Distributed Power

Distributed Power

(This article first appeared in the NEC Newsletter, published by the New England Coalition on Nuclear Pollution.)

The electrical power grid is a network for delivering power from centralized generating plants to consumers.  In the lower 48 states of the US, it is essentially a single network, with parts that can disconnect from each other in an emergency.

Generally speaking, the generating plants are very large. In the US, the largest generate several thousand megawatts of power.  There are economic reasons why these plants are so large, but they must be understood in a historical context.

In the early 20th century, there were a number of struggles among companies and people who were generating power and building equipment.  One of these was the question of whether alternating or direct current should be made standard.  But another was whether centralized or distributed power would be used.

Leaders in the business saw important economies of scale in generating electricity.  Large power plants could operate on less fuel, lower construction costs, and lower operating costs, relative to the amount of power produced.  There were pioneers in electrical generation and use who believed differently, but the attraction of large scale production, with an inherent monopoly on local power, was attractive to investors who favor the creation of larger utility companies.

There were down sides to this, and they were well understood at the time.  Large power plants could not be built in cities for reasons of health, safety, and geography.  Coal burning plants were smoky, hydro plants went only in places where dams could be economically built. Later, nuclear plants could not be built near cities because of the potential for disaster. But at the same time, long distances between generators and consumers caused line loss, with its inherent inefficiency.

Another problem that arose was one of reliability.  The Northeast Blackout of 1965 was caused by a mistake in setting a protective relay in Ontario.  A few days later, the relay tripped, and the cascade of effects blacked out nearly all customers in Ontario and the Northeastern United States for about ten hours.

One thing to understand about economies of scale is that the electrical generating utilities measured it entirely in terms of electricity sold.  They were not concerned with what happened to the waste they produced.

When we think of waste, we tend to think in terms of landfills and pollution, but in the electrical generating business, most of the waste can be understood in terms of heat.  The Vermont Yankee plant, for example, generates about 4700 GWh of electrical power per year.  But it operates at about 32% efficiency in generating electricity, with the heat loss being equivalent of about 9800 GWh in heat.  This heat is put into the atmosphere and the Connecticut River, and its energy is equivalent to the heat of about 242,000,000 gallons of oil.  The heat loss from coal generating plants is similar. This heat cannot be used productively, because it has to be transported, and the plants need to be sited too far from cities for transporting it to be practical.

A newer approach uses this lost heat, which can be resold, an approach called cogeneration.  If power plants can be sited near or in dense population areas, the heat can be piped to homes and businesses, where it is typically used for both heat and hot water.  This requires more efficient and less polluting plants than coal, and plants with less potential for disaster than nuclear, but it can be done.  As it turns out, it can be done rather easily.

Elsewhere on this blog, we have an article on Güssing, Austria, where Jenbacher engines supply electrical power and heat for a combined efficiency of over 82%, using biomass.  Efficiencies in excess of 90% are now routinely achieved, using generators of newer design.  Power plants such as these are distributed through the town, each putting electrical power on the grid and providing heat to a number of nearby buildings.

There are other types of generators that can be used for distributed power, as well. One we might consider is to use natural gas turbines.  If they are sufficiently small, between a quarter of a megawatt and fifty megawatts, they can be sited close to or within cities.

Natural gas does not mean a large carbon footprint, as the carbon dioxide can be captured and sequestered. The term used is carbon capture and sequestration (CCS), which may sound like it is horribly expensive, but as it turns out, it is not.  Early in 2011, the US Department of Energy (DOE) released its projections for costs of power generation in the year 2016.  Electricity generated by combined cycle natural gas with CCS is expected to cost below that generated by nuclear power, even without the costs of waste management factored in.

Other power sources for distributed power include a variety of biomass, wind, hydro, geothermal, solar, and other sources. The DOE cost projections are that all of these except solar will produce power less expensively than nuclear, and all of them have smaller carbon footprints.  Together they can be more efficient and cost less than more traditional, large generating stations.  They can be cleaner and safer as well.  And they have the added advantage that in the event of a blackout, local power can continue to operate, so the entire grid is more reliable and robust.

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