Here Comes the Sun: Taking Solar Power to Grid-Scale

by Lori Pottinger
Tuesday, March 25, 2008

What renewable energy source is highly reliable and predictable, especially productive during the hours of highest electricity use, can be scaled small enough to power one building or big enough to electrify a town, is a proven technology whose costs keep dropping, creates more jobs than gas or coal, and could, with a major rollout, displace 2-3 billion tons of carbon annually worldwide?

The answer is concentrating solar power, which uses mirrors and the power of the sun to run steam turbines. Unlike some other energy innovations being put forth today - "clean coal," for example - there's no "smoke and mirrors" trickery about it. Just mirrors. Lots and lots of mirrors.

This exciting renewable energy technology has been working reliably in California since the 1980s, when oil was cheap and climate change was for wonks. Today, the political and economic conditions that prevented a major rollout of the technology are, pardon the pun, almost a mirror image of the situation in the 1980s. Today, every indication is that concentrating solar power (CSP) is on the cusp of a renaissance, thanks to increased investments in R&D, tariff support for CSP plants' electricity in Spain, and a growing realization among governments and financiers that the world needs to build renewable energy sources now.

A line-concentrator solar power plant in the Mojave Desert, California.
A line-concentrator solar power plant in the Mojave Desert, California.
Warren Gretz

A surge of development in Spain and the US West is well underway. Two new plants producing 65 megawatts of electricity have been built in the US (adding to California's 355 MW of existing CSP), while Spain has completed 10 MW, has 50 more projects in the pipeline, and intends to develop 500 MW by 2010. The goal of the US National Renewable Energy Lab (NREL) is to help develop up to 4,000 megawatts of CSP in the southwestern US by 2015. "This penetration level is aggressive, but possible if the 30% investment tax credit is extended per the primary recommendation of the task force," says George Douglas, an NREL spokesman.

Elsewhere, plants are planned or being built in Egypt, South Africa, Australia, Libya, Algeria, India, Israel and Morocco. And if a Jordanian prince has his way, tens of thousands of megawatts would be generated in the Sahara for sale to Europe. Renewable Energy World forecasts 6,400 MW installed globally by 2015, leaping to 36,850 MW by 2025. By then, they project an annual installation rate of 4,600 MW/year.

"After over a decade of inaction, CSP is finally taking off," says Sven Teske with Greenpeace's Energy [R]evolution Campaign. "For 2040, CSP has a chance to contribute to the global electricity supply in a double digit range. The main reason for this is good policy. In the USA there are Renewable Portfolio Standards in place, in Spain there are guaranteed tariffs."

How it Works

Dish Stirling solar power systems concentrate the sun’s heat to run a Stirling engine, which drives an electric generator.
Dish Stirling solar power systems concentrate the sun’s heat to run a Stirling engine, which drives an electric generator.

CSP uses sun-tracking mirrors to concentrate solar heat onto liquid-filled tubes or central tower. The liquid is vaporized into steam, which is used to drive turbines to generate electricity. CSP plants act much more like conventional power plants than solar PV or wind farms, which make them more attractive to utilities. There are a variety of types of plants being tested and built, with different advantages to each. Because they are fairly simple to design and build, the plants go up quickly. A new CSP plant near Las Vegas, Nevada took about one year to build. (Permitting and land-use acquisitions add to the process, however.)

CSP still has obstacles to overcome. Most importantly to utilities is its still-high cost. While concentrated solar power is now less expensive than solar PV panels, it is still generally around 15-20 cents/kwh, well above fossil fuels and wind (though windpower is more "intermittent" than a well-sited CSP plant, and generally wind's peak production time does not match peak loads as well). Prices for CSP are coming down, however, and the projected increase in new plants will help drive down prices further. Most companies are shooting for a target contract price of 15 cents/khw in the US, whereas "the price for electricity from new baseload natural gas plants is about 9 cents per kilowatt hour, and rises to 12 to 48 cents/kwh for peak power, depending on what report you read," says Tom Hunt, with the Community Environmental Council. Unlike fossil fuel plants, which are expected to see rising prices over time, CSP plants have no fuel costs, and therefore no future price surprises once a contract is signed.

At least one company says they have already solved the cost issue. The US-Australian company Ausra has a new proprietary design that it says can produce electricity for 10 cents/kWh. Not only is Ausra's design cheaper; the company will also save money by manufacturing units as close to where they'll be installed as possible, to reduce shipping costs. Ausra is now building the "world's largest" CSP factory in Nevada that will be able to churn out 700MW/year in new systems, to supply the hot US Southwest market. Other companies are also trimming the costs of their units by incorporating lighter materials, fewer moving parts, and other innovations.

One factor that would allow CSP to compete on an equal playing field with fossil fuels sooner is a price on carbon. "Everyone thinks an increase in the cost of carbon is coming," said David Crane, CEO of NRG Energy Inc., in a recent article in EnergyBiz magazine. That would make the cost of electricity from coal jump significantly.

The other primary challenge for CSP is the ability to produce energy "24-7," the way fossil fuel plants can. Plants would need 16 hours of storage to generate electricity around the clock. Ausra says it can store energy at its prototype plants for 20 hours - a breakthrough that, if it proves workable outside the pilot-plant stage, will place the company at the head of the pack. Ausra's solar collectors employ a propriety storage system, but the basic idea is to focus light onto tubes filled with water, thus directly producing steam. Storing heat is more efficient than storing electricity: just 2-7% of the energy is lost in heat storage systems, compared with losses of at least 15% when energy is stored in a battery, according to the MIT Technology Review. Ausra will start construction on a 175 MW commercial plant in California later this year.

We Shall Overcome

Transmission issues can be more complex than with fossil fuel plants, as large CSP plants cannot always be built close to where power is needed. An article in Scientific American recently laid out a "grand plan" to massively increase solar power (both CSP and PV) in the US. It called for replacing the existing system of alternating-current (AC) power lines which lose too much energy over long hauls with a high-voltage, direct-current (HVDC) power transmission system, which lose far less energy than AC lines over equivalent spans. "The AC system is simply out of capacity, leading to noted shortages in California and other regions; DC lines are cheaper to build and require less land area than equivalent AC lines," the magazine notes.

Water use is another potential drawback. Some CSP designs require water to cool the plant, which is impractical in the desert. Experts say R&D is needed to find air-cooling innovations. Some types, such as dish units, do not require water for cooling. Plants can also be built near the sea, where they could power desalination plants to produce their own cooling water.

A related environmental issue is the siting of large industrial solar fields in fragile deserts. Clearly, care must be taken to minimize impacts, to prevent CSP from being viewed as an unwelcome visitor in the way that large wind farms have become in some settings.

Another siting issue relates to the relatively large tracts of land needed for these projects compared to fossil fuel plants. Not all CSP plants are equally land-guzzling. "We are more than two times more efficient when it comes to land," said Rob Morgan, Ausra's chief development officer. Morgan states that using Ausra's technology, it would take a square of land 92 miles on a side to "provide all US electric power - the entire US grid - day and night" (US consumption is currently about 25% of electricity use worldwide). "This amount of land is less than 1% of America's deserts, less land than currently in use in the US for coal mines, and a tiny fraction of the land currently in agricultural use," according to the Ausra website. The company notes that CSP also has a much smaller land footprint than large hydro.

These aren't insurmountable issues, but they will have to be addressed for a mass rollout to succeed. Industry experts say that incentives are still important for the near term to help the industry address these challenges. The European Union has spent some €25 million in the past decade to help develop this technology. In the US, an investment tax credit (ITC) provides R&D incentive, but has to be renewed every two years, creating uncertainty for those trying to develop projects.

Another type of incentive is feed-in tariffs, as is being tried in Spain. These more direct forms of subsidy are not as good at encouraging innovations that lead to price reductions, say some experts. "At those prices, it's all project driven, you just want to get projects built," says Arnold Leitner, president of Skyfuel.

Under African Skies

What will it take (besides sunshine) for this technology to reach poorer and middle-income countries? The potential is certainly there for the nations with hot, dry climates. Two of the fastest-growing energy users, China and India, are well endowed with desert solar resources to power their economies. Mexico also has huge solar reserves close to major cities in both Mexico and the US. And of course, the granddaddy of all deserts, the Sahara, has many CSP experts feverish in anticipation.

Last year European engineers unveiled a plan to build thousands of megawatts of CSP plants to connect via high voltage undersea cables to northern Europe - enough to meet up to a sixth of Europe's electricity needs. Engineers with the German Aerospace Center who carried out the feasibility studies see the project "as a win-win scenario creating energy, water and income for the Middle East and North Africa," according to the BBC.

An article in the UK Guardian states: "The Desertec project envisages a ring of a thousand of these stations being built along the coast of northern Africa and round into the Mediterranean coast of the Middle East. In this way up to 100 billion watts of power could be generated: two thirds of it would be kept for local needs, the rest - around 30 billion watts - would be exported to Europe." The plants' superheated steam would be used to desalinate water (normally an energy-intensive operation).

The deserts of Africa would be a natural for CSP for domestic purposes too, but thus far there has been little progress. In Southern Africa, the South African utility Eskom has been studying plans for a 100 MW CSP plant for many years, but the decision to build keeps getting put off. The site chosen for the plant is one of the best in the world for solar. The company hopes to use local producers for materials as much as possible.

A recent major power shortfall has Eskom in crisis mode, however, and it's not clear if the new CSP plant will benefit from or be sunk by the turbulence. What is clear, however, is that Eskom will need to find cleaner ways to produce energy. Currently, coal-fired plants produce about 90% of South Africa's power. According to Eskom's CEO, if Eskom were a country, it would rank 25th among the world's largest emitters of carbon dioxide. The huge utility, which supplies power to neighbors as well, is also looking to build a string of nuclear plants, and the world's biggest dam on the Congo River.

Other Southern Africa nations are farther behind. Morteza Abekenari, the CEO of Solar Power, a Botswana-based company that manufactures solar panels, says he has for years been trying to convince local energy authorities to buy into the idea of concentrating solar power, without any luck. "When we started, we said that the sun was Botswana's diamond that would last forever, but the idea of solar energy was like science fiction here," he told the Francistown Voice.

Go Micro

It's not surprising that a small nation with low energy needs like Botswana might balk at the big outlays of cash required for large-scale CSP plants and the grid extensions they might require. But there is another option that could prove workable for areas where grid expansion is impractical. Micro CSP is a smaller scale version of its big brother that is easier to install and can be cost-effectively shipped long distances.

At least one company, the Hawaii-based Sopogy, has developed a rooftop unit that can power a single building or industrial complex. Unlike standard CSP components, the Sopogy unit was developed with more humid climates in mind, and the company is now beginning to market worldwide for large industrial users and residential/hotel complexes. Their systems range from 500KW-10MW.

"I believe there is great potential for micro-CSP to make a difference in developing countries," says Sopogy's Al Yuen. "This is especially true for the application of process heat for industrial purposes, which can be generated at 60-70% efficiency and would be the lowest cost solar solution."

Clearly, CSP is a very exciting alternative with huge potential - but like other new renewables, it is only part of the solution. "No one thing will be the answer to renewable energy to power the grid. CSP will contribute more and more. Wind's role will grow. And ocean power has tremendous potential. A little further out it might be organic solar cells and solar cells that use nanomaterials. You'll see a combination based on geography and cost," says NREL's George Douglas.

More information: 

Concentrating Solar Thermal Power Now! is a "blueprint for action" that aims to accelerate market introduction of CSP. The 2005 report (now being updated for a late-2008 re-release), written by Greenpeace and the European Solar Thermal Industry Association, "demonstrates that there are no technical, economic or resource barriers to supplying 5% of the world's electricity needs from solar thermal power by 2040 – even against the challenging backdrop of a projected doubling in global electricity demand." Download the report.

Learn more about plans for CSP in the Sahara