December 2006

Alternative Energy — Hype or Real?

By Badrul H. Chowdhury

The latest adventure of fictional secret agent Ethan Hunt in Mission: Impossible III has him flying in a helicopter chase through a wind farm. Even though the movie portrays a fictional wind farm, there is nothing fictional about wind power. The statue of liberty is now served by power generated by wind. A and more than 10,000 MW of grid-connected wind power exists in the United States today, second only to Germany in installed wind power capacity. Although still a magnet for environmentalists' concerns for bird mortality, today wind power enjoys a state of tremendous appeal to power producers and consumers alike. The beginnings of commercially available alternate energy, however, were very modest by today's standards.

In 1982, the first central-station photovoltaic (PV) power plant, rated at 1 megawatt (MW) went online in Hesperia, Calif., and served Southern California Edison's (SCE) power grid. 1984 saw more utility interest in PV, with the most notable being the 2 MW PV power plant at Rancho Seco, Calif., that was connected to the Sacramento Municipal Utility District. In 1985, a third grid-tied PV plant, rated at 6 MW, was completed in Carissa Plains, Calif. This facility also supplied SCE's utility grid.

The 10-MW Solar One concentrating solar plant constructed in 1982 near Barstow, Calif., is an example of the so-called Power Tower technology, which utilizes a vast array of mirrors, aptly named heliostats, to focus the sun's incident energy to a central tower that has a receiver and a means to transfer the energy to electricity.

The world's largest and perhaps the most successful early solar power facility was built in the Mojave Desert near Kramer Junction, Calif., in 1986 as a result of a collaboration between the Department of Energy and private industry. This facility consists of five solar thermal stations with a combined capacity of 150 MW. Solar energy is transferred as heat to a fluid in receiver tubes which is pumped into a power generating block (with a steam generator and a turbine) for conversion to electricity. The facility covers more than 1,000 acres and has a collector surface area of more than a million square meters. This facility continues to operate today, providing clean renewable energy to SCE's customers, but it is one of only a few remaining systems from that era. Most of the others have either been dismantled or their permits have run out. However, the lessons learned from these early ventures have led to an expanding renewable energy industry which has benefited from customer acceptance, which has, in turn, led to lower material cost and further expansion in the utility market. A growing number of impressive renewable and alternate energy installations are cropping up around the world, and the economics continue to look better and more in line with what is needed to make further inroads. To gain a peek into the future of alternative energy, one must look at the development of some of these technologies since the early demonstrations of the 1980s.

Solar Energy

Solar panels are now ubiquitous, found in applications ranging from small highway signs to large building-integrated systems on skyscrapers. Some notable examples follow:

• The Nevada Solar Dish-Engine project, rated at 1 MW, includes a parabolic dish and a Stirling engine for power generation. Although not connected to the grid, the system has demonstrated high efficiencies and holds promise for the future.

• The first commercial power tower plant is planned for construction in Spain. It will be rated at 50 MW and will utilize thermal storage to serve power for up to 24 hours-per-day.

• The building at 4 Times Square, Manhattan, New York, built in the 1990s, includes building-integrated photovoltaic (BIPV) panels on the 37th through the 43rd floors on the south- and west-facing facades.

• In 2002, the largest rooftop solar power system in the United States — a 1.18-MW system — was built at the Santa Rita Jail in Dublin, Calif.

• The world's largest solar electric plant is now operating in Bavaria near Arnstein, Germany. Solarpark Gut Erlasse is a 12 MW PV plant constructed in 2006 from about 28,000 Solon modules mounted on double-axis trackers that continuously track the sun.

• China plans to finish construction of a 100 MW solar PV plant in the northwestern province of Gansu by 2011.

Because of a wide array of activities, international standards bodies like the IEEE have developed new standards or modified existing ones to standardize the application of alternate energy sources. Many of these recommended codes deal with safety and reliability issues, as well as interface procedures, allowable voltages and currents, certification, testing and monitoring issues [1, 2].

In 2005, the lowest system prices in the off-grid PV sector ranged from about $10 to $20 per watt. The average price of grid-connected PV systems in 2005 was $6.6 per watt [3]. Concentrating solar power technologies, particularly parabolic troughs, currently offer the lowest-cost solar electricity for large-scale power generation (10 MW-electric and above). Current technologies cost $2 - $3 per watt, resulting in a cost of solar thermal power of 9 - 12 cents per kilowatt-hour. New innovative hybrid systems that combine large concentrating solar power plants with conventional natural gas combined cycle or coal plants can reduce costs to $1.50 per watt and drive the cost of solar thermal power to below 8 cents per kilowatt hour (kwh).

Wind Energy

Once spurred only by tax incentives and attractive utility buy-back rates, wind energy has come a long way from its post-oil embargo status to enjoy unprecedented growth in recent years. Under federal research funding in the 1970s and 1980s, several "new generation" utility-scale wind turbines were built to be tested for commercialization. Among these, the most notable were the Mod 0A, Mod 1, Mod 2 and Mod 5B designs. These experiments were largely unsuccessful — mainly because several design flaws were eventually discovered. At about the same time in California, private industry installed more than 17,000 machines in wind farms between 1981 and 1990. These machines ranged in output from 20 to 350 kilowatts. Then in the 1990s, with a growing U.S. wind industry buoyed by European success stories, several wind farms started operating in wind-rich U.S. areas. The wind industry has grown at a torrid pace since then (see Fig. 1), currently boasting a total installed capacity of nearly 60,000 MW worldwide. At the end of 2005, total wind power capacity stood at 59,260 MW, whereas total off-grid and grid-connected PV power stood at about 3,700 MW (see fig. 2). The King Mountain Wind Ranch in west Texas, with more than 275 MW capacity boasts as the largest wind farm in the world and rivals many conventional fossil-fired generation plants in size.

With such huge amounts of intermittent generation, operating large windfarms within an existing electric utility system can bring about some uncertainties in both windfarm behavior and network behavior. Studies have proven that, at certain penetration levels, one may start to see problems with interconnection. Some suggest this level to be 15 percent, while others suggest 30 percent. Whatever the penetration level is, it is clear that wind variability will most likely have an impact on system operations, including voltage and frequency and, in general, power quality. A second issue the industry has an eye on is dealing with low-voltage, ride-through capability of wind turbines. Presently, wind turbines are forced to trip out during network disturbances. To counter some of these uncertainties, power engineers are devising new grid codes in many parts of the world, particularly where wind power presence is beginning to be felt in system operations.

Advances in wind-turbine technology have cut the average cost of wind energy to about 4 to 5 ¢/kwh in 2005, from more than 80 ¢/kwh in 1980. With the tax credit, wind energy becomes competitive with natural gas, and even with coal.

Fig. 1. Wind power generation is the fastest growing source of energy worldwide. Source: REPP, Worldwatch 1999.

Fig. 2. A comparison of growth windpower and solar PV.
(Source: PV data from [3] and Wind data from [4]).

Biomass Energy

Energy derived from biomass supplies almost 30 times as much total energy (electric and non-electric power) in the United States as wind and solar energy combined. Biomass is a renewable resource because it is derived from plant materials, such as tree and grass crops and animal and urban wastes. Production of alternative fuels, such as ethanol, methanol and biodiesel are the most common forms of biomass application. However, electric power production using biogas derived from landfills, wastewater treatment facilities, and livestock operations has reached a level comparable to that derived from wind power. As a matter of fact, with about 9,730 MW of installed capacity in 2002, biomass power was the leading alternative generating resource in the country. Since then, of course, wind power has taken over as the leader.

In the year 2000, direct-fired biomass energy cost 7.5 ¢/kwh and gasification-based biomass energy cost 6.7 ¢/kwh. The cost of biomass energy has stayed relatively steady since the 1980s.

Geothermal Energy

Geothermal plants utilize the steam and hot water trapped in underground wells and reservoirs to drive turbines for power generation. Among the advantages are less environmental pollution and very little land use for the amount of power generated. However, the drawback lies in the fact that well-developed geothermal sites are not frequently available. The largest electricity producing geothermal plants in the world are located in the Geysers area in Northern California. Total installed capacity amounts to about 1,100 MW, having peaked at 1,967 MW in 1989. Total worldwide capacity is in excess of 8,000 MW.

The cost of geothermal electricity in the United States ranges from 5 ¢/kwh to 8 ¢/kwh. These costs are steadily declining due to technological improvements. The Geysers sells power at 3 to 3.5 ¢/kwh. A geothermal power plant built today would require about 5 ¢/kwh to be economic.

Fuel Cells

An electrochemical device, a fuel cell converts the chemical energy in hydrogen into electrical energy. It functions similar to a battery, except that the fuel has to be continuously fed into the cell. The fuel cell consists of two electrodes, anode (negative electrode) and cathode (positive electrode) separated by an electrolyte. Hydrogen is fed into the anode where electrochemical oxidation takes place and oxidant (Oxygen) is fed into the cathode where electrochemical reduction takes place to produce electric current that can be directed externally to power a load. Each electrode is coated by a catalyst that speeds up the chemical reactions. Water is the primary product of the cell reaction.

Fuel cells are classified in accordance to the type of electrolyte used. Two popular types of electrolytes are the Proton Exchange membrane, which may be used in low temperature applications such as in vehicles, and the phosphoric acid electrolyte, used in higher temperature applications, such as in combined heat and power.

Hydrogen is attractive as a fuel source, because it has the highest energy density by mass, thrice that of petroleum. However, its energy density by volume is extremely low. Therefore, to get any significant energy production, a very large hydrogen storage volume is required. Hence, a primary concern is the fuel supply. Without a hydrogen delivery infrastructure, one has to depend on reforming natural gas to produce hydrogen.

Although the technology holds great promise, only a handful of examples exist of commercial fuel cell application for stationary power. The country's largest fuel cell power plant in commercial operation is located in Garden City, Long Island, NY. The phosphoric acid fuel cells, produced by UTC Power, are rated at 1.4 MW and provide power and heat for Verizon Communications, Inc.'s office building and call-switching center.

Fuel cell cost is still an issue, as many fuel cells require the use of expensive materials. Catalysts, such as platinum, required to speed up the electrochemical reaction, are often expensive. With only a small number of companies engaged in commercial fuel cell production, this technology does not yet have the advantage of cost efficiencies realized from mass production.

Ocean power

The most commonly known ocean power technologies include: wave power, tidal power, ocean thermal energy conversion, and Ocean currents. Although, these technologies have been researched for several decades (mostly outside the United states), not much progress has been made in commercial applications. The technologies are still beset with high initial costs, making them less attractive in comparison with conventional alternatives.

The Archimedes Wave Swing (AWS) is an example of wave power technology that has great potential in the future. The AWS consists of a cylindrical, air-filled chamber (Floater), which moves vertically with respect to a fixed structure connected to the seabed. A wave passing over the top of the device causes the Floater to bob up and down and this relative motion can be used to turn a turbine to produce electricity. Such a device — a 2 MW pilot plant — is currently producing power off the coast of Portugal and feeding the Portuguese grid.

The first and the largest tidal power station is the Rance tidal power plant completed in 1966 at La Rance, France. It has 240 MW installed capacity. Another, much smaller, facility exists at the Annapolis Royal Generating Station, consisting of a dam and 18-MW power house on the Annapolis River at Annapolis Royal, Nova Scotia. The plant is located on an inlet to the Bay of Fundy on the northeast end of the Gulf of Maine between the Canadian provinces of New Brunswick and Nova Scotia. Like hydro power plants, tidal power is subject to high cost of construction and environmental concerns.

[1] IEEE 929-2000 Recommended Practice for Utility Interface of PV Systems
[2] IEEE 1547-2003, Standard for Interconnecting Distributed Resources with the Electric Power System.
[3] International Energy Agency, Photovoltaic Power Systems Program, www.iea-pvps.org/isr/index.htm
[4] Global Wind Energy council, www.gwec.net/

Badrul H. Chowdhury is a professor of electrical engineering at the University of Missouri-Rolla. Comments may be submitted to todaysengineer@ieee.org.