Design criteria

DESIGN CRITERIA BEFORE DESIGN A SYSTEM

Precaution to consider before start designing

• Before designing,check the components rating availability. 
• According to the availability of market standard products,make the design simple and easy. 
• 4main considerations to take into account:

           >load requirement

           >inverter standard ratings(power,std.voltage ranges of DC input/AC output)

           >battery capacity

           >SPV module Wattage

Efficiency factors to be consider while designing the system

• Overall system efficiency from panel output to terminal loadpoint,which terminated as 77%to82%. 
• Solar panel-take output as 90 to 95% of the STC(standard Testing condition)rating 
• Inverter-consider 95to98% for transformer less inverters,and 80to85%nfor inverter with built-in-transformer. 
• Battery-efficiency due to internal battery losses80to85% 
• Derating factor for the DOD(depth of discharge)60to70% 
• Charge controller 15-25% increase in ampere ratings(overload capacity)
• Cable-consider sizing 115%of the operating current(amperes)in circuits 
• DC and AC circuit breakers-125% of overload current for over load protection and upto 250% of short circuit current in the system 
• And the circuit breakers to be designed and specified for the maximum AIC(ampere interrupting capacity)rating equal to the potential fault current that may flow into the specific circuit section.

Inverter design and sizing:

• Input of the inverter rating which should not be less than the total demand load in watts of the system and care should be taken that the inverter capacity covers the maximum demand/peak load device. 
• For stand alone system-inverter size should be 25-30%larger than the demand load 
• Grid-tie system-the input rating should be same as the PV modules 
• Total demand watt of the system is raised by the inverter efficiency 
• Inverter input DC voltage range:12v,24v,48v,96v,144v,192v,240v,400v…..upto 960v

Solar charge controller and sizing:

• It is typically rated against ampere and voltage capacities. Select cc to match the voltage of pv array and batteries and identify which type of cc is right for your application.make sure that cc has enough capacity to handle the current from PV array.

• For series cc type ,the sizing of cc depends on the total PV input current which is deliverd to the cc and also depend upon PV panel configuration.(series and parallel configuration).

• The ampere is increased by the 15% upto 25% to avoid the losses and overloading

• Ranges in market:10A,15A,82A,85A……250A ans voltage upto 600volts.

• According to standard practice,the sizing of cc is to take the short circuit current(Isc)of the PV array,and multiply it by 1.25(125%) ,CC rating=total short circuit current of PV array*1.25

Battery sizing with backup:

• Determine the total watt-hour energy storage and multiply with the number of days storage requirement.

• Raise such arrived capacity by inverter efficiency,battery efficiency and battery DOD factor and divide by system nominal voltage,to arrive battery capacity in Ah

• Nominal voltage which chosen according to panel output and inverter input voltage

• 12v battery available ranges:25Ah,40Ah,70Ah,100Ah,135Ah,150Ah,185Ah,200Ah

• Req.installed battery capacity=(total watt-hour of energy required for storage)/(batt.effi*batt.DOD*batt.bank operating DC voltage)

Solar Tracking System

SOLAR TRACKING

What is solar tracking?

• Tracking the solar panel or module towards the sun.It helps to reduce the incident angle.

Incident angle-Angle between the module and sun is called incident angle

 

if angle of incidence is zero gives peak power

Efficiency -tracking vs mounting

Depend upon the sun traveling tracking is classified into two types they are

Single axis tracking:

This type of tracking is used for track the sun in one direction -East-West

 

• Increase solar yield up to 34%
• Simple, effective design
• Low maintenance
• Lower cost compared to dual axis
• Minimal points of failure

Dual Axis Tracking:
This type of tracking is used for track the sun in bi- direction -East to west and North to South 

• Increases solar yield up to 37%
• Complex design – more motors and sensors
• Higher maintenance
• Higher cost due to additional parts and installation time
• Additional points of failure

Back Tracking:
 array of single or dual axis solar tracker panels can be made more efficient by the use

of

backtracking.To minimise shading and maximise the power so that the maximum amount of solar energy can be harvested



Efficiency using backtracking

 

 

TYPES OF SOLAR INVERTER

Solar panels output is Direct Current but it is not directly used for home appliances and cannot connected to the grid so it is need to convert Alternating current by using inverter.It has several types

they are explained below

solar system works:

Micro Inverter:

It consist small box behind the solar panel .micro inverter converts DC to AC from each panel.

 

Prons:

• Longer Warranty- warranty of 20-25 years – 10-15 years longer than central inverters.

• Easily Expandable-you can expand the solar panel later easy with micro inverter.

• No Single Point of Failure-if any one of the solar panel is affected the solar system is unaffected and running continuously.

Cons:

• Increased complexity in installation

• Increased maintenance costs due to there being multiple units

• some micro-inverters may have issues in extreme heat.

String inverter:

it has large box placed distance from array.This type is used in home and solar plants.

Pron:

• 3 phase variations available 
• Low cost
• Allows for high design flexibility 
• High efficiency
• Possibility to extend warranty to 20 years

Cons:

• High voltage levels present a potential safety hazard
• Higher DC watt unit cost.
• More inverter connections

Central inverter:
This type of inverter designed for large application like industrial and solar power plants.it has very large size .arrays outputs are collected and given to the central inverter.
 
Prons:

• Low capital price per watt 
• High efficiency 
• Comparative ease of installation

Cons:

• Large size

• More noise

• if the potential low at single area, the entire system is failure.

• 10-15 year warranty it is less compare to other inverter

 

 

 

solar panel connection

SOLAR PANEL WIRING

Solar energy system having different type of connection depends on the required output

Series connection of solar panels:

• series connection gives more voltage

 

in series connection voltage is added and current is same

V=V1+V2+V3.....

I=I1=I2=I3......

FOR EXAMPLE:

if panel1=12V,panel2=12V,panel3=12V

output voltage is 12V+12V+12V=36V

Parallel connection of solar panels:

• in parallel connection current is added and voltage is same

I=I1+I2+I3...

V=V1=V2=V3....

Example and connection is shown in the below figure

output current is 4A+4A+4A=12A

 

Series and Parallel connection:

• in some places need both connections .To attain voltage and current efficiently use these type of connections.

 

in this connection both voltage and current added.

V=V1+V2+V3.....

I=I1+I2+I3...

V=12V+12V=24V

I=10A+10A+10A=30A

 

solar inverter

INVERTER 

what is solar power inverter?

In electrical systems,current has different types they are,

• Direct current (DC): Current always flows in the same direction between those two terminals.

•  Alternating current(AC): The direction of the current reverses, or alternates, 60 times per second or 50 times per second

 How do solar inverter works?

By connecting the DC system to input part, AC power is obtained from the output part.Solar inverters are composed of two different units: 

•  Convert Unit: Here, the voltage comes as DC to the system and is converted into AC by means of MOSFET and other electronic components.

By switching alternating MOSFET we mean, when the first signal is positive, the second signal will be negative and when the first signal becomes negative, the second signal becomes positive.This process is periodically and get AC output. 

• Amplifier Unit: Transformers are electrical components that are used to increase or decrease the AC values on the grid.

for example:there is a system connected to the input of the transformer which is 200V,4A but 1000V voltage is required from the output. What is the output current?

P (power) = I (current) x V (Voltage)
P-input = 200 x 4 = 800W
P-out = 1000 x (I-out)
800 = 1000 x (I-out)
I-out = 0.8A

In the picture below, you can see how a transformer unit works and turns ratio

 

Types of Solar Panel Power Inverters

There are two different power inverter types according to the grid connections:

• stand alone(off-grid)inverter:They are the inverters that work separately from the grid. Electronic devices are connected to the inverter output directly. The main reason why they work separately from the grid is because there is no hardware that would enable them to work synchronously with the grid.

Stand-Alone inverters have DC input and AC output units. Output wave doesn't necessarily have to be full sine. 

• Grid-tie(synchronous)inverter:These are the inverters that are connected to the grid. The grid tie inverter must synchronize its frequency with that of the grid (e.g. 50 or 60 Hz) using a local oscillator and limit the voltage to no higher than the grid voltage.In the picture below you can see grid-tie power inverter connection.Grid-tie inverters are also designed to quickly disconnect from the grid if the utility grid goes down,the grid tie inverter will shut down to prevent the energy it transfers from harming any line workers who are sent to fix the power grid. You can find grid tie inverters in the market with more power and voltage options. It is a more commonly used product.Grid tie inverter having galvanic isolation and Maximum power point tracking(MPPT).

Working principle of Grid tie inverter:
 
DC to DC converter: The input voltage is first raised by the boost converter formed with inductor L1, MOSFET Q1, diode D1 and capacitor C2.By switching of Power MOSFET Q2-Q5 ,Q3-Q4 alternatively at the periodic time get isolating converted output DC voltage.T1 can be a so-called step-up type to amplify the input voltage
DC to AC converter:conversion stage turns DC into AC by using another full bridge converter. It consists of IGBT Q6-Q9 and LC-filter L3, C4.The IGBTs Q6-Q7,Q8-Q9 work as electronic switches that operate in PWM mode. This topology requires anti-parallel freewheeling diodes to provide an alternate path for the current when the switches are off. These diodes are either included within IGBTs or added externally.Solar panels provide different power in different points of their volt-ampere (V-I) characteristic. The point in the V-I curve where output power is maximum is called maximum power point (MPP). The solar inverter must assure that the PV modules are operated near their MPP. This is accomplished with a special control circuit in the first conversion stage called MPP tracker (MPPT).

construction of solar panel

 CONSTRUCTION OF SOLAR PANEL

• The basic requirement of the solar panel is Photo Voltaic(PV) cell.Different type of solar cell is used in solar panel.They are monocrystalline,polycrystalline,thin film.

 
Cell:

• It converts sunlight into direct current (DC)electricity.

Module/Panel:

• To achive desire voltage ,number of PV cells are seriesly  interconnected  together.

For example: To obtain 12V Panel  36 cells connected in series and 24V panel 72 cells connected in series.

Array: 

• PV array, individual PV modules are connected in both series and parallel.

.

     Main components are used in the construction of the solar panel  

• Frame :Mechanical support for entire components(glass,cell,Back sheet)

• Solar glass: Protect cells from environment while allowing the light energy to pass through
• EVA Film:Ethylne vinyal acetate polymer act as encapsulation material.

• PV cell: It converts light into electricity.

• Bus ribbons:used to carry the elecrical current throughout the PV module.

• EVA Film:Ethylne vinyal acetate polymer act as encapsulation material.

• PV back sheet:Laminate protects PV module from UV rays,moisture,weather while act as an insulator. 

PV Ribbon