Should the Trend of Larger Turbines Continue Offshore? An Analysis of the New York Bight Floating LIDAR
As an industry, we are exceptionally skilled at optimizing energy production of onshore wind farms. But what happens when the wind resource offshore no longer supports our usual tricks of the trade? In this blog, DNV GL explores the energy benefits of utilizing larger rotors and higher hub heights for improved energy capture based on the measured wind resource in the New York Bight.
DNV GL, under contract with New York State Energy Research and Development Authority (NYSERDA) to provide met campaign siting, data management and wind resource assessment services, has conducted a preliminary data analysis of the two floating LiDARs located approximately 70 miles off the Atlantic coast of New York, also known as the New York Bight. The LiDARs will gather data for two years, which will be used to better understand the meteorological and oceanographic (“metocean”) conditions for the development of offshore wind farms. The locations of the floating LiDARs and wind map are shown in Figure 1 below.
Figure 1 – New York Bight Call Areas
Wind resource in the New York Bight
A preliminary analysis of the first seven months of floating lidar data show exceptionally favorable wind speeds in the region – an average of approximately 10 m/s at 120 m. That’s about 20% windier than the average site in Texas and 50% windier than the average onshore site in New York! While these are exciting findings that provide additional evidence of great wind resource offshore, it is important to dive deeper into the data to understand potential nuances of offshore wind resource that may differ from what we’re used to onshore.
Further analysis of the floating lidar data show that measured shear is only 0.10 in the New York Bight. By comparison, typical shear onshore ranges between 0.15 and 0.35. While the low shear is not surprising given the relatively frictionless surface, this made us wonder – will the trend of larger rotors and taller towers that we see onshore make sense offshore?
The case study
Traditionally, increases in hub height have offered two major benefits: higher wind speeds and additional space for a larger swept area. Higher wind speeds have been the priority given the cubed relationship with power production, but as shown in Figure 2 below, marginal increases in wind speed are expected with increases in height in the New York Bight, which relate to minimal power gains with height. The next best option is then to take advantage of the squared relationship of the radius of the swept area to power.
Figure 2 – Normalized wind speed with height
To investigate this further, we compared the energy benefit of increasing the rotor diameter and hub height by 10 m and 15 m, respectively, while keeping the same rated power, in three regions in the US: the New York Bight and onshore sites in New York and Texas. We found meaningful boosts in energy production of 12% and 22% at the onshore sites in Texas and New York, respectively, but only a 6% increase in the New York Bight! The results are summarized in Table 1 below.
Table 1 – Summary of results
Given the relative cost of larger offshore wind turbines, a 6% energy production gain is an interesting twist that reminds us not to underestimate the little guy. As we move to new wind regimes (e.g. offshore), wind developers must do their due diligence during the turbine selection process to account for the unique site characteristics.
Although a bigger turbine at the same megawatt rating may not have the same energy gain pay-off offshore as it does onshore, offshore wind developers will be looking at larger and higher rated turbines to reduce the number of turbines that are necessary to achieve the target project capacity, thereby lowering the overall dollar per megawatt-hour. Stay tuned for the next blog post in this series, where we factor the approximate cost of the wind turbine, tower and foundation of larger and higher rated turbines into the equation.
If you’d like to conduct your own analysis of the New York Bight floating lidar data, they are publicly available through DNV GL’s Veracity platform.
Disclaimer: NYSERDA has not reviewed the information contained herein, and the opinions expressed in this report do not necessarily reflect those of NYSERDA or the State of New York.