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For several years, there have been ongoing developments on improving the output, efficiency and relative cost of solar thermal and various solar photovoltaic technologies. At the present time, photovoltaic and concentrated photovoltaic technologies appear to be gaining the upper hand as the technology achieves higher conversion efficiencies combined with reduced capital costs. One especially attractive feature of modern solar PV technology is that is can easily and cheaply be installed on to sloped roofs in the urban environment.
A complimentary solar PV technology is transparent is combined with tinted window technology. It may be installed as solar PV windowpanes into large office towers, while a complimentary metallic based solar PV technology can be installed as siding on to buildings. As the price of PV technology drops and its efficiency increases, it becomes an attractive option for decentralized power generation.
Advancing solar PV technologies have recently made inroads into solar thermal markets, notably the scaling back of solar thermal projects involving solar-steam and solar-Stirling-cycle conversion in the SW USA. Solar PV technology has a secure market niche in the urban environment, as do certain forms of solar thermal technology. Solar water heaters have definite application in the urban environment and such heaters can energize absorption refrigeration cooling systems. There may still be potential for some forms of large-scale solar thermal power conversion outside of urban areas.
Solar-Steam Technology:
Functional solar powered steam power conversion technologies operated on a demonstration basis in the USA during the 1920's. For the decades that followed, solar steam was without a solar competitor. For a brief period during the late 1950's and early 1960's, the solar battery showed some promise, except interest in that technology quickly faded. Solar steam power made a small-scale resurgence during the 1970's and over the decades that followed. The technology has its critics and it has its drawbacks:
Coal-fired power generation was much cheaper
Solar steam power was only available for part of the day
The extensive high-pressure piping systems associated with solar steam power increases the need for blow-down, to remove impurities upstream of the turbines. In arid regions, lack of available make-up water restricts solar thermal steam power conversion.
Large-scale, reliable, competitively-priced thermal energy storage technologies have until recently been unavailable
Competing solar-Stirling conversion technologies involve high cost relative to relatively low output that is the nature of the technology. A California-based energy research group attempted to compete with Stirling-cycle technology by developing a closed-cycle, solar-heated Brayton-cycle micro-turbine engine of 7kW at 30% efficiency that like Stirling engine technology, used air as the working fluid. The particular technology involved high cost and was aimed at small power users.
Ocean thermal power conversion (OTEC) showed some promise as it involved generating power from the difference in temperature on the ocean surface off the coast of Hawaii and cooler ocean water located at greater depth. The technology involved low efficiency and high capital cost relative to power output. At the present day, there is ongoing research involving OTEC is off the coast of India, a nation that has great need to increase electrical power generation.
Possible Niches for Solar Thermal Power:
One solar thermal project to show some promise involves a solar heated Organic Rankin Cycle (ORC) engine of 1MW output in Hawaii. The pressurized working fluid used in such engines typically involves lower operating temperatures and a fraction of the latent heat of vaporization as water to convert from liquid to superheated vapor. The technology requires fewer solar reflectors. It is also easier and cheaper to condense the working fluid using ocean water at coastal locations.
The low vaporization temperature or refrigerants used in ORC engines can allow for the use of pressurized saturated water (in the liquid state under 70-psia) to collect solar thermal energy at temperatures of under 150° C or 300° F form solar-trough collection technology. Such installations involve typically lower cost than comparable high-pressure, high-temperature technology needed to superheat steam to 600° F at 250-psia. The water-based heat collection and heat transfer has absolutely minimal need for make-up water. The externally heated ORC engines are compatible with low-cost form of solar thermal energy collection and storage technology, being salt ponds.
Unlike potable water or low-salinity water that would reflect the infrared solar spectrum, high-salinity water captures infrared light, heating the floor of the salt pond to 65° C to 95° C (150° F to 200° F). Oceanside coastal salt ponds are a low-cost, low-tech form of solar collector and thermal storage medium that can operate for decades, provided that the saline concentration is continually optimized to maximize thermal collection and thermal energy storage. It is also possible to purposefully build solar salt ponds that collect brine from thermal desalination installations or that use rock salt from salt domes that have been flushed to store natural gas or compressed air.
Special piping made from corrosion-resistant material that also has high thermal conductivity would be installed under the floor of the salt ponds to carry pressurized liquid, including seawater that would transfer heat to one or more ORC engines. The combination of salt pond solar collection and solar troughs can heat the pressurized liquid to 150 C or 300 F to energize the ORC engines. An array of coastal salt ponds can serve as the collector and storage system for a battery of multiple ORC engines or provide thermal energy for a single large-scale engine of higher output.
Air-Based Solar Engines:
While most ORC engines are rated for up to 1MW output at up to 14% peak efficiency, there is a cross over point where it becomes feasible to replace a bank of multiple ORC engines with a single large air-based engine. There are 2-possible air-based technologies that can operate on the heat collected by an array of solar salt ponds located in arid regions near an ocean coast. A 50kW scale model of such a technology has been in operation at Manzanares in Spain and serves as a proof of concept that a thermal chimney may be heated by solar thermal energy and generate electric power.
Large-scale versions of solar chimney technology can operate on much lower temperatures such as the levels that occur on the floors of solar salt ponds. There are two versions of the technology called vortex engines that involve chimneys built to vertical heights of some 200-ft or 60m. These chimneys may be built with the equivalent of large ducts that guide the incoming air to flow into a vortex or stationery cyclone. Theoretical research has indicated that vortex engines could generate 50MW to over 200MW as heated air is pulled through air turbines built into inlets located at the base of the chimney. There are 3-groups researching competing non-vortex chimneys of 1000m to 1500m in vertical height that may deliver 200MW of 300MW of output.
The leaders of the groups include Roger Davey at Enviromission in Australia (200MW, 1000m chimney), Prof. Wolf-Walter Stinnes at Green Tower (300MW, 1500m chimney) in South Africa and Prof. Christos Papageorgiou at University of Athens (200MW, 1000m floating chimney). These chimney concepts can operate on heat collected by an array of solar thermal salt ponds or they may operate on heat collected by a gigantic greenhouse (of up to 6-miles or 10-Km in diameter) that surrounds each chimney. While the chimney-based solar thermal engines will involve high capital cost, they are believed to be cost-competitive in a per megawatt basis with photovoltaic technology for grid-scale power generation, in remote locations.
High-Temperature Air Solar:
There have been advances in high-temperature stainless steel technology, in ceramic technology (silicon carbide) and in high-effectiveness and in high-temperature heat exchanger technology (the annular-counter-flow design). The combination of these technologies can sustain the efficient operation of solar powered, externally heated Brayton-cycle turbine engines. The main drawback of such technology is that in Brayton-cycle engines, the turbine sustains the operation of the turbo-compressor that can consume 55% to 70% of the total turbine output.
Ongoing developments in energy storage technologies can offer an alternative to the high power consumption of turbo-compressors. Worldwide, there is interest in and ongoing developments involving mega-scale compressed air energy storage (CAES), especially in geographic locations where oil and natural gas occur. Such regions are also home to salt caverns and salt domes that may be flushed of salt, with the remaining cavity being capable of storing either compressed natural gas or compressed air at pressures as high as 3000-psia.
During the overnight and seasonal off-peak hours, electrical energy generated by wind farms, oceanic power conversion technologies and thermal power plants would drive the air turbo-compressors. There is often productive overnight and seasonal use for the heat of compression at many locations. During power generation periods, air will flow from storage through a pipeline distribution system to a heating system where concentrated solar thermal energy would superheat the air prior to its expansion in turbine engines. Operating free from the loads of turbo-compressors during these periods assures that maximum solar-electric power would be available to the grid.
Combined-Cycle operation:
A solar-heated air turbine system can deliver grid-scale power output at competitive cost and at high efficiency when operating on compressed air. Such an approach can offer a competitive niche to high-temperature, concentrated solar thermal power technology. The heated exhaust air from such a system may be put to productive use such as desalinating seawater at coastal locations or sustaining the operation of an air-based bottom-cycle engine such as a vortex engine or a thermal chimney engine.
The combination of a solar-heated air turbine operating on compressed air and a vortex engine or a chimney engine operating on its waste heat could offer an efficient and potentially competitive concentrated solar thermal power generation concept. Such air-based solar thermal power systems would be ideally suited for operation in hot, arid locations where make-up water would be non-existent. At coastal locations where make-up would be available, air-based chimney technology may serve as the bottom-cycle engine for the few solar thermal steam installations that may be competitive and viable.
Conclusions:
While solar PV and concentrated solar PV presently appear to have the competitive upper hand in solar power generation, there may still be potential left in concentrated solar thermal power conversion. Lower temperatures involve lower cost and could make ORC engines and air-based chimney engines attractive and potentially viable solar thermal technologies. The combination of compressed air energy storage (CAES) and high-temperature solar energy technology involving solar heated turbines operating in a combined cycle with air-based chimney engines promises to be a viable solar thermal concept. An air-based chimney engine can serve as the bottom-cycle engine for a solar thermal steam power installation at select locations.
For information on purchasing reprints of this article, contact sales. Copyright 2013 CyberTech, Inc.
I'd be interested to see a reference for your assertion that PV is now or may shortly be lower cost per unit output that solar thermal. Recent distributed solar installation in Ontario costs $10 / watt. Solar thermal is presently far ahead of that presently producing "in the range of" 13 cents / kwh, and projected to cross over coal generation costs if it could get int the range of 8 GW installed.
Data from the NETL places solar thermal north of $200/MWH, with photovoltaic’s even higher, and that is in Daggett, California (down load NRTL's Solar Advisor program).
I do a fair amount of financial Pro Forma work and nothing I've seen has solar becoming even remotely competitive. The diffuse nature and intermittency of the energy source are severe drags on making a profit, absent extremely heavy government handouts.
As to Ontario: a classic case of waste of the taxpayer’s money on an ill-conceived government misadventure.
Len Gould 8.17.10
Micheal. The issue with solar thermal is not what it costs from todays one-off demonstration projects engineered and built with long intervals between uses of the fabrication facilities and teams etc. etc. etc., but what would the costs be with optimally sized factories for the collectors, continuous installation teams, and continuous development of minor improvements, going to eg. 8 GW in a very short time. Criticising the entire concept based on todays scattered installations' production costs is like declaring steam power ridiculously expensive and not worth development based on the performance of Watt's water pumps. The real problem is that solar thermal is fully capable of out-competing coal generation everywhere with development, BUT the present coal-generation technology has a 200 year development edge and no shortage of fuel far into the future, so by strict economic rules, will continue to control. IMHO a tragic state of affairs given solar thermal's potential to achieve baseload reliability (83%) at "3.5 to 6.2 cents / kwh" if only it could get a large enough installation demand going, eg. 2 to 8 GW by 2020. (See Sargent and Lundy / NREL)
Len Gould 8.17.10
And btw Southern Ontario, where all the population is, has 20% better insolation than ANY part of Germany, which is the world leader in installations (and production).
bill payne 8.17.10
"absent extremely heavy government handouts"
"Obama's 'Green' energy program an epic failure in Spain"
'Each "green job" comes at the expense of 2.2 traditional jobs."
From: "ABQjournal Biz Desk" To: "bill payne" Sent: Monday, August 16, 2010 4:02:19 PM Subject: Business Insider
From the staff of the Albuquerque Journal and Business Outlook
Hello, bill.
SOLAR OR NO -- Although city leaders say they still hope the Green2V solar startup comes to Rio Rancho, they have started pitching the intended factory site to other companies. And they have committed $7 million to road and sewer improvements to prep the area for future industrial development, even if Green2V never moves in.
If a business brings jobs to New Mexico, then it apparently is good.
Little or no concern as to whether large-scale solar generation of electricity works appears unimportant in New Mexico.
while it is noted that the current Solar Power technolgy is very expensive, i consider that this is a promising technolgy of near future, as this technology will encourage setting up of distributed generation at differnt pockets of the load centre. Initially to encourage more and more enterprises to set up this technology, Government/regulatroy support is needed to contain the current cost of generation and subsidising the tariff to end users. Howvever , PHV is ging to be the technology of future wordwide and tehrfore the costs are expected to go down as in the case of wind generation. Hence , this technolgy will be in the heart of lot of venture capital investors and is going to be the preferred darling for investment. Furtehr, with teh ambitious targets taken under the climate chaneg by all countrieds world wide, Non-conventional energy sources will be the apt windows for tomarrow and for future generations of mankind. Therfore every effort to be done by all stake holders to support such initiative in the interst of Earth Mother
Michael Keller 8.18.10
Len, It does not follow that throwing massive amounts of money at a problem will solve the problem. The laws of thermodynamics and nature mean that solar energy is inherently very difficult to economically harvest.
Technology and manufacturing advancements can help, but the fact remains that renewable energy is currently not competitive (by a very large margin) with mainstream energy sources.
Malcolm Rawlingson 8.18.10
Len,
Whose farms are you going to bury in millions of solar collectors?
And what on earth do you mean by the term "potential to achieve base load reliability (83%). Do you mean capacity factor? Explain.
As Michael says distributed energy sources are not now and never will compete with mainstream energy sources. That is why the government of Ontario offers 80 cents per Kw hour. Twenty times the cost of nuclear power. Dumb idea.
And I will point out once again that in Ontario - just like Germany the Sun inconveniently does not co-operate at night time and output of ALL solar panels falls to nil. Not much good really is it - unless you have a really big battery - or a bunch of Nukes operating to fill the energy void.
But throw enough money around and I am sure someone can figure out a way to make the Sun shine 24 hours a day.
Malcolm
Len Gould 8.20.10
eg. Malcolm: I've asked you to learn something about solar thermal before making broad sweeping statements, before. You should AT LEAST have the grace to include a "BTW, knows nothing about solar thermal" disclaimer on all your nonsense.
Malcolm Rawlingson 8.23.10
Len, You have consistently failed to answer almost every searching question you have been asked about solar thermal power by which I conclude you know very little about the practicalities of actually doing it.
All theory No practice.
Malcolm
Len Gould 8.25.10
ISigh) responding to paragraph numbers in your 8.18.10 post 3 up:
1) Regarding "burying farms". how about 1/300th of the number now used to produce bio-fuels?
2) 83% capacity factor is achievable by tripling the collector area per unit generation (thus tripling the kwh output and reducing kwhr unit cost) using insulated tanks of sand/gravel mix as thermal storage. Cheap, efficient, effictive solar baseload.
3) as shown in S & L / NREL study i've referenced before, present-day solar thermal technology generates at 12 to 13 cents / kwh. With a rate of build targeted to achieve 2.4 to 8.0 GW installed by 2020, that cost will drop to 3.4 to 6.2 cents / kwh. Only approx. 25% of the preposed cost reductions are ascribed to technology advances, 75% to simple cost reductions due to mass manufacturing and continuous installation.
4) Again, confusing solar thermal with PV. ???
5) Is that supposed to be some brilliant new scientific observation on your part?
Pointless, i know. Old dogs and new tricks type stuff i guess.
Malcolm Rawlingson 8.27.10
I too sigh. Bio fuels was, is and always will be a stupid idea. More energy in than you get out. A stupid comparison Len - you know better. False red herring comparisons like that tell me your case is very weak.
So how about solar thermal = thousands of times more land area than a 24 hour a day nuclear plant including the mining operations of uranium mines.
How are you going to move the tons of sand and gravel mix required. Could that be with diesel trucks?
Len if you believe it is an economic proposition put your dollars in to it and make your millions. Clearly you believe it to be a money spinner at the rates and efficiencies you quote. In the meantime I'll put mine into Cameco and Uranium Participation Corporation. If you can produce electricity this way this cheaply you have it made in the shade my friend. If true (and I believe not a word of it) then every utility will beat a path to your door. Seems to me that most utilities are beating a path to the nuclear door. 440 operating, 59 under construction 149 in pre planning and 344 in consideration.
Tell me again how many of this type of thermal plant are operating?
83% capacity factor - except you omitted a very important piece of data - where? You will NEVER get 83% capacity factor in Canada.
Yes I am indeed an old dog - but my tricks are proven to work. Yours don't The new tricks I prefer to learn are using Thorium, recycling used fuel, fast breeder reactors and fusion. Those are real long term energy solutions.
Like I said all theory no practice - if you consider that a brilliant scientific observation I am thrilled - but worried about your sanity.
I have made millions of kilowatt hours of power operating nuclear plants - I know that works. You have made none using your method yet you expect me to believe it will produce these stunning results. 83% CF when the sun doesn't shine more than 50% of the time. You really must be joking or you have developed a new and innovative definition of capacity factor.
If it sounds too good to be true (and this idea does) then it probably is. There is not a single investor that would touch that idea with a 10 foot barge pole.
I would save your pennies and put it into Uranium stocks. With massive impending demand and a current 26% shortfall in supply there is only one way Uranium is going and that is up.
Malcolm
Len Gould 8.31.10
More flawed argument Malcolm. You demand that I invest my "dollars in to it and make your millions." and close with "There is not a single investor that would touch that idea with a 10 foot barge pole." -- You clearly haven't understood the core dilema, which is that IT CAN'T MAKE MONEY UNTIL THERE IS 2.4 to 8 GW installed and a robust continuous manufacturing and installation process in place. OBVIOUSLY no inveastor in their right mind is ever going to fix that problem on their own.
And yes it can work in Canada, simply requires a different set of suplements and auxiliaries that'll need to wait until round two or three to develop.
Len Gould 8.31.10
Its exactly the same problem as your nuclear favourite. Was it private investors who developed our knowledge of fission tech? The reactors for the subs, the processing and enrichment for the weapons? If solar thermal had any military use it would be commercial long since.
