Confidential_Only for review purpose_Pushkar Singh Sani
SOLAR PV SYSTEMS DESIGN
TIPS ENGINEER ZONE�www.tipsengineerzone.in
SOLAR POWER SYSTEM DESIGN�Course content
INTRODUCTION
Solar Power – The Unlimited source of Energy
Limitless solar energy
The sun provides more than enough energy to meet the whole world’s energy needs, and unlike fossil fuels, it won’t run out anytime soon. As a renewable energy source, the only limitation of solar power is our ability to turn it into electricity in an efficient and cost-effective way
Solar energy - a clean source
No greenhouse gas emissions are released into the atmosphere when you use solar panels to create electricity. And because the sun provides more energy than we’ll ever need, electricity from solar power is a very important energy source in the move to clean energy production.
No fuel to burn
After solar panels have been installed, operational costs are quite low compared to other forms of power generation. Fuel isn’t required, and this means that solar power can create large amounts of electricity without the uncertainty and expense of securing a fuel supply.
Types of Solar PV System
A solar PV system is basically of three types:
On-Grid (Grid Connected) Solar PV System:
In On-grid solar PV system the energy generated is directly consumed by the loads running and the extra
energy is fed to the government utility grid. There is no provision of energy storage in this system.
Off-Grid (Standalone) Solar PV System:
In Off-Grid solar PV System the energy generated is stored in batteries for night consumption and simultaneously consumed by the loads running. This system is used where there is no provision for utility grid available, generally used in rural areas. This system is not connected to the utility grid.
Hybrid Solar PV System:
Hybrid solar systems generate power in the same way as a common On-Grid solar system but use special hybrid inverters and batteries to store energy for later use. This ability to store energy enables most hybrid systems to also operate as a backup power supply during a blackout, similar to a UPS system.
Solar PV Grid Connected System
A grid connected solar PV system uses solar module as the power generation source. The power produced is fed into an inverter which changes the DC power output of the solar array to AC power compatible with power grid standards.
The major component of grid connected PV system are as follows:
Other Than that…
ELECTRICAL BASIC
THIS TOPIC COVERS BASIC TERMS AND LAWS USED IN ELECTRICAL SYSTEM.
Voltage OR electric potential difference is the difference in electric potential between two points, which (in a static electric field) is defined as the work needed per unit of charge to move a test charge between the two points. In the International System of Units, the derived unit for voltage (potential difference) is named Volt (V).
When a potential difference causes is a charge to move between two points, the charge in motion is called an electric current. The number of electrons that can be forced to move depends on the potential difference between the two points. The greater the potential difference, the greater the current flow.
Current is the flow of electrons between two points and is measured in Amperes (A).
Resistance is a measure of the opposition to current flow in an electrical circuit. Resistance is measured in Ohms
(Ω).
Ohm's Law is a formula used to calculate the relationship between voltage, current and resistance in an electrical circuit.
V = I x R ………..Formula 1
Electric power is the rate, per unit time, at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt (W).
P = V x I ………..Formula 2
Energy is defined as the capacity to do work. It is measured in watt-hour (Wh).
E = P x T(in hours) ………..Formula 3
In alternating current, the electric charges flow changes its direction periodically. AC is the most commonly used and most preferred electric power for household equipment, office, and buildings, etc.
Alternating current can be identified in waveform called a sine wave, in other words, it can be said as the curved line. These curved lines represent electric cycles and are measured per second. The measurement is read as Hertz or Hz.
Unlike alternating current, the flow of direct current does not change periodically. The current electricity flows in a single direction in a steady voltage. Everything that runs on a battery and uses an AC adapter while plugging into a wall or uses a USB cable for power relies on DC. Examples would be cell phonesEverything that runs on a battery and uses an AC adapter while plugging into a wall or uses a USB cable for power relies on DC. Examples would be cellphones, electric vehicles, flashlights, flat-screen TVs, electric vehicles, flashlights, flat-screen TVs
Electric power is the rate, per unit time, at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt (W).
P = V x I ………..Formula 2
Energy is defined as the capacity to do work. It is measured in watt-hour (Wh).
E = P x T(in hours) ………..Formula 3
In alternating current, the electric charges flow changes its direction periodically. AC is the most commonly used and most preferred electric power for household equipment, office, and buildings, etc.
Alternating current can be identified in waveform called a sine wave, in other words, it can be said as the curved line. These curved lines represent electric cycles and are measured per second. The measurement is read as Hertz or Hz.
Unlike alternating current, the flow of direct current does not change periodically. The current electricity flows in a single direction in a steady voltage. Everything that runs on a battery and uses an AC adapter while plugging into a wall or uses a USB cable for power relies on DC. Examples would be cell phones, electric vehicles, flashlights, flat-screen TVs, electric vehicles, flashlights, flat-screen TVs
Alternating Current | Direct Current |
AC is safe to transfer longer distance even between two cities, and maintain the electric power. | DC cannot travel for a very long distance. It loses electric power. |
The rotating magnets cause the change in direction of electric flow. | The steady magnetism makes DC flow in a single direction. |
The frequency of AC is depended upon the country. But, generally, the frequency is 50 Hz or 60 Hz. | DC has no frequency of zero frequency. |
In AC the flow of current changes its direction backwards periodically. | It flows in a single direction steadily. |
Electrons in AC keep changing its directions – backward and forward | Electrons only move in one direction – that is forward. |
The frequency of an AC waveform is defined as the number of times that the voltage cycles per second
(Hertz, Hz). It is the rate at which current changes direction per second.
The power which is actually consumed or utilised in an AC Circuit is called True power or Active power or Real power. It is measured in kilowatt (kW). It is the actual outcomes of the electrical system which runs the electric circuits or load.
The power which flows back and forth that means it moves in both the directions in the circuit or reacts upon itself, is called Reactive Power. The reactive power is measured in kilo volt-ampere reactive (kVAR).
The product of root mean square (RMS) value of voltage and current is known as Apparent Power. This power is measured in kilo volt-ampere (kVA).
The Beer Analogy
part you want.
Power factor (PF) is the ratio of working power, measured in kilowatts (kW), to apparent power, measured in kilovolt amperes (kVA). Denoted by cosφ.
Power Factor (cosφ) = Active Power(kW)
Apparent Power (kVA)
In solar, generally the power factor is always unity.
S OLAR RADIATION
THIS TOPIC COVERS BASIC TERMS USED IN SOLAR ENERGY FIELD.
Solar radiation or irradiance is radiant energy emitted by the sun from a nuclear fusion reaction that creates electromagnetic energy. The spectrum of solar radiation is close to that of a black body with a temperature of about 5800 K. About half of the radiation is in the visible short-wave part of the electromagnetic spectrum. The other half is mostly in the near-infrared part, with some in the ultraviolet part of the spectrum.
This is measured in Watt/Square meter (W/m2).
As sunlight passes through the atmosphere, some of it is absorbed, scattered, and reflected by Air
molecules, Water vapor, Clouds, Dust, Pollutants, etc. this is called diffuse solar radiation.
The solar radiation that reaches the Earth's surface without being diffused is called direct solar radiation. The sum of the diffuse and direct solar radiation is called global solar radiation.
It is the total quantity of radiant solar energy per unit area received over a given period, e.g. daily, monthly or annually. This is measured in kilowatt-hours/Square meter (kWh/m2).
The term "peak sun hours" refers to the solar insolation which a particular location would receive if the sun were shining at its maximum value for a certain number of hours. Since the peak solar radiation is 1 kW/m2, the number of peak sun hours is numerically identical to the average daily solar insolation. For example, a location that receives 8 kWh/m2 per day can be said to have received 8 hours of sun per day at 1 kW/m2.
The conditions under which the solar modules output is rated are:
Air Mass: 1.5
Solar Radiation: 1000W/m2 Cell Temperature: 25˚C
Air Mass: 1.5
Solar Radiation: 800W/m2
Cell Temperature: 20˚C Wind Speed: 1m/s
The Air Mass is the path length which light takes through the atmosphere normalized to the shortest possible path length (that is, when the sun is directly overhead). The Air Mass quantifies the reduction in the power of light as it passes through the atmosphere and is absorbed by air and dust. The Air Mass is defined as:
AM=
1
cos(𝜃)
The location of the sun is specified by two angles:
Altitude (γ)
Altitude refers to the angle between the sun and horizontal (or ground), and is always an angle between 0˚ and 90˚. The sun is higher in the sky in summer and lower in the sky in winter due to the natural tilt of earth with respect to the sun as the earth orbits the sun throughout the year.
Azimuth (α)
The angle between the north and the sun’s position. The sun moves from East to West across the sky through the day. The angle between north and the point of the compass where the sun is position is called azimuth angle. In general, the azimuth is measured clockwise going from 0˚ to 359˚. East is 90˚, South is 180˚ and west is 270˚.
Module Tilt Angle (β)
Solar Module should be placed so that the amount of radiation collected is a large as possible. To achieve this, when facing either true south or north (depending whether you are in the northern or southern hemisphere), the solar modules should be tilted at an angle to the horizontal such that there is 90˚ angle between the sun (at solar noon) and the solar module as shown in figure.
To point a module directly towards the sun at all times would require a solar tracking frame to be installed. This can be expensive, so it is not common practice in grid connected PV systems, particularly on a small systems. The most common approach is there for install the system at an angle which will provide the highest annual yield. This involves installing the module at tilt angle that is perpendicular to the radiation at solar noon on the equinox that is at an angle that is equal to the latitude of the site.
PV C E L LS
This topic covers the basic description of solar cells and PV modules.
What is a Solar Cell?
A solar cell (also known as a photovoltaic cell or PV cell) is defined as an electrical device that converts light energy into electrical energy through the photovoltaic effect. A solar cell is basically a p-n junction diode.
Individual solar cells can be combined to form modules commonly known as solar panels. The common single junction silicon solar cell can produce a maximum open-circuit voltage of approximately 0.5 to 0.6 volts. By itself this isn’t much – but remember these solar cells are tiny. When combined into a large solar panel, considerable amounts of renewable energy can be generated.
Construction of Solar Cell
A solar cell is basically a junction diode, although its construction it is little bit different from conventional p-n junction diodes. A very thin layer of p-type semiconductor is grown on a relatively thicker n-type semiconductor. We then apply a few finer electrodes on the top of the p-type semiconductor layer.
These electrodes do not obstruct light to reach the thin p-type layer. Just below the p-type layer there is a p-n junction. We also provide a current collecting electrode at the bottom of the n-type layer.
How Electricity Generates from Solar Cell ?
The working principle of solar cells is based on the photovoltaic effect, i.e. the generation of a potential difference at the junction of two different materials in response to electromagnetic radiation. The photovoltaic effect is closely related to the photoelectric effect, where electrons are emitted from a material that has absorbed light with a frequency above a material-dependent threshold frequency.
Power Characteristics of Solar Cell
The power produced by a solar cell is the product of the voltage and the current for the particular operating characteristics.
P = V x I
P is zero when I or V are zero. This occurs at Isc (when V=0) and Voc (when I=0). For every voltage along the I-V curve that a solar cell can produce, there can be only one corresponding current output. This means that the power generated by the PV module also vary depending on what voltage the cell is operating at.
If we plot power as a separate axis on the I-V diagram, we can see
how power varies between the two extremes.
The power generated by a solar cell will reach a maximum when the internal resistance of the cell is equal to the resistance of the load and is known as the maximum power point (MPP or Pmax). The voltage and current at this point are referred to as Vmp (voltage at max power) and Imp (current at max power) respectively.
It is important to ensure that solar cells operate at or near the maximum power point, so that the PV system has the highest possible output.
Fill Factor
The fil factor (FF) indicates how much series resistance and how little shunt resistance there is in solar cell and its circuit. The fill factor is measurement of how ‘square’ the I-V curve is.
The fill factor is the ratio of maximum power to the product of Isc and Voc and is an operating characteristics which indicates the performance of the cell. Decreases in fill factor may indicate problem with the cell.
𝐹𝐹 =
𝐼𝑚𝑝 × 𝑉𝑚𝑝
𝐼𝑠𝑐 × 𝑉𝑜𝑐
Factors affecting the performance of Cell
Temperature
As the temperature of solar cell increases, the open circuit voltage Voc decreases but the short circuit current Isc increases marginally. The Vmp of the cell decrease and hence so does the power output.
Cell Temperature = Ambient Temperature +25˚
Irradiance
As the temperature of solar cell increases, the open circuit voltage Voc decreases but the short circuit current Isc increases marginally. The Vmp of the cell decrease and hence so does the power output.
Types of Solar Cell
Basically there are two types of cell available in
market:
Polly Crystalline Cell Mono Crystalline Cell
Crystalline Cell:
Both monocrystalline and polycrystalline solar panels have cells made of silicon wafers. While both of these types of solar panels have cells made from silicon, monocrystalline and polycrystalline panels vary in the composition of the silicon itself. Monocrystalline solar cells are cut from a single, pure crystal of silicon. Alternatively, polycrystalline solar cells are composed of fragments of silicon crystals that are melted together in a mold before being cut into wafers.
Thin Layer (Film) Cell:
A thin-film solar panel is made of thin films of semiconductors deposited on glass, plastic or metal. The films are incredibly thin, often 20 times thinner than c-Si wafers. This makes thin-film solar panels flexible and lightweight. If the thin-film cells are encased in plastic, the product could be flexible enough to mold to a roof’s shape; when glass is used, thin-film panels are more rigid and heavier.
There are three common types of thin-film cell:
Amorphous silicon (a-Si), Cadmium telluride (CdTe) and Copper Indium Gallium Selenide (CIGS) or Gallium-free CIS.
4BB Polycrystalline Solar Cell
Image Source: Renewsys
5BB Polycrystalline Solar Cell
Image Source: Renewsys
6BB Polycrystalline Solar Cell
Image Source: Renewsys
9BB Monocrystalline Solar Cell
Image Source: TW Solar
9BB Monocrystalline Bifacial Solar Cell
Image Source: TW Solar
PV modules
Solar cell are connected in series in solar module.
Classification of Solar Module:
Based on type:
Further:
Poly Crystalline Solar Module
Mono Crystalline Solar Module
Half Cut Mono Solar Module
Bi-Facial Solar Module
Poly Crystalline Solar Module
Module Datasheet:
INVERTERS
This topic covers the basic description of solar inverters.
What is inverter?
Inverter is a power electronic device which converters DC generated from from Solar PV module into
AC.
Types of Solar Inverter
Based on capacity and function:
Based on uses:
Micro Inverter:
Image Source: Enphase
String Inverter:
Image Source: Delta
Central Inverter:
Image Source: ABB
Image Source: ABB
Offgrid Inverter:
Image Source: Waaree
Image Source: Waaree
Inverter Protection Systems
A grid connected inverter will only function if it can detect the grid reference it, meaning that the grid meets certain operating specifications itself (as specified in the Central Electricity Authority (Grid Standards) Regulations, 2010). Therefore if these grid conditions are not present, the inverter will not synchronise with the grid and therefore will not produce any power from the PV array.
Protection in inverters:
Anti islanding Protection, in this the Grid tied inverter will starts exporting power only when it gets reference (in terms of voltage and frequency) from the Grid, once the parameters get synched only then it will start exporting the power, this process takes times (5sec to 5min or more) as per Grid.
MOUNTING STRUCTURE
This topic covers types of mounting structure used in solar.
Module Mounting Structure (MMS)
Any solar system is designed to function for 25 years thus material plays an important role in the overall solution. The strength of the material is defined by the geography and environment of the location being installed. Hence, there is a growing need for highly durable, rust-free, corrosion-resistant materials.
Module mounting structure (MMS) used are generally made up of Aluminum, GI sheets, HDG iron, PosMAC (POSCO Magnesium Aluminum Alloy Coated) material. MMS provides support and required tilt to solar modules
In India the MMS design is done as per IS-875 Part-1,2,3,4 & 5
Types of MMS
Based on location:
1) Roof top MMS
RCC Roof MMS
Shed Roof MMS
Based on tilt:
Module Tilt Angle (β)
Solar Module should be placed so that the amount of radiation collected is a large as possible. To achieve this, when facing either true south or north (depending whether you are in the northern or southern hemisphere), the solar modules should be tilted at an angle to the horizontal such that there is 90˚ angle between the sun (at solar noon) and the solar module as shown in figure.
To point a module directly towards the sun at all times would require a solar tracking frame to be installed. This can be expensive, so it is not common practice in grid connected PV systems, particularly on a small systems. The most common approach is there for install the system at an angle which will provide the highest annual yield. This involves installing the module at tilt angle that is perpendicular to the radiation at solar noon on the equinox that is at an angle that is equal to the latitude of the site.
Module Tilt Angle (β)= 180˚-90 ˚ Altitude of Sun
PV Array Row Spacing
PV array row spacing is the spacing between the front and
rear row, this spacing is used to prevent the shadow cast of
front row to rear side row.
Y= Row Spacing X=Module rear height
X= sin(tilt) x length
angle
2) Take the solar noon timing for determining the azimuth & altitude angle on 21 December (Winter solistic) because at that time the sun is low in the sky and at top of the panels in southern side.
BALANCE OF SYSTEMS
Balance of systems used in solar PV system.
Balance of system
Apart from two main components of solar PV system which are Modules & Inverters the rest key items used in
solar PV system are:
DC Cables
to Array junction
Uses of DC cable in solar PV system:
1) String cables connecting modules box/Inverters
AC Cables
Uses of AC cable in solar PV system:
Array Junction Box
Array Junction Box (AJB) are used to provide protection to the system, this box is having DC fuses, DC
isolators, DC SPD as per site requirement.
Solar ACDB
Solar ACDB or Solar LT panel, here the AC output from all inverters is collected and further transferred/distributed
to load. This panel is having AC circuits breakers (MCB, MCCB, ACB), AC SPD, etc.
Protection & Disconnect Switches
DC fuse holder & fuse
MC4 connectors
DC Isolator
DC SPD
Plastics Cable Gland
Moulded Circuit Breaker (MCB)
Moulded Case Circuit Breaker (MCCB)
AC SPD
Metal Cable Glands
Cable Lugs
Lightning Protection & Earthing System
Lightning protection system is used to protect the solar plant from lightening strikes during thunderstorm.
….To be continued
TIPS ENGINEER ZONE�www.tipsengineerzone.in