The emergence of eolics

How does a "science" emerge? How is it you find yourself in a classroom or a lecture theatre attending a lesson in Astronomy 101, or Introductory Equilibrium Thermodynamics, or whatever course of study you may have elected to pursue? Who decided that this was how human knowledge should be subdivided, and presented to you, and eventually applied by you once you have assumed a role like: mechanical engineer; or computer scientist?

The answer is that the application of the science comes first. At school we often encounter knowledge presented in a well organised theoretical structure, neatly arranged into categories and silos of inter-related facts, before we think about the application of that knowledge for real world purposes. But that way of organising our knowledge only emerged as a result of the acquisition of useful knowledge while in the pursuit of real world applications. The application of a science precedes the codification of the useful knowledge it represents into a "subject", like the kinds of subject that can be studied at schools and universities.

Take, as an example the emergence of thermodynamics. This owes a lot to its application during the development of tools and techniques associated with industrialisation.

Here is a Boulton and Watt steam engine. This was a foundational technology for the Industrial Revolution. On Glasgow Green, in 1765, James Watt was taking a walk, when he came up with the idea of a separate condenser for a steam engine. This idea radically enhanced the efficiency of steam engines, which allowed them to make a crucial contribution to the emerging Industrial Revolution. This in turn stimulated the development of the science of thermodynamics, to describe how engines like these work.

But it was not until nearly a century later that this science was formally defined by Lord Kelvin in 1854 as “the subject of the relation of heat to forces acting between contiguous parts of bodies," and the first textbook on the subject wasn’t written until 1859, by William Rankine, across town at the University of Glasgow.

Nevertheless, we are not considering here “where have we been” but “where are we going”, so we should look for new disciplines emerging now in response to the needs of society today, repeating this pattern I have described. What new applications are stimulating new investigations, measurements and analysis, leading to the development of a knowledge base that may someday be codified as a specific subject?

And when we look for emerging disciplines one area we see is wind power. This is an increasingly important part of the economy.

Where steam power was an engine of change historically, wind turbines (and other renewable energy technologies) are the new engines of our sunrise industries. We see new high tech companies putting in place power purchase agreements with green energy companies, or investing directly in the construction of wind farms, as they try to be responsible consumers of electricity.

This chart shows the growth in the contribution renewable energy makes to our power generation globally as projected by the International Energy Agency. It is projected to exceed one quarter of the total by 2018. And wind power is making up an increasing proportion of that contribution, and is projected to overtake hydro power by 2020. Indeed in many situations, wind is the cheapest form of generation.

But in many important respects wind power is not like other forms of generation. It is unique. We can’t simply adopt the approaches we have used previously for other forms of generation. Entirely new tools and techniques are required. And why is this? You can consider three categories of generation

1. In the first, you are exploiting a relatively simple resource, possibly some fuel you are burning, and the technology required to do this is also relatively simple, so the overall challenge is itself relatively simple
2. In the second category the technology required is complex, for example a nuclear power plant, and so this entails complex challenges
3. Wind turbines are relatively simple objects by comparison and so historically there was an assumption that the challenges were simple. However we now appreciate that in fact wind belongs to a third category in which the resource itself is highly complex.

The wind is uncontrolled, unlike the resources in the other two categories.

We are not exposing our assets to a well regulated resource being consumed at a constant rate under highly controlled conditions but to a highly variable and intermittent resource, directly exposing wind turbines to an energy flux which varies over 3 or 4 orders or magnitude.

The wind is always trying to break your turbine.

So why bother? Well, wind power exploits a renewable resource. It has no fuel costs.

Indeed, when we consider the other categories of generation - ones that rely on purchasing fuel whose consumption can be regulated and controlled - we see that what is really being purchased is, in a sense, not fuel, but simplicity, or rather, the illusion of simplicity, since the complex challenges of dealing with the environmental impacts of consuming that fuel are deferred, for example, to the end of the project life cycle when nuclear power stations have to be decommissioned, or beyond, when we all ultimately have to deal with climate change. We buy a fuel and control its consumption to enjoy simplicity now at the expense of complexity later.

Wind power requires us to tackle complexity up front, head on, now rather than later, as we use a free but uncontrolled resource. But if we acknowledge anthropogenic climate change and attempt to mitigate its effects, later is now. 

So if we cannot control the wind then we have an urgent need to understand it with precision and detail, so that we can design turbines that withstand the loads it imposes, operate them as efficiently and reliably as possible, and predict as accurately as possible the energy generated.

The investigations and analyses we undertake to achieve this are examples of applied science. The question is do we see a science of the wind emerging from this application?

Do we see the emergence of eolics?

One place to look for clues is in the kinds of measurements that are required. There is no science without measurement. And just as the favoured instrument of the astronomer is the telescope, so the instrument of choice for the eolicist is the lidar.

Where the astronomer infers the velocities associated with the expansion of the universe by making observations of distant stars and galaxies using a telescope, the eolicist infers the wind velocity by observing the motion of tiny microscopic dust particles called aerosols that are present in the lower atmosphere, and are entrained with this wind.

If an astronomer is a star-gazer, then an eolicist is a dust-gazer.

However, the astronomer observes objects that shine with their own light. The eolicist must illuminate the aerosols to observe them. This is done using lasers. The system that delivers the laser emissions for this is a lidar.

Here is an offshore wind turbine and here are lidars installed on it to measure the wind as it encounters and interacts with the wind turbine.

These effectively allow us to see the wind. We can use this to deal with key questions, such as

• How efficiently does a wind turbine extract energy from the wind?
• How much energy does it leave in its wake for the next turbine downwind?
• How do the varying wind conditions affect the wind turbine?

So here is a plan view of the wakes of many wind turbines in a wind farm.

This was acquired by a lidar on the nacelle of the wind turbine I showed you a moment ago. And here is a side elevation of the same thing.

If we look at how the wind speed changes with height at different points in this plot as we move downwind (indicated by the vertical lines) we obtain some interesting results.  We see how the wind differs in front of the first turbine, behind the first turbine, and behind the second turbine. When we compare these different profiles we see an energy gap that develops as we move further and further into the wind farm.

It looks like this is where energy is coming down from above the wind farm to balance the cumulative effects of the wakes of the wind turbines which are extracting energy from the wind within the wind farm.

As we move into the wind farm it interacts with and modifies the wind conditions around it, pulling more and more energy down from above as shown here.  The wake losses of an array of N turbines cannot be considered to be N times the wakes losses of one turbine. The wakes are an emergent phenomena that are a property of the array as a whole.

This may look like a computer simulation, but it is important to remember that these images represent measurements, not simulations, and in a sense this is the point.

In simulations we can capture the physics and the theory of the situation in the models and equations that we solve numerically. The computer models we use embody what we know about gravity, mass and momentum, how buoyancy supports or suppresses different wind conditions (for example, the wake recovery results we looked at a moment ago), how energy dissipates from large turbulent structures down to heat at the molecular scale, and many other considerations. The equations that represent this are solved numerically using computer models and simulations to provide us with predictions.

What these lidar measurements provide are observations whose level of detail and precision for the first time matches the sophistication of the theory. This allows us to select between accurate and inaccurate predictions more effectively than ever before.

theory  +  measurement  =  science  ?  eolics

And when theory and measurement come together in this way the result is science – in this instance, a science of the wind, eolics.

So, just as we saw in the case of thermodynamics, eolics is emerging as a result of its application as the wind industry strives to understand the wind resource and the best way of exploiting it.

So we see the distinctions we make between different sciences are artificial. They don’t reflect an intrinsic underlying structure to knowledge. They arise from the use we make of the knowledge they embody. At a deeper level all sciences are connected. This interconnectedness finds an immediate and compelling manifestation at a local level and an urgent timescale.

Last year the Intergovernmental Panel on Climate Change issued reports warning in the starkest terms so far about the hazard posed to human society by anthropogenic climate change. The concentration level of carbon dioxide in the atmosphere is now the highest it has been for 800,000 years, and this is changing the climate. We are confronted with a significant rise in global temperatures which can only be limited with an immediate expansion of renewable energy generation that consumes no fuel and emits no carbon dioxide as a result.

Where the development of thermodynamics was stimulated by the needs arising from the narrow imperatives of nascent industrial capitalism as it accelerated the rate at which we consume resources and short-circuited the carbon cycle, we now see the emergence of eolics is stimulated by a wholly more comprehensive set of needs that have arisen as a consequence. The needs we must now respond to transcend short term commercial interests, or class interests, or national interests, or even our species’ interest. The needs of the planet as a whole are now paramount.

Industrialisation has catapulted us into a situation where we exceed the carrying capacity of our environment and we can no longer recklessly and unsustainably exploit it. Indeed, recent mathematical models have suggested that the only way to avert disaster is to restore the sustainability of our environmental impacts and reduce the economic inequalities of our societies.  If we want to continue as a society we have to become responsible stewards of the planet we share with each other and temper the trespass we inflict on its habitats.

And, in this, eolicists (that is, the engineers and scientists engaged in the collaborative inter-disciplinary endeavour of making wind power a success), and the investors and the policy makers, and the consumers, have an important role to play.

A science exists because it is needed. And now we need eolics.

(This article is based on a talk given at TEDx UniversityOfStrathclyde on 25th April 2014, accessible here)