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Super Soaker Inventor Aims to Cut Solar Costs in Half
Posted on Wednesday, January 09, 2008 @ 18:42:10 UTC by vlad
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Solar energy technology is
enjoying its day in the sun with the advent of innovations from
flexible photovoltaic (PV) materials to thermal power plants that
concentrate the sun’s heat to drive turbines. But even the best system
converts only about 30 percent of received solar energy into
electricity—making solar more expensive than burning coal or oil. That
will change if Lonnie Johnson’s invention works. The Atlanta-based
independent inventor of the Super Soaker squirt gun (a true
technological milestone) says he can achieve a conversion efficiency
rate that tops 60 percent with a new solid-state heat engine. It
represents a breakthrough new way to turn heat into power.
Johnson, a nuclear engineer who holds more than 100 patents, calls his
invention the Johnson Thermoelectric Energy Conversion System, or JTEC
for short. This is not PV technology, in which semiconducting silicon
converts light into electricity. And unlike a Stirling engine, in which
pistons are powered by the expansion and compression of a contained
gas, there are no moving parts in the JTEC. It’s sort of like a fuel
cell: JTEC circulates hydrogen between two membrane-electrode
assemblies (MEA). Unlike a fuel cell, however, JTEC is a closed system.
No external hydrogen source. No oxygen input. No wastewater output.
Other than a jolt of electricity that acts like the ignition spark in
an internal-combustion engine, the only input is heat.
Here’s how it works: One MEA stack is coupled to a high- temperature
heat source (such as solar heat concentrated by mirrors), and the other
to a low-temperature heat sink (ambient air). The low-temperature stack
acts as the compressor stage while the high-temperature stack functions
as the power stage. Once the cycle is started by the electrical jolt,
the resulting pressure differential produces voltage across each of the
MEA stacks. The higher voltage at the high-temperature stack forces the
low-temperature stack to pump hydrogen from low pressure to high
pressure, maintaining the pressure differential. Meanwhile hydrogen
passing through the high-temperature stack generates power.
“It’s like a conventional heat engine,” explains Paul Werbos, program
director at the National Science Foundation, which has provided funding
for JTEC. “It still uses temperature differences to create pressure
gradients. Only instead of using those pressure gradients to move an
axle or wheel, he’s using them to force ions through a membrane. It’s a
totally new way of generating electricity from heat.”
The bigger the temperature differential, the higher the
efficiency. With the help of Heshmat Aglan, a professor of mechanical
engineering at Alabama’s Tuskegee University, Johnson hopes to have a
low-temperature prototype (200-degree centigrade) completed within a
year’s time. The pair is experimenting with high-temperature membranes
made of a novel ceramic material of micron-scale thickness. Johnson
envisions a first-generation system capable of handling temperatures up
to 600 degrees. (Currently, solar concentration using parabolic mirrors
tops 800 degrees centigrade.) Based on the theoretical Carnot
thermodynamic cycle, at 600 degrees efficiency rates approach 60
percent, twice those of today’s solar Stirling engines.
This engine, Johnson says, can operate on tiny scales, or
generate megawatts of power. If it proves feasible, drastically
reducing the cost of solar power would only be a start. JTEC could
potentially harvest waste heat from internal combustion engines and
combustion turbines, perhaps even the human body. And no moving parts
means no friction and fewer mechanical failures.
As an engineer, Johnson says he has always been interested in
energy conversion. In fact, it was while working on an idea for an
environmentally friendly heat pump (one that would not require Freon)
that he came up with the Super Soaker, which earned him millions of
dollars in royalties. That money allowed Johnson to quit NASA’s Jet
Propulsion Lab (where he worked on the Galileo Mission, among other
projects) and go independent. His toy profits have funded his research
in advanced battery technology, specifically thin-film lithium-ion
conductive membranes. And that work sparked the idea for JTEC. Besides,
he jokes, “All inventors have to have an engine. It’s like a rite of
passage.”
Source: http://www.popularmechanics.com/science/earth/4243793.html
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Re: Super Soaker Inventor Aims to Cut Solar Costs in Half (Score: 1)
by vlad on Wednesday, January 09, 2008 @ 20:19:15 UTC
(User Info | Send a Message) http://www.zpenergy.com | New nanostructured thin film shows promise for efficient solar energy conversion
In the race to make solar cells cheaper and more efficient, many
researchers and start-up companies are betting on new designs that
exploit nanostructures--materials engineered on the scale of a
billionth of a meter. Using nanotechnology, researchers can experiment
with and control how a material generates, captures, transports, and
stores free electrons--properties that are important for the conversion
of sunlight into electricity. More: http://www.physorg.com/news119024680.html [www.physorg.com] |
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Re: Super Soaker Inventor Aims to Cut Solar Costs in Half (Score: 1)
by Koen on Friday, January 11, 2008 @ 05:54:29 UTC
(User Info | Send a Message) http://no.nl/tesla | Also see http://www.johnsonems.com/jhtec.html
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Solar Cells Can Take the Heat (Score: 1)
by vlad on Wednesday, January 09, 2008 @ 18:45:45 UTC
(User Info | Send a Message) http://www.zpenergy.com | Solar cells have attracted global attention as one of the cornerstones
of alternative energy. In theory, it seems to make abundant sense to
tap into the energy of the sun to convert light to electricity with
little or no emission of noxious pollutants.
However, in practical terms, progress has been
slow because of technological impediments and the many different
factors that need to be optimized to obtain stable and high-efficiency
devices.
Dye-sensitized solar cells based on dye molecules adsorbed onto
titanium dioxide electrodes have emerged as one of the most attractive
solar-cell constructs, combining low cost and relative ease of
fabrication with high-efficiency performance. Indeed, state-of-the-art
solar cells with this architecture show greater than 11%
light-conversion efficiency.
However, the catch is that these high-efficiency solar cells
typically use volatile organic solvents as electrolytes, which
essentially precludes their use in outdoor applications because of the
high vapor pressure of the solvents. Solvent-free solar cells
fabricated so far show poor performance owing to the high viscosity of
the alternative electrolytes.
Now, a team of researchers at the Ecole Polytechnique Fédérale de
Lausanne in Switzerland have fabricated a solvent-free dye-sensitized
solar cell based on a binary ionic liquid electrolyte. These devices
show a light-conversion efficiency of 7.6% under simulated sunlight
conditions, which sets a new record for a solvent-free device.
Shaik Zakeeruddin, Michael Grätzel, and their colleagues have used
a mixture of two ionic liquids as the redox electrolyte in conjunction
with a novel highly conjugated ruthenium-based dye to prepare a
solvent-free solar cell.
Ionic liquids essentially have a vapor pressure of zero, which
makes them preferable even to robust and low-volatile organic solvents.
However, the typically high viscosities of ionic liquids and the fact
that most of the promising ionic liquids are composed of iodide ions
have precluded their application in viable cells since iodide ions tend
to have a deleterious impact upon the photoconversion efficiency by
quenching the dye sensitizer.
Grätzel and co-workers have tackled these
challenges by adding in a low-viscosity ionic liquid comprising an
inert anion. The low viscosity helps to overcome mass-transfer
challenges, whereas the inert anion counteracts the deleterious
influence of the iodide anions.
The obtained solar cells show a record 7.6% conversion efficiency.
More importantly, these cells are stable at 80 °C in the dark and under
visible-light soaking at 60 °C for over a thousand hours, which points
to the possibility of their use in outdoor applications in warm
climates. The solvent-free nature of the electrolyte also suggests that
it may be possible to construct flexible and lightweight devices based
on these electrolytes.
“This is a big step in the search for nonvolatile electrolytes”,
said Zakeeruddin, adding that the performance of devices based on ionic
liquids had lagged so far behind that it was widely thought that these
systems would be limited to indoor applications at low lighting levels.
Grätzel added that the results indicate that it should be possible to
further optimize the performance of these solvent-free systems.
Citation: Michael Grätzel, Stable, High-Efficiency Ionic-Liquid-Based Mesoscopic Dye-Sensitized Solar Cells, Small 2007, 3, No. 12, 2094–2102, doi: 10.1002/smll.200700211
Source: Wiley-VCH
Via: http://www.physorg.com/news119087375.html [www.physorg.com]
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