Distributed Generation of Electricity and its Environmental ...

13 Jan.,2025

 

Distributed Generation of Electricity and its Environmental ...

  • About distributed generation
  • Distributed generation in the United States
  • Environmental impacts of distributed generation

About Distributed Generation

Distributed generation refers to a variety of technologies that generate electricity at or near where it will be used, such as solar panels and combined heat and power. Distributed generation may serve a single structure, such as a home or business, or it may be part of a microgrid (a smaller grid that is also tied into the larger electricity delivery system), such as at a major industrial facility, a military base, or a large college campus. When connected to the electric utility&#;s lower voltage distribution lines, distributed generation can help support delivery of clean, reliable power to additional customers and reduce electricity losses along transmission and distribution lines.

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In the residential sector, common distributed generation systems include:

  • Solar photovoltaic panels
  • Small wind turbines
  • Natural-gas-fired fuel cells
  • Emergency backup generators, usually fueled by gasoline or diesel fuel

In the commercial and industrial sectors, distributed generation can include resources such as:

  • Combined heat and power systems
  • Solar photovoltaic panels
  • Wind
  • Hydropower
  • Biomass combustion or cofiring
  • Municipal solid waste incineration
  • Fuel cells fired by natural gas or biomass
  • Reciprocating combustion engines, including backup generators

Distributed Generation in the United States

The use of distributed generation units in the United States has increased for a variety of reasons, including:

  • Renewable technologies, such as solar panels, have become cost-effective for many homeowners and businesses.
  • Several states and local governments are advancing policies to encourage greater deployment of renewable technologies due to their benefits, including energy security, resiliency, and emissions reductions.
  • Distributed generation systems, particularly combined heat and power and emergency generators, are used to provide electricity during power outages, including those that occur after severe storms and during high energy demand days.
  • Grid operators may rely on some businesses to operate their onsite emergency generators to maintain reliable electricity service for all customers during hours of peak electricity use.

Distributed generation systems are subject to a different mix of local, state, and federal policies, regulations, and markets compared with centralized generation. As policies and incentives vary widely from one place to another, the financial attractiveness of a distributed generation project also varies.

As electric utilities integrate information and communications technologies to modernize electricity delivery systems, there may be opportunities to reliably and cost-effectively increase the use of distributed generation.

Environmental Impacts of Distributed Generation

Distributed generation can benefit the environment if its use reduces the amount of electricity that must be generated at centralized power plants, in turn can reduce the environmental impacts of centralized generation. Specifically:

  • Existing cost-effective distributed generation technologies can be used to generate electricity at homes and businesses using renewable energy resources such as solar and wind.
  • Distributed generation can harness energy that might otherwise be wasted&#;for example, through a combined heat and power system.
  • By using local energy sources, distributed generation reduces or eliminates the &#;line loss&#; (wasted energy) that happens during transmission and distribution in the electricity delivery system.

However, distributed generation can also lead to negative environmental impacts:

  • Distributed generation systems require a &#;footprint&#; (they take up space), and because they are located closer to the end-user, some distributed generation systems might be unpleasant to the eye or cause land-use concerns.
  • Distributed generation technologies that involve combustion&#;particularly burning fossil fuels&#;can produce many of the same types of impacts as larger fossil-fuel-fired power plants, such as air pollution. These impacts may be smaller in scale than the impacts from a large power plant, but may also be closer to populated areas.
  • Some distributed generation technologies, such as waste incineration, biomass combustion, and combined heat and power, may require water for steam generation or cooling.
  • Distributed generation systems that use combustion may be less efficient than centralized power plants due to efficiencies of scale.

Distributed energy technologies may cause some negative environmental issues at the end of their useful life when they are replaced or removed.

Unique technology could turbocharge electrical efficiency

An internal combustion engine similar to the one in your car could play a key role in making electrical generation far more efficient.

A University of Wisconsin&#;Madison team led by mechanical engineering Professor Sage Kokjohn is developing new technology that would use smaller, distributed electrical generation systems roughly twice as efficient as conventional fossil fuel-based power plants and provide more environmentally friendly power.

The technology could also offer an economical way to support the addition of a growing number of renewable energy sources to the power grid.

Most electricity fed into the power grid is generated by large power plants burning coal and natural gas. But these plants turn only about 36 percent of the energy released by their burning fuel into useful electricity. And by the time that electricity reaches customers, the amount drops to 34 percent due to losses over transmission lines.

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Kokjohn is aiming to design a plant that can capture 70 percent of its fuel&#;s energy potential as electricity by integrating two technologies &#; an internal combustion engine and a solid oxide fuel cell &#; into a hybrid system that capitalizes on the unique characteristics of each. The Department of Energy is supporting the research with a $1.7 million grant from its Advanced Research Projects Agency-Energy (ARPA-E) program.

&#;There are certain characteristics of the way that fuel cells operate, such as the partially consumed fuel that exits the stack, that&#;s actually very beneficial for these advanced combustion engines,&#; Kokjohn says. &#;So by coupling these two devices, we can take advantage of some synergies between them and achieve very high efficiency. It&#;ll be very exciting to show a pathway to 70 percent electric efficiency.&#;

Fuel cells are devices that generate power through an electrochemical process instead of by combustion. Certain types of fuel cells can use natural gas as fuel and directly generate electricity with very high efficiency.

However, these fuel cells only consume about 75 percent of the fuel&#;s energy, and the remaining energy in the gases that leave the fuel cell is wasted. Kokjohn sees an opportunity to put that unused fuel to work to boost efficiency. And that&#;s where the engine steps in.

The ability to easily adjust to shifting power demands is especially desirable as more renewable, and highly variable, energy sources like wind and solar are added to the grid.

Kokjohn&#;s hybrid system will direct the exhaust from the fuel cell into an advanced compression ignition engine, allowing the engine to generate additional power by burning the fuel cell&#;s leftovers.

But because the fuel that comes out of the fuel cell is of very low quality, a conventional combustion engine isn&#;t able to effectively burn it, Kokjohn says. To overcome this challenge, his team is investigating several advanced combustion strategies for enabling the engine to use that low-quality fuel.

An engine provides the system with another unique advantage: the ability to easily adjust to shifting power demands. This capability is especially desirable as more renewable, and highly variable, energy sources like wind and solar are added to the grid, according to Kokjohn.

&#;The amount of solar energy that&#;s being added to the grid changes a lot based on the weather,&#; he says. &#;So you&#;d like to be able to shut down the nonrenewable energy source when the sun is really shining, and then come back up when the sun goes under a cloud.&#;

Kokjohn&#;s hybrid system will offer just this kind of responsive flexibility, complementing intermittent renewables like wind and solar by filling in gaps when the sun isn&#;t shining and the wind isn&#;t blowing.

&#;Our system would provide significant benefits not only from an energy perspective but also from an economic perspective,&#; says Kokjohn, noting that it&#;s very challenging and costly for large power plants to respond to changing power demands.

Additional benefits of the technology include a substantial reduction in greenhouse gas emissions.

&#;By going from about 36 percent efficiency to 70 percent fuel-to-electricity efficiency, we&#;d be cutting greenhouse gas emissions in half compared to typical fossil fuel power plants,&#; Kokjohn says.

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