August 02, 2022

Why does wind energy decline during heat waves?

When heat waves hit the western side of the Cascades, power demand surges as folks rev up their air conditioners or heat pumps.  And as the region warms during this century and more people secure cooling systems, the demand will only increase.


As the region and the western U.S. turn increasingly to renewables such as wind energy, an important fact should be kept in mind:  the current distribution of wind turbines in the Pacific Northwest experience a profound DECLINE in output during heat waves.  

Which is not good.  

But why does our energy fall away as the temperatures in western Washington and Oregon rise?

That will be the topic of this blog.

To see the situation, here is a graphic from Bonneville Power Authority showing the regional demand (red line), hydropower generation (blue line), renewable power generation (green line), nuclear (purple line), and fossil fuel/biomass generation (brown line) for the past week.

A few things are evident.  Hydropower is absolutely dominant.  Nuclear and fossil fuel/biomass are about the same as nuclear and almost constant in time.   Renewable energy (almost completely wind power) is highly variable and much less than hydro.


You will note we generate more energy than we need this time of the year, with most of it going to California, which desperately needs our power.

But you will notice something else:  wind generation was extremely low during the warm days of the past week and then surges upward...above nuclear!...during the last day as western Washington cooled down and the demand for AC declined.

This pattern--little wind energy and increasing energy during the cool down--is one I have seen time and time again.   Now let's explain why.

Virtually all of the wind turbines in the region are on the lower eastern slopes of the Cascades or near the Columbia River.
When the winds are from the west, they can push eastward through the gap in the Cascades west of Ellensburg and through the Columbia Gorge.  That is why there are lots of wind turbines around Ellensburg and in and downstream of the eastern side of the Columbia Gorge.

Such westerly (from the west) winds are strengthened by having high pressure west of the Cascade crest and lower pressure over the Columbia Basin: the air can accelerate from high to low pressure.

This pressure pattern is very typical during much of the summer, as cool air dominates western Washington and warm conditions are in place east of the Cascades.   Cool air is denser/heavier than warm air so western Washington has higher pressure than eastern Washington.  

But there is more: a large high-pressure area is typically over the eastern Pacific as well, while lower pressure is found over the desert southwest.  

To illustrate the pressure situation, below is the sea level pressure pattern at 5 PM last Thursday before the heat wave.  The solid lines are isobars of constant pressure and the colors indicate temperatures at around 2500 ft (red/brown/blue is warmer).    High pressure offshore and a big pressure difference across the Cascades.   

The wind turbines were really spinning at this time!  Good wind energy.


But to get a heat wave west of the Cascades, the pressure pattern has to be different. You have to cut off the cool marine air from spreading across western Washington and Oregon!

 The high pressure weakens offshore but builds inland.  The pressure difference over the Cascades weakens or even reverses.  And winds around Ellensburg and near the Gorge die down.  

The pressure and temperature pattern during the start of the heat wave (Tuesday at 5 PM) provides an example (below).   Much less pressure difference across the Cascades.  And other heat wave cases are even more dramatic in such changes.


To further illustrate, here are the wind forecasts by the UW WRF model for the middle of the heat wave and yesterday...both at 5 PM (yellow and reds indicate the strongest winds).  See how much stronger the winds are in eastern Washington yesterday evening?  No wonder power generation surged!


So just when we need more energy to drive our AC in western WA and Oregon, wind energy falters.  And as soon as the west cools down and the normal situation returns, the wind power comes back (as shown above).

And there is another issue.  During the coldest periods in winter, the winds tend to die in eastern Washington, and wind energy generation is very poor.

So if you want to use renewable energy for the times we need it most, what can you do?

You need to diversify.

Regionally, we would need a more varied portfolio of wind turbines in different locations, particularly locations that are windy when the air gets sluggish in eastern Washington.  The Washington and Oregon coastal waters are good examples of favorable locations.


But more than that, a rational national perspective regarding renewable energy is needed, not the ad hoc approach that dominates today.  Starting with a detailed knowledge of the nation's meteorology, one needs to create an optimal system of solar and wind generation that can cover most weather situations and seasons, with massive power transmission capability across the continent to move energy to where it is needed.

And for those periods when renewables are not enough...and there will be substantial periods when this is true-- we need a foundation of power generation, with nuclear power being a prime, carbon-free choice.

Making this happen is an Apollo program times ten type of activity that will not be done by some energy credits and the disorganized approach that is currently dominant.

22 comments:

  1. Not to mention.. these turbines are a blight on the land. They deface 100's of square miles of beautiful natural landscape. I'd like to see them taken down in my lifetime, but I don't have much hope.

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    Replies
    1. No, they aren't. Love seeing them!

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    2. By natural landscape, you mean ugly alfalfa farms and cow feed lots?

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    3. So can you explain what exactly 1000s of acres of corn is doing to the natural landscape? The natural sage brush is perfectly intact all around these green energy producing turbines.

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    4. People love those eyesores until NIMBY comes in to play. I'm with John, let's build lots of safe, clean nuclear energy and take down the wind turbines.

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    5. Except that nuclear is not all it's cracked up to be. Think Chernobyl and Love Island where a nuclear plant failed and contaminated the area around it, making that space inhabitable for many, many years. Then there is the spent rods from said plants that must be dealt with and remain actively radioactive for a very, very long time, like 100's of years.

      Fusion may be the answer but in the meantime, gotta use what technology we have at out disposal today to power the nation as efficiently as we can, and diversify as well the power sources at our disposal. Personally, I don't see any one solution be the answer, but several sources being the way to go in the long run, while reducing the polluting resources (gas and coal) needs to power the grid.

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  2. It sounds as though you are suggesting two substantial generating systems. I favor nuclear, without the wind.
    To produce a major decarbonization (<CO2) by 2050, the country needs to build, commission, and bring on-line the equivalent of 2 Columbia Generating Stations [1,207 megawatts] each day.
    This and other ideas are presented here:
    https://wattsupwiththat.com/2021/01/27/bright-green-impossibilities/

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    Replies
    1. John... is we can get nuclear right....and particularly if we can get fusion to work...we can consider dumping wind turbines completely!....sounds good to me..cliff

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  3. How does air density factor into the turbine's efficiency or is the lower density's impact negligible?

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    Replies
    1. I would guess that power generation varies directly with wind momentum, not speed. Momentum = mass * velocity, so the decreasing density of hot air would be accounted for in the lower momentum imparted by a hot wind than a cold wind for the same wind velocity.

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    2. Wind power is directly related to air density; colder air is more dense and 'pushes' the turbine with greater mass. A wind turbine's power curve generates more power in colder weather than at higher air temperatures at the same wind speed because air density is inversely proportional to temperature. The formula for power is:
      P=1/2 * rho*A*v cubed
      Power = Watts
      ρ (rho, a Greek letter) = density of the air in kg/m 3
      A = cross-sectional area of the wind in m 2
      v = velocity of the wind in m/s

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    3. Start with: https://en.wikipedia.org/wiki/Betz's_law

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    4. Must have hit a wrong key.
      I'll repeat and if a double, sorry.
      Have a look here: https://en.wikipedia.org/wiki/Betz's_law

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    5. It makes sense that warmer thinner air will have less mass to push a windmill blade than cooler denser air, thus adding to the larger meteorological situation Cliff described. Thanks for chewing on this with me.

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  4. That chart from BPA is awesome! I found that chart and all the historical data on their site. Has anyone seen a similar live/detailed dataset for PSE? https://transmission.bpa.gov/Business/Operations/Wind/baltwg.aspx

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  5. I have been wondering about why multiple somewhat unusual heatwaves have been occurring at the same time, globally:

    https://www.startribune.com/what-is-causing-simultaneous-heat-waves/600195189/

    "What Is Causing Simultaneous Heat Waves?
    By Paul Douglas

    Europe's recent heat wave shattered records, and now the Pacific Northwest is experiencing one of the hottest weeks in recorded history. Seattle saw 6 straight days of 90+ for the first time ever. Portland reported 7 straight days of 95+ for the first time ever.

    Scientists increasingly believe these global heat waves maybe linked. Jet stream steering winds have experienced unusual contortions known as a "wave number 7 pattern", with 7 bulges of hot air penetrating unusually far north, simultaneously. This may be another symptom of a warming world."

    thoughts?

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  6. Let's ask the question, is real progress being made on building a practical fusion power reactor, one that can be used in generating commercial quantities of electricity?

    Well, instead of always being fifty years away, scientists and engineers have now made enough progress so that it is always just fifteen years away.

    With some tens of billions of dollars more of further investment, fusion might always be just ten years away.

    And with more billions of dollars of investment, fusion might always be just five years away.

    And with yet more billions of dollars of investment .....

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    Replies
    1. The other currently available technology is energy storage--you store the energy from wind when it generates more than the demand and then when demand is high and wind is low, you pull power from the batteries. These type of hybrid energy projects are already being built worldwide and battery research and technology is making them more economical. Of course fusion will be the real answer but until then, we must use current technology to reduce our reliance on fossil fuels. No need to wait!

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    2. There is no efficient storage at this time

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    3. Despite the hype about breakthroughs (which is attracting a lot of money) there is no practical way to extract the heat generated by fusion without disrupting the magnetic fields or laser pulses that generate the reaction. Fusion can be obtained in the lab with an enormous input of energy but so far that's it.

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  7. Always interesting to see the "environmentalists" who couldn't care less about the West.

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  8. Cliff, this is an interesting topic, and yes there does tend to be a slacking of the local wind under both extreme heat and cold events. I agree the answers to this problem are multi-faceted, involving combinations of new transmission, more battery (or other) storage, offshore wind development, and (something you didn't emphasize much) solar development, which tends to be plentiful, at least during heat waves. Many of these are challenging but should be pursued vigorously. There is some low-hanging fruit: There is a 1.5-gigawatt (that's about 1/4 of a Grand Coulee Dam) coal-fired generation plant in Colstrip, Montana (eastern side of the state). that currently has a transmission line all the way to western WA and helps us considerably during high demand. It is going to be decommissioned, and wind and solar developers are chomping at the bit to build capacity along that transmission line to serve the PNW. This is far enough away that the wind would presumably de-correlate with the hottest temperatures in western WA, plus the solar even more so, and the transmission is already in place.

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Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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