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Wind turbine generators can use doubly fed induction generators (DFIGs) or permanent magnet synchronous generators (PMSGs) based around Rare Earth metals. This data-file captures the trends in DFIGs vs PMSGs over time by tabulating 40 examples, as turbines have grown larger, and different wind turbine manufacturers have adopted different strategies.

How do wind turbines generate electricity? Both doubly fed induction generators (DFIGs) and permanent magnet synchronous generators (PMSGs) retain a balanced market share in modern wind turbines, converting rotational energy into electrical energy.

For an overview of the different designs, please see our overview of magnets, overview of electricity and overview of wind power-electronics.

This data-file tabulates data into forty recent wind turbine designs, sampling across all of the leading wind turbine manufacturers. We have tabulated the model, manufacturer, country, capacity (MW), year introduced (YYYY), rpm, gear system, typical voltages (kV, where available), generator system and other power electronic details.

Capacity trends. The maximum power capacity for DFIG turbines has been hovering around the 6-8MW mark for the past decade, while the trend towards larger 10-15MW turbines, especially offshore, is almost always associated with PMSG turbines.

Why do wind turbines use Rare Earth magnets? The short answer is that Rare Earth magnets have greater magnetic field strengths (flux densities), which opens up direct drive generator configurations with much lower gearing, and without requiring their own input power supply like the electromagnets in DFIGs do.

Advantages of PMSGs are cited by different operators, including higher >96% efficiency, fault ride-through, lower maintenance, more compact nacelles, easier installation.

Elimination of gears is an advantage for PMSGs as it can help to avoid maintenance issues, which typically costs $40/kW of capacity and 1-2c/kWh on levelized cost. For geared turbines, the gearbox is by far the largest source of maintenance issues (data here).

About two-thirds of the PMSGs in our data-file use direct drive to impart rotation into their power-dense magnets (no gears). Almost all of the IGBT turbines use gears, to step up the rotational speed by around 100:1, on average. Some PMSGs retain gears in order to lower the amount of Rare Earth materials/magnets required by up 90% (e.g. Vestas).

More compact turbines are associated with PMSGs, and this is an advantage, as it lowers the costs associated with wind turbine installation, and faster commissioning.

Fault ride-through is one of the most commonly cited issues for using Rare Earth PMSGs rather than DFIG turbines. A DFIG requires a power connection to magnetize the electromagnets in its rotor. If the power input drops, then the power output also drops.

Chinese manufacturers have been gravitating towards PMSGs especially since 2016. For example when Goldwind switched from DFIGs to PMSGs, the company noted it was able to eliminate 13 gears and “hundreds of parts”.

Vestas and GE have been relatively vocal about benefits of permanent magnets. GE back to 1998 (!). Vestas is now using Rare Earth elements in all new grid turbine models (per the Vestas website here).

Conversely, two other European manufacturers stand out as they have been more reluctant to use permanent magnets, and more focused on DFIG designs, especially in smaller turbines and onshore turbines.

Our forecasts for Rare Earth magnet use in future wind turbine’s bill of materials, both in mass terms (kg/kW) and in cost terms ($/kW) is modelled here.

Underlying data behind these observations is set out in the data-file of wind turbine generators. If you want to understand how magnets in wind turbines work, we recommend our overview of magnets. All of our broader wind research is here.

An offshore wind project is likely to cost $2,500/kW, of which c$1,500/kW is turbines and $1,000/kW is offshore wind installation costs. This data-file aims to estimate the breakdown by vessel type, day-rates and costs per turbine.

Estimates range from 25 to 100 vessels being deployed in the installation of a typical offshore wind project, across different studies and technical papers.

Our base case estimate is that each turbine will require 10 days to install, consuming 100 “vessel days”, of which c10% are highly specialized vessels (data here).

The highest day-rates will be commanded by the most specialized vessels, and we think this includes wind turbine installation vessels, cable lay vessels (both intra-wind farm and for the export cable to shore), and foundation vessels that drive monopiles or jackets/piles into the seabed.

Offshore installation costs are sensitive and can realistically range from $800-2,500/kW, depending on project parameters.

These installation costs come on top of the underlying turbine costs, which we think are usually going to be around $1,500/kW per our cost breakdown of a wind turbine.

Economies of scale are achieved by using larger turbines in larger projects. Conversely, costs re-inflate when moving further from shore and into deeper water.

Please see our broader research into wind and solar and the ramp-up of renewables in our roadmap to net zero.

Please download the data-file to stress-test the numbers and see our estimates for the breakdown of offshore wind installation costs by vessel type.

Wind turbine installation vessels are estimated to cost $100-500/kW in the breakdown of a typical offshore wind project’s capex. Total offshore construction time is around 10 days per turbine. Offshore wind installation vessel time per turbine averages around 5 days per turbine. Data from past projects are tabulated in this data-file.

The average offshore wind project comprises 90 turbines. Hence over the entire course of offshore construction, a full turbine is installed every 10-days on average.

However, over 50% of the time is spent on preparations, foundations, cable-laying and commissioning. The average wind turbine installation vessel installs a full turbine every 5-days.

The numbers vary by project. The best installation vessels operating under the best conditions can install an entire turbine upon pre-laid bases/foundations in a single day.

At the other end of the spectrum, installation can take over ten days per turbine, especially amidst bad weather, delays with parts, mechanical issues, and projects that are a long way from ports.

Offshore wind installation vessel time per turbine? Data on the times taken to install an offshore wind turbine are aggregated across 35 offshore wind projects in this data-file. While the data are interesting, there are few correlations to be drawn between simple headline metrics.

Some eagle-eyed readers will have spotted, in the charts above, that some projects appear to have higher WTIV days per turbine than total construction days per turbine, which seems confusing. The reason is that recent large offshore wind projects will tend to have 2-3 installation vessels operating simultaneously. Thus they can achieve 2-3 WTIV-days of work per calendar day. More vessels will mean faster construction. And probably lower total costs. But it will also require booking out more vessels from the total fleet.

Overall, we think that installation vessels and support vessels could be a bottleneck for accelerating offshore wind. Amazingly, some of the largest projects in the history of the industry had 60 – 100 vessels operating at peak construction activity.

For perspective, recent offshore wind projects likely have total installation costs of $2,000-6,000/kW (offshore wind cost data here, breakdown of turbine cost here). Cost is saved by larger turbines. The other large bottleneck is in downstream power electronics for integrating wind with power grids.

Leading companies in offshore wind turbine installation vessels include DEME, MPI, Van Oord, Cadeler, Eneti (Seajacks), and increasingly, private-equity backed vessels gearing up for an expansion of offshore wind, especially in the US.

We have aggregated the power output and power drops across a month of second-by-second wind data, from a 25MW onshore wind farm in Germany (12 x 2MW turbines). We want to use the data to understand the typical second-by-second volatility of wind power, and what kind of power smoothing will be needed to ramp wind power in the energy transition.

As background, our recent research has evaluated the feasibility of powering real-world grid loads using solar power using a similar data-set quantifying the second-by-second volatility of solar power.

We were hoping that the second-by-second volatility of wind power would be less volatile. However, if anything, wind power is more volatile than solar. Volatility events for wind and solar are similarly frequent, but for wind, they tend to be deeper and last longer.

In the average day, the onshore wind farm that we assessed saw 75 power volatility events, where output fell by over 10% from its trailing ten-minute average level (example below). 40% of these volatility events lasted less than 10-seconds. 80% of the volatility events lasted less than 60-seconds.

What is challenging is that the remaining 20% of volatility events (by number) could often last for hours or even days (see below). Indeed, our data-set includes a four-day timeframe with effectively zero wind power generation (examples in the data-file). By contrast, the sun does tend to rise every day, and generates some power even on cloudy days in the dead of winter.

Wind volatility is also more binary than solar volatility, as is visible in the first chart above. Some striking numbers are that solar output tends to drop off by over 90% from its trailing ten-minute average level an average of 0.02 times per day (i.e., very rarely). Whereas wind output dipped by over 90% below its trailing ten minute average level, an average of 10 times per day (i.e., the wind can stop blowing, entirely, and this occurs relatively often).

Arguably, our data-set is also under-estimating volatility. Some days in our data-file showed very few volatility events, simply because wind output was precisely zero for several consecutive hours (example above). Yes, from a purely statistical perspective, this means that a wind power plant can produce the exact same power output for several hours at a time. But so can a potato.

On the other hand, some of the days with high wind output were significantly more volatile than the average day in our sample. For example, the chart below shows a day where output reached nameplate capacity of 25MW. But this day had 163 ‘volatility events’.

We clearly want to ramp both wind and solar power up as much as possible in the energy transition. But powering real world grid loads with the volatile output from both wind and solar is going to create opportunities and challenges in power grids. We think the best solution that is going to emerge is in power infrastructure, inter-connecting large areas, with resilient and long-distance transmission lines.

Definitions. Our wind analysis defined a “power drop” as a >10% reduction from the trailing 10-minute average wind power being generated at the asset. The power drop’s duration is defined as the number of seconds until output returns to 90% of that previous 10-minute average power output. The average power drop is the average reduction in power output during the duration of the power drop, compared to the prior trailing ten minute average. And the peak drop is the maximum reduction in power output during the power drop, compared to the prior trailing ten minute average.

Data sources. It is surprisingly hard to find good, second-by-second data for large, modern wind farms. However, this analysis has been based on an excellent technical paper and underlying data-set into short-term volatility of renewables. Source: Anvari, M., Lohmann, G. Wächter, M., Milan, P., Lorenz, E., Heinemann, D., Tabar, M. R. & Peinke, J. (2016). Short term fluctuations of wind and solar power systems. New J. Phys. 18, 063027.

Wind power operating costs. A breakdown of wind turbine opex is build up in this data-file, using granular data from technical papers, and our other models.

We think a typical wind turbine costs $40/kw per year to run and maintain, equivalent to 1-2c/kWh of opex, depending on the load factor.

The data-file shows how costs can vary, as a function of inputs. A sensible range is $25-75/kW-year. And the single largest way to lower costs is through up-scaling, spreading relatively fixed costs across larger turbines and larger overall assets. Our recent note on up-scaling wind turbines is linked here.

Wind turbine maintenance market? We estimate that around $25/kW of our cost build-up can be described as ‘maintenance’. Hence across 825GW of global wind capacity (at the end of 2021), the wind turbine maintenance market would be worth >$20bn per year.

This maintenance ‘after-market’ is typically controlled by wind turbine manufacturers. Larger operators can lower costs by self-managing, albeit this comes at the risk of lower uptime.

The data-file includes a build-up of maintenance costs across 19 different categories — drives, generators, hydraulic systems, blades, hubs electricals (chart below)– multiplying their annual failure rates by the sum of their replacement costs (i.e., parts) and the time spent by technicians.

Another surprisingly large cost component is lubricants, around $1-2/kW-year.

Full details on wind power operating costs are split out across 6 tabs, including our highlights from the best technical papers that crossed our screen in the ‘notes’ tab. We have also drawn on other data-files assessing wind turbine capex costs, typical plant sizes, land use, and land costs.

Key conclusions on the opex of a wind power project were also highlighted in a research article sent out in August-2022 to our distribution list.