Hydrokinetic energy conversion systems and assessment of horizontal and vertical axis turbines for river and tidal applications: A technology status review

Abstract

The energy in flowing river streams, tidal currents or other artificial water channels is being considered as viable source of renewable power. Hydrokinetic conversion systems, albeit mostly at its early stage of development, may appear suitable in harnessing energy from such renewable resources. A number of resource quantization and demonstrations have been conducted throughout the world and it is believed that both in-land water resources and offshore ocean energy sector will benefit from this technology. In this paper, starting with a set of basic definitions pertaining to this technology, a review of the existing and upcoming conversion schemes, and their fields of applications are outlined. Based on a comprehensive survey of various hydrokinetic systems reported to date, general trends in system design, duct augmentation, and placement methods are deduced. A detailed assessment of various turbine systems (horizontal and vertical axis), along with their classification and qualitative comparison, is presented. In addition, the progression of technological advancements tracing several decades of R&D efforts are highlighted.

Introduction

The process of hydrokinetic energy conversion implies utilization of kinetic energy contained in river streams, tidal currents, or other man-made waterways for generation of electricity. This emerging class of renewable energy technology is being strongly recognized as a unique and unconventional solution that falls within the realms of both in-land water resource and marine energy. In contrast to conventional hydroelectric plants, where an artificial water-head is created using dams or penstocks (for large-hydro and micro-hydro, respectively), hydrokinetic converters are constructed without significantly altering the natural pathway of the water stream. With regard to ocean power utilization, these technologies can be arranged in multi-unit array that would extract energy from tidal and marine currents as opposed to tidal barrages where stored potential energy of a basin is harnessed. While modularity and scalability are attractive features, it is also expected that hydrokinetic systems would be more environmentally friendly when compared to conventional hydroelectric and tidal barrages.

In addition to worldwide interest, recent initiatives by North American entities have also seen a greater momentum [1], [2], [3], [4]. Resource and technology assessment by EPRI in US [5], BC Hydro/Triton [6] and NRC in Canada [7] have given newer perspectives of North America’s tidal current energy potential. While a number of projects are being actively pursued, notable progress has been made in Bay-of-Fundy (Nova Scotia) and in Puget Sound (Washington) [8], [9]. Recently (2003–2007), preliminary investigations on the use of hydrokinetic technologies for in-land water resources have been conducted by organization such as, US Department of Energy [10], EPRI [11], Idaho National Laboratory [12], and National Hydropower Association [13]. In response to interests from a number of project developers, US Federal Energy Regulatory Commission (FERC) has stated this technology as of tremendous potential [14]. Also, the US congress has endorsed the Energy Independence and Security Act of 2007 (the “EISAct” [15]) bringing further encouragement to the development of this technology. At the same time various projects and proposals are in place within a number of jurisdictions in North America ([16], [17], [18], [19], [20]).

While the enthusiasm in this field is obvious, skepticism on technological viability is also prevalent. In addition to several fundamental inquiries (resource availability, definition of technologies, field of application, etc.), a number of technology-specific questions (such as, what converter type is best suited, whether duct augmentation is worth attempting, how to place a turbine in a channel) are continuously being put forward. In this paper, based on a comprehensive technology survey, the approach of a number of technology developers as well as R&D institutions are analyzed in light of the questions above. Discussions on performance analysis and modeling issues are beyond the scope of this work and will be addressed through separate publications (such as, [21]). While a complete converter system may incorporate various important sub-systems (such as, power electronics, anchoring, and environmental monitoring, Fig. 1), this work mostly deals with the front-end process of hydrodynamic-to-mechanical power conversion.