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re: concentrator questions & clarifications
22 apr 1997
anco s. blazev wrote:
>mike page wrote:
>:|>(and once you have more than 6:1 concentration, who needs pvs? why not just
>:|>make steam with a black target?)
>
>: anyone care to follow this suggestion up? how would small-scale steam
>: to electric generation fare in relation to the pv systems that have been
>: proposed?
>
>first, it is up to the market to determine what's needed: pv, or steam.
>during my 20 years in the field i have not encountered too many demands
>for solar steam generation...
perhaps you arrived in this field a bit late :-)
howard reichmuth, pe, one of the inventors of the copper cricket, the ecotope
concentrating greenhouse, etc. suggested the 6:1 ratio. and the 1976 book
applied solar energy by meinel and meinel has this on pages 4-34:
the earliest attempts to convert solar energy into other forms revolved
around the generation of low-pressure steam to operate steam engines.
august mouchot pioneered this field by constructing and operating several
solar-powered steam engines between 1864 and 1878. evaluation of one built
at tours by the french government showed that it was too expensive to be
considered feasible if constructed on a scale sufficient for the practical
needs of commerce. another was set up in algeria, and mouchot described
some of this experiments with it in an 1869 publication.
in 1875, mouchot made a notable advance in solar collector design by
making one in the form of a truncated cone reflector. the spherical or
parabolic mirror arrays of his predecessors had focused all the light at
one small spot in space where the absorber or specimen was placed. mouchot's
cone, called an "axicon" in modern usage, focused light uniformly along
the axis of the cone so that a tube could by used for the energy-absorbing
surface, as shown in figs. 1.1 and 1.2. since the light was more diluted
than when it came to one small spot, the maximum attainable tempearature
was much lower, but then an engine designer is not interested in melting
a hole in his boiler if by accident the water level should drop too low!
mouchot's axicon consisted of silver-plated metal plates and had a diameter
of 540 cm and a collecting area of 18.6 m^2.; the moving parts weighed
1400 kg. it allegedly collected and focused 87% of the sun's heat on the
boiler enclosure. the steam engine was claimed to deliver 1.5 kw, but this
meant it was using less than 3% of the heat received... coal-fueled steam
engines of the day produced work with an efficiency of between 9% and 11%,
principally because they could work at a higher boiler temperature.
abel pifre was a contemporary of mouchot who also made solar engines and
who had a flair for demonstrating them before the public eye. pifre's solar
collectors were parabolic reflectors made of many small mirrors; they looked
rather similar in shape to mouchot's truncated cones. in 1878 at the paris
exposition, pifre exhibited one of his solar engines operating a printing
press, as shown in fig. 1.3. he had hoped to find customers for his solar
engine by this means and was no doubt disappointed to find much curiosity
but no buyers. later in 1882, he set up the engine in the gardens of the
tuileries palace, where he again demonstrated it operating a printing press.
john ericsson, of civil war fame for his role in the development of the
warship monitor, also gave his attention to solar-powered engines between
1871 and 1884... his 1883 model, one of seven that he constructed, is shown
in fig. 1.5. it used a cylindrical reflecting surface bent into a parabolic
shape, in which thin glass plates, silvered on the rear surface, were bent
into shape by iron ribs. the device pivoted about a vertical axis to follow
the sun. this device...claimed 0.7 kw for 9.3 m^2 of reflecting surface.
ericsson was able to look critically at the question of practicability of
solar engines, perhaps because he was spending his own money! during the
course of his experiments, he spent some $90,000, a very sizable sum in
those days. he concluded after his last engine that solar-powered engines
cost 10 times more than conventional engines and that their use could be
economically justified only for remote areas of "the sun-burnt regions
of our planet."
...patents for solar engines were issued in india to w. adams in 1878, in
germany to e. j. molera and j. c. derbrain in 1880 and to c. tellier in
1885, and in the united states to w. calver in 1882 and 1883. a general
summary of current ideas and work as of 1885 was published in scientific
american by charles h. pope, who also was an experimenter with solar engines.
...a lull in activity followed the advances made by mouchot, pifre, ericsson,
and adams, and it was almost the 20th century before a new surge of activity
began. ambitious ideas were forming, however, as indicated by a patent
issued in 1896 to c. g. o. barr for a very large solar engine. barr's engine
used a semiparabolic mirror array mounted on railroad cars on a circular
track, with a fixed boiler at the focus of the system. the engine was a
precursor of some ambitious soviet designs in the 20th century, and also of
the united states' "power tower" systems. the barr engine was not built,
and the soviet system was abandoned.
...because of the efficiency problems that mouchot and ericsson had
encountered, experimenters were using more sophisticated engines. some used
below-atmospheric pressure engines to help vaporize the working fluid. this
new concept was introduced in patents issued to e. h. mchenry in 1900 and
1911 and to e. c. ketchum in 1905 for engines that used two fluids; water
to collect the heat, and a working fluid of lower boiling point than water
to drive the engine.
in 1901... patents were issued to a. g. eneas. he built some very large
engines that were attracting wide attention... m. m. baker for solar
engines... in 1905, e. p. brown and carl gunther obtained patents on
solar steam boilers, as did w. maier and a. remshardt in 1907.
h. e. willsie and john boyle, jr. pursued a different approach to solar
engines from 1902 to 1918. instead of using mirror reflectors... they used
what we now call flat-plate collectors. sunlight entered the system through
a glass window and was absorbed by a thin layer of water flowing over a dark
bottom. the hot water was then used to vaporize a volatile liquid such as
ammonia, ether, or sulfur dioxide... the first willsie engine was built at
olney, ill, out of rather unsophisticated materials. the absorber was a
shallow wooden tank covered with two layers of window glass. the tank was
insulated with hay and the bottom lined with black tar paper... temperatures
were obtained that even in cold, raw october weather that were high enough
to vaporize sulfur dioxide for the engine.
the second willsie engine, built in arizona... used sand rather than hay
as an insulator. the tests were sufficiently encouraging that willsie
decided to form the willsie sun power company. in 1904 this company built
an ammonia-powered system at st. louis, mo, incorporating a 5 kw engine.
it is interesting that willsie prudently provided for the water to be
heated on cloudy days by burning fuel... 1905 at needles, ca... this 15 kw
system operated an irrigation pump that also supplied cool water for the
condenser of the engine. the sulfur dioxide-powered engine developed about
11 kw from a total collecting area of about 186 m^2. although the willsie
engines were a commercial failure, they were a technical success since they
demonstrated that the flat-plate collectors were not as sensitive to
cloudiness as the mirror systems used previously...
frank shuman began work in 1906 on a solar engine concept that, like
willsie's, used flat-plate collectors. by 1907 he had completed his first
engine. it developed 2.6 kw from a collecor of 110 m^2 that heated water,
which in turn vaporized ether. in his 1911 system, built at tacony (near
philadelphia), shuman added a... flat mirror along the north and south edges
that... doubled the energy output. this system... had a total collecting
area of 960 m^2 and yielded 32 kw with steam as the working fluid.
in 1912, shuman, in collaboration with c. v. boys, undertook to build the
world's largest solar pumping plant in egypt. the original boiler exploded
but was replaced in 1913 with a stronger one... the meadi system [used]
long parabolic cylinders to focus sunlight on a long absorbing tube... each
was 62 m long, and the total area of the several banks of cylinders was
1200 m^2... the shuman-boys solar engine developed 37 to 45 kw continuously
for a 5 hour period. the project, however, was abandoned in 1915 as a dual
casualty of wwi and the competition of cheaper sources of power that became
available about that time.
shuman and boys obtained a patent on their solar engine in 1917, as did
r. a. fessenden for a vapor engine to operate at lower than atmospheric
pressure. new engine ideas were popular during this period: three patents
were issued to t. f. nichols from 1912 to 1915, one to c. e. burnap in 1914
for an engine operating with ammonia as a working fluid, and one to
m. koller in france in 1913.
a solar engine idea was patented by w. j. harvey in 1921, by l. h. shipman
in 1928, and four by robert h. goddard, of rocket fame, from 1929 to 1934...
cesare romagnoli in italy did develop a working engine in 1923, using hot
water at 55 c (130 f) to heat a second liquid of lower boiling point,
ethyl chloride.
.. house heating--first appeared in the mid 1930s... unfortunately the
glowing predictions of solar-heated houses did not materialize. in 1955
it was predicted that several million homes would be heated by solar energy
by 1970. the actual count in 1970 may, in fact, be lower than it was in
1955. the hard facts of economics defeated the dream of solar-heated homes.
h. delecourt... developed and constructed a solar engine in 1930 that used
ethyl chloride... patents for solar engines were issued in 1930 to d. h.
drane for an ammonia engine, in 1931 to g. w. dooley, in 1932 to w. l. r.
emmet, whose solar collector, mirrors and all, was inside a vacuum envelope;
and in 1935 to f. a. gill...
solar cells also got a lot of attention when l. bergmann, in 1932 and 1936,
and g. bail, in 1938, studied the effects under sunlight of semiconductors.
time passes...
we soon learned a fundamental problem about the distillation of water.
the "heat of vaporization" for water is very high... even though this heat
is reemitted when the steam condenses to water, its temperature is exactly
the same as that of the boiling water, so it is impossible under these
conditions to cause the heat to flow from the condensing steam to the
boiling water. we did devise a way to solve this problem--by compressing
the water/steam before condensation so that it condensed at a temperature
above that of the boiling water in the next stage... the work done in
compressing... was considerably less than was regained from condensation...
when we came to the question of economics, we soon learned one of the
basic facts that has arrested all attempts to use solar energy: the cost
of the equipment, installation and maintenance is greater than the cost
of doing the same task by cheap fossil fuels...
it is interesting that solar energy was then, as today, classified as an
exotic topic and that the devices that are constructed are still very much
in the category of curiosities, except in one very important area: the use
of silicon chips, mounted thousands to a panel, used to provide dependable
electric power for spacecraft. their efficiencies are quite respectable,
early ones having about 8% conversion efficiency and the current ones [1976]
12% to 15%. we must note here that while these efficiencies of conversion
of solar heat into power are less than the 35% to 40% for modern steam
turbines powered by fossil fuel heat, they are far higher than the 1% to 3%
more characteristic of the solar engines of the eneas era:
...the machine was exhibited at the edwin cawston ostrich farm, and has
attracted the attention of a vast number of people, especially as southern
california is now thronged with tourists... a reflector thirty three feet
six inches in diameter at teh top and thirteen feet on the bottom. the inner
surface is made up of 1788 small mirrors... a section of a cone... focused
on... the boiler, thirteen feet six inches in length... holds one hundred
gallons of water, leaving eight cubic feet for steam... the questions asked
were remarkable. one man assumed it had something to do with the incubation
of ostrich eggs... up to the present time the motor has produced results
equal to about ten horse power, but fifteen is claimed for it...
...almost ten years of effort resulted in nothing but some interesting
pictures in the newspapers and journals of the day, now gathering dust
in the archives of libraries...
...can we see a message in the failures of these noble efforts?...
electrical energy was available in the cities to a limited extent, but
electrical distribution lines were not available in the areas of low
population density. it seems hard for us now to realize that even in the
early 1930s rural electrification was only a dream. a reason for failure
was the the discovery... of oil fields in california and texas...
internal combustion engines could deliver the power to pumps with a
very compact device that was easy to operate and maintain (although
gasoline engines oin the 1920s and 1930s did try the patience...)
another factor... is that solar power from the eneas engines could be
obtained only during the daytime on clear days. pwer, therefore, was not
available at the click of a switch or the turn of a starter crank... the
limitation clearly was real to the boston group, since its members promised
that this problem would disappear with the cheap and long-lived storage
batteries "just around the corner." well, 70 years later we still have not
turned that corner...
the story goes back to 1917 in pasadena, california, and to c. g. abbot
and his colleague g. e. hale, astronomer and founder of observatories...
both were then working on war research at hale's latest observatory, the
mount wilson observatory... [professor] goddard and abbot discussed another
challenge to mankind--solar energy. goddard reacted with enthusiasm and
vision, and the first of five patents on solar energy was issued to him on
10 july, 1924. goddard's contribution through this and four subsequent
inventions was not in basic new ideas but in engineering innovations
designed to render earlier ideas practical...
the devices designed by goddard were supposed to increase the energy
utilization from the usual 3 % to 4% up to, he claimed, 50%. his approach
seemed sound. he would increase the efficiency by increasing the temperature
of the working fluid, the carnot efficiency... goddard's patent drawings
show nozzles... for increasing the velocity of the vapors emitted from his
"solar accumulators." in 1929, the sunday new york times carried an article
that attracted much attention to goddard's publication of an article in the
october 1929 popular science monthly entitled "a new invention to harness
the sun." it was the last word from goddard on solar energy...
time passes...
in 1960 farrington daniels of the university of wisconson and t. finkelstein
of the battelle memorial institute made an improvement in the solar-type
stirling engine by replacing the heat-conducting head of the cylinder by a
sunlight-transmitting quartz window. since the heat still must get into the
working gas of the engine, this modification was less effective than it
first appeared. one needs an opaque working gas plyus the quartz head to
improve the stirling cycle enough for practical application...
harry tabor of the national physical laboratory in israel developed a
turbine engine to use solar energy in the 1960s. for a working gas he
substituted a heavy hydrocarbon molecule, monochlorobenzene... his turbine
operated at 150 c, at 18,000 rpm, and produced electricity at 50 cycles
per second. he estimated the cost of the power generated to be $0.035/kwh.
his collectors consisted of inflated plastic sylinders, clear on top to
admit sunlight and aluminized on the bottom to focus the light on a
heat-collecting tube. he estimated that 75% of the cost of his system
was due to the plastic collector...
...a turbine driven by ethyl chloride was used in libya in 1954 by
l. d'amelio. another... was built by enzio carlivari on the island
of ischia that is reported to have developed 3.4 kw...
nick
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