Impact of Solar PV Penetration on Grid
Renewable energy is gaining
huge importance among all forms
of energy resources and is being
given emphasis and thrust across
the globe. Climate change due to
global warming and the depletion
of fossil fuel reserves are two
major challenges being right now
faced by the planet earth.
Immediate cut down in the usage
of fossil fuel resources and
reduction on its dependency are
the need of the hour to bring
down the emission of greenhouse
gases and to secure the
energy for the future. Switching
to renewable energy is a
promising solution for the
present crisis.
The high cost of renewable energy electric conversion systems has been a main
hindrance to its development till now. But in order to promote the renewable energy
installations, the policies and regulations are being modified in its favor in all major countries.
Also, due to the recent advancements in technology and research, the cost of renewable
energy electric conversion systems has been continually decreasing with the most significant
price drop being observed in solar, which is 80% over the last seven years. Solar energy (especially
solar Photovoltaic (PV)) and wind energy are two major sources among the renewable energy
resources which have been commercially wellestablished and are proven technologies for
clean electricity generation. By the end of 2015 the global installed capacity of solar PV stood at
227 GW out of 785 GW of total renewable
installations. The renewable energy based power
generation is growing at a faster pace recently,
especially, solar PV. It recorded a huge growth
rate of 28% in 2015. The advancements in the
field of PV panel manufacturing and the inherent
advantages of solar PV over other sources and
technologies have paved way for such a
tremendous growth. The statistical projections
indicate that the global solar PV installations will
grow at even faster pace in the coming years. The
situation is same in India which has set an
ambitious target of 100 GW of solar power by
2022. But these renewable energy resources
when implemented in large scale without any
specialized controls is found to impact the integrity, reliability and stability of the grid. Solar
PV power penetration into the grid is on
continuous rise and plants of order of hundreds
of MW are coming up in India and at global level.
The large upcoming utility scale solar plants are
expected to behave similar to the conventional
plants and support for managing grid stability.
With such an extensive growth in the deployment
of the solar PV, power system operators are
expected to deal with a new set of issues due to
the different nature of the generation. Hence, it is
important to study and analyze the impact of the
large-scale penetration of solar PV power into
the grid.
In this article, the impact of large solar PV
penetration on the steady state performance of
the grid is discussed. The steady state bus
voltages are the main parameters that are
affected by the inclusion of the solar PV plants
into the system. As a consequence, undervoltages
or over-voltages may occur across the
system, because voltages may either increase or
decrease. This analysis helps in identifying the
buses with high or low voltages and the buses
with voltages closer to critical levels, thereby,
preventive action can be taken. Hence, system
reliability and stability can be improved and one can be assured that the system is operating
within the permissible voltage limits.
Thevariation in system losses, and real and reactive power loading of transmission lines at various
penetration levels have also been examined.
IEEE 9-Bus System – Standard Bus System for Analysis
The IEEE 9-bus test system, which is also known as P.M Anderson 9-bus system, has been
modelled in ETAP software. It represents a simple approximation of the Western System Coordinating Council (WSCC) system with 9 buses and 3 generators. Solar PV plant has been integrated into this system. The single-line diagram of the
WSCC 9-bus system is as shown in Figure 1. The voltage levels and transmission line impedances
are also indicated in the same. This test system also includes 3 two-winding transformers of 100
MVA each, 6 lines and 3 loads (135.532MVA, 94.45MVA, and 102.64 MVA). The base kV levels
are 13.8 kV, 16.5 kV, 18 kV, and 230 kV.
Developing Model of Solar PV Plant Integrated to IEEE
9-Bus System in ETAP
The complete test bus system has been first constructed in ETAP. Then a model of a typical
solar PV plant is developed with the help of PV array block. Many small PV panels of 200 Watt
each have been combined in series and paralle combinations to arrive at a PV array with a maximum power of 24.5 MW (MPP power) roughly and a DC bus voltage around 1000V
(Vdc). Each of the PV arrays has an inverter unit with an AC rating of 11kV and 26.2 MVA roughly.
Several such PV arrays have been created and pooled into a common 11kV bus called solar bus.
The output of the solar bus is then given to a station transformer which steps up the 11kV
generation voltage to 230kV, which would be suitable for penetration into transmission bus.
Initially, this solar plant setup has been integrated into the Bus No. 5 of the IEEE 9-bus system as
shown in the Figure 2.
integration has been considered as the base case with 0% solar penetration. Then solar plant has
been integrated into bus-5 first as it has the largest load connected to it. The base case slack
bus power (Generator G1) has been taken as reference for the calculation of solar PV
penetration percentage. The power injected by solar PV plant into the grid through bus-5 is
slowly increased from 0% till around 100% in steps of 10% approximately. Load flow calculation has been performed in each step and various parameters are noted. Steady state power flows
in lines, bus voltages, generation details, and system losses were observed. The process is
repeated with solar PV integration into other buses namely bus-8 and bus-6
Effect of Solar PV Penetration on Steady State Voltages
Three different cases of solar PV integration
namely penetration at bus-5, bus-6 and bus-8
observed. The complete bus data for all solar PV penetration levels from 0 MW till 243 MW are
considered for all three cases. The bus voltages are plotted with respect to the penetration level.
The bus voltages of 11kV solar bus is also indicated. Buses 1, 2 and 3 are excluded from the
plot as they are constant throughout the penetration. This is because Bus 1 is modelled in
swing mode and buses 2 & 3 are modelled in voltage control mode. The plots for all 3 cases are
as shown in Figures. 3, 4, and 5. As seen in plots of bus voltages, the voltage
profile seemed to be improving initially as the solar penetration is increasing but it starts
dropping beyond a certain percentage. Similar trend of voltage variation is observed in all three
cases. The voltage starts collapsing as the solar penetration beyond a certain point causes the
line drop to increase. But the intensity of variation in voltages varied with the location of penetration. The maximum of the variation in bus voltages
observed in all three cases is listed below, • Case 1: 2.5% variation of voltage @Bus 5
• Case 2: 3.35% variation of voltage @Bus 4• Case 3: 8.35% variation of voltage @Bus 5;