Performance parameters of Savonius type hydrokinetic turbine – A Review

Abstract

Energy crisis and high emission of fossil fuels are major driving forces for developing renewable energy based technologies. In order to meet growing demand for energy, hydropower can be one of the sustainable alternatives. Further, the hydrokinetic turbine is considered as one of the most emerging technologies which harness energy from flowing water. In this paper, an attempt has been made to review hydrokinetic energy theory for energy conversion system from water currents analogous to wind power system. The most widespread classes of hydrokinetic turbines are discussed in detail with respect to their benefits, drawbacks and desirable conditions for applications. It has been found that in spite of some prevailing downsides of vertical axis turbine like of self-starting and lower efficiency, vertical axis turbines are appealing for many riverine applications. One of the prominent turbines of its kind is the Savonius hydrokinetic turbine that has the capacity to self-start at a very low fluid velocity in the river, canal etc. However, Savonius type hydrokinetic turbine inherently has poor efficiency. A number of experimental and numerical studies with a large number of physical designs and parameters have been carried out in the area of Savonius rotor to enhance its efficiency. Under this study, review of different parameters affecting the performance of Savonius hydrokinetic turbine has been carried out and presented in this paper which may be useful for future studies to improve the efficiency of such turbines.

Introduction

Energy is a significant factor which impacts on the economic and social growth of a nation. Due to increased pace of urbanization and industrialization in the developed and developing countries, energy consumption rate per capita is increasing day by day. The sources of energy are broadly categorized as conventional (fossil fuels) and non-conventional [1], [2]. Fossil fuels are not only limited and inadequately distributed on the earth's crust but are also associated with serious environmental problems [3], [4], [5], [6], [7]. The growth of energy demand and depletion of oil reserve and environmental problems related to fossil fuels as well as rising oil fuel prices are the major issues encouraging the use of renewable energy technologies. Among all the renewable energy sources available, hydropower generation (large and small scale) holds leading position as regards of input to the world's electricity generation [8], [9], [10], [11]. Due to their negative environmental impact, large-scale hydropower stations equipped with large dams and huge water storage reservoirs received considerable criticism [11], [12] while small hydropower (SHP) is regarded as an environmentally friendly technology for rural electrification.

In most of the cases, conventional micro hydro systems work on run-of-river type scheme that lacks the reservoir capacity to store water which causes necessity of backup electricity supply due to seasonal variations resulting in severe output power drop [8], [13]. While conventional hydroelectric technology does well in harnessing the potential energy of water, the kinetic energy of moving water is disregarded. The technique to extract kinetic energy from different water currents such as tidal, ocean, river and irrigation canals is known as hydrokinetic energy technology which is a new category of hydropower energy. It does not require large dams or diverted flow to produce electricity [14], [15], [16], [17]. In order to capture as much potential in water masses as possible with low velocity, large flow openings are required in free flow turbines [18].

Many remote villages might be located in close proximity to rivers with little or no elevation. For such cases, hydrokinetic technology is considered to be suitable to install in comparison to the traditional hydropower generation [19]. High energy density, good predictability and minimal environmental impacts are the key subjects encouraging the use of hydropower technology [20], [21], [22].

The hydrokinetic energy technology may provide inevitable and secured power extracted from free streams. That's why; interest in the development of this technology has been grown-up extensively since the last couple of decades [23]. So far, a number of technological innovation, scientific research and development and the elaboration of public policies have been carried out to insert this Hydrokinetic technology within the rural electrification programs [24]. Due to these efforts, the pilot phase of hydrokinetic projects having an array of full-scale devices was installed in various part of the world. These projects exhibit advantages and disadvantages associated with Hydrokinetic technology. However, Hydrokinetic technology (HKT) has a number of advantages over other renewable sources. One of the most notable advantages is its ability to use existing infrastructure and avoid long-term construction for projects [25]. It leads to the reduction of the installation cost of the small-scale hydrokinetic project and power production starts much sooner than any other renewable sources such as hydro, wind or solar. As huge land is required for other clean energy sources while necessary land is rarely hindrance for the development of hydrokinetic power. The unpredictable or inconsistent output is the biggest hurdle for all other clean energy sources. Conversely, energy from the hydrokinetic source is much more predictable with only seasonal variations (winter) or variations during unusual events such as floods [26]. Canals and controlled rivers are even more predictable and consistent as stream flow are available 24 hours a day with gradual changes as the seasons change. HKT offers unique characteristic of base load power source for a remote community which can provide reliable power for critical applications such as refrigeration, medical, or schooling [26]. This makes hydrokinetic power generation as a strong alternative to meet energy demands of a remote location which improve regional economy [27]. HKT is effective at low water speed even at 1 m/s.

There is no greenhouse gas (GHG) emission and any audible noise at the surface during the operation phase. As a result, there is no anticipated impact quality of life. But there is GHG and atmospheric contaminant emissions during infrastructure manufacturing and installation phase which is one of the disadvantages of HKT [28]. Because of being in the earlier stage of testing, unknown issues i.e. durability of technology and true overall cost arise as a major obstacle to the development of HKT. These unknown issues make investing a risky decision for some business owners. HKT also adversely disturbs environmental issues such as impacts on habitats, flora, and fauna, salinity, dissolve oxygen, faecal bacteria level, sediment transport, seabed scour, structural instability, and disturbance of marine life [23]. As a result of the installation of Hydrokinetic turbine, uses of water body in various activities such as fishing, water sports, coastal tourism, commercial and military navigation, archeological work, communications (submarine cables) and aquaculture are affected and conflict arises between relevant agencies [28]. Due to this conflict, clearance is required from relevant agencies which almost require additional research, time [29].

As per Electric Power Research Institute (EPRI), recoverable hydrokinetic resource of rivers in the USA is estimated as 119.9 TWh per year [30]. EPRI expects that hydrokinetic technology may add 13,000 MW of new generation capacity to the United State by 2025 [31]. The problem associated in this area is its poor conversion efficiency. Therefore, it is a challenge to improve the performance of hydrokinetic turbines. A number of studies have been carried out and are available in the literature. Under the present study, an attempt has been made to review the performance related parameters of Savonius type hydrokinetic turbine considered most suitable under low-velocity water stream.