Solar thermal energy technologies make major strides
Since the early 1860s, when French engineer and inventor Auguste Mouchout used a glass-enclosed cauldron, a polished parabolic dish, and the sun’s heat to produce steam for the first solar steam engine, solar thermal energy (STE) technology has come a long way. Today, an assorted range of technologies is in use or on-line — including parabolic troughs, power towers, and dish/engine systems — and several others are in development. The spate of announcements about solar thermal energy this October and November showed how diverse that range can be and how far those technologies have come.
Next generation CSP
Ausra Inc. has launched the Kimberlina Solar Thermal Energy Plant in Bakersfield, Calif. — the first solar thermal power plant built in California since FPL Energy put up its nine Solar Energy Generating Systems (SEGs) in the Mojave Desert in the late 1980s and early 1990s. The 5-MW (electric) Kimberlina uses what Ausra calls next generation concentrating solar power (CSP) technology, and the company said it is modeled after its Liddell solar thermal facility in New South Wales, Australia.
The plant, consisting of rows of 1,000-foot-long mirrors, was built in seven months by 150 workers (Figure 1). The collector lines will generate up to 25 MW of thermal energy to drive a steam turbine at the adjacent Clean Energy Systems power plant. Ausra said that it had dropped costs by simplifying the system’s design and by mass-producing the mirrors at its factory in Las Vegas, Nev.
Cheaper, quicker, stronger. Ausra’s Kimberlina Solar Thermal Energy Plant in Bakersfield, Calif., consists of rows of 1,000-foot-long mirrors. The collector lines will generate up to 25 MW of thermal energy to drive a steam turbine at the adjacent Clean Energy Systems power plant to produce 5 MW of electricity. Courtesy: Ausra Inc.
Kimberlina is just a start for solar thermal power in California. Ausra is now developing a 177-MW solar thermal power plant for Pacific Gas and Electric Co. in Carrizo Plains, west of Bakersfield. In addition to that plant, the California Energy Commission is reviewing proposals for five large solar thermal plants, including Stirling Energy Systems’ SES Solar Two Project (750 MW), BrightSource’s Ivanpah Solar Tower (400 MW), Beacon Solar’s 250-MW solar trough project in Kern County, and two hybrid projects that would use solar troughs to produce a total of 112 MW. All six projects would add 1,689 MW to the grid. The federal Bureau of Land Management is also studying requests from developers to build 34 more solar plants in Southern California, all of which would produce some 24,000 MW.
Solar tower steam turbines
Siemens Energy said it would supply an industrial steam engine to one of the world’s first commercial solar tower power plants, Sener’s 19-MW Solar Tres project near Seville in Spain — a project that the company started seven years ago. The solar power plant will bundle sunlight using sun-tracking mirrors (heliostats) placed in arrays around the tower and reflect the light directly into a receiver at the top of a tower about 400 feet high.
The heliostats will be arranged over a surface area of 320,000 square meters, about the size of 60 football fields. The project will use salt for heat transfer in the interior of the receiver instead of the thermo oil typically used. Sunlight concentration will produce temperatures of over 1,562F at the solar receiver. The salt, heated to approximately 1,049F as a result, flows in a molten state through a heat exchanger, in which sufficient steam is produced to operate a steam turbine generator.
Siemens, which makes turbines for parabolic mirror solar thermal pants, customized the two-cylinder reheat SST-600 turbine to meet the technology requirements for the Sener solar tower project. The company said the reheat will enhance the plant’s overall efficiency. It also worked with Sener to create a concept that protects the steam turbine from cooling down too much at night.
Glass-free parabolic mirrors
Whereas most parabolic trough mirrors are made of heavy curved glass, the SkyTrough, unveiled recently by start-up company SkyFuel Inc. and scientists from the National Renewable Energy Laboratory, is made from SkyFuel’s own ReflecTech, a highly reflective and shatterproof silvered polymer film that is laminated to thin aluminum sheets (Figure 2). The film offers several advantages: It allows for larger and fewer panel segments than in previous trough designs; according to SkyFuel, it cuts the costs of the parabolic trough concentrator by 35%; and it can be manufactured in high volumes.
All that reflects is not glass. The SkyTrough designed by SkyFuel Inc. and the National Renewable Energy Laboratory uses a highly reflective and shatterproof silvered polymer film that is laminated to thin aluminum sheets in place of glass. The trough is 375 feet long, 20 feet wide, and, according to SkyFuel, it features the largest parabolic trough modules ever built. Courtesy: SkyFuel Inc.
Unlike solar power competitors Ausra and BrightSource, SkyFuel said it is reluctant to build its own power plants using this technology. It is in talks with several companies looking to build solar thermal plants in the U.S. Southwest, however. The company is also working on its own version of the linear Fresnel technology — using molten salt as the heat transfer fluid.
Solar thermal energy hybrid
The Electric Power Research Institute (EPRI) began conducting a case study this October at two natural gas combined-cycle facilities — one at Dynegy Inc.’s Griffith Energy Facility in Kingman, Ariz., and the other at NV Energy’s Chuck Lenzie Generating Station near Las Vegas — to help power companies add solar energy to fossil-fueled electric power plants. As part of the larger study, EPRI will also conduct a parallel study at coal-fired power plants next year, although the sites for the study have yet to be determined.
The 12-month projects will involve adding steam generated by a solar thermal field to a conventional fossil fuel – powered steam cycle, either to offset some of the coal or natural gas required to generate power or to boost overall plant power output (see POWER, July 2008, Options for reducing a coal-fired plant’s carbon footprint, Part II).
As EPRI reasoned, 27 states in the U.S. have enacted renewable portfolio standard policies, and some include specific mandates that a percentage of the requirement be met with solar energy. However, most current solar applications are not cost-competitive with other power-generating options. Using solar to augment coal or natural gas potentially is, according to EPRI, the lowest-cost option for adding solar power to the generation fleet, as it utilizes existing plant assets. And because the highest-intensity solar energy typically is within a few hours of peak summer loads, it makes solar augmented steam cycles an attractive renewable energy option.
Sunday, August 26, 2012
how to make solar superheated steam
Demonstration and measurements on superheated steam produced with a self made linear parabolic concentrator using a mirror and an evacuated tube solar collector. Easily tracked concentration of about 1:15.
Steam from the sun on a small DIY home made scale could be used to clean drinking water or to make electricity. I don’t think that I have seen it done quite this way.
Before now, my solar concentrator efforts have related to heating a home swimming pool. Making steam was something that happened by accident, usually when we forgot to turn on the circulation pump. Making steam was generally not a good idea around a swimming pool. Besides, that system was designed for high volume, low temperature rise and it does that job well. Making steam on purpose requires some changes.
Yesterday I made steam with the sun intentionally on purpose. My test is crude but it shows what is possible with determination, a few tools and a hardware store.
I set up this test specifically to make steam and to measure the amount produced using the Gen2.0 design DIY solar concentrator. This is only a starting point, a first test.
Last year, I had shown with a similar setup that temperatures of over 600degF (316degC) could be reached in the evacuated tube at the FOCUS of my home made parabolic trough. I was a bit concerned that there might be trouble with the glass when the relatively low temperature of boiling water was initially introduced. Would it crack and implode the evacuated tube?
(click any pic to enlarge)
In a way, this was an unremarkable test. Once I learned how to start the process and to set the operating point of my equipment, the steam production was steady and reliable.
Because it was a bright sunny day, the steam at the outlet was almost invisible. I don’t have the obligatory astonishing pic/vid of large plumes of steam to show you, but it was there. Most times, the only way I could see the steam was to place a dry mirror at the outlet. The mirror would be instantly covered with beads of condensed water from the steam that I couldn’t see. Steam production was steady and it was extremely HOT. I measured temperature of 472.2degF (245degC)!
I tried again two days later and the steam is NOT VISIBLE. I measured over 500F. If it has not occurred to you that this is DANGEROUS, you should not read any further. seriously. I take no responsibility. Please be careful if you think you are going to try this at home.
Steam that is hotter than the boiling point of water is dry steam or superheated steam. There is no liquid water in the steam. This is good. If you want to have absolutely clean water or you are running a turbine to make electricity, you want dry steam.
Because this is a focused collector, it needs to face the sun. I had attached my home made reflector motor drive and tracking but I didn’t use it. During the one hour test duration, I simply nudged the reflector position about every 15 minutes or so. Position and therefore FOCUS did not seem to be very critical but that deserves more attention. This was a pretty rough test.
By the end of one hour I turned about 1-1/2 cups of water (actual was.334 KG) into steam. That works out to a heat input to the water of 208 watt-hours or 750KJ. I don’t address efficiency in this test.
Equipment Description
Here is my test setup for the steam test. I am using a four foot (122cm) version of the Gen2.0 parabolic reflector with a six foot (180cm) glass evacuated tube suspended at the 10 cm focal line. The reflector can pivot around the evacuated tube on ball bearing mounts. The test stand has been used in previous tests and is described here.
On top of the ladder is an open top reservoir of water, actually the windshield fluid tank from a 1990 Honda Accord. I had intended to use the small pump on the tank to inject water into the collector but ended up not doing that but simply relying on gravity and the vertical position of the tank to inject water up to a desired level in one arm of the collector (the boiler or up leg). Moving the tank to different steps on the ladder accomplished that quite nicely.
I am re-using the rather burnt-out looking collector assembly that I last used for the stagnation test. Although it had over-heated previously since it had no cooling (a definition of stagnation), the solder joints did not fail and it does not leak so I decided to put it to one more good use for this test.
At the yellow arrow, you can see that I have attached a thermocouple (the silver object) to the copper collector by over winding tightly a short length of copper wire. This thermocouple I have called T4 and its purpose is to show the temperature of the steam just before it exits to the air. The fitting to the bottom left will be the outlet, the fitting to the top left will be the inlet. The yellow bung of fiberglass wool is shown wound between and over the collector pipes and the thermocouple wires. When the collector is inserted into the evacuated tube, the bung seals the opening in the tube creating a solar oven inside the evacuated tube. The water and the steam will not touch the inside surface of the glass but remain inside the copper tubing. The copper mesh provides some heat coupling between the collector and the inside of the evacuated tube. The mesh may not be necessary.
details on the construction of this collector.
This schematic view shows my test setup. At the left is the open top water reservoir coupled to the inlet of the collector through a short length of poly tube. The collector forms an inverted U inside the evacuated tube. The outlet of the collector is simply vented to the air as you can see in the first picture above. Also in that pic, you can see the location of the inlet temperature monitor T2 under the green masking tape which holds T2 to the inlet coupling. The purpose of T2 is to show the temperature of the water going into the collector.
The schematic shows the collector as vertical but in fact, the collector, the evacuated tube and the reflector are tilted approximately 45 degrees on the test stand to make them normal to the direction of the sun at my latitude. I did not attempt to get the orientation EXACTLY right. As I said, this was a rough test. I used the shadow of the reflector counterweight to show that the orientation was more or less correct.
T1, the ambient temperature thermocouple is located in the shade under the small table.
T3, the boiler temperature thermocouple is located on the collector up leg, attached in the same way as T4, approximately co-incident with the top of the reflector or about at the top of the concentrated beam from the reflector. It was intended to show the temperature of that portion of the collector, in the steam above the boiling water.
In a perfect world, I would have the reflector length match the length of the evacuated tube but I have these fine 180cm evacuated tubes to work with as well as 122cm reflectors so the evacuated tube sticks out of the top of the reflector beam for about 20% of its length. A refinement to make for a future test would be to have the reflector better match the evacuated tube and collector. Evacuated tubes are commonly available in standard sizes as I discussed in more about evacuated tubes.
I believe that it is desirable for a home DIY project to have a type of flash boiler in which the water that enters is almost immediately flashed into steam. This would mean very little stored energy in the boiler (safer operation) and a short thermal time constant, meaning that the system would start to operate quickly as there was not a lot of water in the boiler to heat to the boiling point before steam could start to be produced.
Ideally, water would be injected into the inlet at a constant rate to match the rate at which steam is produced. I had planned to do this by regulating the speed of the reservoir pump by changing the supply voltage. Then I realized that a simpler approach was also possible with some compromise to the flash boiler concept and that is the approach described above with setting the reservoir on different steps of the ladder to achieve different fluid levels in the boiler.
As I said above, I had intended to use the small reservoir pump to feed the collector boiler but I was concerned about introducing water into an already hot collector and also about matching the rate of evaporation with the feed rate of the pump. My attempts to feed water in short bursts or at a slow rate simply lead to angry bursts of steam from the outlet and then nothing as the collector cooled down and evaporation essentially stopped until the collector (and the water it contained) heated up again.
The compromise was to try different vertical levels of the reservoir and to not use the pump. Lifting or lowering the reservoir causes the fluid level to correspondingly rise or fall in the collector, like with a fluid manometer. As water boils and evaporates, replacement fresh water will flow in and the level will stay the same as the level in the reservoir.
With the reservoir at the top of the ladder, the water level was too high and the steam that resulted came in bursts with burbles of liquid water, often in violent bursts. You can see the water on the table in this enlargement. The puddle was actually quite a bit larger earlier in the test. I interpret this as liquid water being kicked over the top of the U and then exiting the outlet with the steam. Liquid water is not good in the output of a steam generator. Operation was not steady.
With the reservoir a couple rungs down the ladder, the steam flow was steady but seemed to be coming at a lesser rate. So by trying a few variations, I found the second step from the top of the ladder, or a water level in the collector about 1/2 way up the boiler section of the up leg gave steady steam with no burbling, in other words, no water at all coming out at the outlet, just steam.
To start, I set the reflector out of FOCUS. The evacuated tube was fully exposed to the sun but not concentrated sunlight. This allowed the interior of the tube to heat without solar concentration as it would normally do in the water heating application where these tubes are typically used, without a reflector. I left it this way for about one hour to preheat.
It is interesting that in this condition, without the reflector, no detectable steam was produced. In other words, the collector did not get hot enough to boil. In my previous stagnation test, the collector was empty and the the collector temperature soared. By keeping the boiler about 1/2 full of water it is heated close to the boiling point but did not reach that (without concentration). T3. the temperature at the top of the boiler, was about 250degF (121degC) and T4. the outlet temperature was similar at about 235degF (113degC). Hot enough to boil water if there was any water at those levels but there isn’t. I am speculating that there is sufficient convective loss through the water out the inlet fitting to suppress further rise in temperature or phase change. The temperatures shown in the pic are at this stage.
Spinning the reflector into FOCUS changed everything. Within only a few minutes, I saw wisps of steam and within maybe 10 minutes, I could see a steady jet of steam at the outlet of the collector by using the hand mirror.
At this point, with steam produced at a uniform rate and no liquid water exiting the collector, I weighed the reservoir using a digital scale. Then I left everything alone except for checking FOCUS periodically to match the sun’s travel and checking the temperatures.
At the end of an hour, I had 0.334KG less water in the reservoir by weight than at the start of the test. There were no water leaks. My conclusion is that 0.334 KG of water had been turned into steam and had left the system through the outlet.
The temperatures during the steam test (while using the concentrator) were quite interesting. The ambient temperature T1 has risen just a bit to 103.7degF (40degC). It was a hot day (no clouds, no wind) and the test was just before solar noon. T2, the inlet temperature at 116.8degF (47degC) is a bit higher than ambient since the liquid water at the inlet is being heated from the boiler above it. T3, at the top of the boiler is about the same as without the reflector at 224.6degF (107degC). The outlet temperature is the really surprising one. Yes, you see that correctly in spite of the bad pic, 472.2degF (245degC)!
My interpretation of the outlet temperature is that the down leg of the collector heats substantially in the focused beam raising the possibility that the steam is being superheated before it exits the collector while also vaporizing any errant liquid water that happens to burble over the top of the U.
Not a bad first attempt I think to mock up a potentially viable and practical solar steam source using a DIY approach while keeping things relatively safe.
As I said, this was a crude effort. Regardless, I was pleasantly surprised by the number of interesting things the test showed me and I have tried to describe them here. There are lots of rough edges and things that could be improved and re-tested.
This is a work in progress. I am grateful for any Комментарии и мнения владельцев or suggestions you may have.
Thank you for your interest. George Plhak Lion’s Head, Ontario, Canada
Solar thermal power plants use the sun’s rays to heat a fluid to high temperatures. The fluid is then circulated through pipes so that it can transfer its heat to water and produce steam. The steam is converted into mechanical energy in a turbine which is then converted into electricity by a conventional generator. There are three main types of solar thermal power systems:
Parabolic trough.
A parabolic trough collector has a long parabolic-shaped reflector that focuses the sun’s rays on a receiver pipe located at the FOCUS of the parabola. The collector tilts with the sun as the sun moves from east to west during the day to ensure that the sun is continuously focused on the receiver.
Because of its parabolic shape, a trough can FOCUS the sun at 30 times to 100 times its normal intensity (concentration ratio) on the receiver pipe located along the focal line of the trough, achieving operating temperatures higher than 750°F.
The solar field has many parallel rows of solar parabolic trough collectors aligned on a north-south horizontal axis. A working (heat transfer) fluid is heated as it circulates through the receiver pipes and returns to a series of heat exchangers at a central location. Here, the fluid circulates through pipes so it can transfer its heat to water to generate high-pressure, superheated steam. The steam is then fed to a conventional steam turbine and generator to produce electricity. When the hot fluid passes through the heat exchangers, it cools down, and is then re-circulated through the solar field to heat up again.
Solar dish.
A solar dish/engine system uses concentrating solar collectors that track the sun, so they always point straight at the sun and concentrate the solar energy at the focal point of the dish. A solar dish’s concentration ratio is much higher than a solar trough’s concentration ratio, and it has a working fluid temperature higher than 1380°F.
The power-generating equipment used with a solar dish can be mounted at the focal point of the dish,making it well suited for remote operations or, as with the solar through the energy may be collected from a number of
Solar power tower.
The energy can be concentrated as much as 1,500 times that of the energy coming in from the sun.Energy losses from thermal-energy transport are minimized because solar energy is being directly transferred by reflection from the heliostats to a single receiver, rather than being moved through a transfer medium to one central location, as with parabolic troughs.
Power towers must be large to be economical. This is a promising technology for large-scale grid-connected power plants. Power tower technology is in the early stages of development compared to parabolic trough technology.
Parabolic solar steam generator
This photo is a section of a telephoto shot of an industrial, grid connected solar steam electrical generating station just east of Boron, California. The air temperature was about 40 degrees F.
One of the downsides of these generators. more are scheduled for construction. is that they require fresh water for the steam condensation towers. losing the water to evaporation.
But my hat is off to California for being a hotbed showcase of steam solar, photovoltaics, and wind power. Only by trying out these technologies will we be able to improve them, and find ways around fossil fuels.
Closed steam loop solar gens need wet cooling towers
I received the following question by email so I thought it helpful to post the question here. as my original Комментарии и мнения владельцев about water use by solar steam generators was not clear. Thanks for the interest!
Question: How do these generators work. why isn’t water in closed system? I was thinking solar heats enclosed water steam drive turbines(??) condense repeat. Obviously not the case. maybe you could expand.
Response: The steam loop is closed. It is important to keep the steam loop closed because, if it were open, minerals would be deposited in the steam pipes when the water in the loop evaporated, eventually leading to clogged piping (just like the minerals which deposit in the bottom of your tea pot).
However, because the ambient air temperature can vary between 32 and 120F in the desert, the difference in temperature between the very low pressure waste steam and the air is not sufficient to create an efficent condenser in a small pipe to air radiator envelope (which would at least need to be shaded and fan cooled). It is much less costly to construct a wet cooling tower, where water circulates in contact with (but on the outside of the steam loop). The cooling water condenses the steam back to a liquid so it can be pumped again through the solar heaters. The warmed cooling water is then sprayed down through a natural draft (hyperbolic shaped like Perry Nuke) or fan drafted cooling tower. Some cooling water evaporates, taking away heat into the air, and the rest of the air cooled cooling water is collected and recirculated.
At the Boron solar steam electric facility fan drafted wet cooling towers are used. It is from these cooliing towers that large amounts of moisture are lost throught evaporation (see two towers of 6 at the facility in photo with Joshua tree above).
The same type of evaporative loss takes place from the Perry Nuclear generator. millions of gallons per day of Lake Erie water are evaporated from Perry. and lost from the Great Lakes Basin. These evaporative losses were one of the main water diversion issues addressed recently by the Great Lakes Basin Compact signed into law on October 3, 2008 by President Bush.
Here is a link to a list of SEGS plants from NREL You will notice to to ensure dispatchability these plants have natural gas powered back up generation. so they are not entirely green facilities.
way to post headers
Kudos to you Jeff for posting a header with notes. Not only do we learn about what we’re looking at, we also learn via discussion and dialogue.
Whomever sent the question, I hope you will continue your inquiries here and add your knowledge. Sometimes questioning is the more powerful aspect of knowledge building, eh? At least, in this case, it was for me.
We also learned that someone found the header images link and perchance the contact form. Cool!
Solar Heaters work on two
Solar Heaters work on two principles. First the absorption of Solar energy by black surface and Second is the Heat trapping principle called Greenhouse Effect.