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Renewable Energies

Geothermal

Geothermal comes from the Greek words geo, meaning earth, and therme, meaning heat. The center of the earth is believed to be approximately 5,500º C (almost as hot as the surface of the sun); only a couple of miles below earth’s surface, temperatures can be over 200º C. Geothermal power is energy generated by tapping the heat stored beneath the earth’s surface.

Wind Power

Wind power

Wind power is the fastest growing global alternative energy source. Currently, in the United States and the European Union (EU), it is the second source of new power generation after natural gas. Although wind power provides less than 1 percent of the electricity in the United States today, it is growing rapidly, with production around 13 megawatts (MW)—enough to power over 3.4 million homes—and currently reducing carbon dioxide emissions by 19 million tons annually.

 

Hydropower

Hydropower

Hydropower presently supplies approximately 19 percent of the world’s electricity needs (more than700,000 MW). This energy source can be far less expensive than electricity generated from nuclear or fossil fuel sources while producing no harmful emissions. However, hydropower is not slated for much future expansion because most suitable sites in the United States either have been developed or are unavailable for development.

Wave Action Generation

Wave Action Generation

Wave action generation, also referred to as wave or tidal generation, uses the energy of the ocean tides/waves to generate electricity. Currently, this type of power generation technology is not widely used. Although Portugal has announced plans to have the world’s first commercial wave farm, the technology is being researched and tested globally.

Renewable Energy Resources

Purchasing green power does not imply that the specific electricity generated off-site is transmitted directly to the green power purchaser.  Rather it involves taking advantage of one of several methods to track renewable energy generation and stimulate more renewable energy generating capacity.

Where available, green power programs sponsored by local utilities can be a simple way to purchase renewable energy.  Some electric utilities offer customers the option of purchasing renewable energy for part or all of their electricity consumption.  The utility usually offers green power at a premium, and this premium goes toward developing new renewable energy generation or purchasing credit for renewable energy generated at existing facilities. 

When utilities purchase “credit” for renewable energy generated, these are referred to as Renewable Energy Certificates or Renewable Energy Credits (RECs).  Utilities are not the only entities that buy and sell RECs.  Building owners can purchase RECs directly from brokers to cover part or all of their building’s energy use.Renewable Energy Certificates, also called “green tags” or Tradable Renewable Certificates (TRCs), are intangible assets created whenever electricity is generated from a renewable source.  TRCs are essentially the “credit” for generating power from a sustainable source.  REC brokers purchase RECs from energy generators and market them to consumers, utilities, and others.

All RECs are not necessarily created equal. RECs are classified in several ways, including type of renewable energy generation (solar, wind, hydro, biomass, geothermal, etc.).  Some customers, for example, value solar RECs over large-scale hydro RECs because solar technologies generally have fewer negative environmental impacts.  RECs are also classified by the location where the energy was generated.  To track and verify the generation of renewable energy and the associated RECs, an independent certification program such as Green-e is necessary.  Green-e, operated by the non-profit Center for Resource Solutions, provides certification and verification of renewable energy across the country (see the Resources section below for more on Green-e).

For some designers or owners who have space for renewable energy installations at their sites but do not want to be burdened with the cost, Power Purchase Agreements (PPAs) are an option growing in popularity.  Through a power purchase agreement, a renewable energy contractor will generally install, operate, own and maintain a renewable energy installation at a host site.  The system owner will then sell energy generated by the system to the host at prices determined in the PPA.  This can be an effective way to host a renewable energy system without being burdened by the up-front cost.  Be aware, however, that the “credit” associated with generating electricity renewably (the RECs) are generally retained by the system owners and sold elsewhere through brokers

Today, three geothermal power plant technologies are being used to convert hydrothermal fluids (steam or water) to electricity: flash, dry steam, and binary cycle. The type of conversion used depends on the state of the fluid and its temperature. Temperatures are classified as low (less than 90° C or 194° F), moderate (194–302° F), or high (greater than 302° F).

• Flash steam plants are the most common type of geothermal power generation plants in operation today because most reservoirs are hot water reservoirs with water temperatures greater than 360° F that is pumped under high pressure to the generation equipment at the surface.
• Dry steam power plants were the first type of geothermal power generation plants built. They use steam from the geothermal reservoir as it comes from wells and route it directly through turbine/generator units to produce electricity.
• Binary-cycle geothermal power generation plants differ from dry steam and flash steam systems in that they use a heat exchanger. Heat is transferred from the geothermal water to a secondary liquid that never comes in contact with the turbine/generator units. The geothermal water is then injected back into the underground reservoir.

Wind power

In the past 15 years, the cost of wind energy has more than halved, and its production per unit of capacity has more than doubled. A single modern wind turbine produces, on an annual basis, approximately 180 times more electricity at less than half the cost per kilowatt-hour than its equivalent did 20 years ago. Wind turbines are rated by their maximum power output in kilowatts (kW) or megawatts (1,000 kW, or MW). For commercial utility-sized projects, the most common turbines sold are in the range of 600 kW to 1 MW (large enough to supply electricity to 600–1,000 modern homes), while the newest commercial turbines are rated at 1.5–2.5 MW. The power that can be generated from a modern wind turbine is related to the cube of the wind speed. This means that a site with twice the wind speed of another site will generate energy eight times as much. Currently, in the United States, 46 states offer wind resources suitable for commercial development.

Hydropower
Hydropower plants use the energy of falling water to generate electricity. The water falls on turbines, which in turn spin a generator that produces electricity. The farther the water falls and the more water falling through the turbines, the more power is generated. In addition, the greater the flow of water down a river at a hydropower site, the greater the energy the plant can produce. Today, in the United States, hydropower capacity is roughly 95,000 MW and supplies approximately 28 million households with electricity—the equivalent of nearly 500 million barrels of oil.

Wave Action Generation

The amount of energy that can be tapped from waves depends on the wind speed, the time the wind is moving over the waves, and the distance it covers. As this process continues, the energy is concentrated more and more, and the wave can produce over 100 kW of power per meter of wave front. The two main types of technology that tap the energy of the waves are sitters and floaters. Given proper care in siting, installation, and operation, wave action generation may be one of the more environmentally friendly electricity generation technologies.

Flash, Dry, and Binary Cycle Power Plant Diagrams

Geothermal

• Flash Steam Power Plants: Hydrothermal fluids above 360° F are sprayed into a tank held at a much lower pressure than the fluid, causing some of the fluid to rapidly vaporize, or “flash.” The vapor then drives a turbine, which drives a generator to create electricity. If any liquid remains in the tank, it can be flashed again in a second tank to extract even more energy. In flash plants, both the unused geothermal water and condensed steam are injected back into the reservoir to sustain the life of the reservoir.
• Dry Steam Power Plants: This is the oldest type of geothermal power plant. It uses hydrothermal fluids that are primarily steam. The steam goes directly to a turbine, which drives a generator that produces electricity. The steam eliminates not only the need to burn fossil fuels to run the turbine but also the need to transport and store fuels. Steam technology is used today at The Geysers in northern California, the world’s largest single source of geothermal power. These plants emit only excess steam and very minor amounts of gases.
• Binary-Cycle Power Plants:  Most geothermal zones contain water temperatures below 400° F (moderate temperature).Hot geothermal fluid and a secondary (“binary”) fluid with a much lower boiling point than water pass through a heat exchanger. Heat from the geothermal fluid causes the secondary fluid to flash to vapor, which then drives the tur-bines. Binary technology allows the use of lower temperature reservoirs, thus increasing the number of reservoirs that can be used. Because this is a closed-loop system, virtually nothing is emitted to the atmosphere. Because the most common geothermal zones contain moderate-temperature water, most geothermal power plants in the future will likely be binary-cycle plants.

Wind Farm

Wind

Commercial-scale wind power is generated at a wind farm. A wind farm consists of a number of wind turbines in and around a set location. Individual wind turbines are interconnected with a voltage of around 34,500 volts and then stepped up to a higher voltage to integrate into the grid system. The overall production of electricity at a wind farm depends on prevailing wind patterns, the siting of the turbines, and overall power capacity of the wind turbines. Knowing that wind does not blow all the time in all locations, the EU has proposed to interconnect wind farms across Europe, the idea being that EU countries would benefit from a system that captures wind energy anywhere wind is blowing at various EU wind farms. This way, European countries tied to the system could still reap the rewards of wind power electricity generation even if their particular country is not currently producing wind energy. In the United States, many new wind farms are appearing on existing farmland. Power can be produced from these wind farms without hindering the ability of the land to produce crops for food.

Hydropower

A hydropower plant uses the force of falling water to make electricity and consists of three main systems: a dam that can be opened or closed to control water flow; a reservoir (lake) where water can be stored; and an electric plant where the electricity is produced. The amount of electricity that can be generated at a hydropower plant is determined by two factors: head and flow. Head is the distance from the highest level of the dammed water to the point where it goes through the power-producing turbine (how far the water drops). Flow is how much water moves through the system; the more amount of water moving through a system, the higher the flow. One of the biggest advantages of a hydropower plant is its ability to store energy. Water can be stored in a reservoir and released when needed for electricity production. During the day, when people use more electricity, water can flow through a plant to generate electricity, while at night, when less electricity is demanded, water can be held back in the reservoir. Storage also makes it possible to save water from winter rains for summer generating power or to save water from wet years for generating electricity during dry years.

Wave Action Generation

A numbers of companies have devised systems capable of generating power with the waves and tides of oceans and rivers. Because water is more than 800 times denser than air at sea level, slow-moving waves or tides have the potential to generate far more electricity than wind turbines, even if the wind blew at 100 miles per hour. Ocean power also remains far more predictable than other alternative energy sources because waves can be tracked from far offshore, allowing computer models to predict electrical output several days in advance. Tidal power is also predictable because tides are dependent on the gravitational pull of the moon. Currently, potential sites around the world are being investigated for commercial application of this technology.

A few applications of wave action generation going on today are listed below:

• Pelamis

  Finavera Renewables and AWS Ocean Energy have created wave power systems that rely on buoys that act as hydraulic pumps. Waves push the buoys down, which drives a turbine. When the wave passes, the buoy returns to its normal spot, only to be pushed again by the next wave.
• Ocean Power Delivery is testing the Pelamis, a device (395 feet long) that looks like a segmented snake. When the segments bob up and down, buoys attached at their joints generate hydraulic pressure. The company has built a 2.25-MW system off Portugal consisting of three 750-kW Pelamis wave-energy

  Wavegen Limpet

  converters and is aiming to build 5-MW and 3-MW systems off the coasts of England and Scotland in the next few years.
• Wavegen, a division of Voith Siemens Hydro Power Generation, is experimenting  with the Limpet (a large cement tube submerged in the ocean, but not attached to the bottom). Water rushes into the tube from waves and cranks a turbine. The company is installing a Limpet in Mutriku, Spain, that will produce 250 to 300 kW when opened in late 2008/09. Wavegen has had a prototype running off Scotland since 2000.

Emerging Trends

Geothermal

Currently, in more than 20 countries worldwide, electric power plants driven by geothermal energy provide more than 44 billion kilowatt-hours of electricity per year, with world capacity growing at approximately 9 percent per year. In the United States, a recent, comprehensive study of the potential for geothermal energy within the country found that mining the huge amounts of heat that reside as stored thermal energy in the earth’s hard rock crust could supply a substantial portion of the electricity the United States will need in the future, probably at competitive prices and with minimal environmental impact. An 18-member panel led by the Massachusetts Institute of Technology prepared the 400+ page study, The Future of Geothermal Energy. Sponsored by the U.S. Department of Energy, it is the first study in 30 years to take a new look at geothermal, an energy resource that has been largely ignored.

The goal of the study was to assess the feasibility, potential environmental impacts, and economic viability of using enhanced geothermal system (EGS) technology to greatly increase the fraction of the U.S. geothermal resource that could be recovered commercially. Although geothermal energy is produced commercially today and the United States is the world’s biggest producer, existing U.S. plants have focused on the high-grade geothermal systems primarily located in isolated regions of the West. This new study takes a more ambitious look at this resource and evaluates its potential for much larger scale deployment. The study suggests that 100,000 MW of electrical generation capacity can be met through EGS within 50 years with a modest investment in research and development (R&D) and recommends the following: More detailed and site-specific assessments of the U.S. geothermal energy resource should be conducted; field trials running three to five years at several sites should be done to demonstrate commercial-scale engineered geothermal systems; the shallow, extra-hot, high-grade deposits in the West should be explored and tested first; other geothermal resources such as coproduced hot water associated with oil and gas production and geopressured resources should also be pursued as short-term options; on a longer time scale, deeper, lower grade geothermal deposits should be explored and tested; local and national policies should be enacted that encourage geothermal development; and a multiyear research program exploring subsurface science and geothermal drilling and energy conversion should be started, backed by constant analysis of results.

Wind

According to the U.S. Department of Energy (DOE), good wind areas, which cover 6 percent of the contiguous U.S. land area, have the potential to supply more than one and a half times the current electricity consumption of the United States. Estimates

of the wind resource are expressed in wind power classes ranging from class 1 to class 7, with each class representing a range of mean wind power density or equivalent mean speed at specified heights above the ground. Areas designated class 4 or greater are suitable with advanced wind turbine technology under development today. Class 3 areas may be suitable for future technology. Class 2 areas are marginal, and class 1 areas are unsuitable for wind energy development.

Although transmission availability, siting and permitting conflicts, and other barriers remain, the American Wind Energy Association (AWEA) expects continued strong growth in wind power capacity. With backing from industry and government, new efforts to explore ambitious long-term targets for wind power are underway. A joint DOE–AWEA report (due for completion this year) will explore the possible costs, benefits, challenges, and policy needs of meeting 20 percent of the nation’s electricity supply with wind power. In the European Union today, wind power is saving over 50 million tons of carbon dioxide a year, and wind power installations are on track to deliver one-third of the EU’s Kyoto Treaty commitment by 2010.

Hydropower

Although most potential large-scale projects have been in the developed nations, large potential is estimated in such regions as Africa, Asia, and South America, where several countries have hydropower facilities either planned or under construction.

Asia and India have about 12,020 MW of hydroelectric capacity under construction. China also has a number of large-scale hydroelectric projects under construction, including the 18,200-MW Three Gorges Dam project (expected to be fully operational by 2009) and the 12,600-MW Xiluodu project on the Jisha River (scheduled for completion in 2020, as part of a 14-facility hydropower development plan). Brazil has plans for a number of new hydropower projects that the country hopes to complete to keep up with electricity demand after 2010, including the 3,150-MW Santo Antonio and 3,300-MW Jirau projects on the Madeira River.

Wave Action Generation

This is still a new technology, as wave power was delivered to the electrical grid for the first time in August 2004. The electricity was generated by a full-scale preproduction Pelamis prototype in Orkney, Scotland, by Ocean Power Delivery Corporation. Presently, in Europe, an array of tidal turbines are being built and tested at various locations. Both wave and tidal energy devices will soon begin tests at the new European Marine Energy Centre (the largest facility of its kind in the world), located in the Orkneys Islands north of Scotland. The Scottish government has pledged that the country will generate 18 percent of its power from renewable resources by 2010. Currently, research and testing are also taking place in the United States, with several wave action generation sites currently under investigation. In New York City, Verdant Power is installing six 36-kW tidal turbines in the East River, with the installation of the first two turbines to be completed by the end of this year. The six tidal turbines will power a shopping center and parking garage on Roosevelt Island, which is located between the boroughs of Queens and Manhattan. In addition, the city of Tacoma, Washington, is investigating the tidal energy potential of the Tacoma Narrows of Puget Sound. These low-impact tidal current turbines, which resemble underwater versions of wind turbines, are still going through R&D and are mostly in the experimental stage, borrowing largely from concepts learned from wind energy technology.

Fuel Cells

Fuel cells are electrochemical devices that combine hydrogen and oxygen to produce electricity, with water and heat as the by-product. As long as fuel is supplied, the fuel cell will continue to generate power. Because the conversion of the fuel to energy takes place via an electrochemical process, not combustion, the process is clean, quiet, and highly efficient—two to three times more efficient than burning fuel. In addition to low or zero emissions, benefits include high efficiency and reliability, multifuel capability, siting flexibility, durability, scalability, and ease of maintenance. Fuel cells operate silently, so they reduce noise pollution as well as air pollution, and the waste heat from a fuel cell can be used to provide hot water or space heating for a home or office. Fuel cell systems have been installed all over the world in buildings and utility power plants, either connected to the electric grid to provide supplemental power and backup assurance for critical areas, or installed as a grid-independent generator for onsite service in areas that are inaccessible by power lines. Fuel cell power generation systems in operation today achieve 40 percent fuel-to-electricity efficiency using hydrocarbon fuels. When the fuel cell is sited near the point of use, its waste heat can be captured for beneficial purposes (cogeneration). In large-scale building systems, fuel cell cogeneration systems can reduce facility energy service costs by 20 to 40 percent over conventional energy service and increase efficiency to 85 percent.

• Reduce the overall energy use in your building
  • Reducing the overall energy use of a building will put less demand on conventional and/or renewable sources providing the energy, whether purchased or otherwise
• Specify energy-efficient equipment and technologies
  • Using energy-efficient equipment and technologies as part of the overall building design process will further decrease the load the local power plant must provide while reducing overall emissions.
• Use renewable strategies and purchase green power
  • Use of electricity sourced from alternative sources or the purchase of green power can reduce a building’s overall carbon and emission footprint.
• Educate building owners, operators, and occupants
  • On where their sourced power comes from and its implications

Resources

Geothermal:

• U.S. Department of Energy (DOE): http://www1.eere.energy.gov/geothermal/overview.html
• Geothermal Resource Council: www.geothermal.org
• Geothermal Energy Association: www.geo-energy.org
• 2006 MIT Research Report—“The Future of Geothermal Energy”: www.geothermal.inel.gov/publications/future_of_geothermal_energy.pdf

Wind:

• American Wind Association: www.awea.org
• Wind Energy Works: www.windenergyworks.org
• North American Wind Farms: www.windpowr.info

Hydropower:

• International Hydropower Association: www.hydropower.org
• National Hydropower Association: www.hydro.org
• The International Journal on Hydropower and Dams: www.hydropower-dams.com

Wave Action Generation:

• The Renewable Energy Centre:  www.therenewableenergycentre.co.uk/wave-and-tidal-power
• British Wind Energy Association (BWEA):  www.bwea.com/marine/resource.html
• Inform Web site (Ocean and Tidal Power Generation news): www.inform.com/Ocean+and+Tidal+Power+Generation

• Epicenter, Artists for Humanity

 Epicenter, Artists for Humanity
 Photo Credit: Richard Mandelkorn

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