DE vs. Utility Supplied Power | DE Technologies

As described in the DE Overview and Technology sections, DE is represented by a vast assortment of systems and equipment, reflecting a myriad of end uses, services, and applications. When assessing the environmental impacts of any energy system, effects on such issues as air quality, noise, and land use must be considered. It is important to understand how the different DE technologies affect the environment and this section discusses each major kind of technology. It is also important to examine how these impacts compare to typical central plant power generation that the DE power is replacing, so that decisions to deploy DE can be made in the proper context.

DE vs. Utility Supplied Power Environmental Impacts

DE generally replaces grid power, and electricity from the grid affects the environment in a variety of different ways. At each stage of the process - from the generation of electricity to the high voltage long-distance transmission of that electricity to the final low voltage distribution to customers-there are a number of real or potential impacts.

Utilities increased the size of central plants throughout the 20th century seeking economies of scale to lower installed cost per kW of capacity and often achieving small increases in plant efficiency. The goal was to produce electricity over the life of the plant at less cost. However, as electric use expanded, we saw the number of plants, and their size, greatly increased. The end result has been a major increase in total fuel consumed and emissions.

The type of fuel being burned has also contributed to the worldwide increase in power plant emissions. The new larger power plants being built were most often fueled by coal. Due to coal's lower cost per kW, thousands of new coal-fired plants where constructed worldwide coal, particularly in areas where it is either abundant or can be transported inexpensively by train or ship. According to the International Energy Agency, coal is the leading fuel for electric power generation. As it has twice the carbon content of natural gas and is the second leading source of carbon dioxide (CO2) emissions by fuel. Additionally, coal produces nitrogen oxides (NOx), sulfur oxides (SOx), and a multitude of other airborne pollutants.

As plants increased in size and based near their fuel source, be it a mine or a port, the length of transmission increased. The longer the transmission line required, the greater the loss of power (called line losses) that results. This reduction means that more electricity needs to be generated to compensate for the line losses, thereby reducing the overall efficiency of the system. When there is congestion during times of heavy electric usage, line losses will increase further. To make matters worse, older and dirtier peaker plants are used during periods of peak demand.

Except in rural or under developed areas where the grid does not exist, DE systems usually replace a part or all of the electricity that comes from the grid for a specific building or facility. Therefore, the efficiencies, emissions, land impacts, and other environmental considerations for DE need to be placed in the context of how these systems compare to electricity from the grid.

With this in mind, the following discussion of environmental impacts focuses on (1) how DE affects the environment compared to traditional means of generating electricity (i.e., central power generation); and (2) how individual DE facilities affect the surrounding environment.

1. Emissions - With concern over global climate change (primarily linked to CO2), acid rain (from SOx), smog (from NOx), and other airborne pollutants, there is a real need to find low or non-emitting electric generation technologies.. Some DE resources, like diesel combustion engines, are valuable as peaking or back-up generating devices and these units generally operate for short periods of time. Diesel is a particularly dirty fuel from an emissions standpoint. Promising research is being conducted with support from the Department of Energy into the production of low sulfur diesel fuel. Low-sulfur diesel fuel will be available in the U.S., Western Europe, Japan and other parts of the world in the next several years, but will typically only be required for highway vehicles. Use of the cleaner fuel will be voluntary for diesel engine and turbine applications. Other DE resources like solar cells or wind turbines emit no harmful emissions. It is important to consider the environmental impacts of a specific technology as well as the length of time a particular piece of equipment will be operation in order to determine consequences for the environment.

The emissions impact of any DE technology can be evaluated by reviewing the product specification sheets or contacting the manufacturers. The DE Forum lists over 600 DE products currently being manufactured with links to manufactures to facilitate this review. In general, those technologies that are based on fossil fuel combustion tend to have higher emissions of the main categories of pollutants (SO2, NOx, CO2, and particulates) than non-combustion technologies. Natural gas fired technologies have the lowest emissions of the combustion fuels, with fuel cells producing far lower emissions per kWh.

2. Land Impacts - Since DE systems are generally small scale, they typically have much smaller land impacts than utility grid power. DE systems do not need high voltage transmission wires or medium voltage distribution lines, since generation typically occurs inside the fence of the facility. The primary exception to the generally small footprint of DE is wind turbines. Through technological advances, wind turbines have been getting larger and more efficient. Some individual wind units today generate more electricity than ten of the most efficient units a decade ago. Wind turbines have an advantage of having the rotors high in the air, so that the actual "footprint," the area taken up on the ground, is small. A number of farmers have taken advantage of this small footprint by having turbines placed in their fields or pastures. The greater efficiencies have come mostly from size and height (the stronger and steadier winds are at higher altitudes). However, the enormous size of new wind farms can cause concern about the visual impacts and the physical effect on birds. New technologies are being tested to mitigate the effect on birds.

3. Fuel Use - DE resources that rely on fossil fuel combustion have achieved gains in efficiency while reducing pollutants per unit output, resulting in a double reduction in overall air emissions. Nonetheless, fossil fuels have the greatest environmental impact though the various fuels have different impacts. The fuel with the highest sulfur content and the lowest energy density is coal, making it the dirtiest of the fossil fuels. Over 50% of electricity generated in the United States comes from coal through large central power plants. Liquid fuels (gasoline and diesel) have a higher energy content than coal, but still release high levels of sulfur, NOx and CO2. Natural gas is the cleanest burning of the fossil fuels as it contains no sulfur, produces less NOx per kWh compared to liquid fuels, and has half of the carbon atoms per molecule of coal. Renewable technologies such as wind and solar collect their energy input from natural thermodynamic cycles. The operational limitations imposed by the variable quality of these sources of energy (only when the sun is shining or the wind is blowing) limits the time that electricity can be produced. Finally, hydrogen, which is used in fuel cells, could be by far the most abundant fuel resource since it is part of the water molecule. Hydrogen used in fuel cells is converted to electricity, but it can also be combusted as with the space shuttle rocket boosters using liquid hydrogen.

4. Innovative Uses of DE Technologies - Working to the advantage of the environment is the trend towards greater efficiencies in generation. DE is flexible, customizable, and adaptable, which makes it a more efficient resource than the "one size fits all" service from the grid. The more efficient the system, the less the environmental impact since less fuel is used. New DE technologies are ideal for use in advanced systems such as combined heat and power (CHP) and combined cycle (CC) systems, both of which use waste heat to increase efficiency. Some technologies such as combustion turbines and fuel cells can be merged to create systems with exceptionally high efficiencies and low emissions. Other hybrid systems combine generation and storage technologies so that excess electricity can be generated during optimal times while electricity is used from the storage at other times.

DE Technologies

Each DE technology has its own environmental characteristics. The following charts highlight the environmental benefits while allowing comparison among technologies.

Table 1. Zero Emissions Technologies

Table 2. Technologies for Gaining Greater Efficiencies

Table 3. Innovative Configurations