ABSTRACT: INVELOX is a wind delivery system suitable for wind power harnessing. One of its innovative features is its capability of incorporating multiple wind turbine generator systems in the Venturi section. INVELOX captures wind flow through an omnidirectional intake or multi-unidirectional intakes and thereby there is no need for a passive or active yaw control to orient the wind turbine. It accelerates the flow within the Venturi section which is subsequently expanded and released into the ambient environment through a diffuser. This allows for harnessing wind power at multi-stages. When two or three turbines are in the Venturi section, the second and third turbine harness the wind power that otherwise cannot be harnessed by the first turbine due to its power conversion limitations. The objective of the present work is to report on measured performance of the system when single, double and triple turbines are placed in the Venturi section. The results show that it is possible to harness wind power using multi-stage turbine configurations, therefore increasing the total harnessed power of the system.
Three turbines were tested to ensure they have identical output when subjected to the same input, environmental, and load conditions. All three turbines appeared to have identical performance. The testing was multi-phased. The successful data from a single turbine in the INVELOX system led to testing two and then three turbines. Data was collected over a 24 month period.
Results for voltage of the two turbine test is above. V1, 12 (red) shows the voltage output of the first turbine generator, V2, 12 (orange) shows the voltage of the second turbine generator. V12 (blue) is the combination of V1 and V2 to represent the total voltage of the system. The addition of the second turbine was found to generate 70% more voltage. It should be noted that the downstream turbine was not expected to harness more that the upstream because the available power in the incoming flow is smaller than in the upstream flow, therefore the total output of the two turbines cannot be more than 2.
Results for voltage of the three turbine test is above. V1, 12 (red) shows the voltage output of the first turbine generator, V2, 12 (orange) shows the voltage of the second turbine generator, V3, 12 (green) shows the voltage of the third turbine generator. V12 (blue) is the combination of V1, V2, and V3 to represent the total voltage of the system. The combination of 3 turbines produced 2.2x the voltage of the single turbine.
The findings of the above graph are very noteworthy. Installing 2 and 3 turbines downstream did not affect or influence the output of the first turbine in any case.
INVELOX: Description of a new concept in wind power and its performance evaluation
INVELOX with No Turbine – In order to compare the field data with those generated by the CFD (Computational fluid dynamics) models; we collected wind speed data when the turbine was not placed inside the Venturi section of INVELOX.
Figure 1 shows the measured free stream and Venturi wind speeds for 24 data sets with Sunforce turbine inside the Venturi section of INVELOX. The instantaneous speed ratio (SR) and average SR are also displayed. It is noted that SR varies from 1.5 to 2.1 with an average value of about 1.8. The SR values are in satisfactory agreement with those predicted by the CFD models. The average mass flow was determined to be about 34.30 Kg/s; this value is in satisfactory agreement with those predicted by the CFD models.
INVELOX with Turbine – Figure 2 shows one of the two fielded demos tested in Chaska, Minnesota in 2012. Pressure and velocity were measured at free stream and right before the turbine inside the Venturi. Five cup anemometers were installed: one was used to measure free stream wind speed at 8 feet above the top of the tower, and the other four were used to measure the wind speed right at the intake (see Figure 2). Four hotwire anemometers were used at the turn of the pipe and three were used at entrance, middle, and exit plane of the Venturi. This set up gave us wind speed data before and after the turbine. At the same location as the wire anemometers, pressure sensors were installed. The diffuser faces north. The INVELOX system was constructed in the Chaska industrial park and is surrounded by buildings. The unit has been tested with four different turbines installed inside the Venturi to date and two more will be tests in 2013. A load bank is used to dissipate the generated energy. The results presented in this paper are from a 3-bladed turbine with power rating of 600W at 12.5 m/s. Sample results are presented.
Table 1 shows the specification of the two systems. As it was pointed out, the turbine, generator, control panel, load bank, all sensors (current, velocity, speed) are all the same for the turbine on the traditional tower and turbine inside INVELOX.
In order to make meaningful comparisons with traditional turbines, additional measurements were carried out by placing the same turbine used in the INVELOX, on top a conventional turbine tower system as shown in Figure 1. The same electrical conversion system and same load bank was used as in the case of INVELOX. Thus, the performance of this set up with the turbine placed on the top of a traditional tower in the same location could be directly compared with the INVELOX data.
Figure 3 shows that higher wind speeds were maintained even when a turbine was placed inside the Venturi section of INVELOX. In addition, recorded data shows that the intake is indeed omnidirectional; the system performs well in all wind directions. Furthermore, Chaska, Minnesota is generally considered a class 1 or 2 wind area which is verified by free stream wind speeds recorded as shown in the figure. However, wind speeds recorded inside the Venturi section of INVELOX show that winds are converted to class 3.
Figure 4 shows the daily energy production improvements of INVELOX with respect to the traditional WTG system. The results show INVELOX generated 80% to 640% more electrical energy than the traditional WTGs. The total energy production of INVELOX over 8 days is about 314%.