Abengoa’s IST Thermal Trough
About half the energy burned in the U.S. is used to make hot water and heat (most of which is below the boiling point), yet PV solar and wind energy do little to provide it aside from electric water tanks and inefficient baseboard heaters.
Does that mean natural gas is here to stay? Solar thermal, as the term is generally used, is a bit of a misnomer, since the thermal output is used to make electricity. It becomes part of the same process as a conventional steam or gas turbine plant, but instead of burning natural gas, or coal, the steam comes from a liquid heated by concentrated sunlight.
In the case of troughs, the so-called concentration ratio is about 60 to 1. Three to five ‘suns’ from a magnifying glass will start a fire. Sixty suns will produce enough high quality steam to run a power plant. (PV power comes from one-sun, i.e. what you see is what you get). Concentrated sunlight is no trifling matter. A few years ago in London, windows on a curved high rise focused enough light on a Jaguar to start melting it. Did it have to be such an expensive car, in sun-starved London, of all places? The story would have made more sense if it had been a pickup truck in Phoenix. (Assuming the Haboob season had ended.)
There is a legend that in 212 BC, Archimedes and friends pointed enough polished shields at a Roman sailing ship to set it on fire. Today we would call that a heliostat array, and it concentrated the power of many suns. This was applied math at its best but the Romans were not amused and they caught and killed Archimedes.
In this article, unless otherwise indicated, solar thermal will refer to thermal-only, i.e. heat, for the sake of heat, hot water and even air conditioning. The ‘light water reactor’ referred to in the title simply means that sunlight is concentrated on a steel tube, filled with water and painted black, at the focal point of a trough. And in the case of troughs, the ‘focal point’ is actually a line, which runs parallel to the trough itself. (I see a steel pipe and I want to paint it black -- with apologies to Mr. Jagger, a former student at the London School of Economics.)
The term ‘light water reactor’ generally refers to a type of nuclear power plant design. In this case, though, the reactor is a trough collector where the sunlight meets water running through a pipe, courtesy of the reflective surface that defines the trough. The phrase was coined, tongue-in-cheek, by Dr. Barry Butler who was the first head of the Solar Thermal division of SERI (the Solar Energy Research Institute established by the Carter Administration), which later changed its name to NREL. It seems there were other renewable sources of interest than the sun.
The trough above is the brainchild of Ken May, who was once a technician under Dr. Butler’s wing at SERI. Mr. May founded IST (Industrial Solar Technology) in 1983, which was bought by Abengoa in 2006, and he is now the head of the Spanish giant’s Thermal division, based in the U.S. Abengoa is currently building the world’s first large scale solar desalination plant in Saudi Arabia. That plant will use PV to drive the standard reverse osmosis process. However, it is possible to get salt out of water using heat, and time will tell if the price of water will be set by the cost of power from the sun or simply from solar heat, which may turn out to be cheaper, and will certainly be able to produce fresh water on a smaller scale.
75 MW trough array provides steam for 3.7 GW FPL Martin (Next Era) gas power plant
“Florida Power & Light’s Martin Next Generation Solar Energy Center, with 75 MW of parabolic trough CSP [concentrated, or concentrating solar power], is the first hybrid combined cycle natural gas + concentrating solar power plant to be developed in the United States and is also the world’s largest such hybrid power plant. At the time of its completion in 2010 it was also one of the world’s largest parabolic trough solar CSP plants. The hybrid renewable energy power plant includes a field of 190,000 parabolic mirrors that heat a synthetic oil thermal fluid to temperatures of 398C. The superheated thermal fluid is run through a heat exchange system and used to generate steam to supplement the existing natural gas/ oil plant’s (4) combined-cycle steam turbine units.” Related: Unorthodox Plays For The Savvy Energy Investor
The troughs below, now also owned by Next Era, were built at Kramer Junction in the Mojave Desert 30 years ago. The steam output is used to make power; the Kramer Junction array is rated at 310 MW and feeds the grid via Southern California Edison.
Image Source: Nextera
Though power markets came first for big trough arrays, it is worth noting that large scale thermal only applications are coming on line. The most impressive may be the massive 1 GW thermal (GW) enhanced oil recovery (EOR) project in Oman, Saudi Arabia’s neighbor, being built by a company called Glasspoint.
The recent Renewable Energy World article on this project explains: “At an astonishing 1,021 megawatts, Miraah is almost three times the capacity of Ivanpah, which at 377 MW is currently the world's largest CSP project delivering electricity. Yet not only will Miraah (mirror in Arabic) produce steam at gigantic scale, but it does so at much lower cost than CSP and about half the cost of gas. The 1 GW project will cost a mere $600 million.”
Another way to crunch that number is to say it costs 60 cents per Watt. Though the Watts are thermal and not electric, that price is in line with the ‘China price’ of PV cells, which still need to be set in place, connected to an inverter, and then hooked up to the grid. Utility PV in the U.S. is coming in at just under $2 per Watt now, but developers, planners and dreamers alike should be aware that a trough, that will produce steam for 50 years, using a rudimentary steel pipe, costs about the same as the inverters alone for a power project. Inverters do not last 50 years so you must pay for the replacement units.
It is reasonable to assume that solar steam will be eventually able to supply a majority of the hot water and heat needed in the U.S. and elsewhere at roughly the equivalent of $2 per MMBtu natural gas, though this has yet to be demonstrated at scale. In fact, it is possible that solar steam will eventually become the hurdle gas must clear in order to stay in the game. This arithmetic may yet save the world -- FOB Light Water Reactors.
According to John O'Donnell, Glasspoint’s VP of Business Development, “Two thirds of all industrial energy used is thermal. The biggest thermal energy user in the world is the oil industry; 98 percent thermal energy, only 2 percent electricity. This is why Glasspoint has focused on EOR, by far the biggest industrial steam market.”
However, using solar steam for EOR (also known as tertiary recovery – first, the well pressure is great enough to blow the oil out of the ground; second, water (the Saudi’s use seawater) is pumped in to maintain pressure, and; third, steam, usually produced by burning natural gas, or CO2 is injected into the well to get the leftovers) does not help much when it comes to mitigating climate change. Furthermore, large trough arrays take up a lot of real estate.
The best news from this project, though, is that it proves an important point. Commercial grade steam may be produced at a reasonable price because the process eliminates the most expensive aspects of the solar thermal power plant. According to Renewable Energy World: “Glasspoint now uses only pipes and lightweight mirrors to create steam: each glasshouse is a steam generator - with no power block.”
Power plants require higher temperatures, meaning that tubing along the focal line is much more expensive. In addition, the fluids used in those pipes are generally very corrosive and flammable, meaning the cost of maintenance is much higher. Steel tubes painted black, which is where the light reacts with water, are cheap. The water is in a closed loop so it does not require continual resupply, and the maintenance is simple, cleaning mirrors occasionally and making sure the pipes don’t rust, i.e. more black paint.
There are plenty of other applications that are well suited to low cost troughs, among them: Air conditioning, which is provided by steam being fed to absorption chillers (it is worth pointing out that the need for AC is greatest when the sun shines in the afternoon – tracking troughs are therefore an elegant, and possibly the lowest cost way to solve the utility industry’s biggest headache), and; hot water for space heating. This may be accomplished either with a small unit in your back yard, on a commercial rooftop or with larger community arrays using a proven method known as seasonal heat storage. Related: A September To Remember?
Even at latitudes that include Norway and Alaska, the summer sun may be stored in the ground, simply by drilling holes, filling them with hot water and retrieving it for use in the winter. The U.S. Department of Energy reckons the efficiency of this process is close to 98 percent. And if you think that solar hot water is some failed science project that a bunch of hippies tried to pull off 40 years ago, think again. 200 Chinese GW can’t all be wrong. If it plays in China, that is because it is low cost and durable.
District heating is nothing new, and piping systems in northern cities still exist from the late 1800s that can deliver steam underground. In many cases the fuel came from wood wastes but solar steam is more scalable than trees. District steam heating has been appreciated in New York City since the Blizzard of 1888 (the Great White Hurricane). “Con Edison operates the largest CHP [combined heat and power system] in the United States. The system contains 105 miles of mains and service pipes, providing steam for heating, hot water, and air conditioning to approximately 1,700 customers in Manhattan.”
Perhaps the most critical application of all for thermal troughs will be turning seawater, or brackish water around farmland, into fresh water. News from America’s drought-stricken front in June tells the tale: Solar Thermal Desalination Now Underway in Water-hungry California, reads the Renewable Energy World headline of June 23.
“Regional droughts are being exacerbated by climate change, which is mostly caused by what is tasked with bailing them out — fossil fuels. Israel, Australia, and now southern California have all turned to expensive energy-guzzling seawater desalination projects after historic droughts. . . . The controversial Carlsbad desalination project’s latest projected cost is now $1 billion. It will suck in 100 million gallons of San Diego’s seawater a day and force it through a series of filters to produce 50 million gallons of [fresh] water a day using high-pressure reverse osmosis. . . . A modest solar thermal desalination alternative now quietly undergoing permitting inland would produce 5 million gallons of water, about one tenth of that of Carlsbad, but at a much lower cost of just $30 million, using a solar distillation process.”
So, that’s ten percent of the output from the thermal only plant, but three percent of the cost, making it 70 percent cheaper. (Carlsbad: $20 per gallon per day. WaterFX/SkyFuel: $6 per gallon per day.)
A 5 ft-wide roll of silver-coated aluminium Reflectech slides into each unit making up SkyFuel's
20 ft wide parabolic trough used on the solar collector field creating steam for the WaterFX solar still
“WaterFX will use a 24-MW trough-type solar thermal field supplied by NREL-collaborator SkyFuel to create direct steam from the sun to run multi-effect distillation, desalinating enough agricultural water for reuse to keep 2,000 acres of farmland irrigated each year. . . . [The company will] be focused on reusing agricultural drainage water because agriculture is California's biggest water user. . . . The agricultural sector uses about 80 percent of all the water in California," says Aaron Mandell, the company’s Chairman. "If only 20 percent of the water is being used for municipalities, and you reduce that water consumption by 50 percent, you've only made a 10 percent impact overall. Reducing agricultural use has a much bigger impact." Related: Saudi Oil Strategy: Brilliant Or Suicide?
Another advantage of the thermal only system is that it leaves less brine for disposal – seven gallons of brine per 100 gallons of intake water whereas the Carlsbad reverse osmosis project appears to leave 50 gallons per hundred (100 million gallons of seawater in and 50 million gallons of freshwater out).
Furthermore, the company says that the brine includes gypsum which can be used in construction and selenium which is used in semiconductors. “We can actually separate and refine certain components for resale,” says Mr. Mandell.
Somewhere Over the Rainbow
In all the excitement over the renewable David knocking back the Goliath of fossil fuel providers and large scale users, it is only beginning to dawn on observers and investors alike that renewables will eventually provide too much of a good thing. It is wonderful to say that an energy source will be too cheap to meter or that it will turn back the meter, but when that happens it no longer becomes interesting, profitable, or even possible to finance the next kilowatt-hour of electricity without losing your shirt. At that point, sun and wind power may still be cost-effective and scalable, but they may not be bankable. At that point, what’s a photon to do?
A Financial Times headline dated August 3 reads: Renewable energy sector runs the risk of overpowering market. “Another day, another billion-dollar renewable energy deal. . . . But what if the extra-clean electricity eventually generated is doomed to make no money? Or to be more precise, not enough money to keep the companies producing it profitable without a lot more renewable subsidies?. . . The idea is not hypothetical. When hurricane-strength winds swept across Germany in March this year, wind and solar generators produced about as much as 30 nuclear power plants at one point in the afternoon, briefly making wholesale electricity worthless. This is happening when wind and solar have a 21 per cent share of electricity in Germany. So what happens if that proportion rises?”
On August 11, Greentech Media struck a similar chord: How Wind and Solar Will Blow Up Power Markets. The article cites a recent MIT report which reads: “It is worth noting that price reductions from solar PV production are systematically most significant during the same hours when solar generators deliver maximum output . . . As a consequence, higher levels of solar penetration lead to lower revenues per kW of installed solar capacity. For this reason, at any given per-kW installation cost of solar PV, there is a system-dependent threshold or limit beyond which adding further increments of PV capacity will not break even from a cost perspective.”
This phenomenon may turn out to be a boon to solar thermal power plants with storage, such as the 377 MW Ivanpah heliostat array mentioned above. However, in the short run, it seems that wind projects could suffer the most, at least until there are enough EVs in the garage to take the midnight gales that give coal operators in the Midwest fits. And that will take some time (0 to 60% market share in 15 years?). As for the sun, there is no need to wait for storage if the thermal output is taken during times with too much PV power, which is another way to say: times with too much sun. If used for AC, desalination, hot water and seasonal storage that will heat buildings in the winter, then there is no such thing as too much sun.
One of Aesop’s fables is about a contest between the North Wind and the Sun to see who was stronger. They wanted to find out who could get a traveler to remove his coat. The North Wind blew and the harder he blew the tighter the traveler wrapped his coat. The Sun tried a different approach, using heat rather than power, and before long the traveler took it off.
Thanks to German subsidies and Chinese manufacturing, most of the headlines and animal spirits devoted to renewable energy over that past 10 years have been focused on photovoltaic solar power. But in the post-subsidy age that starts now, the best bet in renewables is likely to be solar heat. And with about half the world’s energy needs coming in the form of hot water and heat, solar thermal seems like a winner. Steam from a mirror, fancy that.
By Henry Hewitt for Oilprice.com
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