Green power

Summary: Green power is a subset of renewable energy that represents resources with the highest environmental benefits when compared to conventional power sources.

Green power is a subset of renewable electricity that is generated from resources that have the highest environmental benefit, such as solar, wind, geothermal, biomass, and low-impact hydropower facilities. The term green power is used as a way to develop a market for renewable energy, through the sale of green power in the form of certificates that bring green power to electricity markets in which end users have direct access only to conventional power. Green power technologies are the only electricity options that can be used to obtain renewable energy certificates. These certificates are then traded on the open market.

The increasing availability of green power programs gives electricity customers the option of buying green power in markets that do not have renewable options. Green power programs accelerate installation of renewable energy technologies when looking at a country as a whole. While some regions may not get power from renewable generation, they can still participate in the development of renewables by purchasing renewable energy certificates created by green power. When green power sources are developed in a few places, displacing conventional generation, the overall environmental impact associated with electricity generation will be significantly reduced.

Green power programs would operate much differently if a smart integrative grid existed. In the United States of the early twenty-first century, most electricity markets remained segments. Grids are not integrated completely; thus, some grids do not have access to green power because it may not be economical to produce green power in the region. Certificate programs allow for green power to be brought to market virtually.

While renewable energy is any form of energy whose source can be replenished as quickly as it is used, green energy goes further, in that it has a low environmental impact. For example, traditional biomass, such as wood burned for fire, is renewable in that it can be replaced as quickly as a forest grows, but biomass may not necessarily be considered green, because of the particulate matter that is released into the environment when it is burned. Thus, the term green power is distinguished both by the fact that it refers to electricity and by the fact that it has a net environmental benefit when compared to conventional power.

The exact method of measuring green power is dependent on how the programs are defined. Many programs base certification of green power on its source and on the amount of electricity it generates. For example, the amount of electricity that solar panels generate over a particular period of time can be rendered as a certificate that can be traded on the open market. In many ways, green power is a vernacular term for sustainable electricity that is assessed and measured by some sort of regulatory body or privately certified company. The power companies that, in the end, sell these certificates market them as green power.

Although the environmental impact of green power is generally much lower then that of conventional power, green power sources still do have some effect on the environment. For example, biomass resources are converted to electricity through combustion, which emits air pollutants. Hydroelectric dams can flood the surrounding land and impede the passage of fish. When compared with conventional power, renewable power has a net positive benefit by significantly reducing the adverse environmental impacts of electricity generation. Therefore, screening methods and life-cycle assessments of green power sources are needed to make it possible to compare green power to conventional power sources.

Environmental Impact

No form of electrical power generation has zero impact on the environment, but electricity generated from green power has proved to be environmentally preferable to electricity generated from conventional energy sources such as coal, oil, nuclear power, and natural gas. Green power contributes to cleaner air and water by avoiding emissions and pollutants that would result from conventional power generation. On average, every kilowatt-hour of renewable power reduces the emission of more than one pound of carbon dioxide when compared to conventional power sources.

One aspect of green power is that not all green power sources have the same environmental benefit. Indirect and embodied energy in manufacturing the components in an electricity-generating system often are generated from conventional power sources. Thus, environmental impacts of the creation of the green power source must be taken into account before it is possible to compare green power sources with one another. One way to do this is by measuring what is called energy payback time (EPBT). EPBT is the time it takes for an energy technology to generate enough useful energy to offset energy consumed during its lifetime. Using EPBT to determine when green power becomes green allows for the accounting of fossil fuel needs and emissions as an energy infrastructure is transformed from a carbon-intensive to a low-carbon system.

EPBT can be applied when doing a life-cycle assessment of a green power installation. In a lifecycle assessment, the energy expenditures and environmental impacts of not only the manufacture of the installation but also its decommissioning are taken into account. The following sections look at green power by type of renewable and outline the environmental impacts that should be taken into account.

Solar Power

Solar power systems generate no air pollution during their operation. However, solar power systems are energy intensive during their manufacture and installation. When fossil fuels are used for this purpose, emissions will be released. The primary environmental, health, and safety issues are involved in how solar components are manufactured, installed, and ultimately disposed of or recycled.

The EPBT should be short if solar is to be considered green. The EPBT of a solar panel is determined by the energy required to manufacture it and the placement of the solar panel. Scaling of solar photovoltaic (PV) panel manufacturing and efficiencies is reducing embodied energy. The energy intensity and cost of PV systems are closely related, and as the costs are dropping the energy requirements are also dropping, making solar PV systems more attractive as green power. In 2000, the EPBT for PV systems was in the range of eight to eleven years, compared with typical system lifetimes of around thirty years. By 2010, however, the EPBT had dropped to between three and five years, depending on where the panel was placed. Reports on solar panel EPBT in the early 2020s from areas around the world indicated that in some places, the EPBT was lower than three years or, in some cases, even one year.

Materials used in some solar systems may have health and safety hazards for workers. Traditionally, the manufacturing of PV cells has required hazardous materials such as arsenic and cadmium. That is why decommissioning of solar PV panels should also be taken into account, to ensure that toxins are not released into the environment. A solar energy system cannot replace air pollution with water pollution, for example, if it is to be considered green power. At the same time, reports indicated that by the 2020s, material usage in the manufacturing of panels, due to advancements in design, had decreased significantly.

Land-use change is another issue that arises in considering solar installations. For example, the cutting of trees in order to ensure direct sunlight for generation of electricity releases carbon into the air that was sequestered in the biomass. Additionally, open areas that may be conducive for solar farms may be already serving an ecosystem service by functioning as open land for wildlife. Such issues have made urban roofs attractive for solar PV installations, as such placement has no impact on land use.

Wind Power

Among all the renewable energy technologies, wind power systems are estimated to be the lowest lifecycle emitters of greenhouse gases, making wind the greenest power source. Wind speed is a key factor in determining life-cycle emissions, which are highly dependent on the location of windmill installations. Other benefits of wind are that it does not change land use significantly; farming and natural regions, for example, can coexist with wind installations.

Issues do arise with regard to noise pollution, however. Windmills are extremely loud, and the full impact of the noise, including on any nearby wildlife, remained unclear. Many wind farms are zoned only in areas that are not authorized to support residential communities. This means that wind generation has to happen outside urban areas and energy must be transported long distances from where it is created to where it is needed. Additionally, migratory birds are at risk near small wind power plants. The shorter blades of the windmills used in these installations must spin faster to generate the power needed and thus pose a danger to birds. Larger wind blades, however, are greatly reducing the impact of wind farms on bird populations.

Biopower

Biopower is derived from the burning of plant matter or from methane released during the decomposition of biomass. Biopower raises the most environmental issues, in that it can be either clean or dirty, depending on how it is developed. Combustion of biopower and biomass-derived fuels produces air pollution, but these pollutants can be offset by the production of biomass. If biopower is generated in a sustainable fashion, it could greatly reduce emissions of greenhouses gases; many countries have already been investing in such sustainable technological advancements in biopower production.

The amount of carbon dioxide released when biomass is burned is very nearly the same as the amount required to grow the plants to produce the biomass. Thus, in a sustainable fuel cycle, there would be no net emissions of carbon dioxide. However, in the early twenty-first century, fossil fuel inputs were still required for planting, harvesting, transporting, and processing biomass. The attractiveness of biomass is that it can be added to current facilities and burned in place of fossil fuels.

Geothermal Power

Emissions from geothermal electricity generation are composed mostly of the emissions associated with production of the facility and emissions during operation. The operational emissions are highly dependent on the composition of reservoir gas and whether an open or closed system is used. Most geothermal plants are built with open systems, where the gas is vented to the atmosphere during electricity generation. These gases then can spread pollution via emissions that previously were sequestered underground. It is environmentally preferable to use closed systems, which extract only heat and keep gases and steam sequestered. In the 2020s, major producers of geothermal energy such as the United States continued to research more cost-effective means of generating this energy at a larger scale, including development of "enhanced geothermal systems."

Hydroelectric Power

Large hydroelectric resources can have environmental trade-offs associated with issues such as fisheries and land use. The dams built to create reservoirs for large-scale hydropower cause formerly dry areas of land to be submerged below water.

These areas can include forests, farmland, wildlife habitats, scenic areas, and even towns. This inundation results in a mass die-off of vegetation, which releases carbon formerly sequestered in the plant materials. Additionally, dams can cause radical changes in river ecosystems, both upstream and downstream, causing ecological impacts. Smaller hydropower plants that work with the flow of the river (called run-of-the-river plants) have smaller environmental footprints and are considered green power. By the 2020s, increased frequent and severe droughts throughout the world also threatened the productivity of hydrolectric plants and dams as water sources experienced shrinkages.

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