Power plants

Discussion in 'Off-Topic' started by atferrari, May 15, 2014.

  1. atferrari

    Thread Starter AAC Fanatic!

    Jan 6, 2004
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    For years I have been wondering what is, in different power plants, the relationship between the fuel you spend to keep them running ready for the consumers and the actual power consumption.

    While I do not expect this to be explained here, what to google for?

    Wondering what would be more expensive: the cost of keeping a portable Honda generator running continuously to feed my home with a minimal ammount of appliances, a power plant in a small city of maybe 100K people or the power plant(s) for a megacity?

    I am used to the concept used in passenger vessels where in case of an emergency you shutdown non-essential services to avoid a general black out but here is the oposite; to cope with a somewhat unpredictible demand, you keep running a certain number of turbines or whatever, just in case.

    Maybe all boils down to statistics and practical rules of thumb.
     
  2. Kermit2

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    Feb 5, 2010
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    Spinning standby

    Is the search term you will need.
     
  3. alfacliff

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    around here, they use huge coall fired plants continously. and only use the gas turbine plants for suplying extra power at peak use times. the gs turbines are much more "throtelable" than the coal plants. the coal plants much stay hot and take time to heat up and cool down. the most eficient would be a supply for your house that starts up when you need the power, but that is beyond the technology we have now. the newer small generator/invertors slow down the engine to whats needed without any problems of engine rpm affecting frequency, but that dosnt translate to city or larger plants.
     
  4. Alec_t

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    Similar to the UK. Gas turbines can be spun up from zero in minutes.
    Here in Wales we also have a pumped storage hydro station making use of two lakes at different altitudes. At peak times the water in the top lake flows down through generators to the lower lake. Off-peak the generators are run in reverse to pump water back up to the top lake. IIRC the turn-on time is < 1min.
     
  5. Sparky49

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    Jul 16, 2011
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    I remember a documentary on the national grid, the controllers apparently increase capacity for the exact moment (within 10's of seconds) that Eastenders finishes. This is when there is a sudden increase of people turning on kettles, stoves, lights, etc. He mentioned that they often do this with hydro electric plants in the Highlands and Wales, as well as buying in electricity from the French.

    It's amazing how finely tuned the whole process is.
     
  6. JoeJester

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  7. alfacliff

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    they pump water from a low lake to a higher one to store for peaking times. dosnt that sound real efficient? use electricity to pump water, whats the effiecency there? run downhill to generate electricity, another loss of efficiency. but who cares, they can always charge the customer more. and dont have to shut down or startup their old dinosaur coal plants, just keep them running 24 hours a dsy at the same output.
     
  8. Alec_t

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    Yes, the pumped scheme is not as efficient as some others, but its real purpose is an energy storage system to meet rapid peak demands for short periods. Cheaper than having a spare coal/oil-fired/nuclear plant on standby just to meet those demands.
     
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  9. Sparky49

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    I believe the biggest scheme in the UK is around Loch Ness. Seen the output when we go fishing. A drop of 900m from a reservoir in Glendoe. Alec is spot on. It's not meant to generate energy, rather store it for when daily demands increase. You can't just expect powerplants to suddenly increase output at 7pm every day, but a nation of people switching on appliances creates an immediate demands for more energy.

    My last electrical engineering lecture was on power stations. Turns out gas has the shortest startup time, but this is still many hours. Think of the vast quantities of water that needs to be boiled, and under high pressure, and then needs to start turning turbines. Coal is only slower than nuclear stations. However, by using energy generated during off-peak times (think early morning), water can be pumped up mountains. Then, when the 7pm demand kicks in, the water is allowed to turn the turbines and within a span of couple of minutes, demand is met.
     
  10. #12

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    Nov 30, 2010
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    There is an efficiency of scale. A hundred thousand local generators big enough to start motors several times a day or one generating station that knows a hundred thousand motors will be started several times today.

    The minimum load for a city is fairly steady. Peak hours are well known. When the local utilities are looking at 5 days of rain followed by 35 C, they know that air conditioners which barely ran for 5 days will come on maybe 50% of the time on the 6th day.

    Much like other professions, the people that work every day with load adjustments for a city get surprisingly good at it.
     
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  11. atferrari

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    Hola Joe,

    Could you show pictures of them?

    I recall seeing those brands in vessels. Deck officer myself, used to peek in engine rooms from time to time. Got used to engineers complaining of the flaws of each brand. They did repairs inhouse. Very seldom a workshop was called to assist.

    Once in Buenaventura, Colombia, going to downtown with two engineers, they were delighted to see one Cummings engine in a truck at the port entrance. Seemed to be the same model of one of those installed on board. The spent quite some time talking to the driver.
     
  12. tracecom

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    Apr 16, 2010
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    TVA is the utility company that produces electricity for most of Tennessee plus parts of several other states. They have an extensive web site; here is one page with a lot of links that have to do with fossil fuel power generation.

    http://www.tva.com/power/fossil.htm
     
  13. alfacliff

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    we have quite a few large generator sets here, to keep the power on if necessary. the comuter rooms use ups's rated at quite a few kva, with generators to back them up. one mistake made here is to size a generator the same as the ups, when the generator starts, the ups has discharged its batteries a bit and wants to pull power too. you have to double the size of the generator. we have several 1200 kva caterpiller sets (24 cylinder naural gas fueled) and even some on trailers to move as needed.
    after the tornado hit here in 2012, someone shut off the natural gas supply, and all the generators quit. made a mess.
     
  14. WBahn

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    Mar 31, 2012
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    Before we jump on the "evil power companies don't care about their customers" bandwagon, let's take a moment to think. First off, this line of reasoning requires the phrase "they can always charge the customer more" to be true. If that is the case, then they can charge the customer the higher price whether they operate more efficiently or not. That being the case, what motive do they have for operating less efficiently since that reduces their net profit?

    Then consider that, in many cases, the alternative is to charge their customers a hell of a lot more in order to increase generation capacity by building or expanding the power plant infrastructure, including all of the environment impact statements and years of hearings and studies and delays.

    Instead, they can run the existing generating facilities at their point of peak efficiency and use the excess during low demand to store energy in a form that is readily accessible to augment the system during high demand.

    And there can be an overall efficiency gain, too. During the low times, the plant is generating not only the energy that is going to be used to pump the water to the high reservoir at peak efficiency, but it is also generating the energy being delivered to customers at peak efficiency. So the energy savings from the higher efficiency of the delivered energy is available to be spent to cover the efficiency losses of the stored energy system. Similarly during peak hours, even assuming that the plant could deliver the peak demand, the energy that it does produce is at peak efficiency and so that energy savings is also available to cover losses in the stored energy system. Because the base load is such a large fraction of average load and because efficiencies can fall off pretty quickly as you move away from the optimal operating point, the net result is often an overall improvement in efficiency, lower costs to the customers, and less fuel consumed by the utility.
     
  15. JoeJester

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    Rarely do the SNIPES (engineer types) have enough of them in one location for some good BS sessions about their profession, so they take it where they can get it, even on liberty.

    I'll have to dig through the old photographs to see where the copies are as I haven't been on that unit in 20 years, but for the time I was Officer in Charge, they were mine.

    Every day, twice a day, I would see when a very large business would begin and end the workday. It was manifested by brownouts or over voltage spikes. That's the problem with being towards the end of line from the generating plant. The ATS (auto transfer switch) monitored the incoming power and if there were a few cycles off, the generators would start. The same for power lags or over voltages.
     
  16. AnalogKid

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    Aug 1, 2013
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    No it isn't. Two of my neighbors have whole house generators - 10-20Kw-ish generator tied to a 4 cylinder engine converted to run on natural gas. Auto start and changeover after a programmable startup delay, runs for a few hours each month to maintain the oil coatings, and sends an email when it is time for service.

    It is an excellent system, a trimmed-down versiion of industrial co-generation plants, but around here electricity still is cheap, and there's no way one of these things is as efficient as a traditional power plant on a city-wide scale.

    ak
     
  17. shortbus

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    Since I have two gas wells on my property, and get free gas, I half heartedly looked into doing this. But the small amount of savings would take forever to pay off. Especially since my electric bill is only ~$60 a month.
     
  18. Wendy

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    Mar 24, 2008
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    A friend of mine is leasing solar panel on her roof. It should provide her power during the day, and at night she buys here power. She is having to switch power companies to ones that will buy back the excess.

    Volt will be selling their car batteries for a total house UPS which will dovetail nicely with this system.
     
  19. Wendy

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    Depending on time of year, mine averages between $200-400 per month.
     
  20. JoeJester

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    Apr 26, 2005
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    Agustín,

    Here were the two generator sets at my last unit.

    [​IMG]
     
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