuel for several cars, and with energy left over to sell.
This scenario is significantly enhanced if we are presented with the
hybrid option, which would be to use the hydrogen output as an
intermediate fuel, and the electric output to power a laser, such that
the Holmlid effect can be implemented. We end up massive amounts of
heat/hydrogen/kWH, and at moderate cost and off-grid. The one drawback
is that the energy is not fully renewable, in that some hydrogen is
annihilated or converted into dark matter.
Even a few grams per year, per person would be problematic... in a few
billion years <g>.
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The bond enthalpy of OH-H is 268 kJ/mol or 2.78 eV which is
essentially in the UV range for photons. Most UV is captured by the
atmosphere but enough gets through to make it interesting. The band
gap of silicon for photovoltaic is only 1 eV but the coupling losses
are huge so the comparative efficiency is below 20%. Thus splitting
water via sunlight would be viable, especially for automotive uses
once the problem of storage is solved. Moreover, the "waste" visible
sunlight not robust enough to split water can still produce
electricity so a combined facility would be advantageous.
To put this new report about overunity water splitting into
perspective - it should mean that making hydrogen as well as making
electricity are complementary processes - and once the storage problem
is solved, hydrogen could be the favored output. Fortunately, there is
a German company which seems to have solved the hydrogen storage
problem in a unique way - as a solute not requiring pressurization.
http://www.hydrogenious.net/en/energy-storage/
This has "automotive" applications written all over it. Will the new
Tesla be a German startup which is quickly snatched up by VW or Mercedes?
