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More Costs and Higher Prices

November 11, 2011

Renewables, such as wind and solar, generate electricity intermittently, where it’s impossible to predict when the wind will stop blowing or the sun will be clouded over.

The need for costly back-up power is well documented.

Not so obvious is the impact that intermittency has on existing coal-fired and natural gas combined cycle (NGCC) power plants.

NGCC and coal-fired power plants are designed to run at a steady load, except for planned maintenance periods where they are carefully shut down at the beginning of the maintenance period and slowly brought back on line when maintenance is completed.

The advent of renewables has resulted in these plants being cycled, up and down, to accommodate the variables caused by intermittent wind and solar power plants.

This cycling has resulted in less efficient use of the power plants, as well as costly damage to the plants.

This means higher costs and higher prices to the consumer for electricity.

The first casualty of cycling these plants is lower capacity factor. This means that these units are producing less electricity than they could. In other words, efficiently generated electricity is being replaced by inefficiently generated electricity from renewables.

The next casualty is damage to components from thermal cycles. In other words, components that are designed to operate at more or less stable temperatures, after being slowly brought up to operating conditions, are whip sawed between lower, then higher temperatures. These unplanned thermal cycles damage the boilers and turbines.

This damage causes increased spending on preventative and corrective maintenance, which results in higher costs to consumers.

The next casualty is to the pollution control systems. The changes in load result in changes to flu-gas temperatures and pressures that result in less efficient operation of these systems. In addition, the cycling of temperatures also damages this equipment.

Coal-fired power plants receive the most wear and tear from this thermal cycling.

Some examples.

  • Headers in boilers are thick, expensive and hard to reach components that have been cracked as the result of thermal cycling.
  • The boiler structure that supports firewalls and water-tubes expands and contracts at different rates than the firewalls, etc. This uneven expansion and contraction causes severe damage to the firewalls and tubing.
  • Different expansion rates cause damage to the super heater tubes and their supporting structures.
  • Boiler water chemistry is altered when boilers are operated under variable temperatures and pressures. Boiler water chemistry is crucial to preventing chemical attack of boiler tubes.
  • Steam turbine rotors consist of huge, solid forgings. Gas turbines have buckets mounted on diaphragms keyed to forgings. These rotors, unless designed for thermal cycling, must be brought up to speed slowly so as not to be deformed by changing temperature. The coefficients of expansion between components are also different, which requires steady operating temperatures under load. Clearances are tight and deformation could cause rubbing and damage.

These are merely a few examples of the problems caused by operating coal-fired and NGCC power plants in anything other than steady conditions.

As an aside, I have worked inside the fire-box of marine boilers to point-up the brickwork, and to clean the tubes using a handheld steam lance. For a long while, I had the scar on my left arm from a burn caused by the high temperature of the steam hose.

The public isn’t aware of these problems and higher costs. All they hear about are the so-called “Green” benefits of wind and solar.

In the real world, renewables cause problems, and increase the price of electricity to consumers.

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4 Comments leave one →
  1. Mark permalink
    November 12, 2011 10:47 am

    Morning Donn,

    I cleaned out a few water treatment tanks back in my youth- luckly for me the tanks were cold vs the the hot boilers you worked on! My local paper had an interesting post on renewable energy projects out here in CA that you might find of interest-

    “Firms gobble ‘green’ subsidies.”

    The price that PG&E is noted as paying for the PV electrons at the site of their generation is likely an average price. In order to get the revenue side of things to work for investors CA was paying a premium for green energy at peak times in the summer. Last I checked this equated to something like $.22 a kwh for PG&E contracts. If the PV farm operated at night the electrons would only be worth something like $.08 a kwh……………….

    NRG is investing in the market to supply CA with it’s green energy needs- most recently as noted in a Genentech media article that shows their purchase of First Solar’s projects (with the associated loan grants, tax breaks, etc. and most importantly the fixed contract PPA for 20 years).

  2. November 12, 2011 12:07 pm

    Thanks Mark:
    The Sacbee article from the NY Times was very interesting. The subsidy for NRG was a huge windfall.
    Re the financial announcements by Sun Power and First Solar, they’re not doing well even with all the subsidies and high prices they receive for their electricity. Basically, most renewables are a bad investment for the United States and for consumers.

    • Mark permalink
      November 12, 2011 1:57 pm


      Thanks for the catch- the article actually written by folks at the NY Times. Your comments on the effect(s) of having to cycle up and down natural gas or coal fired plants got me to thinking how someone like SCE or PG&E would deal with the consequences. I take it that they can come back to the public utility agencies that set their utility rates (in CA it would be the CPUC) to pass along the extra costs associated with added maintenance costs and shorter life expectancy of their equipment. Does this sound about right to you?

      Out here in CA CARB is finalizing it’s CAP and trade program for our reduction in CO2 goals. Our big utilities are part of this program. Your comments indicate that a natural gas fired generation facility (or a coal one) is kind of optimized to run between some X and Y percent of full capacity. Do you happen to have any data on how less efficient the plant would be running when it goes below X? Thanks, the reason I am bringing this up as I am interested in understanding SCE thoughts about how to address system wide issues in regards to capturing the true costs of adding in a lot more RE. Their thoughts on the subject are referenced and elsewhere.

      CA is aware that the intermittency of most forms of RE and their inability to be ramped up or down (dispatch ability) compared to our traditional forms of electrical generation. There is a upcoming meeting (on the 15th) at our energy commission on energy storage that should be rather interesting. In case your interested the reference info on the “Staff Workshop on 2020 Strategic Analysis of Energy Storage in California.”//
      Workshop Notice, Posted November 3, 2011
      2020 Strategic Analysis of Energy Storage in California, PIER Program Final Project Report.
      Posted November 9, 2011. (221 pgs, 3.1 megabytes)


  3. November 12, 2011 3:42 pm

    Thanks. I have downloaded the two papers you referenced and will read them. I scanned them and they look interesting.
    Storage is a key issue. SCE has taken an objective look at the topic, identifying needs matched to possible solutions. Uninterruptable power is a necessity in today’s electronic age.
    But that isn’t the case with storage because of intermittent wind and solar generated electricity.
    That’s what the uproar is really all about.
    I’ll probably write more on the subject after I have studied the SCE paper and am sure I have all the facts.

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