On Mar 24, 2012, at 11:35 AM, [email protected] wrote: <snip>
> > > (5) Transmission: With the present fossil-fuel-powered > system, transmission lines from the large-scale fossil fuel > or nuclear power plants to the consumers are needed. This > transmission and distribution network has tree structure: > electricity always flows in one direction, from the > generator to the consumers. snip> > This is how I see it. I may have overlooked things. > Please comment. > > Hans Hans, what I sent a few minutes ago implied what I'll add here. I disagree that Transmission has a tree structure, or only one direction of flow. The interties between the Northwest and Southwest are a simple example. In general the seasonal loads, North vs South, are opposite -- peak in the North in the winter, peak in the South in the summer. So both areas have larger baseload capacity than they need for much of the year, and employ that year round by the swap that transmission enables. It is also true that adjoining utilities all over the country plan their systems with contracts with neighbors that enable them to build and run the most appropriate system. Let me make up an example. Suppose utility A sees a need for new capacity in the near future amounting to 400 mW. And suppose the most efficient (in the heat rate sense) plant on offer from manufacturers is 700 mW. If utility A anticipates future load growth beyond 400 mW, it might build the 700 mW plant and contract with a neighbor to buy 300 mW for the first year of operation, 250 in the second year, 150 in the third year, etc. And utility B, the purchaser, might meanwhile make plans and then begin building a new plant of its own, larger than its own needs (at first) and selling its expected excess to utility A in the far future when utility A begins to need capacity beyond what the 700 mW plant will provide. This was for decades a very common planning practice among utilities, often involving more than a simple pair. Gene
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