Opportunities for and challenges to further reductions in the “specific power” rating of wind turbines installed in the United States

Abstract

A wind turbine’s “specific power” rating relates its capacity to the swept area of its rotor in terms of Watt per square meter. For a given generator capacity, specific power declines as rotor size increases. In land-rich but capacity-constrained wind power markets, such as the United States, developers have an economic incentive to maximize megawatt-hours per constrained megawatt, and so have favored turbines with ever-lower specific power. To date, this trend toward lower specific power has pushed capacity factors higher while reducing the levelized cost of energy. We employ geospatial levelized cost of energy analysis across the United States to explore whether this trend is likely to continue. We find that under reasonable cost scenarios (i.e. presuming that logistical challenges from very large blades are surmountable), low-specific-power turbines could continue to be in demand going forward. Beyond levelized cost of energy, the boost in market value that low-specific-power turbines provide could become increasingly important as wind penetration grows.

The hidden value of large-rotor, tall-tower wind turbines in the United States

“…Note that while the costs associated with the first two transmission needs (spur lines and interconnection costs) are generally borne by wind plant owners, the third category is often socialized, and not paid directly by the wind plant owner. Finally, to estimate the benefits of increased transmission utilization (and so lower transmission build, for a given MWh of wind), we assume an average capacity factor of 42% for the 2018 average turbine and 55% for the low-SP, tall turbine (Bolinger et al, 2021). This results in different estimates of the US$/MWh cost of transmission depending on the turbine employed.…”

“…A typical wind turbine installed in California in the 1980s featured a 0.1 MW generator, a tower height of 18 m, and a rotor diameter (RD) of 17 m. The resulting ''specific power,'' (SP) defined as the nameplate capacity of the generator divided by the swept rotor area of the blades, was 440 W/m 2 . In 2018, the average turbine installed on land in the United States was 2.4 MW in size, with a hub height (HH) of 88 m and a RD of 116 m (Bolinger et al, 2020; see Figure 1 for recent trends). The average SP had fallen to 230 W/m 2 , demonstrating that the wind industry has prioritized blade length and growth in swept rotor area even more than increased nameplate capacity.…”

“…This growth in the size of wind turbines deployed on land has brought many benefits, not least of which has been a progressively lower levelized cost of energy (LCOE) (Bolinger et al, 2020;Wiser et al, 2011). Larger capacity turbines drive lower LCOE by spreading any per-turbine fixed costs-whether upfront capital expenditures or ongoing operating costs-over a larger number of megawatts.…”

“…The result is more megawatt hours of electricity generated per MW of capacity installed, yielding a higher capacity factor. The sum total of these turbine design trends has been a steep historical decline in the LCOE of land-based wind, from the early 1980s to the present (Bolinger et al, 2020;Duffy et al, in press;Veers et al, 2019;Williams et al, 2017).…”

“…Wiser et al (2016) surveyed some of the world's leading wind experts, and found that continued growth in turbine size-capacity, rotors, and towers-is expected to be the single largest driver of LCOE reductions by 2030. More recently, Bolinger et al (2020) employed geospatial analysis across the United States and found that, under reasonable assumptions, turbines sized at 5 MW and with a SP of 150 W/m 2 and a HH of 140 m may have an LCOE advantage of US$6/MWh (on average), when compared with equivalent turbines with a SP rating of 230 W/m 2 . Yet, the degree to which these LCOE advantages are ultimately realized, and at what point turbine size plateaus, will be determined by the success of continued design and materials optimization, by social acceptance and regulatory hurdles, and by the logistical constraints and costs of transporting and erecting even-larger blades, towers, and nacelle components (DNV, 2019;DOE, 2015;McKenna et al, 2016).…”