New Berkeley Lab study finds a dramatic increase in estimated project output coupled with a decrease in surrounding sound levels for future turbines as compared to those installed in the past.
Multiple technological, social, and market factors of wind power are evolving rapidly. Most notably, significant wind turbine scaling in height and size is occurring and is forecasted to continue. While the larger turbines expected to be deployed in the future are more powerful and efficient, they are also expected to operate with higher sound emissions than those installed in the last decade. Due to their taller heights, larger rotors, and higher sound power levels, future wind turbines will require larger setbacks from homes and greater inter-turbine spacing, resulting in fewer turbines deployed for a given land area. These competing technology and siting trends - and their associated impacts - are not well understood.
The new Lawrence Berkeley National Laboratory analysis “Effects of land-based wind turbine upsizing on community sound levels and power and energy density” simulates the development of 22 unique projects at two different prototypical sites using eleven different wind turbine models to extract output, nameplate capacity, numbers of turbines and receptor sound level patterns between projects using older, current, and future turbine models sited within a fixed land area.
The study, published in Applied Energy in open-access format, is available here. The authors will host a webinar covering the results of the study on April 13, 2023, at 1 PM Eastern / 10 AM Pacific. Register here: https://lbnl.zoom.us/webinar/register/WN_ljqJqmyWQEaSl0nC99kDdQ.
A summary of the key findings follows:
The analysis finds, unsurprisingly, future turbines are more than 60% taller than those installed most frequently in the last decade. Relatedly, 60% fewer turbines are expected to be able to fit in the same land area in the future as they were in the past.
From the Then period (using the most frequently installed turbines in the last decade in the US, 2011-2020) to the Future period (turbines that are expected to be installed in the next three to five years, 2023-2025), wind turbine heights are expected to increase an average of 60%, from 122 m to 202 m (Figure 1). This increase in turbine total height, coupled with larger rotor diameters and sound power level increases, decreases the number of turbines that can be developed in the fixed land area at our two prototypical sites. Accordingly, the average number of turbines decreases by 60% (from 222 to 89) at those sites. (See Figure 1 caption for more details on periods.)
Despite fewer turbines, plant layouts using future turbines result in projects with higher installed capacities and annual energy output for a given land area.
Despite 60% fewer turbines for the given land area at the two sites, the total installed nameplate capacity for Future projects increases by roughly 11% (from 395 MW to 437 MW), and estimated annual energy output increases by almost 60% (from 1,146 GWh/yr to 1,825 GWh/yr) over the Then period. These average trends are shared among all the manufacturers and across both sites, with some variation in the size of those trends (not shown). These output increases are driven, in large part, by significant increases in rated capacity and efficiency of the turbine models used in the Future period.
Community sound levels at homes are expected to be significantly lower in the future, despite overall louder turbines.
Even though serrated trailing edges (STE), which lower sound levels by approximately 1.5 dBA, are expected to be applied to the blades of all future turbine models, turbine sound levels (at the hub) for Future turbines are higher (105.3 dBA) than for Then turbines (104.3 dBA). Despite this predicted increase, sound levels at homes surrounding the turbines are estimated to be 18% lower in the Future period. This decrease is the result of increases in setbacks from the homes which scale as a multiple of turbine height and a factor of turbine sound power, as well as fewer wind turbines being constructed in the same land area.
Figure 1. Mean total wind turbine height, numbers of wind turbines, total project capacity, project output, and loudness among the periods examined. Those periods were chosen to represent, respectively; Then: turbines most frequently installed in the last decade in the US (2011–2020); Now: turbines most frequently installed in the last two years in the US (2019–2020); and, Future: turbines most likely to be installed in the next three to five years in the US (i.e., 2023-2025). All Future turbines are expected to have serrated trailing edges to reduce sound levels (STE), so separate projects were designed using turbines representing the Now period with STE (Now with STE) and all Future turbines contain STE to align with manufacturer expectations.
These lower sound levels occur not only for homes neighboring projects, but also those very close to turbines on parcels hosting turbines.
A commonly mentioned potential nuisance for homes very near wind projects are turbine sounds. Yet our research finds that average estimated receptor sound pressure levels (SPL) (a measurement of what neighboring home inhabitants might hear) surrounding the projects in all periods show consistent decreases from those estimated in the Then period (Figure 2). This is especially pronounced for the Future period, where decreases are between 1.5 and 3 dB. Participating homes, which are located on parcels where turbines can be hosted, tend to be closer to wind turbines and are also subject to higher noise limits when designing the projects relative to non-participants’ homes. But, our research finds a reduction in SPL in all periods occurs for those homes, as well as their nonparticipating neighbors. This implies that future turbines might significantly reduce a common potential nuisance.
Figure 2. Average change of overall A-weighted sound pressure levels (SPL) measured are receptor homes referenced to Then (i.e., starting) SPL by participation. Nonparticipants, those near the projects, are shown as solid lines and participants, those with parcels where turbines can be located, are shown as dashed.
Myriad other benefits appear likely as a result of increased adoption of taller higher capacity turbines in the future.
Because of their increased size, turbines installed in the future will be situated further from homes and property lines given often required setbacks based on total height. Additionally, fewer turbines used for future projects might provide enhanced flexibility as to where turbines are placed on the land, therefore, potentially, creating greater opportunity to avoid sensitive viewsheds. Further, higher project capacities and output could lead to higher local economic benefits (e.g., taxes and income).
A number of areas for future research are suggested such as: examining aesthetic tradeoffs of fewer larger turbines vs. more numerous smaller turbines; the need to examine outcomes at other sites (ridgelines and alternative wind regimes); and, the value of conducting economic analyses using turbines to be installed in the future.
We thank the U.S. Department of Energy’s Wind Energy Technologies Office for their support of this work, as well as the numerous individuals and organizations who generously provided data, information and reviewed our study.