Brennan T. Smith

Assessment of Energy Production Potential from Tidal Streams in the United States

Tidal stream energy is one of the alternative energy sources that are renewable and clean. With the constantly increasing effort in promoting alternative energy, tidal streams have become one of the more promising energy sources due to their continuous, predictable and spatially-concentrated characteristics. However, the present lack of a full spatial-temporal assessment of tidal currents for the U.S. coastline down to the scale of individual devices is a barrier to the comprehensive development of tidal current energy technology. This project created a national database of tidal stream energy potential, as well as a GIS tool usable by industry in order to accelerate the market for tidal energy conversion technology. Tidal currents are numerically modeled with the Regional Ocean Modeling System and calibrated with the available measurements of tidal current speed and water level surface. The performance of the model in predicting the tidal currents and water levels is assessed with an independent validation. The geodatabase is published at a public domain via a spatial database engine and interactive tools to select, query and download the data are provided. Regions with the maximum of the average kinetic power density larger than 500 W/m2 (corresponding to a current speed of ~1 m/s), surface area larger than 0.5 km2 and depth larger than 5 m are defined as hotspots and list of hotspots along the USA coast is documented. The results of the regional assessment show that the state of Alaska (AK) contains the largest number of locations with considerably high kinetic power density, and is followed by, Maine (ME), Washington (WA), Oregon (OR), California (CA), New Hampshire (NH), Massachusetts (MA), New York (NY), New Jersey (NJ), North and South Carolina (NC, SC), Georgia (GA), and Florida (FL). The average tidal stream power density at some of these locations can be larger than 8 kW/m2 with surface areas on the order of few hundred kilometers squared, and depths larger than 100 meters. The Cook Inlet in AK is found to have a substantially large tidal stream power density sustained over a very large area.

Burden on hydropower units for short-term balancing of renewable power systems

There is a general need to change hydropower operational regimes to balance the growing contribution of variable renewable energy sources in power systems. Quantifying the burden on generation equipment is increasingly uncertain and difficult. Here, we propose a framework combining technical and economic indicators to analyze primary frequency control (PFC) on a timescale of seconds. We develop a model integrating hydraulic, mechanical, and electrical subsystems to characterize efficiency loss, wear and fatigue, regulation mileage, and frequency quality. We evaluate burden relief strategies under three idealized remuneration schemes for PFC, inspired by those used in Sweden, the USA, and China, respectively. We show how burden and compensation vary under future scenarios of renewable power systems. Our framework can be used by producers to develop favorable operation strategies that reduce burden and increase economic value, and by transmission system operators to provide insights on the relation between incentive structures and regulating performance.Quantifying burden on hydropower units for balancing variable renewable energy sources has been uncertain and difficult. Herein Yang et al. propose a framework and characterize the burden, performance and compensation of hydropower regulation of renewable power systems.