**10. Conclusion**

*Wind Solar Hybrid Renewable Energy System*

can reduce the size of central storage devices.

**9. Long-distance transmission**

but the DC system has higher energy efficiency with improvement up to 10% [96] with less number of conversion stages taking generation from RES. The important communication system, not less than the brain makes it all possible in a coordinated manner. It communicates with the smart metering system present on the MG and on the EV charging station, through Modbus on TCP/IP connection, using the

When the market penetration of uncoordinated plug-in electric vehicles (PHEV) is studied by [97], it is encouraged for load control by smart charging. It

a cooperative manner that helps the voltage control and reduces congestion. The PHEVs as dynamically configurable dispersed storage can operate in vehicle-to-building (V2B). Based on the distinctive attribute of the battery, the benefits of using PHEVs as energy storage for DSM and outage management are deliberated by Pang et al. [99]. The faster-charging are yet to come up. The parking

Clement-Nyns et al. [98] have investigated charging and discharging of PHEV in

All countries emphasize on use of clean and alternate energy. As discussed in previous subsections, with the rapid development of RES fresh set of technological requirements pops up on the grid: the location of RE resources distant from load centers, and the power-variability. The characteristics and its control of the electricity grid need a modification to integrate RE [100]. At present many countries lack affordable storage facilities for renewable power. But on a positive note, the excess power is transmitted through the national grid by internal transmission lines. However, connectivity to the national grid should be even or balanced. The large scale intermittency demands to switch in fast-acting conventional reserves on the basis of climatic forecasts on short to long time frame; by setting up grid-scale storage or; by long-distance transmission of RE generation connecting to larger reserves for resources in order to equalize regional and local surplus or shortfall. This section discusses opportunities for renewable energy transmission over a long distance. Long-distance transmission capacity is necessary to despatch a huge quantity of renewable power a thousand kilometer or more across the country. The construction of transmission tower is given low priority by historically low investment in transmission, community concern over the required right of way in more dense urban areas. Further many long transmission lines are aged and of inadequate capacity. Both remote solar PV and wind energy generation require "Green power Superhighways." HVDC transmission [100] and use of superconductors [100] are costly alternatives as RE itself cost more to the user. HVDC lines offer transient as well as short term voltage stability. Variability of the source can be well managed via an extensive and robust transmission line network. The transmission capacities based on power electronics devices starts to change the grid characteristics and control requirements. The key power electronic technology has a high impact on the power quality because of its fast control and sensitivity to fault and other abnormal

So, research is still going on HV superconducting cable for long-distance transmission of RE [101]. Anyway, in the present day of renewable energy, the grid has to serve national character. With more urbanization and industrialization, the reduction of carbon dioxide emission has been essential and requires long-distance delivery of renewable power [102]. Rooftop PV can reduce the need for long-distance transmission, but have a higher cost than wind or concentrating

internal LAN, and with the ES converters, through the CAN protocol.

time can be utilized for charge or discharge mode when required.

**130**

conditions of the grid.

Renewable energy is environmentally, socio-ethically and economically sustainable compared with the dominant centralized and non-renewable energy generation systems. However, the techno-economic limitations for ever-growing renewables' share of power generation in the majority of the countries are alike.

The RES is not currently cost-competitive with base load coal-fired power, and geographically dispersed. However, it leads over a conventional generation in low emissions of air pollutants, free fuel, and a low gestation period.

Traditionally, the electric power system is not intended to handle RE generation and storage. But with the rapid growth in the alternate energy sector, the integration of the DE and RES into an electric power grid can be done in many ways along with power quality solution. The power electronic technology plays a significant part in the integration of RES into the electrical grid. They offer exclusive competence over conventional interconnection technologies. They further provide additional power quality and voltage/reactive power support.

This chapter describes the various aspects of grid interface for wind energy systems and solar PV systems and some other DERs for electrical system compatibility by reducing the effects on fault, and flexibility in functioning with various other DERs, while minimizing the interconnection costs.

Around 100 research papers in various problems of grid connection have been surveyed but claims in no way to be complete. This particular subject is definitely emerging in nature and attracts many researchers towards it.

It has been discussed that utility RE investments are typically evaluated from regulatory, project finance, and engineering viewpoints. The regulatory evaluation focuses on ensuring utility conformance to RES and that expenses are kept judiciously limited. From a finance perspective, the return on the investment within disjunctive limits of the funding and cash flows for a particular project is evaluated. The technical evaluation determines the engineering and operational safety of the project and the specific technologies deployed. While these approaches are essential for investors, utilities, regulators and ratepayers, they do not scope out the goodness that a RES can convey beyond the boundaries of a given project, such as the usefulness of transmission and storage and the organizational plus point of bringing an integrated grid.

Variability of RES occurs due to the nature of the climate. Thereby the uncertainty in the generation is affecting up to 70% of day time solar capacity due to passing clouds, and 100% of wind capacity on calm days, is much greater than the somewhat expected variations of a few per cent in demand that system operators handle. This has been discussed. It necessitates a more complicated voltage and frequency regulation. The larger the RE entrant, the more complicated (sometimes unattainable) is the management of this challenge.

Spatial aggregation of RES greatly lessens forecast errors, just as it lessens variability. This may be due to spatial smoothening effect. The forecast error rises further as the time range of the forecast is expanded. Forecasting techniques are improving constantly. But this requires better weather model and better data collection and processing.

In contrast to the convention fossil fuel power sources, selecting a site to exploit certain RES has few or no degrees of freedom. In other words, RE such as wind and PV, are site-constrained. Transmission needs to be extended to these sources, not the other way around. Future distribution systems will contain MGs and hence it is necessary to understand the steady-state and transient operating conditions of such systems to appraise their effects on the present grid.

Control system is the key element for flexible operation, high efficiency and superior power quality in RE integration. In this regard, the control system fetches real-time states through local measures and via the communication, takes actions to attain the control objectives (for instance, maximum power extraction, output voltage and frequency regulation, reactive power compensation, etc.), and at last send commands to the actuators, usually power electronic converters. Challenges in control design and realization, energy management strategies, communication layout and protocols, and topologies for power electronics-based distributed RES are all addressed in brief here.

The value of energy storage by batteries in grid-level applications that guides both transmission and generation services to the grid. It mitigates the unpredictability of generation. It has been emphasized to conduct a review of the technological potential for a range of battery chemistries.

Lastly, it is reiterated again that because of some demerits and irrevocable externalities in conventional energy production, it has become essential to go for and uphold technologies and insist for RES. Power generation using RES should be enhanced in order to reduce the per unit price of generation.
