A Metric Space with LCOE Isolines for Research Guidance in wind and hydrokinetic energy systems

Abstract

This paper introduces a new Metric Space to guide the design of advanced wind energy systems and hydrokinetic energy converters such as tidal, ocean current and riverine turbines. The Metric Space can analyse farms that combine different or identical turbines and stand-alone turbines. The first metric (M1) of the space considers the efficiency of the turbines in the farm, which is also proportional to the specific power per swept area at a given wind/water velocity (W/m 2 ). The second metric (M2) describes the specific rotor area per unit of mass of the turbines (m 2 /kg). Both metrics depend on the primary design characteristics of the turbines, such as swept area, system size and mass, materials and efficiency, and are independent at first from external characteristics, such as atmospheric and ocean site conditions, cost of materials and economic factors. Combining both metrics, and for a given set of external characteristics, the resulting Metric Space M2/M1 displays the Levelized Cost of Energy (LCOE) standards as isolines. This graphical representation provides a quick understanding of the cost and state of the technology. It also offers a practical guidance to choose the research tasks and strategy to design advanced wind and hydrokinetic energy systems. The paper applies the new Metric Space to several case studies, including large and small onshore wind turbines, floating and bottom-fixed offshore wind turbines, downwind rotors, multi-rotor and hybrid systems, airborne wind energy systems, wind farms and tidal energy converters. KEYWORDS hydrokinetic energy systems, Levelized cost of energy, performance metrics, research strategy, tidal energy systems, wind energy systems, wind farms, wind turbines | INTRODUCTIONMetrics play a critical role in research and technical innovation. Optimal and practical metrics are often not easy to find. When found, they certainly help to quantify the performance of the technology and to discover new ways to improve design and operation.Over the last few decades, the Levelized Cost of Energy, or LCOE, is been used to characterize the technical capabilities and economic opportunities of wind and water energy systems. The LCOE has shown to be particularly useful for selecting the site between different options for a given wind or water turbine technology, and for comparing different technologies at the same point in time, avoiding the dependence of economic factors on the temporal variability. Every year, international agencies and centers publish detailed reports of the LCOE achieved by wind and water energy systems over different regions and countries in the World. As described in these annual reports, the LCOE for onshore wind energy systems has been constantly reduced, from over $0.60/kWh in the early 80s to $0.03-0.05/kWh at the end of 2018.

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