As recently noted, at least one experienced venture capitalist favors centralized, utility-scale solar power. According to Red Herring, Vinod Khosla specifically believes the greatest opportunity is with the application of concentrator technology. This blog was unaware that one solar thermal electric power plant produces 90% of the world’s commercially produced solar power.
Solel, an Israeli company, operates the plant, which covers 1000 acres in the Mojave Desert in Southern California.
At 354 MW, SEGS (Solar Energy Generating Systems) is not only the largest operational solar thermal energy system, but the largest solar power system of any kind. SEGS is a trough system; linear parabolic mirrors concentrate sunlight upon a receiver running along the focal line of the collector. Each mirror has a diameter of almost 20 feet concentrating solar energy upon a 4 inch diameter specially-insulated tube filled with oil. There are seven different production units (SEGS III to SEGS IX) with 400,000 mirrors.
Each mirror is able to heat the oil to almost 750 degrees Fahrenheit. The heated oil circulates through a heat exchanger. The last stage is similar to a conventional steam turbine generator.
Khosla is not alone in favoring concentrated solar power. A number of industry observers have included thermal solar, when suggesting that solar energy finally may be coming into its own. Or, at the very least, solar power is becoming competitive with traditional load-following / peaking generation, particularly as the costs of natural gas and diesel fuel increase and air quality standards are raised. (If it ain’t the Feds, it’s the States.)
Particularly in the Southwestern United States, utilities have been more amendable to thermal solar systems and have been investigating ways to increase their efficiency.
Studies have indicated that the use of Stirling engines for generation or combined cycle generation is somewhat more efficient than just using steam turbines for generation. Back in February 2006, Jim Fraser commented that Stirling Energy Systems , without any incentives, was able to demonstrate the cost effectiveness of a Stirling installation for Southern California Edison.
Studies also have indicated an advantage to thermally integrated systems, a.k.a., ISCC (Integrated Solar Combined Cycle), whereby recovery of heat from a gas turbine is combined with solar thermal energy and used to power a steam turbine. The example previously used in this blog was combining the gasification of waste biomass with a solar thermal.
Combined heat and power generation show the highest system efficiencies. Still there is considerable variability in reported efficiencies depending upon what usage is made of the process heat, e.g., absorption cooling, desalination, district heating or industrial applications. Reducing transport losses is key to higher efficiencies.
The optimum capacity of a solar thermal power plant is smaller than coal or nuclear powered generation. On the other hand, utility-scale solar thermal needs to be on a sufficiently large enough scale to justify the capital cost. The use of two turbines with ISCC adds significant cost, which is one reason for research into other lower cost generation.
Nonetheless, material costs for thermal solar are less than for photo voltaic systems. Since this translates to a quicker ROI (Return On Investment) on solar thermal power, there would seem to more monies available for investment in large scale, thermal solar projects.
According to a 2005 policy analysis from Greenpeace, the five most promising regions in the world for development of large scale, thermal solar projects are:
- Spain
- Middle East
- North Africa
- Australia
- the South Eastern and South Central United States
There is even greater market potential since other areas throughout the world, typically arid, semi-desert areas, receive a great deal of sunlight. The challenge is to lower the cost of technology; simpler solar power systems are indicated where materials are scarce and costly to import. These other areas are located in South America, Southern Africa and India.
4 Comments
The waste heat/CSP hybrid you mention reminded me of another combination I’ve been thinking about: Geothermal/CSP. In the US, areas of good geothermal resource overlap nicely with the best areas for CSP, and a low-grade geothermal resource often can’t be used to generate electricity directly, but it might be a good way to boost the output of a concentrating solar plant.
Well, I lack specific geological knowledge, so it is difficult to reject the concept completely.
While it makes sense to combine heat sources, there would seem to be the need for comprehensive risk assessment, especially as to loss of either or both sources with seismic activity.
From what I understand, today’s turbines are machined to fine tolerances and balanced extremely well to perform at high efficiencies. The turbine companies, like General Electric or Westinghouse design a specific platform, so we are back to capital cost, particularly when construct materials, turbines, etc. must come long distances to these remote areas.
Note that I am assuming from your statement about geothermal, you are referring to heat from volcanic activity, e.g., Iceland. I have thought that using ground temperatures for cooling might work with solar thermal, but it may be that the size of the field is prohibitively expensive compared with other methods of cooling.
Some areas with a great deal of sunlight and low use land are also near large bodies of water that could be used for cooling. Yet, there are other ecological issues to consider depending upon site.
I also have wondered if there was some use that could be made of expended oil fields, either for a coolant loop or as a means of thermal energy storage.
Hybrid Solar / Diesel Power Plants
By Dr. Hussain Alrobaei
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Currently, the medium-speed diesel is already one of the most efficient simple cycle sources of electricity, especially with lower grade fuels. The combustion process of a modern diesel engine is efficient and narrowing the gap to theoretical limits. To obtain further reductions in fuel consumption, the focus is expected to be moved from the combustion process onto converting waste heat to mechanical work.
The waste heat generated by Internal Combustion Engines (ICE) can be recovered to produce additional power, steam or hot water. In addition to that Integrated Solar Combined Cycle power Plants (ISCCP) with their capability of thermal energy storage and of solar/bio or fossil fuel hybrid operation can provide firm capacity and thus are a key element for grid stabilization and power security in such a well-balanced electricity mix. This has led to a rather rapid development of ISCCP to achieve good performance at all modes of operations and to increase the shear of solar power generation, and subsequently an increase in the thermal and environmental effectiveness of the plant.
From this standpoint, the author proposes a new approach to prospective ISCCP. This approach includes a proposed design for increasing the specific output at sunny periods, and off design performance at cloudy periods and at night, of the Hybrid Solar / Diesel Power Plant (HSDPP). The desired effect of integrating an ICE with a Solar parabolic trough Power Plant (SPP) is not just to add the power produced by the ICE to that produced by the SPP but indeed to augment the latter.
The HSDPP uses the waste heat from the ICE to supplement solar heat from Parabolic Solar Collector Array (PSCA) in order to augment power generation in the steam turbine unit. In this design, the ICE provide four waste heat streams that can be used as heat sources by a bottoming cycle: the exhaust gas, the charge air, the jacket water (i.e., the engine cooling water) and the lubricating oil. The charge air is cooled to increase the power output of the engine. Consequently, the SPP cycles were changed in order to use these heat sources efficiently and maximize the power output. The ICE waste heat is used for feed water preheating, to generate additional steam, and for steam superheating and solar energy is generally used for direct steam generation into PSCA.
This combination does not reduce the solar energy source to negligible role as most integrator of large fossil-fuelled power plant but places both sources on approximately the same level and allows the power plant to operate independently of the solar field.
Dr. Alrobaei, thank-you for the informative comment, particularly on the subject of Integrated Solar Combined Cycle. No argument from me that diesel engines are efficient.
In the transportation sector there is considerable research into engine thermodynamics and better use of hot air and exhaust gases. Better efficiency can indicate better environmental impact, i.e., less fuel used, less GHG emissions.
Unfortunately, economics prevails, so people sometime refer to better efficiency when they mean better price. Fossil fuel is an existing paradigm that while dominant, ultimately may prove unsuccessful for the continuation of life.
So, while it is good to see extrapolation from the transportation sector to the power generation sector in an effort to achieve more efficiency, from an environmental viewpoint, I would rather see the diesel oil used for heat transfer than for combustion to offset peak load or for back up / emergency use.
On the other hand, if, in an emergency, I have no electric power and someone comes along with a diesel generator, then I quite likely will overlook my GHG emissions. So it goes.
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