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.