More on Wind Capacity

The other day I wrote to beware of rated capacity for wind and solar, because such plants tend to run way below their rated capacity on a 24-hour average.  MaxedOutMamma reads the wind report of the largest utility in Germany, which is as a country is among the largest adopters of wind power.  She finds this interesting bit:

wind power capacity rises, the lower availability of the wind farms
determines the reliability of the system as a whole to an ever
increasing extent. Consequently the greater reliability of traditional
power stations becomes increasingly eclipsed.

a result, the relative contribution of wind power to the guaranteed
capacity of our supply system up to the year 2020 will fall
continuously to around 4% (FIGURE 7). In concrete terms, this means
that in 2020, with a forecast wind power capacity of over 48,000MW
(Source: dena grid study), 2,000MW of traditional power production can
be replaced by these wind farms.

This is an even lower substitution factor than I mentioned previously, and is so because this report looks not just at the percent of time wind is blowing at full speed, but also at the peak load conventional power plants that must be kept running on standby due to the unreliability of wind.  At this 24:1 substitution ratio, folks like Al Gore and Boone Pickens will bankrupt us.  But of course, their investment portfolios, laden with alt-energy investments, will be paying off.


  1. James Barlow:

    A good rule of thumb is that turbines achieve about 25-30% of their rated capacity.

    On Wind Power and a Sustainable approach to Carrot Crunching

  2. diz:

    Typical grid reliability planning suggest you want a 20% reserve margin. This means that you want installed capacity in MW that is 120% of your peak hour load. Peak hour load is probably in most cases about twice that of avergae load. So, even when you are using fossil fuel plants (many of which have the advantage that they can be tripped on and off with seconds notice), reliability generally demand more than twice as much capacity aas the average load.

    Factor in intermittency and all other things being equal the number goes up many many multiples of that. For the record, ERCOT applies an 8.7% factor to wind generation for the purposes of its reserve margin calculaiton:,_Demand,_Reserves_Report_FINAL.xls

    I think realistically to pull off Gore's no fossil fuels plan with current levels of reliability you probably need at least 150% of average load in wind/solar, and maybe 80%-90% of peak load available in pumped or compressed air storage facilities. [This is just a wild ass guess because this in unchartered territory we are talking about here as we have not heavily relied on these sorts of facilities due to their very high cost.] Plus, you probably need a lot of new transmission to get power from places where the wind blows/sun shines to where the people live.

    If you were not pursuing an artficial political goal of 100% of electricity from non fossil fuels, you would almost certainly rely on gas fired generation for the grid's peaking/intermittency coverage. Particularly since you already have it installed!

  3. Rolo Tomasi:

    The 25-30% would be an average capacity factor =(MWh produced per year)/(8760*MW capacity). This is the percentage of power produced compared to how much would have been produced if the turbine was generating its rated capacity continuously through the year.

    The 8.7% reserve margin is the amount ERCOT plans will be available if they need to call up more generation than is normally required.

    If there is a demand spike, the first thing that pops into ERCOT's head will not be "let's turn on some wind."

    Note: 8760=hours per year

  4. Nobrainer:

    I think there is a bit of confusion here.

    The amount that conventional plants are going to be running on standby will be a function of the largest system contingency. For example, the biggest plant in the state of New York, which has it's own operating system, is about 1.2GW (that plant is Nine Mile Point 02). At any given time, the New York Independent System Operator, the NYISO, tries to maintain an operating reserve margin of 1.8GW. Included in those reserves are plants that are running and that have the ability to increase output if necessary. It also includes plants that are off and that can be turned on in either less than 10 minutes or less than 30 minutes.

    In the former case, a 400MW generator may generate 200MW of power and provide 200MW of spinning reserves. In that case, the unit isn't operating at peak efficiency (which is probably when it generates 90-95% of it's full capacity), but it is providing reserves at what a cost that is a fraction of the going rate for 1 MW of actual power.

    In the latter cases, the units will basically be paid just to be ready. Most days, the only fuel they'll burn is the gasoline in the trucks of the workers who show up just in case they have to turn the generator on. Again, the cost of reserves is a fraction of the cost of actual power.

    However, as more wind is added and it becomes a larger fraction of installed capacity, it will become the largest contingency, and the operating reserve requirement will increase. This means that the low substitution factor won't let us mothball a bunch of old fossil fuel burning plants. It simply means that we need to keep them around just in case and that we'll run them far less frequently. In all likelihood, this means that when wind farms dominate the reliability metric, reserve requirements will increase and reserve costs will increase. However, this may be offset by a couple factors. The first is that, in a competitive market, such as NYISO's, any power produced by wind will have the effect of shifting the supply curve to the right and lowering actual power costs. [Side note here: any reduction in power costs results in savings of ($/mw_savings * system_load_mw), whereas the increase in reserve costs is approximately ($/mw_reserve_price_increase * reserve_requirement) where reserve_requirement ~= 10% of system_load_mw).] The second factor is that wind failure, although it may be large and sudden, is likely to be less sudden than the unplanned loss of a nuclear or large coal plant, which can, will, and does happen. Therefore if the failure of wind requires a response rate lower than that of other contingencies, then the quality of reserves can be lower and therefore cheaper.

    Please don't mistake me as an ardent supporter of wind power. It certainly has its downsides. I just wish to highlight actual downsides and not ones that are the result of being misconstrued or made up.

  5. John Moore:

    I have to agree with Nobrainer... one needs a realistic look at this. Just looking at generating capacity isn't the full story, because when that generating capacity is idling, it isn't using much fuel.

    I'd like to see a cost analysis using the sort of analysis Nobrainer suggests. On the plus side (perhaps), the wind power when available, is presumably cheap. If you subscribe to the anti-Carbon religion, it is also low carbon emissions. On the negative side, a lot of capital is tied up in reserve plants, as is their continuing non-generating perating costs.

    Take all of that together, and I have no idea what it looks like, but it is not as grim as Coyote makes it sound.

    Numbers please? Cost/KwH of Wind Power? Cost/KwH of other sources? Cost for idling? Include amortization and operation of reserve capability?

    Anyway, wish I had time to dig out the nums.

  6. dearieme:

    The need to keep old kit running as back-up implies that some day it will have reached the end of its life and that new thermal plant will have to be built to replace it. In that sense wind power isn't "sustainable", since it exploits the temporary existence of back-up plant. Isn't "sustainability" a key requirement of the new religion?

  7. Corky Boyd:

    The first commenter on this post stated "(wind) turbines achieve about 25-30% of their rated capacity." This isn't borne out by statistics in the e.on report MaxxedOutMama references.

    In the box on the bottom of page 4, the report shows Installed wind power capacity on their system as 7050MW and the Average fed-in wind power capacity as 1295MW. This works out to 18.4%. The other statistic that is mind boggling is this (also on page 4):

    "Their dependence on the prevailing wind conditions
    means that wind power has a limited
    load factor even when technically available. It
    is not possible to guarantee its use for the continual
    cover of electricity consumption. Consequently,
    traditional power stations with capacities
    equal to 90% of the installed wind power
    capacity must be permanently online in order
    to guarantee power supply at all times."

    This appears to mean they must have about 6300MW (90% of 7050MW) of online power backup for a system that on average yields about 1300MW. (assuming all wind units are "up")

    No wonder GE is in the wind business. They can sell 2 or 3 million dollars of gas turbine peaking units for every million of wind power.

  8. Corky Boyd:

    I have been doing research on wind power and the e.on/netz report I found very helpful. But I find hard statistics very difficult to come by. Some come from trade associations or manufacturers in the wind power business and they cite very favorable, but totally undocumented, figures.

    Does anyone here know where there is good source material? I have found Wikipedia to be unreliable when covering controversial subjects. Here are some questions I have:

    When the EU sets a goal of 20% wind power by a certain date, is this installed capacity, actual delivered power or some other metric?

    What is the average capital cost per newly installed MW of nuclear, coal, gas turbine peaking, wind, photovoltaic (fixed and steerable)?

    What is the average delivered cost for the above?

    Just post here if you can help me. Thanks.

  9. diz:

    The 25-30% would be an average capacity factor =(MWh produced per year)/(8760*MW capacity). This is the percentage of power produced compared to how much would have been produced if the turbine was generating its rated capacity continuously through the year.

    The 8.7% reserve margin is the amount ERCOT plans will be available if they need to call up more generation than is normally required.

    I didn't mean to imply that ERCOT assumes the wind will only run 8.7% of the time.

    ERCOT's reliability assessment isn't about average run times. It's about ability to cover the peak.

    When that peak occurs, the wind may be running at 100% or it may be 0%. Since the wind is spread around the state somewhat, I imagine they feel comfortable only counting on 8.7% for reliability planning purposes.

    Wind is usually considered "must run" power. That means essentially, that when it is available it will be fed into the grid -- and the ISO will call on other units to cover the peaks and valleys. Up to a certain point this fairly benign -- wind is after all a zero fuel cost source. But there is diminishing marginal value to the grid to adding more and more wind.

  10. markm:

    Wind speeds vary constantly and widely, and wind energy varies with the cube of the speed. That is, if a turbine is rated for 1 MW at 40 mph, it is at half-power (0.5MW) at 32 mph, and at 1/8 power (0.125MW) at 20 mph. However, 41 mph, that turbine's output is probably zero. The rated output comes at the maximum wind speed the turbine and tower can handle without being overstressed, and when the wind blows just a little stronger, the turbine has to shut down to preven damage. So where a coal or nuclear power plant can run at it's full rated power most of the time (given a market for the power), the wind turbine hardly ever hits full power, and I would expect averages of far under half power in most locations.

    Second, nuclear and fossil-fuel power plants do have to shut down for maintenance now and then - but nearly all of this maintenance is scheduled far in advance, after considering the expected availability of other plants and the expected system load. Wind speeds go up and down unpredictably and without regard to the need for power.

  11. Bob Smith:

    I'm surprised that a bunch of eco-nuts who rail against "sprawl" from human habitation are a-ok with wind and solar, both of which consume far, far more land area (several times as much, in fact) for power generation than nuclear, gas, or coal.