Renewable energy generates a larger portion of the world’s electricity each year. But in relative terms, solar power generation is hardly a blip on the energy screen despite its long history of technological development. Solar-generated electricity has one major advantage over it’s more ubiquitous cousin wind power: electricity is generated during typical peak demand hours making this option attractive to utilities that value solar electricity for peak shaving. However, the capital cost of all the solar technologies are about $5,000/kW and higher and projects are moving forward only in particular regions within the U.S. with tough RPS requirements and subsidies from states and the federal government.
In Part I, we reviewed the enormous scale and capital cost considerations of photovoltaic projects and then introduced the standard taxonomy of central solar power generating plants. By far the favored technology for utility-scale projects is the concentrated solar power (CSP) option that either produces thermal energy that produces electricity in the familiar steam turbine process or by concentrating the sun’s thermal energy on an air heat exchanger to produce electricity via a gas turbine. In this Part II, we review a sampling of recent projects. In sum, CSP and Stirling engine technology appears to be favored in the U.S., while the “turbine on a stick” projects are gaining a foothold elsewhere.
The final post will explore the latest developments in hybrid projects that combine many of the available solar energy conversion technologies with conventional fossil-fueled technologies. Hybrid projects offer the opportunity for utilities to reduce fuel costs, while simultaneously helping utilities cope with onerous renewable portfolio mandates.
Pacific Gas and Electric Co. (PG&E) was the most solar-integrated utility in the U.S. last year, followed by Southern California Edison and San Diego Gas & Electric, according to new rankings released earlier this year by the Solar Electric Power Association (SEPA). It’s no great surprise all three utilities serve California residents.
PG&E interconnected 85 MW of new capacity—a number representing 44% of the survey total, the trade group found in its “2008 Top Ten Utility Solar Integration Rankings.” The report surveyed 92 utilities, identifying those that have the most significant amounts of solar electricity integrated into their portfolio. On a cumulative solar megawatt basis, Southern California Edison was ranked first, followed by PG&E, and Nevada utility NV Energy. “This year, the report demonstrated that the utility segment is making a major investment to increase the amount of solar energy in power portfolios, with many utilities doubling the amount of solar power in their portfolio in just one year,” SEPA said. The overall installed solar capacity of the top 10 ranked utilities rose from 711 MW to 882 MW, reflecting a 25% growth. SEPA cited renewable portfolio standards, impending carbon policy, and fluctuating costs of power generation and fuel resources as primary factors driving this growth.
Participating utilities had an average of 11 MW in their cumulative portfolio, and the top 10 utilities represented 93% of all solar capacity. Because of their head start, the large investor-owned utilities in California are likely to retain a lead in the overall cumulative rankings even as the year-to-year rankings shift, SEPA said.
California utilities have contracted for renewable solar electricity from a variety of plants that are now or will soon be under construction. Let’s review some of the more interesting projects, in no particular order.
Focus is California for New Solar Projects
First up is Kimberlina, the first and only CSP project built in California in 20 years. Next are a slew of projects in the development phase, including five large solar thermal plants, including the two Stirling Energy Systems’ (SES) projects (850MW and 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. 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.
Kimberlina Leads the Charge
Ausra’s Kimberlina Solar Thermal Energy Plant in Bakersfield, Calif., consists of rows of 1,000-foot-long mirrors that focus the suns energy on collector lines that generate thermal energy in this CSP plant (Figure 1). The collector lines can 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. Ausra is also developing a 177-MW solar thermal power plant for Pacific Gas and Electric Co. in Carrizo Plains, west of Bakersfield using the familiar CSP technology. On September 30, Ausra was selected to provide the solar steam boiler for a proposed 100-MW CSP project JOAN1 under development in Ma’an, Jordan. This project, expected to enter commercial service in 2013, would become the largest CSP project in the world.
1. Ausra is developing a 177-MW CSP project in Bakersfield, California. Courtesy: Ausra Inc.
SkyFuel seeks to build SkyTrough
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.
2. 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 pictured is 375 feet long, 20 feet wide, and, according to SkyFuel, it features the largest parabolic trough modules ever built. Courtesy: SkyFuel Inc.
Elsewhere, utilities such as the San Francisco-based Pacific Gas and Electric Co. have signed gigawatts of contracts to buy solar power. One of its solar thermal power suppliers, Oakland, Calif.-based BrightSource Energy, is set to start construction in early 2010. But it only recently began to disclose how it would finance a 440-MW project in California’s Mojave Desert. BrightSource has lined up San Francisco-based engineering firm Bechtel as a project investor and general contractor.
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.
Using the Stirling Engine for Solar Power
Since Robert Stirling invented the Stirling engine in 1816, it has been used in an array of specialized applications. That trend continues today. Its compatibility with clean energy sources is becoming apparent: It is an external combustion engine that can utilize almost any heat source, it encloses a fixed amount of a gaseous working fluid, and it doesn’t require any water — unlike a steam engine.
A good example is Phoenix-based Stirling Energy Systems’ (SES) newly designed solar power collection dishes that were unveiled at Sandia National Laboratories this July. Called SunCatchers, these dishes are the next-generation model of SES’s original system. With a high rate of production and cost reduction, they will be used in commercial-scale deployments starting in 2010.
The modular concentrated solar thermal (CSP) SunCatcher uses precision mirrors attached to a parabolic dish to focus the sun’s rays onto a receiver, or heat exchanger, which heats the engine’s working fluid, in this case hydrogen, and rejects heat at ambient conditions. As the gas heats and cools, the working fluid’s pressure rises and falls. This change in pressure drives the piston inside the engine, producing mechanical power, which in turn drives a generator and makes electricity.
The improved design stems from a collaboration between Sandia’s CSP team and SES. The new SunCatcher is about 5,000 pounds lighter than the original, is round instead of rectangular to allow for more efficient use of steel, has improved optics, and consists of 60% fewer engine parts (Figure 3). The revised design also has fewer mirrors — 40 instead of 80 — and the reflective mirrors are formed into a parabolic shape using stamped sheet metal similar to the hood of a car.
Because the mirrors and engines are made by using automobile manufacturing techniques, the improvements will result in high-volume production, cost reductions, and easier maintenance. But it also minimizes land development and has numerous environmental advantages, said Chuck Andraka, the lead Sandia project engineer. “They have the lowest water use of any thermal electric generating technology, require minimal grading and trenching, require no excavation for foundations, and will not produce greenhouse gas emissions while converting sunlight into electricity.”
Tessera Solar, SES’s sister company and the developer and operator of large-scale solar projects using the SunCatcher technology, plans to build a 60-unit, 1.5-MW plant by the end of the year either in Arizona or California. SES would sell the equipment to Tessera Solar, the project development company set by SES earlier this year. Tessera has taken over the projects that SES had worked on since its inception in 1996, and is now developing more than 1.5 GW of projects.Stirling Energy Systems this July unveiled four newly designed solar power collection dishes at Sandia’s National Thermal Test Facility. The next-generation SunCatcher is about 5,000 pounds lighter than the original, is round instead of rectangular to allow for more efficient use of steel, has improved optics, and consists of 60% fewer engine parts. The engine’s sealed system is filled with hydrogen.
SES said that the proprietary solar dish technology will then be deployed to develop two of the world’s largest solar generating plants in Southern California — a 750-MW project to sell electricity to San Diego Gas & Electric located in the Imperial Valley that will require SES to install 34,000 SunCatcher dishes. SES is applying for a loan guarantee from the U.S. Department of Energy to offset half of the cost of the $2.2 billion project. The second is an 850-MW project to sell electricity to Southern California Edison in the Mojave Desert. SES predicts these projects will produce 1,000 MW by the end of 2012. Both projects have faced delays and are still undergoing the permitting process to secure federal and state approval (the projects are located on federal lands—more on that later in this post). Tessera officials are hoping to secure the permits by next spring.
SkyFuel’s Uses a Glass-Free Parabolic Trough
SkyFuel Inc. has signed an agreement with Sunray Energy Inc., a subsidiary of Cogentrix Energy, for the installation of SkyTrough collectors at Sunray’s 43-MW parabolic trough generating plant near Daggett, Calif.
The plant was formerly known as Solar Energy Generation Systems I and II (“SEGS I & II”). The agreement with Sunray Energy allows for the first commercial installation of the SkyTrough, an advanced parabolic trough concentrator that uses glass-free ReflecTech Mirror Film reflectors.
The agreement allows SkyFuel to integrate an array of SkyTrough solar collector assemblies into the Sunray plant to demonstrate their commercial viability in a full-scale, solar generating plant application. The SkyTrough installation is to be operational later this year. No business terms were disclosed.
The SkyTrough, first introduced to the market in October 2008, offers a departure from the prior state-of-the-art for parabolic trough concentrating collectors. A key difference is that the SkyTrough does not use glass mirrors. Instead, is uses a new mirror system with an advanced material developed with scientists at the Department of Energy’s National Renewable Energy Laboratory. The goal was to replace traditional glass mirrors that could shatter under operating conditions—resulting in considerable expense to replace the mirror panels and any receiver tubes damaged by flying glass shards.
Construction of the SkyTrough installation at Sunray’s plant will begin in the current quarter with completion and commercial electricity production scheduled for the end of 2009.
Interior Department to Fast-Track Solar Development on Public Lands
The favored location to site new solar electricity plants is in the sunny southwestern U.S. and given the enormous amount of land necessary, that means leasing land from the Department of the Interior—historically a time-consuming process. That is about to change, according to Secretary of the Interior Ken Salazar. In the future, federal agencies will work with western leaders to designate tracts of U.S. public lands in the West as prime zones for utility-scale solar energy development, fund environmental studies, open new solar energy permitting offices, and speed reviews of industry proposals.
Salazar added that the DOI is evaluating nearly two dozen areas that could generate about 100,000 MW of solar power although Salazar has a history of confusing theoretical with practical potential for generating electricity. “With coordinated environmental studies, good land-use planning and zoning and priority processing, we can accelerate responsible solar energy production that will help build a clean-energy economy for the 21st century.”
Under one initiative, 24 tracts of Bureau of Land Management (BLM)–administered land located in six western states—known as Solar Energy Study Areas—would be fully evaluated for their environmental and resource suitability for large-scale solar energy production. The objective is to provide landscape-scale planning and zoning for solar projects on BLM lands in the West, allowing a more efficient process for permitting and siting responsible solar development.
Those areas selected would be available for projects capable of producing 10 or more megawatts for distribution to customers through the transmission grid system. Companies that propose projects on that scale in areas already approved for this type of development would be eligible for priority processing. The BLM may also decide to use alternative competitive or noncompetitive procedures in processing new solar applications for these areas.
Salazar also announced the opening of a new DOI renewable energy coordination office (RECO) in Nevada, the first of four, with the others located in Arizona, California, and Wyoming. The offices will help to expedite processing of the increased number of applications for renewable energy projects on U.S. lands.
To date, BLM has received about 470 renewable energy project applications. Those include 158 active solar applications, covering 1.8 million acres, with a projected capacity to generate 97,000 MW of electricity. The BLM has said it will continue to process existing renewable energy applications, both within and outside of the solar energy study areas. The DOI is also is coordinating with states to expedite permitting for a number of solar power projects nearing approval, Salazar said. The BLM will begin site-specific environmental reviews for two major projects in Nevada that would have a combined capacity of more than 400 MW of electricity: the NextLight Silver State South array is planned to produce 267 MW; NextLight Silver State North would produce about 140 MW. The DOI also continues to work with the Western Governors Association to develop renewable energy zones and transmission corridors.
The Solar Energy Study Areas, located in Nevada, Arizona, California, Colorado, New Mexico, and Utah and outlined in maps encompass about 670,000 acres. Only lands with “excellent” solar resources, suitable slope, proximity to roads and transmission lines or designated corridors, and containing at least 2,000 acres of BLM-administered public lands were considered for solar energy study areas, the DOI said. Sensitive lands, wilderness, and other high-conservation-value lands, as well as lands with conflicting uses, were excluded.
An ongoing federally funded environmental evaluation of potential solar energy development on public lands in six Western states, known as the Solar Programmatic Environmental Impact Statement, or PEIS, will be expanded to include an in-depth analysis of the potential impacts of utility-scale solar energy development on public lands in the 24 Solar Energy Study Areas. This enhancement will be supported by additional federal funding under the American Recovery and Reinvestment Act. The BLM will continue to process the 158 active solar applications during preparation of the PEIS. The bureau will also continue to accept new applications both within and outside of the Solar Energy Study Areas. However, these applications will be subject to any decisions made from the Solar PEIS.
DLR to Commercialize Technology from Solar Tower Demonstration. A solar thermal demonstration power plant in Jülich, Germany, that was developed by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR), was formally handed over to its future operator, the Jülich Department of Works this August. The solar power plant, developed as a complete system, will now be used as a reference for future commercial power plants. DLR said in a statement that, in particular, the plant will play a major role in the Desertec Project, the €400 billion proposed project that seeks to establish 6,500 square miles of concentrated solar power plants and high-voltage transmission lines in the vast deserts of North Africa and in the Middle East. (More on the Desertec Project later in this post).
“Of course, the sun does not shine as often in Jülich as in North Africa, but for an experimental power plant in which the technology is to be further developed, having good connections to the research institutes is more important than continuous operation,” said Professor Hans Müller-Steinhagen, head of DLR’s Institute for Technical Thermodynamics.
The project consists of 2,153 heliostats with a total area of almost 18,000 square meters that are arranged over about 8 hectares, or 20 acres and produces 1.5 MW (Figure 4). Tracking the sun, these concentrate solar radiation on a receiver that is about 22 square meters in size, installed at the top of a 60-meter tower. The receiver is made of porous ceramic elements through which incoming ambient air flows. In passing through the receiver, the air is heated to around 700C. This heat is then delivered to the water-steam cycle in a heat-recovery boiler. The steam generated there drives a turbine, which produces power via a generator.
4. German Aerospace Center in August handed over a full-system solar thermal demonstration project to a local department of works. It now plans to use the tower to develop commercial power plants for sunny regions in southern Europe and for the €400 billion multi-company solar project in North African and Middle Eastern deserts. Courtesy: DLR
A heat storage module that extends across two stories of the tower is integrated into the plant. This heat storage module contains ceramic filling material through which hot air flows, and which can thus be heated. When discharging, the process works in reverse: The heat storage module releases its energy so that power can also be produced when clouds pass overhead.
DLR said that it would set up a research platform on one story inside the tower (at about half the height of the tower) to place experiments behind a 3 m x 7 m opening onto which the power plant’s heliostats can be focused. Included among the planned activities are tests for new receivers and experiments on the thermochemical manufacture of hydrogen using solar energy.
Acciona Inaugurates 50-MW Parabolic Cylinder Plant in Spain. Spanish energy firm Acciona in late July inaugurated a 50-MW concentrating solar power (CSP) plant in Alvarado, Spain. The €236 million plant uses parabolic cylinder technology — the same as Acciona’s Nevada’s Solar One CSP plant, which has been in operation since June 2007. The Alvarado I CSP plant covers more than 130 hectares. Solar energy is reflected by 184,320 mirrors aligned in rows to 768 solar collectors with a total length of around 75 km. Construction of the plant began in February 2008 and involved shifting more than a million cubic meters of earth. An average of 350 people worked throughout the 18-month construction period. A team of 31 will make up the plant’s operation and maintenance team.
Saharan Solar Project Heats Up
Plans to install a series of solar thermal power plants in the Sahara Desert to power Europe and North Africa are heating up. The idea was discussed in May as part of the newly formed Mediterranean Union, launched at a summit in Paris, and it now has the backing of both UK Prime Minister Gordon Brown and French President Nicolas Sarcozy.
More recently, Germany’s Wuppertal Institute for Climate, Environment and Energy and the Club of Rome issued a study that said the project could generate some €2 trillion worth of power through 2050. And this July it received yet another major boost, with 12 companies congregating at the request of German insurance firm Munich Re and formally agreeing to analyze and develop a multidimensional framework for the €400 billion project. The Desertec Industrial Initiative, as the 12-company coalition is now called, includes European giants Deutsche Bank, Siemens, ABB, and utilities E.ON, RWE, and Abengoa Solar.
At the heart of the ambitious Desertec project is the goal to establish 6,500 square miles of concentrated solar power plants in the vast African and Middle Eastern deserts, along with a super-grid of high-voltage transmission lines, to supply countries in Europe and Africa with electricity. The project could supply continental Europe with up to 15% of its total energy needs — producing a stunning 20 GW by 2020, as Guenter Gloser, Germany’s deputy foreign minister, told Reuters in June. The first possible power station would be a 2-GW solar thermal power station in Tunisia with power lines to Italy, a project that would take five years to build.
According to the Desertec Foundation, satellite studies conducted by the German Aerospace Center show that by using less than 0.3% of the entire desert of the Middle East/North Africa region, enough electricity and desalinated seawater can be produced to meet the growing needs of these countries and of Europe (Figure 5). The German Aerospace Center also assumes that in 10 to 15 years, electricity from solar power plants will be able to compete with medium-load electricity from fossil power plants.
5. Several European countries are backing an ambitious project that seeks to establish 6,500 square miles of concentrated solar power plants and a super-grid of high-voltage transmission lines in the vast deserts of North Africa and in the Middle East. Courtesy: Desertec Foundation
But not everyone is convinced that the project is feasible. Vattenfall prefers not to support the undertaking, because “it costs too much money” and “transmission costs are too high,” as the Swedish state-owned utility’s CEO Lars Josefsson told the Financial Times in June. “I don’t think it’s realistic,” he said, adding that securing Europe’s future energy needs should be focused on developing carbon capture and storage technology for coal-fired power plants.
Even Munich Re — which spurred a media frenzy about the project by publicly inviting Europe’s energy giants to discuss the project — recognizes the cost obstacle. The insurer said recently in a statement that, “despite the use of known technologies, implementation of such a visionary concept will require substantial initial financing. Therefore, DESERTEC can probably only be put into practice if suitable incentivisation mechanisms are in place to make such investments worthwhile for investors.”
Other critics have expressed concerns about becoming energy dependent on politically unstable North African countries in the Sahara and about the concept of centralized transmission lines, which could be vulnerable to terrorist attacks. Project proponents counter by saying that the EU already imports energy from regions and sources that are not risk free.
Portions of this article appeared in POWER magazine. Sonal Patel, Senior Writer, originally prepared several segments of this article.