wind turbine is a device converting wind energy into useful power. There are two technologies of wind turbines: horizontal-axis wind turbine (HAWT) and vertical -axis wind turbine (VAWT). In a HAWT, the turbine shaft axis is parallel with the ground. While in a VAWT, the turbine shaft axis is perpendicular to the ground. Both turbines are shown in Figure 1.
Except the difference of the wind flow direction with the shaft axis, HAWTs and VAWTs have some differences and impacts in construction, economy, and environment. In HAWTs, the huge towers and large blades result in a high cost and trouble in the environment. After several decade of developments, HAWTs are becoming the bigger and the taller. The huge HAWTs are not suitable to locate in the areas of metropolitan, community, and resident, etc. Therefore, VAWTs become more attractive and practical in such areas. VAWTs are more convenient for installation and maintenance in which the electric system is on the ground. A summary of major differences between HAWTs and VAWTs are shown in Table 1.
From Table 1, it can be seen that HAWTs have advantages of efficiency and commercial availability;
VAWTs, however, have the advantages which can compete with HAWTs, in application location, environment effect, etc.
Figure 4 shows some locations and areas being suitable for VAWTs application. In 2010, two VAWTs were successfully installed on the Eiffel Tower, Paris, shown in Figure 5. They were installed 400 feet up on the 2 nd tower level and provided 10,000 kWh of green electricity each year. It was an iconic application of the VAWT.
© 2020 Global Journals
Most of VAWTs have unique characteristics: replaceable and stackable. The replaceable characteristic allows an existing VAWT to be altered to another type amazingly and the stackable characteristic lets the VAWT be upgraded conveniently to meet the load requirements. Figures 6 and 7 illustrate the two characteristics, respectively. A Novel Design of VAWT Green power tower (GPT), a novel VAWT design, is developed. The GPT is a stackable type and has no exposed rotating components.
Figure 8 shows the configuration of the GPT. Air stream horizontally blows into the channels to drive the shaft by rotating turbine blades. The air stream will flow out on the top of the GPT. The GPT is packable and can have multiple levels to meet the power requirement. The shaft at the tower center drives the electric generator on the bottom. To evaluate the performance of the GPT, the scaled prototypes were built and tested with different wind blades. Figure 9 presents the tests conducted in the wind tunnel and at the site, respectively. At the site tests, the GPT was installed on the top of the moving vehicle. The driving speed of the vehicle is the velocity of the wind blowing. Where P out -power output from a wind turbine (kW) P in -thepower of the wind (kW), P in = ??d 2 v 3 /8 ? -density of air (kg/m 3 ) d -diameter of wind turbine (m) V -electrical voltage generated by a wind turbine(V) I -electrical current generated by a wind turbine (A)
In the test, both V and I were measured by a multimeter, respectively.
The tests were performed for both GPT and HAWT for comparison. The prototype data are listed in the following Table 2.
Test results of GPT performance and comparison are shown in Figure 10. The tests revealed all VAWTs performance were better than HAWTs. GPT-2 output power is about 200-250% higher than HAWT-2. These two prototypes are equivalent in terms of the swept area. The difference is about 104% when GPT-1 and HAWT-1 are compared, although the swept area of GPT-1 is about 44% smaller than HAWT-1. It can also be observed that higher wind speed leads to a bigger gap between GPTs and HAWTs.
C p converges on higher wind speeds. In lower wind speed, GPT with more levels outperforms the fewer number of levels, which was expected. There is also an irregular jump in GPT-1 for low wind speeds, which could be explained by the different cut-off speed of the system when there is only one level of GPT. The difference between GPT-2 and HAWT-2 in terms of C P when wind speed is about 30 mph, is about 250%, where GPT-2 has a better performance.
The test data also indicates the in low wind speeds GPT-1 can have a better performance compared to the horizontal propeller of GPT, although in higher wind speeds it shows a negative impact. It seems that VAWTs with small length blades have better performance and efficiency than HAWTs, which maybe be a reason HAWTs need large size and get larger and larger.
Large HAWTs may have more efficiency than VAWTs. Large HAWTs are more attractive in the application of wind farms in which large open area is available. Further study will be necessary to help with this evaluation.
The GPT has all advantages and characteristics of the VAWT. Also, the GPT doesn't have exposed rotating parts. All rotating parts are covered in enclosures. Therefore, the GPT is much safer than other VAWTs. The GPT can have many applications, for instance, on buildings, towers, and bridges, including wind farms. Some of the application is illustrated in Figure 11.
Comparing to HAVTs, VAWTs have advantages of without long length blades and giant towers and no needing large open areas so that VAWTs can be applied in the areas, such as metropolitan, community, and resident. In the areas, VAWTs not only can efficiently utilize the wind energy but also may have cosmetic effects for the buildings and surroundings.
Most of VAWTs have unique characteristics: replaceable and stackable. The replaceable character allows an existing VAWT to be altered to another type amazingly and the stackable character lets the VAWT be upgraded conveniently to meet the load requirements. The GPT, a novel VAWT design, has no exposed rotating components which are completely covered in enclosures. The GPT prototypes were tested and the performance was significant, which showed the GPT could extract more wind energy comparing to the similar size HAWTs. The novel VAWT can have many potential applications, such as on buildings, towers, and bridges, including wind farms.
Renewable Energy: The Next Generation of Wind Turbine Technology. Thesis of Master Degree, December, 2017. New York Institute of Technology (NYIT
Vertical-Axis Wind Turbine (VAWT) and Its Uniques. Annual Seminar of Engineers Joint Committee of Long Island (EJCLI) February 13, 2019.