An urgent need for power around the world is seeing more and more power facilities running on the fast track. In the case of developing countries like India, these installations can provide a boost to grid power or bring off-grid power to people who have none. In developed nations, they can enhance energy security and support the transition to a renewable-based power mix. India with potential for renewable energy (RE) requires supporting policies, renewable purchase obligations, and it is good to note that other incentives have already been set up for reducing carbon footprint for mitigation of greenhouse gas (GHG) emissions and to empower rural areas of the country. The Ministry of New and Renewable Energy is already active to fulfill and to meet the target of installation of 175 GW renewable energy capacities in India by 2022. Until recently, the most widely adopted procurement strategy for attracting renewable energy involved feed-in tariffs (FiT). This article presents a novel integrated hybrid system of solar and wind energy for off-grid power generation in non-interconnected areas or remote isolated communities.

Proposed System

Hybrid systems based on microgrid provide ways to use renewable energy in an efficient way. A key challenge in the deployment of renewable sources is their intermittent nature. In the present work, the dynamic component models, a simulation model for the proposed hybrid energy system has been developed. The overall power management strategy for coordinating the power flows among the different energy sources is presented in this work. Simulation studies have been carried out to verify the system performance under different scenarios using a load profile and weather data. The results show that the overall power management strategy is effective and the power flows among the different energy sources and the load demand is balanced satisfactorily. Therefore, this system can tolerate the rapid changes in load and environmental conditions, and suppress the effects of these fluctuations on the equipment side voltage.

Fuel cell system

The proton exchange membrane fuel cell (PEMFC) is one of the most promising and certainly the best known of the fuel cell types satisfying the above requirements.

Electrolyzer system

Water can be decomposed into its elementary components by passing electric current between two electrodes separated by an aqueous electrolyte.

Ultra-capacitor system

Ultra-capacitors are essentially used in power applications requiring short duration peak power. An ultracapacitor is an energy storage device. Its construction is similar to that of a battery. This subsection, presents the model of the ultra-capacitor bank to perform load sharing with the fuel cell system. When they simultaneously operate with the wind turbine and solar cell, fuel cell systems exhibit good power supply capability during steady state operation. The response of fuel cells during instantaneous and short-term peak power demand periods is relatively poor. In these periods, the ultra-capacitor bank can assist the fuel cell system to achieve good performance reducing the cost and size of the fuel cell system. Ultra-capacitor modules are connected in parallel with the fuel cell to reduce its voltage variation due to sudden load changes. Ultra-capacitor has transfer function base model.

Typical Information about the Project

With ever-increasing concerns on energy issues, the development of renewable energy sources is becoming more and more attractive. Then, a new stand-alone wind–PV hybrid generation system is proposed for application to remote and isolated areas. For the wind power generation branch, a doubly excited permanent magnet brushless machine is used to capture the maximum wind power by using online flux control. For the PV power generation branch, a singleended primary inductance converter is adopted to harness the maximum solar power by tuning the duty cycle. The simulation results confirm that the proposed hybrid generation system can provide high efficiency with the use of maximum power point tracking (MPPT).

This system has 75 W solar cells, a 400 W wind turbine, a 500 W proton exchange membrane fuel cell, ultracapacitors, electrolyzer, and a power conditioner. It is used to step up ultracapacitor voltage to DC 200 V and invert to 120 Vrms, 60 Hz AC.

When wind speed is 12.5 m/s, then wind turbine produces maximum power 400 W. Solar cell has maximum power is 75 W. Capacitance C=108.75 μF, series resistance Rc=16 mΩ, and stray resistance Rs=0.01 Ω. Figure 1 gives the layout of the project.

Hybrid System Simulation Result

Simulation results with step changes in load demand, wind speed, radiation, and ambient temperature are analysed. The initial wind speed is 10 m/s. Wind speed increases, at t=10 s from 10–12 m/s and decreases to 8 m/s at t= 16 s. The solar cell initially supplies power at the radiation 500 W/ m2 and temperature 25°C. At 15 s, the radiation increases to 600 W/m2 and temperature also increases to 28°C. Solar power, wind power, and fuel cell power variation with time are shown in Figure 2. The load demand changes from 360 W to 225 W at 10 s. The power tracking performance of the hybrid topology with respect to load demand change and environmental variations is shown in Figure 2.

Fuel cell current variation at t=0s to t=10s is due to start-up transients and load demand, as the solar cells and wind turbines contribution are limited and fixed. During t=10s to t=16s, the fuel cell current decreases to zero because load demand is reduced and the wind turbine increases output power. After t=16s, variation in fuel cell current is due to changes in power demand from the fuel cell with varying availability of wind energy. When wind speed is decreased to 8 m/s at t= 16 s then the contribution of the fuel cell starts at t=19.1 s. With changes in load and environmental conditions, there are variations in the fuel cell current as shown in Figure 3.

The use of an ultra-capacitor in parallel with the fuel cell reduces the stack’s output. With variations of the ultra-capacitor voltage between 49 and 62 V, the power converter unit regulates the load voltage. The controller in the boost converter adjusts the duty ratio so as to attain a fixed 200 V DC in the inverter’s input. The inverter, on the other hand, delivers 120 Vrms to the load. Figure 4 shows variation in UC voltage with time. Hydrogen is used as a fuel in fuel cell. The electrolyzer electrolyzes water to produce hydrogen by the excess power of the system and stores it from t=10s to t=19.1s. The variation of hydrogen in storage tank is shown in Figure 5. The system can circulate supply load demand and renewable energy will not be wasted.

Conclusion

To overcome the deficiency of the solar cell and wind system, the appropriate way is by integrating them with the fuel cell (FC) and ultra-capacitor (UC) system, which has been explored in this work. PID controller is also used to control the fuel cell voltage by varying the H2 and O2 flow rates. Modelling of various components of this isolated system is presented in this work. The voltage variation at the output is found to be within the acceptable range. The output fluctuations of the wind turbine varying with wind speed and the solar cell varying with both environmental temperature and sun radiation are reduced using a fuel cell. Therefore, this system can tolerate the rapid changes in load and environmental conditions, and suppress the effects of these fluctuations on the equipment side voltage. The proposed system can be used for offgrid power generation in non-interconnected areas or remote isolated communities. It reduces the dependence on one single source and increases the reliability. Hence an attempt is made in this work to improve the efficiency of the system as compared with their individual mode of generation.

In this work, the fuel cell is an accessory generator in this system and supplies insufficient power. Supply and load demand are to keep balance but when supply is bigger than the load demand then the electrolyzer model electrolyzes water to produce hydrogen and store it for further usage, so this system can circulate supply load demand and energy will not be wasted.

Therefore, this system can tolerate the rapid changes in load and environmental conditions, and reduce the effects of these fluctuations on the equipment side voltage. The proposed system can be used for off-grid power generation in noninterconnected areas or remote isolated communities.

THE PROPOSED SYSTEM CAN BE USED FOR OFF-GRID POWER GENERATION IN NON-INTERCONNECTED AREAS OR REMOTE ISOLATED COMMUNITIES. IT REDUCES THE DEPENDENCE ON ONE SINGLE SOURCE AND INCREASES THE RELIABILITY. HENCE AN ATTEMPT IS MADE IN THIS WORK TO IMPROVE THE EFFICIENCY OF THE SYSTEM AS COMPARED WITH THEIR INDIVIDUAL MODE OF GENERATION.

The Way Forward

The hybrid system modelled in this work is efficient, durable, and cheaper as compared to the hybrid system with that of using battery. The parameters of the proposed model in this work can be further improved or advanced control method can be used. A computer measurement and control bus may also be added to the system. Computer controlled relays will allow all the major elements of the system to be switched in and out of the system through computer programmes. These provisions will help in the better study of more complex issues such as power faults, caused by sudden over voltages like lightning. In future, the effort to improve the stability and dynamics of grid connected Wind-PV generator may also be made.

Shri Radhey Shyam Meena (Member IEEE, CIGRE, IAENG, Associate Member IET) is JTT in the Ministry of New and Renewable Energy, New Delhi,Email: [email protected]