Bacon's Rebellion

Democracy Thrives in Sunlight

Wind Power’s Big Problem: Erratic Output

—

by

James A. Bacon
in

Source: PJM Interconnection
Wind forecast and output across the PJM system on Sept. 3, 2015. Source: PJM Interconnection

The great thing about wind power is that the fuel is free. The bad thing about wind power is that you can’t count on getting it when you want it. Wind power may be an economically competitive source of electric power in parts of the country, like the plains states, where wind is strong and steady, but it’s not so competitive where its output is intermittent.

Yesterday afternoon, I captured this image from the PJM Interconnection website, which shows the fluctuations in wind generation compared to forecasts over 24 hours. (Both Dominion Virginia Power and Appalachian Power Co. are integrated in the PJM regional grid.) Here is the explanation that PJM provides:

Because wind is an intermittent resource, it requires its own forecasting and monitoring methods to plan for its reliability. This graphic chart displays both instantaneous power (in megawatts) being produced and forecasted power for every five minutes. It is updated hourly. The data is measured at each wind farm every minute and then is aggregated for this tool. Dispatchers use this display to monitor trends in wind power production.

The fact that PJM’s service territory spans parts of 13 states and the District of Columbia helps even out the power output. Local fluctuations sometimes cancel each other out. Even so, wind output varied from roughly 200 megawatts to 1,600 megawatts over the 24-hour period. In this particular day, wind turbines were cranking out the energy when it was needed least, during the night, and took a steep dive in the late morning when electricity demand was high and rising.

If wind power can’t be relied upon to produce electricity when needed, or at the very least on a predictable basis, the electric grid needs substantial backup capacity, maintained at great expense, to fill in the gaps. That’s why, over and above the local Not In My Back Yard resistance to wind farms, on-shore wind power doesn’t make much sense in Virginia. Even if Virginia wind power can crank out electricity competitively on a stand-alone basis, measured by the cost per kilowatt hour, basis, that’s not especially helpful to an integrated grid designed for system-wide reliability.

Solar energy is a very different story, as I will explain later today. Solar is intermittent as well, but it is intermittent within narrower parameters than wind. Solar plants generate zero electricity during the night, when electricity demand is lowest, and they reach maximum capacity during the afternoon, which coincides with peak electricity demand. My sense is that solar will play a much bigger role in Virginia’s energy future than wind.

— JAB

(Hat tip: TomH)

Share this article

ADVERTISEMENT

(comments below)

ADVERTISEMENT

(comments below)

Comments

20 responses to “Wind Power’s Big Problem: Erratic Output”

  1. John B Avatar
    John B

    The graphic’s profile sure looked like a call for installation of more pumped storage (obviously depending upon the topography).

    In the wee hours demand is low and output is high.

    What’s not to like other than the enormous investment required?

    1. Acbar Avatar
      Acbar

      Re smoothing out wind power fluctuations, I’d go with batteries before pumped-storage hydro. One of these days battery technology will make sense for grid use, and with a battery you get nearly all the power back (>90%) that you put in. Pumped storage, unfortunately, is in the range of <30% recovered. You use the electricity to pump water up a hill and that incurs big energy losses; you use the water's fall down the hill to generate electricity later and that incurs big losses; the result is big losses x2.

      Pumped storage hydro generation made sense in the 1970s when paired with nuclear power which generated power in excess of the customer load at night, because getting something, even an inefficient 30%, back later was better than nothing. The difference today is, due to load growth and a better-connected grid, it's rare when nuclear baseload generation exceeds the nighttime load, so there's rarely a time when you'd really just throw away that power if you didn't use it to pump water up a hill, so it rarely makes economic sense today to use it for that purpose.

      Batteries are too darned expensive today and have too limited a life cycle and impose too much environmental cost to make and to dispose of; but the technology is changing fast. It seems like a battery revolution is always just a few years away but there is amazing new stuff happening, like the flexible aluminum and graphite battery announced recently at Stanford, that has huge development potential.

      1. TooManyTaxes Avatar
        TooManyTaxes

        While I’m certainly not an engineer by any means, Acbar’s comments about batteries are well taken. If I had a spare billion, I’d invest it in battery research.

      2. John B Avatar
        John B

        Acbar, I’d be interested to see your citation for percentage losses. Admittedly 30% efficiency does seem surprisingly low.

        My suggestion was based on the profile showing that wind power seems most available when least needed.

  2. LarrytheG Avatar
    LarrytheG

    think of a natural gas plant sited right next to a coal or nuke plant.

    now think of the gas plant modulation its generation according to how much more is needed over and above the output from the coal/nuke.

    now add a wind turbine to the site where it generates power.

    as the wind increases or decreases – the natural gas plant would do the same thing it does when it responds to demand over and above what the coal/nuke is providing.

    it’s the same concept just on the generation side.

    think of the coal plant … having 2 boilers and one goes down and the plant only generates one half of what it was before the boiler crapped out.

    the onsite natural gas plant would then increase it”s generation to compensate for the loss of the boiler.

    once the boiler is fixed and comes back up – the gas plant then starts reducing it’s generation in response to the coal plant doubling its output from the fixed boiler.

    now change the coal plant with 2 boilers to a wind turbine that goes up then down and back up according to how much wind is blowing.

    as the wind turbine input increases output – the gas plant decreases in response. Once the wind dies, the gas plant increases output to compensate.

    where have I got this wrong?

    1. TooManyTaxes Avatar
      TooManyTaxes

      I think Larry has the concept correctly – multiple generating technologies working together to produce reliable, safe and inexpensive electric power. That’s what we need to keep the economy going and growing. If all sources are reliable and affordable, power companies can alter the mix to achieve optimum results.

      It also strikes me that other states will have better access to land-based wind and solar power than Virginia. (Too bad we cannot share the hot air that comes from legislators and lobbyists in Washington.) But we have an eastern border on the Atlantic. Basic and applied research on ocean-based wind and current(?) power sources should be conducted. Who knows – there might even be a cost-efficient way for ocean vessels to be powered by the very currents in which they travel. Back to the future? We need disruptors, not bureaucrats, pushing us forward.

      1. Acbar Avatar
        Acbar

        Yes, agreed, the concept is right; this is in fact the principle that PJM and other ISOs work to carry out every day, balancing one type of generation against another and against the forecasted load due to weather conditions etc. But there is a tradeoff between the ability to vary a generator’s output and the efficiency with which the generator converts fuel into electricity. So called “cycling” units are not as efficient as “base load” units. A natural gas unit is typically of the cycling type, but add on combined cycle features (NGCC) and make it bigger and more efficient and it gets harder to change its output. Simply put, wind power is very hard to accommodate efficiently on the Grid because it’s SO variable.

        1. Rowinguy Avatar
          Rowinguy

          The overall concept is indeed correct. But, as always, the devil resides in the details. As Acbar notes, there are indeed cycling gas plants, The large baseload units now being built by Dominion and others are not these types. They are baseload and require an enormous and constant supply of gas; hence the proposed interstate pipeline proposals we’ve discussed at this site. You couldn’t just double the output of an idling baseload plant when, in Larry’s hypothetical, a coal boiler crapped out. The gas would not have been “nominated” by the generator and thus would not be physically immediately available.

          This is where the concept of the regional network, such as PJM comes into play. Units already running elsewhere can be ramped up to collectively replace the power from the crapped out boiler (or the tripped off nuclear unit, for that matter). So, you don’t need different types of generation all co-located so long as they are available somewhere in the system. Power pushed onto the grid from anywhere flows according to the laws of physics–new electrons coming from the west of a particular load means less power needs to flow from the east to serve that load and will be available to be consumed by another load.

          There are, of course, numerous caveats. The grid does not operate perfectly everywhere. That’s why new lines and power stations are needed from time to time. Nonetheless, I believe PJM thinks it can accommodate quite a bit of intermittent power because of the resiliency of its grid and the numerous sources of stand by power.

  3. TBill Avatar
    TBill

    Because I am not a utility load distribution expert, I do not have a good feel for how useful wind power is for Virginia. Seems obvious to conclude that wind and solar are probably more expensive in Virginia compared to the most favorable sites in other states.

    Even so Dominion has already moved ahead with some wind projects such as in the West Virginia wind corridor, and the recent in-state proposal getting resistance in the Tazewell region.

    With the EPA CPP program, I assume Dominion’s and other wind proposals may now get siting support from Virginia and the EPA. This may include improved host community benefits, on the kind and gentle side, to, on the “hard ball” side, possible legal pushing in the courts. I’ve certainly experienced states using “hard ball” to push coal plant construction…it could be nicer to push wind projects with similar gusto.

  4. LarrytheG Avatar
    LarrytheG

    If wind and solar are truly not usable power then I no more would require it than I would burning cantaloupes for power.

    but when wind and solar are “on” – they do generate real power so the issue is how can we efficiently and reliably harvest that power because that power is just as valuable as power that comes from coal, nukes, gas or efficiencies.

    think of it like what we did when oil and gas wells played out and even though there was still oil/gas – getting what was left – out, was uneconomical – until technology came along that allowed getting the rest out.

    thats what needs to happen with wind and solar. we need to figure out how to efficiently ..economically – access it rather than looking at it as “unreliable”.

    1. Acbar Avatar
      Acbar

      I agree with you Larry but it’s not trivial figuring out that last part: “how to efficiently — economically – access it.” Natural gas units are part of the solution, but only part. As you yourself have mentioned, batteries are another part; but they are not yet ready for “prime time.”

  5. Rowinguy Avatar
    Rowinguy

    Both wind and solar make economic and operations sense in many places right now and that area will only expand as technology improves to deal with their intermittency, I don’t think Virginia is the next place that that happens, but it will happen here eventually.

    I hope soon enough that Dominion doesn’t have to build another nuclear unit at North Anna

    1. James A. Bacon Avatar
      James A. Bacon

      Clearly, the technology is evolving rapidly, and many of the problems I highlight now can and will be solved. I, too, question the wisdom of sinking $10 billion (give or take a couple billion) into a nuclear plant with a 40-year life that could be obsolete in four or five years. Right now, I think the best policy is creating a grid that optimizes flexibility.

      1. Acbar Avatar
        Acbar

        I think it’s highly unlikely that any nuclear plant, once built, will become obsolete in its lifetime, unless shut down despite economics (for political/regulatory reasons). Sharing baseload power is the principal reason-for-being of the Grid; everything else is built around/on top of that foundation. What’s much more questionable is whether CONSTRUCTING any nuclear unit today makes sense. It should make sense; but the up front costs including the financial and regulatory risks are very, very high.

        1. TomH Avatar
          TomH

          Acbar,

          “I think it’s highly unlikely that any nuclear plant, once built, will become obsolete in its lifetime, unless shut down despite economics (for political/regulatory reasons).”

          It’s time we discussed a little bit more about nuclear since it comprises about 20% of the generation in the U.S. and is a large component of our generation in Virginia. When a new nuclear plant is authorized, it is granted a 40-year operating license by the Nuclear Regulatory Commission (NRC). To operate longer than that, the plant must be granted a 20-year extension of its original license. More than half of the U.S. fleet (99 reactors) has surpassed or will soon surpass the 40-year lifespan envisioned when the licenses were awarded—most of them have already secured 20-year extensions.

          For some, their owners chose not to apply for an extension. Further complications were caused by a June 2012 court ruling that blocked the NRC from issuing new reactor licenses or renewals until it sufficiently assesses the risks of storing spent radioactive fuel at nuclear plant sites. Two of the plants, the Vermont Yankee reactor and Wisconsin’s Kewaunee reactor, were felled by stiff competition. One plant, San Onofre in California, was shuttered amid safety concerns and severely damaged steam generators. And the other, Florida’s Crystal River, was done in by structural damage. Duke Energy Corp.’s decided to shelve plans for two new reactors in Levy County, Fla. (in addition to permanently closing Crystal River).

          Analysts say economic woes make at least 10 other plants vulnerable enough to follow suit. Almost all of those are among the nation’s 47 “merchant” nuclear plants, which, unlike regulated plants, operate in open markets and have to beat out other power suppliers to win customers and long-term supply contracts. The especially vulnerable facilities cited by analysts are at greater risk for closure because their power is too expensive to sell profitably in wholesale markets or because their output is too small or too unreliable to support rising operating and retrofit costs.

          Wall Street firm Credit Suisse set the tone with a report that described the aging U.S. fleet of nuclear power plants as “facing declining performance, higher costs and inevitable mortality.” Given the outlook for age-related extra costs, new safety and security expenses, sluggish electricity demand and stiff competition from power plants burning cheaper natural gas, Credit Suisse said, “losing another 1-5 plants in 2013 would not shock us.”

          Mark Cooper, a senior fellow at the Vermont Law School’s Institute for Energy and the Environment, was more pessimistic. Cooper, a longtime critic of nuclear power economics, argued that competition from natural gas as well as carbon-free wind and solar power producers could push more than 30 U.S. reactors “to the brink of economic abandonment.”

          Cooper believes market conditions are so unfavorable that premature closures will not be limited to plants that have to compete for customers. He said closures will also hit nuclear plants that operate in regulated markets, where they are mostly protected from the competitive forces that drove the Kewaunee and Vermont Yankee plants out of business.

          Nuclear plants in regulated markets are typically owned by the region’s incumbent utility, so they have an automatic buyer for their output and don’t have to compete against lower-cost power producers. State regulators decide how much the utility can charge its customers for electricity, not based on market prices, but based on how much it costs the utility to provide the power, maintain the plants and facilities and operate the utility—plus a specified profit margin. What’s more, regulated utilities that undertake big-ticket projects, such as replacing a nuclear plant’s steam generators, can pass those costs on to its customers by raising rates.

          Increasingly, though, state regulators are questioning the economics of pricey retrofits and upgrades, and some states have begun pressing utilities to pay for cost overruns and expensive mistakes on projects.
          “Economic pressures have become so severe that regulators have been forced to take action,” Cooper said. More than 50 reactors run in regulated markets, and now that government officials are keeping a closer eye on costs, about three dozen of them are “on the razor’s edge,” he estimated.

          David Lochbaum, director of the nuclear safety project at the Union of Concerned Scientists, added that with so many older plants still operating—20 have been online for more than 40 years—equipment problems and safety issues are becoming inevitable. Increasingly, companies and regulators won’t be able to justify the cost of the necessary fixes.

          “The underlying factors are similar everywhere. They’re not making buckets of money every day, and it’s very tight,” Lochbaum said. As a plant operator, “you’re basically one surprise away—one component [problem] away—from not having the economics favor you.”
          The market setbacks and stark projections have put an emphatic end to talk of the U.S. “nuclear renaissance” that was still being touted by industry supporters as recently as 2010. A few years ago, the NRC received its first formal application for a new nuclear reactor in decades. It was followed by more than two dozen more, as well as a host of proposals to boost the output of existing reactors, and a steady stream of requests for 20-year extensions on plant operating licenses.
          More than half of the 28 proposed new reactors have since been officially cancelled or halted, and most of the others are stalled. Many projects that would have sharply increased power production from existing reactors suffered a similar fate. Four new reactors are under construction, two at Georgia’s Vogtle plant and two at the Virgil C. Summer plant in South Carolina. Both projects are behind schedule and substantially over budget—and being paid for in large part by taxpayers and electric customers.

          Reactors recently closed or scheduled for closure:
          •Vermont Yankee, Vermont
          •San Onofre, California
          •Kewaunee, Wisconsin
          •Crystal River, Florida
          •Oyster Creek, New Jersey

          More are on the chopping block:
          Indian Point – NY
          Ginna – NY
          Fitzpatrick – NY
          Three Mile Island – PA
          Davis Besse – OH
          Pilgrim – OH

          The U.S. still has no federal repository for nuclear waste. With the need to keep the waste isolated from the environment and human contact for 10,000 years, this is not an inconsequential issue. The fight over plans to create such a repository under Yucca Mountain in Nevada has dragged on since the 1980s and the idea has recently been abandoned by the federal government with no alternative proposed. Instead, the waste is stored at the plants, where the owners are responsible for keeping it secure.

          Many of the shutdown decisions are being made because of the low cost of natural gas. What happens when we begin exporting LNG and our domestic prices begin to approach the world prices? Often the license renewals are not pursued in order to get at the decommissioning fund. The owner of a plant in shutdown mode has access to the decommissioning fund that was set up at the time the plant was built and into which additional funds have been added over the years of operation. In the case of Vermont Yankee, the decommissioning fund balance is $582 million. Tapping that fund will allow the company to book more revenue.

    2. TomH Avatar
      TomH

      Wind located on ridge tops is probably the lowest cost source of new generation in Virginia at this time. If the economics did not make sense the projects would not be moving forward (although many will encounter opposition because of views). In general, it is more available at night because wind depends on changes in temperature and pressure which are most pronounced at night.

      On the whole, the southeast is a low quality wind resource region compared to other areas in the U.S. Ridge top and some shoreline locations do provide enough wind to make the economics work. An investment in a wind farm in the Texas panhandle will still yield much more energy than the same investment in wind in Virginia, however. Very little land is required for their operation. Typical activities, such as agriculture, can continue as before. This is not the case for a gas plant or a solar array for example.

      The greater night time output makes wind a good complement to solar so that together they provide a more consistent source of energy. Pumped storage is a useful resource to complement renewables, as well. The largest facility of its type in the world (3000 MW) is in Bath Co. These units are typically 70 – 80% efficient. If your price differential between wind and intermediate or peak power is more than 20 – 30% (usually it is far more than this, often 200 – 300% or more) it makes sense to utilize wind to the maximum extent it is available.

      I think the various opinions are converging on the important point. A diversity of geographically distributed generation sources, each used to optimize its strengths, will provide us with the lowest costs and greatest reliability.

      By the way, 40 MW of utility scale battery storage was installed in the U.S. in April, May and June of this year. A total of 250 MW is expected to be installed by the end of the year. Utility scale battery storage is cost-effective today in certain situations and costs are rapidly declining. These units are valuable not only for energy storage but for a variety of grid regulation and stability services as well. ISO’s such as PJM are beginning to price these services much as they do generating plants, so this contributes to the speed of adoption.

  6. Acbar Avatar
    Acbar

    TomH, agree with the thrust of your comments but take issue with one detail: you say, “The largest facility of its type in the world (3000 MW) is in Bath Co. These units are typically 70 – 80% efficient.” That’s more than double the highest efficiency I’ve ever heard of for pumped storage. A pumped storage unit changes electrical energy into kinectic/potential energy, then back again. Maybe Bath Co can come close to 70% efficiency in one direction, but double that loss of efficiency or more for a full cycle (electricity>pumping the water up-hill to store it, then drawing it down on demand>electricity).

    Yes, PJM will pay for battery power as much as for any other source that can deliver bulk power on demand; they even pay a premium for quick-responsiveness, which of course a battery has.

  7. TomH Avatar
    TomH

    Acbar,

    I was using that figure from my experience with a pumped storage project in Ludington Michigan. However, here is a reference for you that gives approximately the same answer:

    “The round-trip efficiency (electricity generated divided by the electricity used to pump water) of facilities with older designs may be lower than 60%, while a state-of-the-art PHS system may achieve over 80% efficiency.”

    http://people.duke.edu/~cy42/PHS.pdf

    Pumped Hydroelectric Storage Chi-Jen Yang Duke University, Durham, North Carolina

  8. LarrytheG Avatar
    LarrytheG

    pumped storage could me the ultimate battery for places with rivers because if you’re using solar to pump water upstream – continuously – you don’t need a reservoir.

    Reservoirs basically are needed for “storage” for runoff that would be lost if not captured and then used to drive turbines.

    but think of solar pumping water upstream during the day boosting the flow in the river – the energy of which can be captured as it flows downstream.

    run-of-the-river “turbines” would “work” like wind turbines – as long as there is flow in the river – it would drive the turbines. that can happen also in tidal areas.

    the key to wind or water turbines is slower speeds that do not harm critters… and screw turbines –

    like these : goo.gl/IjZM6R

    https://youtu.be/1Nm0aaCZ4iY

    and vertical axis wind turbines like these

    https://youtu.be/qeRwmI1gLhI

    the current conventional wisdom is that you need a lot of head and a lot of windspeed to efficiently generate power.

    perhaps more research should go into how to harvest low speed/low head energy which would change the landscape of what are considered
    “good” sites!

  9. TomH Avatar
    TomH

    These are good solutions for low-power applications in remote locations. Run-of-river hydro is usually one of two types:

    High-head – which diverts a portion of the flow of a stream which is a short distance away but at a much higher in elevation. A small amount of pondage is required upstream to keep the penstock covered at all times. It would be hard to recover energy from water pumped back upstream unless you built a bigger pond. Advantages – no fuel costs. Disadvantages – construction damage in mountainous terrain for intake pipeline, generator and transmission. Most of power is generated during lowest use period (spring).

    Low-head, high-flow – larger rivers are used, but usually a low dam or weir is required. Most of these were built 100-years ago. It’s harder to get approval to disrupt waterways in any way now. It is even getting tougher in Canada.

    You are right to point out the many innovative turbine designs that have been developed. However, most of these applications don’t have value for large utilities. To them, a major value of hydro (besides cost) is that they can be activated quickly, whenever they need them. Run-of-river units don’t provide that flexibility and flows are lowest during the peak summer and winter seasons.

    Savonius rotor wind turbine designs are very interesting. I worked on a few designs in Hawaii because we wanted to reduce the visual impact. We considered mounting them horizontally at the top of buildings and also looked at “wings” around the rotor that would increase wind velocity. Unfortunately, this design is hard to scale and needs a complex geared generator unit because it doesn’t rotate faster than the wind.

    Because the power that can be extracted from wind is a cube of the wind speed (2x faster wind yields 8x the power), the higher you put the wind turbines – the faster and more consistent the wind. The huge new wind turbines developed for utility use now are traveling at 180 mph at the tip of the blades.

Leave a Reply

Read More