The physical ceiling for innovation is here.
An unfounded statement, yet one that has been used time and time again - and often to the chagrin of the naysayers!
However, the ability to meaningfully increase the efficiency of wind turbines through technological innovation are physically impossible to continue.
All forms of energy are subject to physical limitations.
Solar has its physical limitation - the Shockey Queisser (SQ) Limit - though is far from being reached based on today’s commercial solar cell efficiencies.
Oil and gas are also limited in their efficiency. Aside from the extraction, processing, transportation, and refining process, its combustion in an engine or plant extracts only a portion of that fuel’s energy potential - known as the conversion efficiency.
Fossil fuel plants cannot run at 100% efficiency due to the Carnot Efficiency Limit, with energy lost as waste heat during the conversion of heat into mechanical work.
The future ubiquity of renewable energy is entirely based on forecasts that assume innovation will continue to run on an exponential growth curve. A dangerous assumption to make in the face of these physical limitations.
Just as with fossil fuel plants and solar cells, wind turbines encounter a physical limitation too - The Betz Limit. With every gust of wind, they approach an abyss, nearing the final state of maturity.
Imagine fading Newton?
Betz Limit - derived from Newton’s Law of Motion - states that wind turbines cannot convert > 59% of the wind’s kinetic energy into electric energy.
Let’s keep it simple. A turbine, which captures energy from the wind, cannot ‘grab’ all of that energy. As the wind passes through the turbine blades, it gets slowed down, causing a kind of ‘traffic'.’ This means there’ll always be some energy left in the wind that the turbine cannot catch.
A 59% energy conversion efficiency would not be bad compared to other forms of energy. It would place wind 3rd in the below chart’s list of capacity factors.
But keep in mind - wind will only generate electricity ~35% of the day given its intermittency - meaning the wind doesn’t always blow. This is unlike nuclear, geothermal, and to a lesser extent natural gas plants which provide a more reliable stream of energy.
So, why is a 59% conversion efficiency problematic for wind turbines? Wind turbines in 2023 have achieved efficiencies of nearly 50%, so any incremental improvement in technological efficiency won’t be enough to move the needle in terms of economic viability.
Even at the impressive 50% conversion efficiencies wind turbines have achieved today, they’re still not economically sustainable. The sheer amount of raw material needed to be mined, processed, refined, constructed, transported, operated, and dismantled requires a lot of energy.
Surprise! More EROI talk
The energy generated wind turbines are only slightly enough to offset the energy needed for the manufacturing and dismantling processes.
Because wind is intermittent in nature, a battery storage facility is needed to “bank” excess energy generated from the turbines during nighttime - when wind is at its strongest - to smooth out the electricity dispatch to demand centers overtime.
The inclusion of a battery storage system, which has its own complex and energy-intensive supply chain, only adds to a wind plant’s economic woes.
Some say that over the the Energy Returned on Energy Invested (EROI) of a wind plant + battery system is about 7:1.
(Natural resource investors Goehring & Rozencwajg have suggested this could actually be closer to 2.5x)
In other words, the energy generated by a wind turbine is 7x the amount of energy that was put into its creation. We talk about the concept of EROI and at length here and here given its fundamental nature and utmost significance in extrapolating the potential realities of transitioning to lower EROI energy sources.
An EROI of 7:1 may sound like a lot - but 7x is actually just below the EROI threshold on the “Net Energy Cliff” chart (Mearns 2008).
Studies have shown that an EROI of 8x is about the minimum level of energy return we need from an energy source to maintain a functional and sustainable society.
Perspective: Foragers were estimated to have an EROI of about 10x. This was enough to innovate, evolve, and achieve higher quality of life - albeit over a VERY long period of time.
Therein lies wind energy’s fatal limitation. Going from a 50% efficiency to 59% will not move the needle much in terms of achieving an EROI necessary for continued prosperity and increasing quality of life.
On the brighter side..
Recognizing the dangers of putting limits on human ingenuity and innovation, there could still be many ways in which wind energy’s EROI increases despite Betz Law’s limitation. And that is by improving the efficiencies of the mining, manufacturing, processing, refining, and transporting of the raw materials used to build the wind turbines.
Significant efficiencies in this area would make a substantial impact on wind turbine’s long-term economic (and societal) viability, as well as other energy sources and processes.
This is, in fact, where most of the focus has been directed - towards lowering material costs, adjusting blade lengths, optimizing turbine distance etc. to get system level costs as low as possible.
Again, this shift in focus towards lowering input costs is because modern turbine designs have evolved enough to be bumping into the physical limitations of Betz Law.
Until significant progress can be made in enhancing the process of material extraction and refinement, wind turbines will continue to be subsidized heavily to ensure economic viability.
Unresolved Enigmas Remain
How long can subsidies occur before inflationary pressures redirect capital towards more promising energy sources?
Can significant efficiencies in the supply chain process materialize enough for wind generation to stand on its own?