Hydrokinetic and ultra-low head turbines in rivers: A reality check

Abstract

Despite a lot of optimism about the potential of hydrokinetic turbines in rivers, the reality is that very few are currently deployed in rivers, delivering power to those who need it. Barriers to their widespread deployment include, above all, the cost per kW actually delivered in rivers which rarely flow at more than about 1 m/s, far short of the 3 m/s at which rated power is typically quoted. Although designers of grid-connected systems aim for maximum annual energy yield, small off-grid systems with limited storage capacity should generally aim for minimum cost per continuous kW delivered. A further factor is that few fast-flowing rivers are deep enough to accommodate axial flow turbines greater than about 1 m diameter. A source of confusion and erroneous power prediction is the mistaken assumption by some researchers that hydrokinetic turbines are “zero head” turbines. Finally, there is a lack of interaction between researchers, who may have the necessary theoretical knowledge but lack awareness of real conditions, and potential users who may have the necessary hands-on practical skills but lack theoretical knowledge. This paper examines these factors, suggests measures to address them and describes a simple low-cost horizontal axis cross flow turbine with much greater swept area and able to generate more power than an axial flow turbine of similar diameter.