Electricity grids are slowly getting smarter. Simultaneously, the use of distributed generation is increasing. Though smart grid advocates tout the ability of a smarter grid to enable greater deployment of distributed resources, the benefits could flow in both directions.
In decades past, distributed generation (DG) consisted of a smattering of off-grid generation sources, industrial and commercial grid-connected generation—including backup supply and combined heat and power (CHP), and strategically located utility-placed generation for grid reliability. DG was fairly predictable.
Today we are seeing an expansion of the types of technologies that fall under the DG umbrella (see the sidebar “Distributed Generation Is Up—Way Up”). In addition to the familiar diesel- and gas-fired engines and microturbines, wind power and rooftop solar generators are proliferating across not just North America and Europe but on every continent. (Yes, even Antarctica’s research stations use solar and wind power.) Electric vehicles are starting to both take from and give back to the grid. Small and micro-size nuclear power generation promises to become a DG power source in the foreseeable future. And pole-mounted solar generation starts to blur the very line between distributed generation and distribution lines.
Some of these new DG technologies are being developed in anticipation of a more widespread, smarter grid. But others are proliferating for other reasons, and the grid—whether “smart” or “dumb”—will have to deal with them. Accommodating increased DG, especially sources that are not under full-time, direct utility control, would be easier with a smarter grid. More energy storage options would help, too (see p. 30, “Energy Storage Enables Just-in-Time Generation”).
Though many of the distributed resources discussed below likely would have materialized without the prospect of a smarter grid, a smarter grid promises to maximize their value to both their owners and the greater grid. But the grid stands to benefit from increased DG as well. From peak load management to voltage support, smart grid operators are likely to welcome the ability to interact with small generation sources located in or near load centers.
Old and New Types of Distributed Generation
Wind and solar power have become common enough to count as “old-style” DG, even though solar photovoltaics (PV) have not been around as long as reciprocating engines. And although new wind turbine designs are proliferating (see p. 38, “Changing Winds: The Evolving Wind Turbine”), the basic principles and constraints (such as variable generation) are familiar.
System operators may not always have the most precise tools to predict and control such resources’ contribution to supply, but all of the major North American regional transmission organizations are already using central wind power forecasting programs, and tools to predict output from solar generation are being developed. For example, researchers at the University of California, San Diego and Merced are working on solar forecasting techniques that would help any large or small grid operator predict and plan for variable solar generation.
For the purposes of this article, “distributed renewables” are those that do not require new transmission and that are connected to the existing distribution grid, when they are grid-tied. That includes an increasing number of residential installations that may or may not be utility-owned. An overview of less-familiar DG options follows.
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