Re: Hydrogen economy will never exist
From: william mook (william.mook_at_mokindustries.com)
Date: 07/16/04
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Date: 16 Jul 2004 08:52:03 -0700
bri1600bv@hotmail.com (brianb) wrote in message news:<68a6629.0407150208.4fb9ca6@posting.google.com>...
> william.mook@mokindustries.com (william mook) wrote in message news:<407c5321.0407141619.14d198e9@posting.google.com>...
> > > While large its a smaller cost energy wise than ripping the carbon
> > dioxide apart or ripping the water apart. The benefit of mining air
> > for water and CO2 - even in the desert - is that you don't have a
> > complex and costly supply chain.
>
> If you get CO2 from the air, don't you have to split off the C to
> combine it with the H? What is the cost of that per kg?
The there are two ways;
(1) Sabatier Reaction and
(2) Electrolytic decomposition of CO2
http://www.methanol.org/pdf/HydrogenEconomyReport2003.pdf
http://www.nap.edu/books/0309057442/html/22.html
http://ares.ame.arizona.edu/publications/961597.pdf
http://ares.ame.arizona.edu/publications/ices96-paper.pdf
Electrolytic processes achieved separation of C and O2 is 3.1 kWh per
kg of CO2 or 11.4 kWh per kg of Carbon.
The Sabatier process takes hydrogen and reacts it directly with CO2 in
the following equation;
CO2 + 4H2 --> CH4 + 2H2O
Here half the hydrogen used to create water vapor, half CH4, a
hydrocarbon. Of course the H2O can go back to the electrolyser again
to be separated. If divided by the mass of carbon processed this
again is about 11 kWh per kg of carbon.
Methane can be run through zeolites to produce synthetic liquid fuels
http://www.osti.gov/dublincore/gpo/servlets/purl/83041-saf5HI/webviewable/83041.pdf
This process has additional costs but also produce additional hydrogen
to balance that cost;
8CH4 --> zeolite --> C8H18 + 3H2
The energy is applied by direct pressure of methane gas against the
membranes.
The price and longevity of those membranes, along with issues of
fouling and maintenance are the main issues here.
>
> >
> > > And
> > > what percentage of oil is carbon and hydrogen? I'm thinking it's
> > > (oil) is about 12% hydrogen.
> >
> > http://www.santos.com/production/marketing/downloads/elang_crude.pdf
> >
> > Depending on grade it ranges from 14% to 16% by weight.
> >
> > Octane is a good representative molecule, its formula is C8H18 - which
> > means its about 15.79% hydrogen by weight.
> >
> > Here are the physical properties of the various hydrocarbons in oil;
> >
> > http://www.creative-chemistry.org.uk/alevel/module3/documents/N-ch3-04.pdf
> >
> > Octane compares well to the bulk properties of the highest grade oils.
> >
> > > Also, what efficiency and cost are your electrolyzers?
> >
> > Wet chemistry electrolyzers with KOH electrolyte and stainless steel
> > electrodes. Very inexpensive.
>
> What is a wet chemistry electrolyzer?
Electrolysis applies low voltage DC electricity to water to separate
it to its component parts. To achieve this you can use Proton
Exchange Membranes with platinum elctrodes
http://www.electrochem.org/publications/interface/winter2003/IF12-03-Pages40-43.pdf
or containers of water with Potassium Hydroxide using simple
stainless steel electrodes.
http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=6380653
PEMs are more efficient and are ideal for mobile applications and are
reversible, making them ideally suited for fuel cells.
Water containers (wet chemistry electrolyzers) are ideal for
stationary applications and one way production of hydrogen at very low
cost (about 1/1000th the cost of fuel cells!)
> > > Also would I
> > > assume that a 1MW electroloyzer works at average 25%, for 6 hours of
> > > sun per day?
> >
> > No.
> >
> > > At peak sun it's taking in 1MW of electricity and there
> > > are an average of 6 sun hours per day?
> >
> > No.
> >
In Nevada where the bulk of our land in the US is located we have an
average of 6.6 hours of sunlight per day. That's 6.6 kWh per day.
Over 24 hours that averages out to 0.275 watts of output per peak watt
of input.
If there are 6.6 hours of useful energy per day means there are 24 -
6.6 = 17.4 hours of output at 0.275 watts (assuming 100% efficiency,
which ain't the case - in actuality we end up with 1/4 watt averaged
output per peak watt of input) In any case, for each watt we need
about 0.275 * 17.4 = 4.785 Wh of energy.
Now, sealed lead acid batteries cost around $0.20 per Wh of energy
storage. This means that we need $0.96 of batteries per peak watt.
These may also be charged and discharged only 1,000x before they're
replaced. So, life span is 3 years.
Sodium sulfur batteries have the potential to cost 1/5th cent per Wh
of energy storage. This means that they cost 1 cent per peak watt of
output. Further, advanced batteries may charged and discharged up to
7,000x before they're replaced. This gives them 20 years lifespan.
This allows us to produce a combined battery and PV system at a cost
of less than $0.05 per peak watt (with 2,410 hours per year of
operation) which amounts to $0.20 per averaged watt (with 8,766 hours
per year of operation)
Why spend all this time and energy on batteries?
Because this allows us two things;
(1) to reduce the size of follow on equipment to 1/4th the size
needed otherwise;
(2) to increase utilization of downstreamequipment to 4x that of
equipment operated intermittently;
Combined these features improve our capital efficiency of downstream
components 16x. In regions where there is half the sunlight battery
costs increase to 2 cents per peak watt, but downstream efficiencies
are improved by 64 times!
So, low cost, long lived batteries are important to operating
efficient solar based systems.
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