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Efficiency

A wind turbine is a relatively simple concept, a motor is spun by the force of the wind and this in turn generates electricity. It’s of course a little more complex than this, but that is enough to get the basic idea. Next we an take a look at efficiency:

Accordingly, Betz’s law gives the maximal achievable extraction of wind power by a wind turbine as 16/27 (59.3%) of the rate at which the kinetic energy of the air arrives at the turbine.

It’s worth noting this is not really a bad thing at all. 100% conversion would mean zero wind speed after reaching the turbine, which could have a dramatic impact on the environment, etc. It would also mean it wouldn’t be possible to have them so close to one another.

Wind-to-rotor efficiency (including rotor blade friction and drag) are among the factors affecting the final price of wind power. Further inefficiencies, such as gearbox losses, generator and converter losses, reduce the power delivered by a wind turbine. To protect components from undue wear, extracted power is held constant above the rated operating speed as theoretical power increases at the cube of wind speed, further reducing theoretical efficiency. In 2001, commercial utility-connected turbines delivered 75% to 80% of the Betz limit of power extractable from the wind, at rated operating speed.

As you can see, higher wind does not equal higher return, only higher wear on the turbine parts. There is also some inefficiencies that simply cannot be removed from the system. 75% - 80% of the theoretical upper limit of energy conversion seen in the field is highly impressive. Bare in mind, some of the most efficient engines out there only see numbers like 50% efficiency in normal operating conditions.

Analysis of 3128 wind turbines older than 10 years in Denmark showed that half of the turbines had no decrease, while the other half saw a production decrease of 1.2% per year.

It’s quite interesting to see that there appears to be some form of degradation in operating performance over time, similarly seen in solar power. Something like nuclear power or fossil fuel power stations will pretty much provide just as much power year after year (within limits). Part of this is because they are simply more maintainable and the conditions they operate under are more controllable. Wind turbine are typically hard to repair (and this has knock-on effects we will discuss later).

Infrastructure

One issue with building wind turbine farms offshore is that there is no existing infrastructure out there. These farms are generating many megawatts or electricity and this needs to make its way inland with massive copper cables. These is resistance in these cables and therefore a voltage drop, further increasing inefficiency.

Wildlife

Unfortunately wind turbines have been shown to negatively impact some wildlife:

Environmental impact of wind power includes effect on wildlife, but can be mitigated if proper monitoring and mitigation strategies are implemented. Thousands of birds, including rare species, have been killed by the blades of wind turbines, though wind turbines contribute relatively insignificantly to anthropogenic avian mortality. Wind farms and nuclear power stations are responsible for between 0.3 and 0.4 bird deaths per gigawatt-hour (GWh) of electricity while fossil fueled power stations are responsible for about 5.2 fatalities per GWh. In 2009, for every bird killed by a wind turbine in the US, nearly 500,000 were killed by cats and another 500,000 by buildings.

Compared to other energy generation methods, the impact on wildlife can be said to be better, but still not ideal.

End of Life

Another consideration is the carbon emissions generated during the production of these massive structures. They have to operate some time before they are carbon-neutral. As many of the parts cannot be recycled, this is a carbon cost that must be considered when considering their ‘green’ nature.

In Germany, wind turbine blades are commercially recycled as part of an alternative fuel mix for a cement factory. In the USA the town of Casper, Wyoming has buried 1,000 non-recyclable blades in its landfill site, earning $675,000 for the town. It pointed out that wind farm waste is less toxic than other garbage.

When decommissioning the wind turbines, it is important to consider that some parts can simply not be recycled, such as the blades. They are often made of some glass composite material and therefore cannot be easily handled either. The only real safe way to deal with them is to bury them or embed them in some material.

Cost

As Wikipedia suggests:

As of 2019, a wind turbine may cost around $1 million per megawatt.

This includes labour costs and material costs, both of which are difficult to reduce further given location and complexities regarding optimal location for wind power generation. These locations can often be inaccessible, if by altitude alone.

This all of course has a cost to energy consumers:

In 2015, it was estimated that the use of wind power in the UK had added £18 to the average yearly electricity bill.

I believe one misconception that is often thrown out there is that renewable energy is somehow a one-time investment into infinitely cheap future electricity. This simply is not true. Renewable energy will be an indefinitely increased cost to the bill/tax payer. As the UK and other Countries switch to renewable sources of energy, their energy costs will increase, not decrease.

Capacity

Of course one major issue with wind generation is meeting the demand, with other less efficient sources being used to make up for demand differences:

In August and September 2021, the UK had to fire-up coal plants, amidst a lack of wind, as power imports from Europe were insufficient to satisfy demand.

Wind generation is very good when it is available, but wind cannot be relied upon to be available at all times. Energy from storage makes up just 0.5% of UK power - which is not even close to being sufficient to make up for dips in wind-based energy production.

Putting more stress on the electric grid demand will be electric vehicles, which could easily see electricity use jump by magnitudes. Ironically, electric vehicles may also be the solution, with massive batteries being attached to the energy grid in a decentralized manner, they could equally be used to pump energy back into the grid at optimal times to make up for generation shortages ¹.