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11.2: Overcoming the Challenges of Wind Power

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    84606
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    clipboard_ec1f86a63d7c8038bf3f8e2ed4cdfa2bc.png
    Figure \(\PageIndex{1}\): generated over the month can be obtaining by calculating the area below the curve (i.e., by integrating), which yields 1,8126 GWh,corresponding to the average power of 2.436 GW (shown as the red line). Source: hourly data published by the operator of the national grid in Poland ”Polskie Sieci Elektroenergetyczne (PSE)” and systematically monitored on Mrs. Jozefa Sokolowska’s blog – chart based on the data collected in her blog, with her permission.

    Above lands, winds can be quite capricious - especially in medium latitudes where different atmospheric fronts often clash with one another. It leads to periods of high winds alternating irregularly with light winds, or even with completely windless periods. An example of electric power generated by wind in March 2019 in Poland, a country located centrally in Europe, is shown in Fig. \(\PageIndex{1}\). It illustrates irregular fluctuations in the power, between the maximum of 5 GW and the minimum of less than 0.5 GW. Such fluctuating patterns are typical for other countries from the same region – in particular, for Germany and Denmark, two nations in which the energy systems rely heavily on the wind power.

    clipboard_ed92b0c89c06bfa0615d662ffa2274ffb.png
    Figure \(\PageIndex{2}\): Upper panel: the total demand for power in Poland on a day in April 2019; lower panel: the power provided by wind farms only in the same day. Over the period in which the wind power ramps down by almost 5 GW, the other available sources – all of them burning fossil fuels – must ramp up by the same amount (Source: as in the Fig. \(\PageIndex{1}\) )

    Is energy storage necessary to deal with such wind fluctuations in Poland? Well, no. Not yet! To explain what we have in mind, let’s take a look at another graph (Fig. \(\PageIndex{2}\)), illustrating the situation in Poland on one day in April 2019. The red curve in the upper plot shows the total generation over the 24-hour period – generation equal to customers’ needs. The lower graph shows that in the morning hours the wind sector delivered about 5 GW, nearly 1/3 of the power demand on 5 a.m. – but then, while the demand was strongly increasing, about 8:00 a.m. the wind power generation started suddenly “ramping down” and over the next 9 hours it fell to less than 0.5 GW.

    This unexpected loss of energy from wind farms forced other sectors of the national utility system (mainly coal-fired power plants) to increase output power to almost it’s maximum capacity. Fortunately, necessary reserves in the coal-fired plants still existed and a power outage did not happen.

    But let’s try to imagine a similar situation in the future. The European Union has set itself the goal of achieving total “decarbonization” by 2050. Poland, being a member of the Union, must therefore gradually reduce the share of coal-fired plants in the entire power generating “mix”. Then, say, in 2040 the coal-fired sector needs to be reduced to about 1/3 of the current power, from about 27 GW to 9 GW. The 27 - 9 = 18 GW power deficit which arises as the result of such transformation must be covered by increased wind farm generation.

    As noted before, currently the wind farm system in Poland is capable of delivering about 5 GW under the most favorable circumstances. But such “most favorable” circumstances may not occur at the moment when all 18 GW are needed. More realistically, one should take into accuont the average of 2.4 GW. So, the existing wind-farm capacity should be increased at least eight-fold or even more to offer sure guarantees that 18 GW will be delivered when needed. Well, but as can be seen in Fig. 11.1, more than once in the month of March 2019 the existing wind farms were able to deliver even less than 0.5 GW. So, it may happen that the enlarged system, even with the capacity increased by a factor as big as 10, will be able to provide only some 5 GW out of the necessary 18 GW. And then what?

    Well, the currently existing utility systems – those still dominated by fossil fuel burning sources – are prepared to deal with sudden dramatically increased power demand. They have special generators in reserve, called “peakers”, capable of switching from zero to full power in minutes. Presently, most of them are natural gas turbines – or, sometimes, huge Diesel engines. Such “peakers” may offer a remedy for sudden “incapacities” of wind farms. But let’s keep in mind that the objective is to reach a full decarbonization, so any “remedies” using fossil fuels are certainly not welcome! But are there zero-emission “peakers”? The answer is yes, there are - such a task can be fulfilled by energy storage devices.

    Note that in the example scenario discussed the number of wind farms is increased so that the average generation meets the needs. Accordingly, there will be periods in which the energy generation will significantly exceed the needs. This is not a small problem! What to do with that surplus energy? In nations which already have a substantial windpower potential (e.g., in Germany), such situations occur from time to time. But, as was emphasized earlier, in an efficient system the generated power must match the needs of consumers: not only there should not be less power, but also there must not be no more than needed! Over-generation would destabilize the grid, potentially leading shutdowns and even to damage of power lines and distribution centers. Therefore, an often used “emergency remedy” is to curtail the wind generation: either by changing the angles of the wind turbine blades to lower their efficiency, or – in a more brutal fashion – by stopping some turbines altogether. Such curtailing, of course, makes little sense, because it is simply a waste of energy. The surplus energy should be stored This excess electricity should be stored in appropriate “rechargeable” reservoirs capable of returning the stored energy on demand. Then such “reservoirs” can act as “peakers” in times when the wind is so weak that wind farms are no longer able to generate the needed power.

    The idea is pretty clear. But it has only recently been realized that with- out the existence of extensive energy storage systems achieving a significant reduction in CO2 emissions will not be realistic. Thus, efforts to create such systems at the scale needed are only now gaining momentum. Fortunately, several viable technologies that can be employed for this purpose already exist and additional opportunities are still emerging thanks to intensive research. An overview of such technologies is presented in the following sections of this chapter - but only after discussing the problems arising from the intensive use of solar energy - which is also characterized by intermittence, but of a somewhat different nature than that in the case of wind.


    11.2: Overcoming the Challenges of Wind Power is shared under a CC BY 1.3 license and was authored, remixed, and/or curated by Tom Giebultowicz.

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