Sea breeze, coastal upwelling modeling to support offshore wind energy planning and operations

Abstract

In July 2014, BOEM issued the NJ Proposed Sale Notice of nearly 344,000 acres designated for offshore wind (OSW) energy development. The BOEM lease auction is expected to take place during the current year. The OSW developer(s) who win the lease(s) will submit their development application to the NJ Board of Public Utilities (NJ BPU). These applications must include a wind resource assessment and economic analysis. One major focus in the NJ BPU OSW rules is that applications “shall account for the coincidence between time of generation for the project and peak electricity demand.” Preliminary data analysis shows two mesoscale processes-coastal upwelling and sea breeze-may have a significant impact on wind generation during peak electricity demand. Tasked by NJ BPU, the Rutgers University Center for Ocean Observing Leadership (RUCOOL) is using the Weather Research and Forecasting (WRF) model to resolve these processes and quantify their impact on the wind resource. The WRF model set-up used is designed specifically for coastal/offshore regions, with three pertinent features for these regions. First, innovative satellite sea surface temperature (SST) composites at 2km resolution are used to resolve coastal upwelling. These composites integrate a) our own declouding algorithm set for the Mid Atlantic Bight to remove cloudy pixels from Advanced Very High Resolution Radiometer (AVHRR) SST scans, and b) coldest pixel composites of the resulting declouded AVHRR SST scans, rather than warmest pixel composites that would effectively remove coastal upwelling. Second, microscale grid spacing (<;1km) is used in WRF to resolve the sea breeze circulation, which can vary at meso- to microscales. Finally, validation of the WRF simulations is performed against coastal/offshore wind monitoring sites with atmospheric heights up to 200m, in order to ensure adequate model performance in coastal/offshore conditions. Three main results will be presented in this paper: (i) Coastal upwelling can produce high wind shear (~8 ms-1 across rotor blade dimensions). These significant shear values could potentially pose engineering challenges and should be considered in wind resource assessments. (ii) Lagrangian Coherent Structure (LCS) methodology can be used to identify key boundaries and fronts within the sea breeze circulation. While the onshore component of the sea breeze is well observed, very little is known about its unobserved offshore component, where OSW turbines will be installed. (iii) Power generation from a hypothetical 3000 MW OSW scenario off NJ was analyzed during three different sea breeze cases (one with strong upwelling, one with weak upwelling, and one without upwelling). Significant variability in power production occurred within each case and across the three sea breeze cases (net capacity factor ranged from 1 to 95%). WRF OSW potential power production data are being ingested by an electricity grid model to evaluate the impact of OSW energy penetration into the electrical power grid along with evaluating the economic portion of the applications. NJ is leading development of such an advanced joint atmospheric-economic modeling capability for determining the viability of OSW projects. Ongoing work includes development of a coupled atmosphere-ocean model (WRF-ROMS, Regional Ocean Modeling System), which will provide improved capabilities to diagnose coastal airsea processes (sea breeze and coastal upwelling) for OSW resource assessment (i.e. lowering uncertainty by including relevant mesoscale processes in simulations), and to more accurately predict these processes for operational forecasting during OSW construction and O&M phases.