solar.pdf

Renewable Energy Resources
KOE-074 Unit-1
Lecture-5,6&7 : Solar Cell Power
Plants.

Contents
I. Learning Outcomes
II. Introduction
III. Types of Solar Cell power Plants
IV. Design of a Solar Power plant
V. Applications
VI. Advantages and Limitations
KOE-074 Unit-1
Department of Electronics & Communication Engineering

1. Learning Outcomes
The students will able to list different kind of solar power plants.
The students will be able to calculate the different parameters in designing a solar power plant.
The students will be able to compare the different kinds of solar power plant.
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2.Introduction
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❖ Solar power plant also known as solar energy system, solar
system, solar power system and solar plant. It is basically a
modern technique to generate electricity by solar panel
using sunlight.
❖ This system consists of an arrangement of several
components including solar panel to absorb and convert
sunlight into electricity, solar inverter to change the
electricity from DC to AC as well as monitoring the
system, solar battery and other solar accessories to set up a
working system.
❖ In other words you can say solar power system is based on
the conversion of sunlight into electricity, either directly by
using photo-voltaic (PV) panel or indirectly by using
concentrated solar power (CSP).

2.1 Module
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❖ The building blocks of a photovoltaic system are solar cells. A solar cell is the
electrical device that can directly convert photons energy into electricity. There are
three technological generations of solar cells: the first generation (1G) of
crystalline silicon cells (c-Si), the second generation (2G) of thin-film cells (such
as CdTe, CIGS, Amorphous Silicon, and GaAs), and the third generation (3G) of
organic, dye-sensitized, Perovskite and multijunction cells.
❖ Conventional c-Si solar cells, normally wired in series, are encapsulated in a solar
module to protect them from the weather. The module consists of a tempered glass
as cover, a soft and flexible encapsulant, a rear back sheet made of a weathering
and fire-resistant material and an aluminum frame around the outer edge.
Electrically connected and mounted on a supporting structure, solar modules build
a string of modules, often called solar panel. A solar array consists of one or many
such panels. A photovoltaic array, or solar array, is a linked collection of solar
modules. The power that one module can produce is seldom enough to meet
requirements of a home or a business, so the modules are linked together to form
an array. Typical panel ratings range from less than 100 watts to over 400 watts.
The array rating consists of a summation of the panel ratings, in watts, kilowatts, or
megawatts.

2.2 DC-AC Inverter
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❖ Systems designed to deliver alternating current (AC), such as grid-connected applications need an inverter to
convert the direct current (DC) from the solar modules to AC. Grid connected inverters must supply AC
electricity in sinusoidal form, synchronized to the grid frequency, limit feed in voltage to no higher than the grid
voltage and disconnect from the grid if the grid voltage is turned off.
❖ A solar inverter may connect to a string of solar panels. In some installations a solar micro-inverter is connected
at each solar panel. For safety reasons a circuit breaker is provided both on the AC and DC side to enable
maintenance. AC output may be connected through an electricity meter into the public grid. The number of
modules in the system determines the total DC watts capable of being generated by the solar array; however, the
inverter ultimately governs the amount of AC watts that can be distributed for consumption.

2.3 Battery
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❖ PV systems increasingly use rechargeable batteries to store a surplus to be later used at night. Batteries used for
grid-storage also stabilize the electrical grid by leveling out peak loads, and play an important role in a smart
grid, as they can charge during periods of low demand and feed their stored energy into the grid when demand is
high.
❖ Common battery technologies used in today's PV systems include the valve regulated lead-acid battery– a
modified version of the conventional lead–acid battery, nickel–cadmium and lithium-ion batteries.
❖ PV systems with an integrated battery solution also need a charge controller, as the varying voltage and current
from the solar array requires constant adjustment to prevent damage from overcharging. Basic charge controllers
may simply turn the PV panels on and off, or may meter out pulses of energy as needed, a strategy called PWM
or pulse-width modulation.

3. Types of Solar Cell power Plants
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3.1 Central Power Station System
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Central PV power stations are conceptually similar to any other conventional central power station. They
feed power to grid. These are being proposed in few MW range to meet daytime peak loads only. Central
PV power stations of up to 6 MWp (peak MW) capacities have already been experimented within USA
and Europe. While the concept has been demonstrated through such experimental plants, the capital costs
are currently somewhat high for their commercial exploitation. Other configurations such as, single stage
configuration as well as multistage (more than two) are also available for certain applications, which have
their own merits and demerits.

3.2 Distributed System
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Distributed form of energy use is unique and much more successful with solar and most other renewable energy sources.
These systems can be further divided into three groups:
(a) Stand Alone or Off Grid
It is located at the load center and dedicated to meet all the electrical loads of a village/community or a specific set of
loads. Energy storage is generally essential. It is most relevant and successful in remote and rural areas having no access
to grid supply. Indicative capacity of such a system is 10 Wp–100 kWp. Various types of configuration for stand-alone
PV system are shown in Fig.
In Config. 1, a dc load is directly connected to PV panel. This is the simplest possible configuration. Power is available
only during sunshine hours and no arrangement is made for power storage. Such type of arrangement may be used for
supplying raw dc load such as minor irrigation.
In Config. 2, a regulated power is supplied to the load. A DC-DC converter is inserted between panel and load. The
converter may be controlled using MPPT algorithm to extract maximum power from the PV panel. Usually when MPPT
is implemented a battery is used to absorb excess power, which the load cannot consume.
Config. 3 is used for loads such as lighting for which battery storage is required. For safe charging and discharging
operation a charge controller is also required. The use of battery ensures uninterrupted and smooth power availability. In
the charge controller operation, MPPT may also be implemented to optimize the use of solar power.

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Config. 4 also includes ac loads for which an inverter is also required. Since most of the commonly available loads
are ac type, this configuration is suitable for most domestic and commercial applications.

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(b)Grid-Interactive or Grid Tied
This system is connected to the utility grid with two-way metering system. It may be a small rooftop system owned and
operated by the house owner or a relatively bigger (rack mounted) system meant for the whole village or a community.
It meets daytime requirements of the house owner without any battery backup and surplus power is fed to the grid.
During peak hours and during nights the energy shortage may be met from grid. The grid serves as infinite source or
sink of energy.

3.3 Hybrid PV system
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These systems are meant for low energy consumer devices requiring power in the range of microwatts to 10 Wp
and mostly designed for indoor applications e.g. calculators, watches, electronic games, etc.
3.4 Small Consumer System
Solar hybrid power systems are hybrid power systems that combine solar
power from a photovoltaic system with another power generating energy
source.
A common type is a photovoltaic diesel hybrid system, combining
photovoltaics (PV) and diesel generators, or diesel gensets, as PV has
hardly any marginal cost and is treated with priority on the grid. The diesel
gensets are used to constantly fill in the gap between the present load and
the actual generated power by the PV system.
As solar energy is fluctuating, and the generation capacity of the diesel
gene sets is limited to a certain range, it is often a viable option to include
battery storage in order to optimize Solar's contribution to the overall
generation of the hybrid system.

4. Design of a Solar Power plant
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A solar PV system design can be done in four steps:
❖ Load estimation
❖ Estimation of number of PV panels
❖ Estimation of battery bank
❖ Cost estimation of the system.

4.1 Load Estimation
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❖ Base condition:2 CFLs(18 watts each),2 fans (60 watts each) for 6hrs a day.
❖ The total energy requirement of the system (total load) i.e Total connected load to PV panel system = No. of units ×
rating of equipment = 2 × 18 + 2 × 60 = 156 watts.
❖ Total watt-hours rating of the system = Total connected load (watts) × Operating hours = 156 × 6 = 936 watt-hours
❖ Actual power output of a PV panel = Peak power rating × operating factor = 40 × 0.75 = 30 watt
❖ The power used at the end use is less (due to lower combined efficiency of the system = Actual power output of a
panel × combined efficiency = 30 × 0.81 = 24.3 watts (VA) = 24.3 watts
❖ Energy produced by one 40 Wp panel in a day = Actual power output × 8 hours/day (peak equivalent) = 24.3 × 8 =
194.4 watts-hour
❖ Number of solar panels required to satisfy given estimated daily load := (Total watt-hour rating (daily load)/(Daily
energy produced by a panel) =936/194.4 = 4.81 = 5 (round figure)
Inverter size is to be calculated as :
❖ Total connected load to PV panel system = 156 watts
❖ Inverter are available with rating of 100, 200, 500 VA, etc. Therefore, the choice of the inverter should be 200 VA.

4.2 Estimation of battery bank
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❖ The battery type recommended for using in solar PV system is deep cycle battery. Deep cycle battery is
specifically designed for to be discharged to low energy level and rapid recharged or cycle charged and discharged
day after day for years. The battery should be large enough to store sufficient energy to operate the appliances at
night and cloudy days. To find out the size of battery, calculate as follows:
a) Calculate total Watt-hours per day used by appliances.
b) Divide the total Watt-hours per day used by 0.85 for battery loss.
c) Divide the answer obtained in item 4.2 by 0.6 for depth of discharge.
d) Divide the answer obtained in item 4.3 by the nominal battery voltage.
e) Multiply the answer obtained in item 4.4 with days of autonomy (the number of days that you need the system to
operate when there is no power produced by PV panels) to get the required Ampere-hour capacity of deep-cycle
battery
❖ Battery Capacity (Ah) = Total Watt-hours per day used by appliances x Days of autonomy (0.85 x 0.6 x nominal
battery voltage)

4.3 Assumptions Taken For Design
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❖ Inverter converts DC into AC power with efficiency of about 90%.
❖ Battery voltage used for operation = 12 volts
❖ The combined efficiency of inverter and battery will be calculated as : combined efficiency = inverter
efficiency × battery efficiency = 0.9 × 0.9 = 0.81 = 81%
❖ Sunlight available in a day = 8 hours/day (equivalent of peak radiation.
❖ Operation of lights and fan = 6 hours/day of PV panels.
❖ PV panel power rating = 40 Wp (Wp, meaning, watt (peak), gives only peak power output of a PV panel)
❖ A factor called „ operating factor‟ is used to estimate the actual output from a PV module. [The operating
factor between 0.60 and 0.90 (implying the output power is 60 to 80% lower than rated output power) in
normal operating conditions, depending on temperature, dust on module, etc.]

Design Equation
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Design Example
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5. Applications
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❖ Grid Interactive PV Power Generation: Presently, the biggest solar PV plant of 579 MW capacity, solar
star project, is located at Antelope valley, Los Angeles County, California. This is followed by a 550 MW
Desert Sunlight Star at Riverside County, and 550 MW Topaz Solar farm at San Louis, Obispo County,
California.
❖ In India, a 221 MW solar PV plant at Chankara, Gujarat is the biggest plant. Another 750 MW plant is
underway at Rewa, MP. A large number of small rooftop grid interactive systems are successfully being
operated in various parts of the world.
❖ Water Pumping:Pumping of water for the purpose of drinking or for minor irrigation, during sunshine
hours, is very successful application of stand-alone PV system without storage. Water pumping appears to
be most suited for Solar PV applications as water demand increases during dry days when plenty of
sunshine is available. There would be less need of water during rainy season when the availability of solar
energy is also low.
❖ Lighting:Next to water pumping, lighting is the second most important and extensive application of
stand-alone solar PV system. As lighting is required when sun is not available battery storage is essential.

5. Applications
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❖ Medical Refrigeration:Many life-saving medical supplies, particularly vaccines, require refrigeration during
storage and transportation in order to remain effective. For life saving vaccines the World Health Organization
(WHO) has laid down ground rules to maintain the cold chain from point of their manufacture to their application.
In many developing countries where such life-saving vaccines are in great demand, electricity is not available to
operate conventional refrigerators. WHO has specified technical details for PV based refrigerators using solar
energy for such applications.
❖ Village Power:Solar PV power can be used to meet low energy demands of many remote, small, isolated and
generally unapproachable villages in most developing countries. Two approaches have generally been used:
(i) Individual SPV system for every household
(ii) A centralized SPV plant to meet combined load demand of the whole village
❖ Telecommunication and Signalling:In hilly and mountainous terrain, radio and TV signals may not reach as they
get blocked or reflected back due to undulating terrain. At these locations, either low power transmitters (LPT) or
very low power transmitters (VLPT) are installed to receive and retransmit the signal for local population. As
these locations are generally remote and normal grid supply is not available, these are powered by solar Solar
Photovoltaic Systems photovoltaic electricity.

6. Advantages and Limitations
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❖ Save up to 100% electricity bills.
❖ One time Investment and free power for life.
❖ 30% to 90% subsidy on solar panel.
❖ Return on Investment in just 3-5 years.
❖ Eco friendly technique of power production.
❖ Increase the value of property and your goodwill also.
❖ Cost effective method of generating electricity.
❖ Easy to install and low maintenance.
❖ Provides backup in off grid and hybrid solar power system.
❖ Benefits of solar net metering is also available.
Limitations
❖ Needs one time heavy investment.
❖ Required only shadow free area for installation.
❖ Regular maintenance is must for regular generation.

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