A Novel Design for a Solar PV-Wind Hybrid System to Improvise Renewable Energy Harnessing – a theoretical study on Indian Subcontinent

Inherently variable nature of renewable sources of energy such as solar and wind, are incapable of meeting continuous supply demand. Combining solar photovoltaic (PV) and wind power could offer a feasible solution to the problem of continuous power supply, particularly in those geographical locations where both resources are available in abundance. The present paper investigates the solar and wind energy potential in Indian sub-continent. The feasibility of harnessing renewable energy per sq. meter of land (i.e. energy density) from a combined solar PV-Wind hybrid system in the selected location Jaisalmer in Rajasthan, is reported. The solar irradiance and wind velocity data for the last three decades for the selected site is collected using PVsyst software. A novel design of PV-wind hybrid system is proposed to gauge the better utilization of the existing space, productivity enhancement, and energy/m2 harnessed from the utilized land. The proposed system would pave a way forward towards developing a more sustainable, effective and rugged hybrid renewable energy systems that could cater the energy needs of the Indian sub-continent and similar geographical locations. Keyword solar energy, wind energy, renewable energy harnessing, hybrid system.


II. SYSTEM DESCRIPTION
The proposed hybrid system consist of a solar PV module mounted across the periphery of the stem/tower of a horizontal-axis wind turbine, a battery bank, converter circuit, controller, and other accessories as shown in Fig.  1. The PV array is mounted on the stem at an angle of -30° with respect to the horizontal to avoid the shadow and hence, attain the maximum incident solar radiation for a particular point of time. The PV array is placed around the stem of the wind turbine at a vertical distance of 30 -40m from the base measure from the inner edge of the mounted system wherein, the average total height of stem is around 110 -120 m. The output of solar PV array is fed to the DC bus. The conditioned output from the wind turbine system is also fed to the same bus. When energy from either of the systems is available, it drives the electronic load. The excess energy generated during peak wind or solar or both, gets stored in the battery bank to meet the power demand during off-peak generation. The converter circuit converts the DC power into AC to meet the load demand. The DC loads are directly fed from the DC bus. Although the proposed system runs similar to the conventional PV-wind hybrid systems however, the new design offers additional advantages discussed in the succeeding section.
III. PROPOSED HYBRID SOLAR PV-WIND SYSTEM Generally, a conceptual PV-wind hybrid system work as independent units connected to the DC bus which lowers the overall energy harness output per m 2 of the land occupied. Therefore, a novel design of PV-wind hybrid system is proposed to gauge the better utilization of the existing space, productivity enhancement, and energy/m 2 harnessed from the utilized land. The efficiency of any given solar PV module depends on the following factors: 1. The operating temperature of solar cell. 2. The cooling arrangement for the cell, and 3. The time of exposure to the sun radiation incident on the cell. All the above factors are cater by the proposed system as the rotating wind turbine blades would generate a draft of air that will aid-in keeping the low operating temperature of solar cell. Moreover, the tilted (angled) design of solar PV array would avoid shadow and hence, provide maximum time and intensity of sunlight exposure thereby generating more power.
IV. SITE ANALYSIS It is viable to install the proposed hybrid system at particular sites where both solar and wind energy is available in abundance. One such site is Jaisalmer in Rajasthan state of India located at 26.9157 latitude and 70.9083 longitude respectively. The solar irradiance and wind velocity data for the last three decades for the selected site is collected using PVsyst software. The input parameters inserted in the PVsyst are given in Fig. 2. The angle of tilt considered here is the angle at which the solar PV array is mounted on the wind turbine stem with respect to the horizontal. The maximum power point (MPP) curve was obtained from the PVsyst software against the inserted input parameters for the proposed PV array around the stem of the wind turbine. The obtained curve helped assessing the maximum power generation capability of the proposed PV system and found to be equal to 3 kW at STC, 2.8 KWdc at 50°C, and 2.1 kWac. It also accounts the overload loss of 36.7 kWh. The results allowed estimating the power sizing and hence inverter output distribution system. Fig. 3 shows the obtained MPP curve and inverter output distribution for the selected site i.e. Jaisalmer. It is evitable to study the solar behavior of the selected site in order to assess the performance of the proposed hybrid systems. In lieu to this, analysis of sun-earth angle, solar azimuth angle in particular, was performed through PVsyt. The effect of variation in solar azimuth angle on the selected tilted plane (30° with respect to the horizontal) is shown in Fig. 4. The obtained results for the selected site throw light on the annual variation behavior of the total received energy, global incidence, ambient temperature, effective global incidence, energy generated, grid-transfer, PV array efficiency and overall system efficiency.  Table II represents the annual wind trends and global incidence data of the selected site (Jaisalmer). The obtained annual wind velocity trends would assist in designing an efficient and durable horizontal-axis wind turbine that is most suitable for the proposed hybrid system. The wind velocity varies through-out the year from 1.4 -5.4 m/s with an average value of 3.1 m/s. The simulation also details about the enhancement in energy harnessing by mounting PV array module around the stem of a horizontal-axis wind turbine. The annual energy need enhancement is projected in Table 5.

V. CONCLUSION
The proposed solar PV-wind hybrid system with site location of Jaisalmer, Rajasthan is a feasible fit due to availability of both solar and wind energy. A simulation was conducted by inserting fixed variable inputs to assess the technical feasibility of the overall system. The simulation results as mentioned in the preceding sections were found to be within the acceptable limits. The obtained results would pave a way forward towards developing a more sustainable, effective and rugged hybrid renewable energy systems that could cater the energy needs of the Indian sub-continent and similar geographical locations.
VI. CONFLICT OF INTEREST The authors of the presented manuscript have contributed significantly in the research work and hereby declare no conflict of interest. The authors mutually agree on the order of name of authors for the presented manuscript.