energies Article Article Large Scale Renewable Energy Integration: LargeIssues Scale Renewable and Solutions Energy Integration: Issues and Solutions G V Brahmendra Kumar 1, Ratnam Kamala Sarojini 1, K Palanisamy 1,*, Padmanaban G. V. BrahmendraSanjeevikumar Kumar 12 and, Ratnam Jens Bo Kamala Holm-Nielsen Sarojini 21 , K. Palanisamy 1,*, 2, 2 Padmanaban1 SanjeevikumarSchool of Electrical *Engineering,and Jens Vellore Bo Holm-Nielsen Institute of Technology, Vellore 632014, India; 1 School of [email protected] Engineering, Vellore Institute (G.V.B.K.); of Technology, [email protected] Vellore 632014, India; (R.K.S.); [email protected] (K.P.) [email protected] Center for Bioenergy and (G.V.B.K.); Green Engineering, [email protected] Department of (R.K.S.) Energy Technology, Aalborg University, 2 Center for6700 Bioenergy Esbjerg, and Denmark; Green Engineering, [email protected] Department (P.S.); [email protected] of Energy Technology, (J.B.H.-N.) Aalborg University, 6700 Esbjerg,* Denmark; Correspondence: [email protected] [email protected]; [email protected]; Tel. No.: +45-7168-2084 * Correspondence: [email protected] (K.P.); [email protected] (P.S.) Received: 16 April 2019; Accepted: 21 May 2019; Published: date Received: 16 April 2019; Accepted: 21 May 2019; Published: 24 May 2019 Abstract: In recent years, many applications have been developed for the integration of renewable Abstract: Inenergy recent sources years, many (RES) applications into the grid have in beenorder developed to satisfy forthe the demand integration requirement of renewable of a clean and energy sourcesreliable (RES) electricity into the generation. grid in order Increasing to satisfy the demandnumber of requirement RES creates of uncertainty a clean and in reliable load and power electricity generation.supply generation, Increasing which the also number presents of RES an createsadditional uncertainty strain on in the load system. and power These supplyuncertainties will generation,affect which the also voltage presents and an frequency additional variation, strain on stability, the system. protection, These uncertainties and safety issues will a ffatect fault the levels. RES voltage andpresent frequency non-linear variation, characteristics, stability, protection, which requires and safety effective issues atcoordination fault levels. REScontrol present methods. This non-linear characteristics,paper presents whichthe stability requires issues effective and coordinationsolutions associated control methods. with the Thisintegration paper presents of RES within the the stabilitygrid. issues and solutions associated with the integration of RES within the grid. Keywords:Keywords:renewable renewable energy sources; energy energy sources; storage energy system; storage voltage; system; frequency; voltage; frequency; grid integration grid integration 1. Introduction1. Introduction The majorityThe of majority countries of acrosscountries the across world the are world concentrating are concentrating on RES, due on toRES, an due increase to an of increase of environmentalenvironmental concerns and concerns depletion and ofdepletion fossil fuels of fossil [1]. Forfuel example,s [1]. For Chinaexample, is aiming China foris aiming RES to for RES to represent somewhererepresent somewhere around 35 percent around of 35 consumption percent of byconsum 2030.ption India hasby 2030. set an India ambitious has set RES an target ambitious RES of 175 GWtarget [2]. The of European175 GW [2]. Union The European and the United Union States and the also Un haveited targets States also regarding have targets RES [3 ].regarding Some RES [3]. countries successfullySome countries integrated successfully large sharesintegrated of RES large in theshares power of gridRES inin 2017,the power and most grid countries in 2017, and most have set targetscountries to receive have set their targets power to generation receive their from power RES generation by 80% in 2050,from asRES is shownby 80% in in Figure 2050, 1as. is shown in Figure 1. Figure 1. Renewable energy share and targets by countries in 2017 and 2050 [4]. Energies 2019, 12, x; doi: FOR PEER REVIEW www.mdpi.com/journal/energies Energies 2019, 12, 1996; doi:10.3390/en12101996 www.mdpi.com/journal/energies Energies 2019, 12, x FOR PEER REVIEW 2 of 17 Energies 2019, 12, 1996 2 of 17 Figure 1. Renewable energy share and targets by countries in 2017 and 2050 [4]. Due Table to 1. the The irregularities comparison of and renewable fluctuating energy features sources (R ofES) RES, with new synchronous challenges generator to the (SG) grid [5]. over a unified anticipated generation have been created. The RES outputs are influenced by meteorological Characteristics Solar Wind SG conditions. These characteristics affect the power system efficacy, power quality, system reliability, load Fluctuations More Less No management, security, and safety in various ways and are also very significant factors to be viewed in Cost for large scale More Medium Low to medium the integration of RES within the grid [6]. This influence is commonly observed with solar and wind Maintenance cost Minimum More Moderate energy, but geothermal, hydropower and biomass energy resources are more anticipated and have Inertia No inertia Low inertia High irrelevant difficulties in their association with the grid [7]. The comparison of RES with a synchronous Capacity factor Very Low Low to medium More generator (SG) is shown in Table1. Annual growth in power industry Very High More More Table 1. The comparison of renewable energy sources (RES) with synchronous generator (SG) [5]. Due to the irregularities and fluctuating features of RES, new challenges to the grid over a unified anticipatedCharacteristics generation have been created. Solar The RES outputs Wind are influenced SG by meteorological conditions. These characteristicsFluctuations affect the power More system efficacy, Less power quality, No system reliability, load management,Cost security, for large scaleand safety in various More ways and Medium are also very Lowsignificant to medium factors to be viewed in the integrationMaintenance of RES cost within the grid Minimum [6]. This influence More is commonly Moderate observed with solar Inertia No inertia Low inertia High and wind energy, but geothermal, hydropower and biomass energy resources are more anticipated Capacity factor Very Low Low to medium More and have Annualirrelevant growth difficulties in power in industry their associationVery High with the grid More [7]. The comparison More of RES with a synchronous generator (SG) is shown in Table 1. The RESRES integratedintegrated with with the the grid grid is is shown shown in in Figure Figu2re. Figure2. Figure2 is incorporated2 is incorporated with with RES, RES, grid andgrid electronicand electronic components. components. The power The power generation generation from RES from to RES the gridto the is unidirectional.grid is unidirectional. The RES The requires RES therequires converters the converters to be connected to be connected to the grid. to Thesethe grid converters. These converters will achieve will effi achievecient operation efficient and operation obtain theand energy obtain quality the energy requirements quality relatedrequirements to the harmonicsrelated to level.the harmonics Also, this allowslevel. theAlso, integration this allows of RESthe inintegration a power inverterof RES in with a power high energyinverter features with high and energy safety. features and safety. Figure 2. RES integration with grid. The remainderremainder of of this this paper paper is organizedis organized as follows:as follows: Section Section2 considers 2 considers the grid the integration grid integration issues withissues a with high sharea high of share RES, of and RES, solutions and solutions for variable for variable RES is discussedRES is discussed in Section in3 Section. The Energy 3. The Storage Energy SystemStorage (ESS)System support (ESS) issupport explained is inexplained Section4 ,in and Section followed 4, and by smartfollowed grid featuresby smart in grid voltage features control in withvoltage RES control in Section with5 .RES Section in Section6 is the 5. conclusion. Section 6 is the conclusion. 2. Grid Integration Issues with a High Share of RES 2. Grid Integration Issues with a High Share of RES As the power generation from RES increases, the installed capacity of power converters increases. As the power generation from RES increases, the installed capacity of power converters By utilizing the large scale of solar energy, the RES system is able to supply power to the grid. Thus, increases. By utilizing the large scale of solar energy, the RES system is able to supply power to the by increasing the capacity of the RES, the grid-connected RES will create a negative impact on the grid. Thus, by increasing the capacity of the RES, the grid-connected RES will create a negative grid when fault or disturbance occurs. Hence, the Point of Common Coupling (PCC) voltage drop is impact on the grid when fault or disturbance occurs. Hence, the Point of Common Coupling (PCC) triggered by a fault in grid power and the RES will become off-grid across a wide area range. Moreover, voltage drop is triggered by a fault in grid power and the RES will become off-grid across a wide these fault impacts cause the grid voltage and frequency collapse, also affecting the safe, stable and area range. Moreover, these fault impacts cause the grid voltage and frequency collapse, also reliable