Roadmap for Small Wind Turbines Deepak Valagam, Technical Director, Vaata Infra Limited, Chennai Introduction With depletion of fossil fuel and ever growing electricity demand, the focus has shifted to renewable energy and small wind turbine is one viable source of energy. The market for small wind turbine (SWT) is gaining global interest. SWTs could be used for residential, commercial and industrial systems. It is seen that the cost of technology, wind evaluation tools and consumer awareness are the driving factors for the future of small wind turbine industry. With the growing concern over the carbon footprint left behind by us in the environment, there is an urgent need for the adoption of renewable energy practices. One such sources of energy is wind power. The extraction of wind energy is done using the Wind Turbines. Wind Turbines are broadly classified into large scale systems and small scale systems. Based on their swept area the international standardization body, the International Electro technical Commission (IEC), defines small scale wind turbines in standard IEC 61400-2 as turbines having a rotor swept area of less than 200, equating to a maximum rated power capacity of 50 KW generating at a voltage below 1000 V AC or 1500 V DC. The small wind turbines are of two types. The Horizontal Axis Wind Turbines (HAWT) and Vertical Axis Wind Turbines (VAWT) Statistics Global installed small wind capacity has already reached 576 MW by 2011. At the end of 2011, a total of 730,000 small wind turbines (SWT) have been installed [1]. The future of the small wind industry depends on the cost of the technology, the enactment of supportive policies and economic incentives, fossil-fuel prices, investor interest, consumer awareness, certification and quality assurance, permitting processes and regulations, and wind evaluation tools. Financial, wind, and energy experts anticipate high growth rates forth production of SWTs if consumer demand increases. SWT Manufacturers by 2011 VAWT (60) 18 % HAWT/VAWT (19) 6 % Data collected from 327 small wind manufacturers from the WWEA Small Wind Manufacturer Catalogue Others (6) 2 % HAWT (242) 74 % 28 Indian Wind Power April - May 2015
The early HAWT technology has dominated the market for over 30 years. Based on the study of 327 small wind manufacturers as of the end of 2011, 74% of the commercialised one-piece small wind manufacturers invested in the horizontal axis orientation while only 18% have adopted the vertical design. 6% of the manufactures have attempted to develop both technologies. As the majority of the vertical axis models have been developed in the past 5 to 7 years, the scale of market share remains relatively small. HAWT STATISTICS Total number of HAWT Manufacturers 242 Total number of HAWT Models < 100 kw 717 Average rated capacity Median rated capacity 10.8 kw 3 kw Percentage of turbines < 10 kw 78.1% Percentage of turbines < 5 kw 66.2% VAWT STATISTICS Total number of HAWT Manufacturers 60 Total number of HAWT Models < 100 kw 157 Average rated capacity 7.4 kw Median rated capacity 2.5 kw Percentage of turbines < 10 kw 88.5 % Percentage of turbines < 5 kw 75.8 % Horizontal Axis Wind Turbines (HAWT) vs. Vertical Axis Wind Turbines (VAWT) Wind turbines come in several forms but are most easily categorized by the position of their axis of rotation relative to the oncoming wind. HAWTs have their axis parallel to the wind direction and are most recognizable as the propeller type wind turbine. A VAWT on the other hand has its axis of rotation pointing in a direction perpendicular to the wind and can resemble an egg beater. While both concepts appear different, they each convert the wind s momentum into a useable torque and are capable of a similar maximum theoretical performance. The VAWT possesses a key advantage in that it does not need to align itself with the prevailing wind direction and can exploit a rapidly changing wind resource which is otherwise difficult for a HAWT to operate in at high efficiency. A lot of debate has been going on over which is the preferable choice for the small scale application, the HAWT or the VAWT. The turbine also permits mounting of generator and drive train at ground level. These characteristics of VAWT offer high functionality in the small scale localized usage of VAWT for power generation. Moreover, while the HAWT has a negative sensitivity to yawed flow conditions (Off axis), the VAWT actually has a range of positive sensitivity to skewed flow. Market Forecast: What is seen today as big wind started in the size which is today defined as small wind. Until mid 1980 s most of the turbines had a capacity less than 100 kw. Most common applications of small wind turbine include: ² ² Residential ² ² Commercial & Industry ² ² Hybrid systems ² ² Pumping ² ² Desalination ² ² Research & Education ² ² Telecom base stations Majority of the wind turbines installed are a grid-tied system with larger capacity. On the other hand, off-grid applications continue to play an important role in remote areas of developing countries. Off grid applications include rural residential electrification, telecommunication stations, off-shore generation, and hybrid systems with diesel and solar. Introduction to VAWT Figure 2: Typical HAWT There are different configurations of VAWT. The major classifications of VAWT in small scale are the Savonius type and Darrieus type. a. The Savonius Type: The Savonius type wind turbine is a class of VAWT invented by the Finnish engineer Sigurd Johannes Savonius patented in 1931. The turbine as shown in figure 3 mainly operates on the principle of drag force. The differential drag causes the Savonius turbine to spin. But one of the major drawbacks of the Savonius turbines is the negative drag exerted on the convex side of the blades. The torque of the rotor varies through a single rotation thus affecting the selfstarting of rotor at different wind angles. April - May 2015 Indian Wind Power 29
Based on the different requirements in initial design phase of wind energy conversion systems (WECs), three main requirements functional requirement, performance requirement and constraints are used. For the trade-offs between the different designs options in order to choose the most suitable solution for the specific application, it is necessary to establish trade-off criteria. In other words, weight factors should be assigned to describe the importance of each requirement during the design phase selections. For the requirements with biggest importance a value of 10 is given, with medium importance are assigned a value of 8 and so on. Trade-off criterion Weight factor HAWT VAWT Figure 3: Schematic of Two-scoop Savonius type VAWT b. The Darrieus type: This type is patented in the year 1931 by Georges Jean Marie Darrieus, a French aeronautical engineer. The full layout of the turbine as shown below is lift based i.e. the rotor movement is caused by the lift forces acting on the blades. This can be further classified into curved and straight bladed type. Straight bladed have span of blade aligned with axis of turbine, whereas curved bladed do not have. Efficiency 8 9 Considered more efficient Availability 8 10 Technologically more mature Safety 10 6 Blades anchored in one point 7 8 9 Blades anchored in two points Noise 10 8 10 Operation in lower tip-speed ratios Omnidirectional Skewed flow 8 4 Need yaw system 8 4 Reduced efficiency in skewed flow 10 Omni directional operation 10 Increased efficiency in skewed flow Aesthetics 6 6 10 Self-start 8 10 4 Not able to self start Risk 10 8 Mature technology 4 Further research neededcomplicated aerodynamics Total score 65 72 Figure 4: Schematic of Darrieus type VAWT Figure 5: WECs Trade-off Criterion [2] 30 Indian Wind Power April - May 2015
Research & Development on VAWT Sandia National Laboratories in New Mexico is also conducting a research on evaluating feasibility of VAWT architecture for large scale deployment in offshore environment. One of the project s lead researcher claims, total estimated reduction in COE from the baseline work is 28%. The most important COE reduction categories are the increased annual energy production and reduced operations and maintenance, support structure, and balance-of-system costs. According to Sandia s findings, road to success of VAWT lies on reliability and performance of VAWT. Several areas have been identified for R&D on VAWT, ² ² Reduce cost ² ² Reduce manufacturing cost ² ² Improve reliability ² ² Power Electronics ² ² Reduction in noise ² ² Improved analytical tools ² ² Distributed generation applications ² ² Improved control theory. In India, VAATA is a company that takes up Research & Development in VAWT. It is developing a wind turbine that goes beyond just being efficient and cost effective to be planet-friendly, across sectors as diverse as recyclable energy and household care. With a goal of transforming extant realities in rural areas in India drives to create products to alleviate problems, like infrastructure limitations, faced by agriculturists/farmers. It focuses on making energy available to farmers for their lifestyle development. Small Art, shortly known as SMART is a small 15 kw VAWT developed from scratch, completely in-house. The main objective of SMART is to provide a low-cost, sustainable and reliable source of energy and income for farmers and rural dwellings. With such intent, Research & Development of this VAWT turbine has been going on for more than 4 years at their R&D centre and they have now reached their goals. Prototype turbines are running in two sites in Tamil Nadu. Also, it can be put in Hilly Terrain and Remote Islands where bigger wind turbines cannot reach. Thus, replacing the need for diesel generated power. SMART is designed for infill within existing wind farms, providing power to rural dwellings and cell-phone towers in remote areas. Several other global research programmes are under study and some are already prototyped for offshore environments. Noticeable among are, Project INFLOW is carried under the 7th European framework for wind energy. The project is a Floating Vertical Axis Wind Turbine (VAWT) with sophisticated semi-submersible platform for offshore environment. Project Deepwind is under research by the European Framework for Energy. The proposed Darrieus 5 MW floating offshore wind turbine concept consist of a long vertical tube that rotates in the water, a vertical axis rotor at the top, a bottom based generator and a sea-bed fixing system at the bottom rotates. April - May 2015 Indian Wind Power 31
Growth in Size of Wind Turbines Figure 6: Growth in Size of Wind Turbines since 1980 and Prospects Wind energy is developing towards a mainstream, competitive and reliable power technology. Globally, progress continues to be strong, with more active countries and players, and increasing annual installed capacity and investments. India and other developing countries in Asia emerge by 2020 as an important market. Adapted from EWEA, 2009 the figure 6 shows Growth in size of wind turbines since 1980. The key point to be noted is scaling up turbines to lower costs has been effective so far, but it is not clear if the trend can continue forever. Hence need for small wind turbines which are highly reliable and robust have already emerged and will become more evident in the near future. Economics of Wind Energy The levelised cost of energy (LCOE) is the primary metric for describing and comparing the underlying economics of power projects. For wind power, the LCOE represents the sum of all costs of a fully operational wind power system over the lifetime of the project with financial flows discounted to a common year. The principal components of the LCOE of wind power systems include capital costs, operation and maintenance costs and the expected annual energy production. Assessing the cost of a wind power system requires a careful evaluation of all of these components over the life of the project. The capital costs and the cost of the energy produced by small wind turbines are still higher than large-scale wind turbines (AWEA, 2011 and IEA Wind, 2010). The cost of small wind turbines varies widely depending on the competitiveness of the market and factors affecting installation, but costs for a well-sited turbine tend to range between USD 3 000 to USD 6 000/kW. The average installed price of a small wind turbine system in the United States Figure 7: Typical Cost of Wind Energy, IRENA Wind Power Report 2012 is USD 4 400/kW and USD 5 430/ kw in Canada (AWEA, 2011 and CanWEA, 2010). Costs are significantly lower in China, and range between USD 1500 to USD 3000/ kw depending upon the quality and reliability. The LCOE of small wind is in range of USD 0.15 to USD 0.35/kWh (IEA Wind, 2010), estimated operations and maintenance (O&M) costs range between USD 0.01 to USD 0.05/ kwh (AWEA, 2011). It is worth mentioning that through continuous Research & Development, the capital cost and cost of energy production can be significantly reduced. References 1. Small Wind World Report 2013, by World Wind Energy Association. 2. Systems and Knowledge Engineering Design of a Urban Vertical Axis Wind Turbine - Charilaos Kotsarinis TU Delft, 2009. 32 Indian Wind Power April - May 2015