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  • Macrogrid and Microgrid

    Posted by David Foster on February 22nd, 2009 (All posts by )

    Last week, I picked up a copy of American Scientist on the strength of a couple of interesting-looking articles, one of them relevant to our ongoing discussion of America’s energy future. It contains a graph which, at first glance, looks pretty unbelievable. The graph is title “U.S. electric industry fuel-conversion efficiency,” and it starts in 1880 with an efficiency of 50%. It reaches a peak of nearly 65%, circa 1910, before beginning a long decline to around 30%, at which level it has been from about 1960 to the present.

    How can this be? Were the reciprocating steam engines and hand-fired boilers of the early power plants somehow more efficient than modern turbines?

    Not at all. The efficiency of the conversion of fuel into electricity has improved, according to the graph, by about 6:1. What has been lost, though, is the efficiency gained through the use of left-over heat. In many early power plants, waste heat was distributed (as steam or hot water) through a network of pipes permitting it be be sold to local homeowners and businesses. This practice is still used in New York City, where it dates back to Edison’s day. But the use of “district heating,” as it is known, has become much less common in the U.S. than it was in the late 1800s and early 1900s. (These systems are still heavily used in some other countries, including Denmark, the Netherlands, and Finland.)

    I have some questions about the efficiency numbers used in the graph. Do they properly account for seasonality?–heating is in much less demand in summer than in winter, though it is still required for hot water and for certain industrial processes. (The heat can also be used to power absorption-type air conditioners, but I doubt there were enough of these around to make much difference over the time period of the graph.) I also wonder if the graph takes into account the relatively new combined-cycle turbines, which have efficiencies close to 60%. (See GE “H System” brochure here.)

    In any event, though, it does seem that there is a lot of heat being wasted by large power plants which could be used for heating and cooling applications. Why is this potentially valuable resource being wasted?

    The authors (Casten & Schewe) identify two primary reasons. First, there is the trend toward building power plants a long way from cities, putting them beyond the practical range of steam or hot-water pipes. Second, there are regulatory policies that make it unprofitable or even impossible for combined heat & power systems to thrive.

    The “stimulus” bill contains provisions to spend considerable money on enhancements to the electric transmission grid, partly for the purpose of bringing solar and wind power over very long distances. Maybe we’d be better off if some of this money was devoted to local networks of steam or hot water pipes, served by modest-sized gas-fired power plants offering very high total-system efficiencies. This won’t work everywhere, because of population density factors, but it could work in a lot of places. I expect that it would be provide a far more efficient ratio of capital per unit energy saved than would building wind or solar farms which require 500- or 1000-mile transmission lines to connect them to their loads.

    Of course, the coalition of lawyers and environmentalists which blocks virtually all infrastructure development in this country would object to a local steam pipe network as vehemently as it objects to a long-haul transmission line.

     

    18 Responses to “Macrogrid and Microgrid”

    1. Marty Says:

      Not sure if it speaks to this issue or not, but you might check out “The Bottomless Well” by Peter Huber & Mark Mills. One of their points is that the evolution of use of energy has been towards greater “purity,” which trades off gross energy for quality—think in terms of the electricity needed to run computers versus that to run large industrial machinery of the 1930s—the modern stuff needs VERY constant, unchanging power supplied to it, which is why computers (for example) have their own “power supplies” to filter the line current into something safe for microchips. But, the 1930s stuff needed a much purer energy than did 19th century steam-powered engines. And so on, back thru history.

      This trend goes back to burning wood and dung and evolution through peat and coal and petroleum and gas and hydro and nuclear, and still continues. Basically, for a given amount of energy at the use end, the purer it is, the more energy you have to put in at the front, and the more is lost in conversion.

    2. Brett_McS Says:

      The company I used to work for, Brown Boveri, had a big section devoted to cogeneration systems, so it is definitely not a lost art. Although it is of course an extra expense, and fitting a cogeneration system to a power plant would only be warranted under certain circumstances. An era of cheap power is not going to generate much call for it.

    3. david foster Says:

      Brett..I doubt that we are entering a lasting era of cheap power. Building of coal plants is being suppressed by regulation and litigation. Ditto for nuclear. Wind and solar–even with technology enhancements–will likely to continue to be considerably more expensive than current electricity prices. Hydro is a niche source that can only be used in certain places, and despite its obvious “renewability”, it is politically unpopular. That leaves natural gas, and although there have been several important new fields recently, I suspect that demand pressures (for transportation and home heating as well as power) will combine with supply limits (hostility to drilling by Democrats) to push up prices considerably.

    4. Rich Says:

      I wonder what the distance involved in transporting power over the grid reflects in the loss of efficiency. Today power lines are everywhere, not true 80 years ago when power was centered around large cities.

    5. Knucklehead Says:

      Marty,

      I’m picking a nit here, but the PSUs in computers have very little, or nothing, to do with the “purity” of the input electricity. Their function (at least in the case of AC units) is to convert incoming AC electricity into low voltage DC (normally several voltage levels) and distribute it to the various components at the proper voltages.

      Surge protectors, line filters, and uninteruptable power supplies are a different matter.

    6. Marty Says:

      Knucklehead–

      fair enough re converting AC to DC, tho my point, not well explained, was that if the computer could use messier power there might be less loss in the conversion process.

      Many large building complexes built pre-WW2 include a central boiler and underground steam pipes–very common on campuses such as colleges and hospitals. Back in my college days we would access the tunnels for purposes of ingesting questionable substances in a mind-altering environment.

      In Chicago, about a decade ago ComEd built a couple of big central cillers in dwntown, that pipe cold water to nearby buildings for air conditioning purposes; I don’t know the economics of this (whether it was subsidized or required by regulators, or was just economically efficient), but hard to believe it doesn’t happen elsewhere, too.

      I remember back in the 1980s or 1990s there was a big deal about superconductors at much higher temperatures than theretofore–originally required liquid He at about 4 Kelvins, and some materials were showing superconductivity at temperatures around 100-150 Kelvins, if memory serves. Big noise about the potential impact on electric distribution if superconducion could be attained at ambient temps. Haven’t heard anything about this for several years. This might actually be worthwhile for some govt funding if not already done, applications abound at the use end as well as transmission.

      Power generating stations used to be located close to the users when possible (obviously not easy with hydro, tho you did get almost co-located aluminum smelters and the like), but with environmental concerns and the cost of urban land, those stations are just about all gone and new ones are located well away from the users–I have no doubt the average distance power is transmitted has grown by at least an order of magnitude since the 1920s.

    7. sol vason Says:

      In the early 1900’s Edison made the decision to sell AC power rather than DC. AC can be transmitted over long distances. DC can be transmitted only short distances. DC power requires many small power plants close to the market. AC allows producers to create huge plants that can serve many markets. AC is ideal for hydro-electric and the Niagra Falls plant influenced Edison’s decision. (Yes. There was a time when the Feds did NOT make every decision)

      European governments adopted DC power for many reasons – foremost being national security. (In Europe the government ptrovided electricity). Today the US is extremely vulnerable to foreign and domestic attacks on our relatively few power plants and our unprotected transmission lines. Europe is not nearly so vulnerable.

      A very expensive way to waste lots of money would be to rewire America for DC and replace all our appliances, tools, gadgeets, widgets, etc that currently need AC power and replace all the megawatt monster plants with neighborhood power plants that develop power from waste from American toilets. That would be stimulating.

    8. david foster Says:

      Sol…Edison was very anti-AC for a long time, and engaged in an extremely vicious political and PR war (against George Westinghouse) to try and get AC suppressed. This included a fear campaign against “killer” AC wires and a successful lobbying campaign to get the AC-based electric chair adopted as the standard means of execution. (He helpfully suggested that electrocution should be referred to as “Westinghousing,” and surreptitiously acquired a Westinghouse AC generator for use at Sing Sing)

    9. mishu Says:

      Actually, DC is now more efficient to transmit over long distances. You don’t have to worry about phase adjustments over the length of the transmission. Because of that, construction costs are lower for the transmission lines. You also don’t need to have everyone convert to a DC system. You can have a converter change the electricity to AC for the local consumer market.

    10. Brett_McS Says:

      David, oh yes, I agree. Brown Boveri and other cogeneration companies are in for a nice windfall as new power plants are stopped because of possible effects on the habitat of the pointy-eared ground quirrel; companies will need to get as much from existing ones as possible. Up until now, cogeneration has not been such a big deal. From now on it may well be. Of course if the pointy-eared ground squirrel supporters and their ilk get shoved down a hole and nuclear takes off, cogeneration will be on the back burner again.

    11. Brett_McS Says:

      Mishu, that’s very interesting. Do you know what technology is behind the turn around of DC vis a vis AC?

    12. david foster Says:

      Brett…but the same people who stop the building of the new power plants will also stop the building of the networks of steam and chilled-water pipes which are necessary to operate cogeneration….Honda does have a home cogeneration system which generates both electricity and heat–runs off natural gas. Hopefully the lawyers & environmentalists will allow us to keep the gas pipelines we already have, though I wouldn’t be too sure even of that…

    13. david foster Says:

      GE was just showing off a new cogeneration plant in China, as part of Hillary Clinton’s visit. In addition to producing electricity, this plant supplies steam and chilled water to a 40km area..not sure if he means 40 square kilometers or 40 kilometers squared, though I’d guess the former.

    14. mishu Says:

      Brett, ABB has a good primer on their product here.

    15. Brett_McS Says:

      Thanks Mishu. Good to see the ol’ ABB on the ball. When I worked with Asea Brown Boveri in Australia, my desk was within earshot of the receptionist (it was a very small office) and she would occassionally have to explain to the caller “No, I didn’t say ‘I see a brown fairy'”.

      David, GE are making a huge push into China. I’m now with a licensee of GE (in Australia), and we are supplying the bogies for new locomotives being delivered to China as we speak.

    16. renminbi Says:

      The Chinese are the only people now buying 6000 HP diesel-electric locomotives-from GE and EMC.

    17. Mrs. Davis Says:

      Efficiency is important for scarce resources. For the last 50 years fuel and capital have been in abundant supply. I can recall when the cartel known as the Texas Railroad Commission used to restrict the flow of tank cars in Texas to keep the price of crude oil up as well as several ultimately unsuccessful efforts by middle eastern producers to control prices through supply control as well. (Paid $1.62 for regular yesterday. Nobody’s even noticing the crashing prices, an indicator of how badly beaten down consumers are.) Likewise the number of asset bubbles of the last 20 years indicates that there was plenty of excess capital unable to find a productive home.

      So it should come as no surprise that there is lots of inefficiency in our power generation and distribution infrastructure without getting into the Edison-Westinghouse history. Now that both fuel and capital appear to be heading into relative scarcity, we may see a renewed respect for efficiency and frugality. Water comes to mind also.

    18. Robert Schwartz Says:

      Let us remember another factor deceasing the efficiency of coal fired plants, which are the pollution controls that have been installed over the last generation. They may be a good thing, but they do have a cost.