Grid Integration of Renewable Energy Sources:

Challenges, Issues and Possible Solutions

Ahmed Sharique Anees

Department of Electrical Engineering, lamia Millia Islamia, New Delhi-II0025, India
shariq.anees@gmail.com

Abstract-India is considering renewable energy resources renewable energy sources. Challenges and issues are
(RES ) like solar and wind as alternative for future energy presented in Section III. Some possible solutions are
needs. As on March 31, 2012 the grid interactive power proposed in Section IV. A Conclusion followed by the
generation from RES is 24914 MW i.e. around 12.1 % of the
references is discussed in Section V.
total installed energy capacity. Further Ministry of New and
Renewable Energy (MNRE) , Government of India is targeting
II. LITERATURE REVIEW
to achieve 20000 MW grid interactive power through solar
and 38500 MW from wind by 2022. However there are
In this paper a literature review is carried out related to
various issues related to grid integration of RES keeping in the
view of aforesaid trends it becomes necessary to investigate
grid integration of RES. Number of authors/researchers has
the possible solutions for these issues. Integration of renewable presented the various issues, challenges and their possible
energy sources to utility grid depends on the scale of power solutions in the context of grid integration. The variability
generation. Large scale power generations are connected to of wind power limits its grid penetration and increases
transmission systems where as small scale distributed power costs. At high penetration levels, the variable output of
generation is connected to distribution systems. There are wind requires utilities to dedicate much of their available
certain challenges in the integration of both types of systems
reserve generation capacity to accommodate this variability.
directly. This paper presents the some issues and challenges
This paper [5] presents research on improving wind energy
encountered during grid integration of different renewable
integration through more effective coordination of
energy sources with some possible solutions.
traditional generation resources and energy storage systems
Keywords-Renewable energy source, grid management, that can optimize wind energy production while also
distributed generation increasing the predictability of wind farm output. The
increasing use of the Renewable Energy Sources (RES) and
I. INTRODUCTION the intermittency of the power generated by them create
stability, reliability and power quality problems in the main
Use of Renewable Energy Sources (RES) is increasing electrical grid [6]. The micro grid is called to be a feasible
drastically due to depletion of fossil fuels and associated alternative to solve these issues. As it is a weak electrical
environmental problems. Since most of the renewable grid, the micro grid is very sensitive to load or generation
energy sources are intermittent in nature therefore it changes. To reduce the effect of these variations and to better
becomes a challenging task to integrate RES into the harness the energy generated by RES, the Energy Storage
power grid infrastructure [1]. This trends leads to Systems (ESS) are used. As the different ESS technologies
numerous technical and non-technical challenges. For that are currently available are not enough to satisfy the wide
maintaining a reliable and cost effective supply, new frequency spectrum of the generated energy, the use of a
efforts have to be undertaken for the management of energy Hybrid Energy Storage System (HESS) is necessary. A
networks, integration of RES and DO in the distribution HESS is usually formed by two complementary storage
networks, for generation and load management and for a devices that can be associated in many different topologies.
range of other technical and socio economic aspects of Of course, the two devices have to be coordinated by an
decentralized energy markets. In this paper PV and wind Energy Management System (EMS). In this work the
energy sources have been considered under study. The different topologies and energy management algorithms that
increasing penetration level of PV and wind systems is have been applied in the RES and microgrid contexts have
raising the concerns of some utilities due to the possible been analyzed and compared. The micro grid can operate
negative impacts of the power fluctuations generated from both connected to the main grid and in islanding mode.
these systems on the network operation [2]. Also, the This system is used to overcome the intermittency and
fluctuation in the power of these systems can lead to uncertainty of the RES. The power converters are used as
unstable operation of the electric network prior to the fault interfaces between the ESS and the micro grid, to control
conditions, high power swings in the feeders [3] and the power flow of the storage devices and operate the
unacceptable voltage fluctuations at certain nodes in the system optimally. However, the power losses of the
electric network [4]. Moreover, the random fluctuations converters (mainly switching losses) and their
of the power output generated these systems does not economical cost are limiting factors for their use. Although
allow for considering them in the scheduling process of there are methods like the soft-switching designed to reduce
electricity generation. the switching losses of the PCS, depending on the
This paper is organized as follows: Section II presents the application, in some cases it is more economical not to use
literature review pertaining to the grid integration of it.

978-1-4673-0934-9112/$31.00 ©2012 IEEE

 A new control strategy for a grid connected doubly fed the stochastic wind power fluctuation into full account so as
induction generator (DFIG)-based wind energy conversion to give a quantitative risk assessment of grid frequency
system (WECS) is presented [7]. Control strategies for the deviation to grid operators, even without using any dynamic
grid side and rotor side converters placed in the rotor circuit simulation tool. The case studies show that this method
of the DFIG are presented along with the mathematical can be widely used in different types of wind power
modeling of the employed configuration of WECS. Battery system analysis.
energy storage system (BESS) to reduce the power Some issues related to grid integration of PV systems have
fluctuations on the grid due to the varying nature and been presented [12]. Further some methods to reduce the
unpredictability of wind is also presented. Further, the fluctuations in PV power output are also discussed. The
detailed design, sizing, and modelling of the BESS are given main issues related to PV systems integration with grid are
for the grid power levelling. Existing control strategies like the fluctuation of PV output power, these fluctuations can
the maximum power point extraction of the wind turbine, negatively impact the performance of the electric networks
unity power factor operation of the DFIG are also addressed to which these systems are connected, especially if the
along with the proposed strategy of grid power levelling. An penetration levels of these systems are high. Moreover, the
analysis is made in terms of the active power sharing between fluctuations in the power of PV systems make it difficult to
the DFIG and the grid taking into account the power stored or predict their output, and thus, to consider them when
discharged by the BESS, depending on the available wind scheduling the generating units in the network. In this paper
energy. This strategy is simulated in MATLAB- SIMULINK three methods have been investigated such as the use of
and the developed model is used to predict the behaviour. battery storage systems, the use of dump loads and
A case study describing the situation of grid integration of curtailment of the generated power by operating the power­
wind energy in German is presented [8]. Due to a new edition conditioning unit of the PV system below the maximum
of the renewable energy law some technical requirements power point. The emphasis in the analysis presented in
must be fulfilled by the wind turbines. These demands and this paper is on investigating the impacts of implementing
the possibilities and efforts of the technical realization are these methods on the economical benefits that the PV
described based on the existing technology. Further, the system owner gains. Integration of renewable energy sources
necessary steps towards an increased power share of wind (RES) brings to the grid not only their benefits but also
energy are introduced. This includes the energy storage in some technical problems, as increase of harmonic currents.
power systems and the retrofit of the existing transmission Compliance with the technical requirements for harmonic
system. current is necessary for successful increase of RES
The application of FACTS device (STATCOM) for power capacity. Scheme to reduce harmonic current for grid­
quality improvement in grid connected wind generating connected PV generation system was developed [13]. This
system and with nonlinear load is presented [9]. The power control scheme effectively reduced harmonic current in the
quality issues and its consequences on the consumer and grid current of the PV generation system caused by voltage
electric utility are also presented. The operation of the control distortions at the grid. Experiments using a prototype of the
system developed for the STATCOM in power conditioning system (PCS) showed its validity. 400
MATLAB/SIMULINK for maintaining the power quality has kW PCSs with the control scheme have been installed and
been simulated. The system has the capability to cancel out have been in service since the end of 2009. In this project,
the harmonic parts of the load current and maintains the three control methods were developed such as generation
source voltage and current in-phase and support the reactive power control for fault ride through harmonic current
power demand for the wind generator and load at PCC in the reduction control scheme and grid voltage stabilization using
grid system, thus it gives an opportunity to enhance the optimal reactive power control. A high performance
utilization factor of transmission line. The integrated wind harmonic current reduction control scheme has been
generation and FACTS device with BESS have shown the presented. Its purpose is to reduce the harmonic current that
outstanding performance. The options for larger scale flows through a PCS by outputting harmonic voltage equal
integration of wind power and other renewable energy to the one contained in the grid. The control scheme does
sources into the grids are demonstrated [10]. In this paper, not use grid current and has low interference with the
the German and Greece experience is reported. existing current control and FRT capability. Extraction
The grid frequency deviation caused by wind power algorithm for the harmonic voltages enables the VSI in the
fluctuation which is a major concern for secure operation of PV generation system to output harmonic voltages that are
a power system with integrated large-scale wind power. very close to the harmonic voltage of the grid. Experiments
Many approaches have been proposed to assess this showed the validity of the control scheme. 400-kW PCSs
negative effect on grid frequency due to wind power with the control scheme were installed at the Hokuto site.
fluctuation [11]. Unfortunately, most published studies are The voltage distortions at the Hokuto site were so small
based entirely on deterministic methodology. This paper that there were not significant differences between the
presents a novel assessment method based on Time­ results of the harmonic currents of PCS with and without the
Frequency Transformation to overcome the shortcomings control scheme. However, the results measured at the
of the existing methods. The main contribution of the paper Hokuto site confirm that the harmonic current reduction
is to propose a stochastic process simulation model which control does not have negative effects even if there is no
is a better alternative of the existing dynamic frequency large voltage distortion at the grid side.
deviation simulation model. In this way, the method takes The distributed generation systems that impose new
requirements for the operation and management of the peak shaving service at the lowest cost. The structure of a
distribution grid, especially when high penetration levels are power supervisor based on an optimal predictive power
achieved [14]. In this paper an improved structure of power scheduling algorithm is proposed. A novel control scheme
conditioning system (PCS) for the grid integration of PV using a variable frequency transformer eVFT) of 100 MW
solar systems is presented. The topology employed consists to effectively reduce power fluctuations of an equivalent
of a three-level cascaded Z-source inverter and allows the SO-MW aggregated doubly-fed induction generator (DFIG)­
flexible, efficient and reliable generation of high quality based offshore wind farm (OWF) connected to an onshore
electric power from the PV array. A full detailed model 120-kV utility grid is presented [IS]. A frequency-domain
is described and its control scheme is designed. Validation approach based on a linearized system model using eigen
of models and control schemes is carried out through techniques and a time-domain scheme based on a nonlinear
digital simulation using the MATLAB/Simulink system model subject to disturbance conditions are both
environment. performed to examine the effectiveness of the proposed
A novel control strategy for achieving maximum control scheme. It can be concluded from the simulation
benefits from these grid-interfacing inverters when installed results that the proposed VFT is effective to smooth the
in 3-phase 4-wire distribution systems is presented [15]. fluctuating active power of the OWF injected into the
The inverter is controlled to perform as a multi-function power grid while the damping of the studied OWF can
device by incorporating active power filter functionality. also be improved. An analysis of the interaction between the
The inverter can thus be utilized as: variability characteristics of the utility load, wind power
1) Power converter to inject power generated from RES generation, solar power generation, and ocean wave power
to the grid, and 2) shunt APF to compensate current generation is discussed [19]. The results show that a
unbalance, load current harmonics, load reactive power diversified variable renewable energy mix can reduce the
demand and load neutral current. All of these functions may utility reserve requirement and help reduce the effects of
be accomplished either individually or simultaneously. With variability.
such a control, the combination of grid-interfacing inverter The continuously growing amount of renewable sources
and the 3-phase 4-wire linear/non-linear unbalanced load starts compromising the stability of electrical grids.
at point of common coupling appears as balanced linear Contradictory to fossil fuel power plants, energy production
load to the grid. This new control concept is demonstrated of wind and photovoltaic (PV) energy is fluctuating.
with extensive MATLAB/Simulink simulation studies and Although predictions have significantly improved, an
validated through digital signal processor-based laboratory outage of multi-MW offshore wind farms poses a
experimental results. This paper has presented a novel challenging problem. One solution could be the integration
control of an existing grid interfacing inverter to improve of storage systems in the grid. After a short overview, this
the quality of power at PCC for a 3-phase 4- wire DG paper focuses on two exemplary battery storage systems,
system. It has been shown that the grid-interfacing inverter including the required power electronics. The grid
can be effectively utilized for power conditioning without integration, as well as the optima usage of volatile energy
affecting its normal operation of real power transfer. This reserves, is presented for a 5-kW PV system for home
approach thus eliminates the need for additional power application, as well as for a 100-MW medium voltage
conditioning equipment to improve the quality of power at system, intended for wind farm usage. The efficiency and
PCC. Extensive MATLAB/Simulink simulation as well as cost of topologies are investigated as a key parameter for
the DSP based experimental results have validated the large-scale integration of renewable power at medium and
proposed approach and have shown that the grid­ low-voltage. Energy storage systems are a promising
interfacing inverter can be utilized as a multi-function solution regarding the integration of fluctuating renewable
device. Moreover, the load neutral current is prevented energy into grids. This paper focuses on small amounts of
from flowing into the grid side by compensating it locally energy with high peak power, which can be reasonably
from the fourth leg of inverter. When the power generated buffered by battery systems. These energy amounts are
from RES is more than the total load power demand, the required when differences occur between prediction and
grid-interfacing inverter with the proposed control production of wind or PV power. Two exemplary battery
approach not only fulfills the total load active and reactive storage systems including the power electronics have been
power demand (with harmonic compensation) but also presented. One could state that the modular medium voltage
delivers the excess generated sinusoidal active power to the system shows slightly higher converter efficiency, resulting
grid at unity power factor. The power quality problems from a multilevel topology. Considering transmission and
associated with the renewable energy based systems and distribution losses from the medium-voltage grid to the
how custom power devices such as STATCOM, DVR, load, the low-voltage solution for domestic use may be
UPQC play an important role in the power quality just as economically viable because of its relatively high
improvement are presented [16]. In this paper PV and efficiency. However, the relative costs of the low-voltage
Wind energy systems integration issues and power quality converter are probably higher due to more overhead.
problems are discussed. Taking transport losses into account, both systems can
An optimal power management mechanism for grid achieve nearly equal performance concerning efficiency
connected photovoltaic (PV) systems with storage is and commercial viability.
presented [17]. The objective is to help intensive As more renewable power sources, such as wind, solar,
penetration of PV production into the grid by proposing and ocean wave, are added to the grid, there has been an
increasing impact on the ability of system operators to deal integration of renewable energy sources and energy-storage
with the added variability that these resources introduce systems are demonstrated.
[20]. Since these types of sources are variable and non­ The integration of small scale solar and wind generation
dispatchable in nature, their continued integration has into distribution networks could cause power fluctuations
required that more and more generating resources be kept due to the intermittent and random nature of these sources.
in reserve to account for unexpected power changes. While This could become one of the significant concern in
wind, solar, and ocean wave share similarities in their future power system operator [22]. Though the
fundamental characteristics as renewable sources, their development of Battery Energy Storage Systems (BESS)
variability and subsequent impact on the grid can often can address effectively the aforesaid concern, the high
differ greatly. In combination, however, it has been shown cost of batteries making it economically less attractive. The
that positive synergistic effects are possible (e.g., in participation of consumers in energy markets actively and
combination, reserve requirements can be reduced allowing some of their equipment to be used in demand
compared to single resource scenarios). This paper utilizes side management operations in future has the potential to
the factorial design methodology to analyze the reserve reduce the capacity requirements of BESS. Wide scale
requirement impacts of combining different resources to implementations of demand side management require the
determine parameters for modeling various grid penetration exchange of information between controllable system
scenarios. The results point to the possibility of determining elements and a demand management controller in near
an optimal mix of wind, solar, and ocean wave resources. A real time. A scheme developed for the coordinated control
methodology for determining model to predict the reserve of system elements to reduce fluctuations caused by
requirements for balancing authority areas with high renewable sources was tested for its performance when
penetrations of wind, solar, and ocean wave. This model information exchange is carried out over a segment of a
includes interaction effects. The results show that the university network connected to the internet. Results
interaction effects between different renewable sources obtained from this study are also presented in the paper.
can result in a lower reserve requirement than would be The assessment of the impact of communication over the
required if the sources are considered in isolation, Internet on the performance of a method to control
although the reduction may be modest. More study on this power systems elements to reduce the power fluctuations
to find the best mix is necessary. Validation of the was done experimentally. The experimental setup used for
presented model with actual data suggests the model is simulation studies was created within a laboratory
accurate. It is also shown that using a reduced model that environment.
ignores interaction effects may be able to provide an Some communication technologies available for grid
acceptable first-order approximation in cases where the integration of renewable energy resources have been
interaction effects are not known. presented in the literature [1]. The communication
The new power-electronic technology plays a very systems used in a real renewable energy project, Bear
important role in the integration of renewable energy Mountain Wind Farm (BMW) in British Columbia,
sources into the grid. It should be possible to develop the Canada are presented. In addition, the communication
power-electronic interface for the highest projected turbine systems used in Photovoltaic Power Systems (PPS) is also
rating, to optimize the energy conversion and transmission presented.
and control reactive power, to minimize harmonic
distortion, to achieve at a low cost a high effIciency over a III. ISSUES AND CHALLENGES
wide power range, and to have a high reliability and
tolerance to the failure of a subsystem component. The Renewable energy sources are intermittent in nature
common and future trends for renewable energy systems hence it is therefore a challenging task to integrate
have been described [21]. As a current energy source, renewable energy resources into the power grid. Some of
wind energy is the most advanced technology due to its the challenges and issues associated with the grid
installed power and the recent improvements of the power integration of various renewable energy sources
electronics and control. In addition, the applicable particularly solar photovoltaic and wind energy

regulations favor the increasing number of wind farms due conversion systems. Further these challenges are broadly

to the attractive economical reliability. On the other hand, classified into technical and non-technical and described
the trend of the PV energy leads to consider that it will be below.
an interesting alternative in the near future when the current A. Technical Issues

problems and disadvantages of this technology (high cost The following are the technical issues are described as
and low effIciency) are solved. Finally, for the energy­ 1. Power quality
storage systems (flywheels, hydrogen, compressed air, super a. Harmonics
capacitors, superconducting magnetic, and pumped b. Frequency and voltage fluctuation
hydroelectric), the future presents several fronts, and 2. Power fluctuation
actually, they are in the same development level. These a. Small time power fluctuations
systems are nowadays being studied, and only research b. Long time or seasonal power fluctuations
projects have been developed focusing on the achievement 3. Storage
of mature technologies. 4. Protection issues
New trends in power-electronic technology for the 5. Optimal placement of RES
6. Islanding continuously fluctuating power gives rise to the security
Apart from aforesaid technical issues some of the non concern to the grid for making stable grid. Solar PV plant
technical issues are also presented in this paper. owner have to install the different type of storage system
B.Non- Technical Issues which gives additional cost to the plant owner. Once the
1. Lack of technical skilled man power storage system is fully charged then this storage elements
2. Less availability of transmission line to accommodate gives no profit to the system owner. Therefore solar based
RES water pumping system may be installed instead of storage
3. RES technologies are excluded from the competition by system.
giving them priority to dispatch which discourage the
installation of new power plant for reserve purpose. V. CONCLUSIONS

IV. POSSIBLE SOLUTIONS In this paper, some issues related to grid integration of
RES and their possible solutions available in the literature
The renewable energy sources such as solar, wind etc. have been presented. To minimize the fluctuations and
has accelerated the transition towards greener energy intermittent problems p o w e r e l e c t r o n i c s devices a r e
sources. The increasing number of renewable energy the viable options. Further, energy storage and use of
sources and distributed generators requires new dump load and MPPT could be used for reducing the power
strategies for the operation and management of the fluctuations in PV systems. In addition to the aforesaid, the
electricity grid in order to maintain or even to improve the up gradation in balance of systems by incorporating the
power-supply reliability and quality. Keeping in view of new materials and storage elements could reduce the
the aforesaid some of the possible solutions have been problems associated with grid integration.
proposed by researchers.
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