" Device ups hydrogen energy from sunlight
Peter Weiss
Here's a recipe for a cleaner, healthier planet: Take some water, add solar energy, extract
hydrogen, and use it to power fuel cells for running cars and other machines. Then, collect their
water emissions and start the procedure again.
One look at the list of ingredients in today's fuel cells, however, shows that this ideal isn't yet
being followed. Because processes that use sunlight to extract hydrogen remain costly and
inefficient, fossil fuels still supply the hydrogen in most fuel cells.
Hoping to break the fossil fuel habit, a team of Israeli, German, and Japanese scientists has
created a device that boosts the efficiency of solar-powered hydrogen extraction by 50 percent.
The group placed a photovoltaic cell on top of two flat, finger-long electrodes. The combination
"is very efficient in converting solar energy [into an electric current] but also provides nearly the
ideal voltage for splitting water" into hydrogen and oxygen, says team leader Stuart Licht of the
Technion in Haifa, Israel. A water molecule splits, or undergoes electrolysis, at only 1.23 volts.
Licht and his colleagues describe their device in the Sept. 14 Journal of Physical Chemistry B.
The gadget converts sunlight to an electrolysis current with 18.3 percent efficiency. In turn, the
current creates hydrogen gas as it passes through acidic water.
The device is "showing the pathway towards higher efficiencies for direct solar-to-hydrogen
production," comments John A. Turner of the National Renewable Energy Laboratory (NREL) in
Golden, Colo. The newly achieved efficiency may already be high enough for commercial
hydrogen generators to be feasible. "That still needs to be figured out," Turner says.
In 1998, he and Oscar Khaselev, then also of NREL, demonstrated a novel apparatus for
solar-to-hydrogen conversion (SN: 4/18/98, p. 246). To achieve unprecedented efficiency, the
device used multiple layers of semiconductor materials. The researchers arranged the layers to
form two active regions, or junctions, that would absorb solar photons that dislodge electrons.
Some of the less energetic photons weren't captured in the first junction but passed to the
second, where they generated more current.
The design gained an energy advantage by combining solar electricity and water splitting into one
unit. Their cell's 12.4 percent efficiency-nearly twice that of any previous solar-to-hydrogen
device-has held as the record until now.
Licht and his colleagues have improved upon that pioneering effort in several crucial ways. In one
sense, the NREL device was all wet: It had to be completely immersed in water to operate. That
feature forced the researchers to select semiconductors that wouldn't break down in solution.
By keeping their stack of semiconductor layers high and dry, Licht and his group were free to
optimize them for both converting sunlight to electricity and water splitting. Their design permits a
low electrolysis current, which also reduces energy waste.
Licht and his coworkers say that besides besting the solar-to-hydrogen conversion record, their
work opens the way to efficiencies not considered possible before. Using measured
photoelectric efficiencies of seven semiconductor combinations not yet tested in hydrogen
generation, they predict maximum solar-to-hydrogen conversion efficiencies of up to 31 percent.
Thermodynamics theory says the maximum could range above 40 percent for a two-junction
converter, but no one has previously predicted better than 24 percent performance for practical
devices, Turner says. Experimentally achieving the new prediction "would be an accomplishment
indeed!" he adds."
Something is happening, but you don't know what it is, do you.....?
>I have differed sharply with Mark Jones over the extent to which
>the environment and the future exhaustion of fossil fuels can be
>made a core political issue. The issue obviously attracts a large
>number of committed activists, and any mass movement will obviously
>have to be structured to include them and their issues. But however
>that may be, Mark's extended study of and commentary on the energy
>problem are of immense importance. I think the following post on
>alternative energy sources is worth careful consideration.
>
>Carrol
>
>-------- Original Message --------
>Subject: [CrashList] Why 'alternatives' are no alternative
>Date: Sun, 17 Sep 2000 10:38:47 +0100
>From: Mark Jones <jones118 at lineone.net>
>Reply-To: crashlist at lists.wwpublish.com
>To: crl <crashlist at lists.wwpublish.com>,"Marxism-Thaxis at Lists.
>Wwpublish. Com" <marxism-thaxis at lists.wwpublish.com>
>
>It is said frequently and often nowadays that the future economy will be
>'hydrogen-driven'. Most of what is written on the subject shows signs
>of
>being untouched by the human mind. For one thing, hydrogen is an
>energy-carrier, not an energy-source. You have to *manufacture*
>hydrogen,
>and it is an energy-intensive process, requiring huge amounts of
>electricity. Where will the electricity come from? One answer is natural
>gas, which in itself is hardly a real answer if you're talking about
>moving
>beyond fossil fuels that pour greenhouse gas into the air. And where
>will
>the natural gas come from? According to some petrogeologists, there is
>no
>shortage of natural gas, particularly in the USA. Eminent member of the
>American Association of Petroleum Geologists, "Skip" Hobbs recently
>assured
>the US Senate that the US has plenty of natural gas (his testimony is in
>the
>Crashlist message archive). But the reality is that existing gas
>reserves
>are depleting at an alarming, and unexpected rate; meanwhile the US
>Department of Energy assumes that a supply of 35 quads of natural gas
>p.a.
>will be found to meet expected demand by the year 2020; that is almost
>double existing US natural gas consumption. Most analysts think the
>target
>is unreachable. In short, natural gas will be (a) scarce and (b) much
>more
>expensive than it is today. Natural gas supplies 20 per cent of world
>energy
>(25% in the US). But to replace petroleum as the prime transportation
>fuel
>will mean finding *double* that amount: in the US it would mean finding
>perhaps 70 quads a year, and even Skip Hobbs isn't suggesting that is
>feasible. But if all the yhpe and public optimism about fuel-cells is
>on
>track, that is exactly what WOULD have to be found. So someone is lying
>somewhere.
>
>Maybe the hydrogen can be found using *alternatives* to produce the
>necessary electricity? The alternatives comprise: nuclear,
>photovoltaics,
>wind and biomass. Together these alternatives today provide less than 5%
>of
>total US energy. Can they be ramped up?
>If alternatives CAN fill the gap left by declining oil, then both
>capitalism
>and the biosphere might be saved.
>
>In this scenario, hydrogen-driven fuel cells will be the motive-power
>source
>of the future; you'll even plug them into your home and power domestic
>electricity with them, so goes the hype which is repeated even by
>responsible and well respected people, for example people like legendary
>James Hansen, the Nasa scientist who practically invented the term
>'global
>warming'. His most recent paper, "Global warming in the twenty-first
>century: An alternative scenario" (James Hansen, Makiko Sato, Reto
>Ruedy,
>Andrew Lacis, and Valdar Oinas) (available from www.pnas.org for $5 or
>for
>free by writing offlist to me). This paper, published in August 2000, is
>already notorious because in it Hansen seems to backtrack on earlier
>global-warming doom-mongering. He is optimistic about reducing
>atmospheric
>CO2, mostly because of a new-found enthusiasm for technology. Hansen now
>beliecves that fuel cells and similar innovations will save the day:
>"Investments in technology to improve energy efficiency and develop
>nonfossil energy sources are also needed to slow the growth of CO2
>emissions
>and expand future policy options," Hansen writes.
>
>Hansen is employed by NASA, which practically invented the things, but
>it is
>clear that when it comes to fuel-cells he doesn't know what he is
>talking
>about, and his new-found techno-optimism is misplaced: natural-gas (or
>methanol) powered fuel-cells cannot replace gasoline engines, and unluss
>there is some other way out, the 'hydrogen economy' is likely to be
>still-born, even assuming fuel-cells can *ever* be manufactured cheaply
>and
>in volume, which remains unproven.
>
>Enthusiasm for alternatives, borne largely of desperation, is widespread
>these days. Even James Lovelock, father of the Gaia theory, believes
>that
>nuclear power is a possible, and necessary, alternative to fossil fuel,
>to
>judge from recent remarks of his (archived in the Crashlist).
>
>To replace the world's existing petroleum-based transportation fleets
>with
>hydrogen-powered systems (assuming this was technically or financially
>possible) will require the construction of around 25,000 new nuclear
>reactors. Oil demand today is about 75 million barrels per day, a power
>equivalent of 5 trillion watts. Supposing the nuclear plants were 40
>percent
>efficient in transferring nuclear energy to gaseous hydrogen, that
>requires
>12.5 terawatts of electrciity-genertaing capacity. But hydrogen must be
>condensed somehow, and this raises the input power by, in the
>representative
>case of cooling hydrogen until it liquefies at ambient pressure, a
>factor
>close enough to 2. This entails an extra global capacity of 25
>terawatts, ie
>about 25k conventional pressurised water reactors of 1 Gw output.
>
>Unfortunately, there is already a world shortage of exploitable uranium.
>Absent viable fusion technologies, such a massive increase in nuclear
>power
>generation is not feasible in resource terms (let alone safety terms).
>Whether such a massive construction of new nuclear power stations would
>be
>socially acceptable and/or politically feasible is a separate and
>interesting question.
>
>
>Others argue for photovoltaics. Actually we can take photovoltaics and
>biomass together, because both entail using available land (and possibly
>ocean) surface areas to capture solar energy fluxes. So far no
>technology
>exists (either by plant-based photosynthesis or silicon-based or other
>photovoltaic technology) which is capable of capturing enough solar
>energy
>to substitute for more than about 10 percent of today's use of fossil
>fuels.
>This leaves wind-power and some other mnore exotic methods (subsea
>turbines,
>geothermal). In all cases even the massive application of known
>technologies
>will provide orders of magnitude less energy than we get today from
>fossil
>fuels. In short, there is no way to make the transition to a non-fossil
>economy without massive social and economic upheaval and dislocation,
>even
>in the *best* case.
>
>Mark
>
>
>
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