Design Aspect of Solar PV System

 

Design Methodology



  • PV systems are designed to meet the demand load as per the requirement.
  • Configuration selections are the most considerable procedure in designing a solar PV plant. 
  • Selection of the quality of a component to maintain project cost within the budget.
  • PV system sizing involves the determination of the sizing and capacity of various components like PV panels, batteries, etc.

Mainly two approaches are used in a PV system design depending upon the level of details used in component sizing

  1. Approximate sizing
  2. Precise Sizing

Design Steps

PV system design proceeds in the reverse direction of energy flow

Step 1: Load estimation
Step 2: Inverter sizing
Step 3: Battery sizing
Step 4: Solar radiation estimation
Step 5: PV panel sizing

Load Estimation

Following parameters are considered while estimating load requirement

  1. Type of load (AC or DC)
  2. Number of Loads
  3. The power rating of each load
  4. Hours of operation
  5. Energy requirement per day(kWh/day)

Selection of Components

To select solar PV system components, we need to consider the parameters which are listed below-

  • Location of the roof,
  • Types of roof i.e. RCC, Tilt, etc.
  • Orientations of the roof
  • Total loads connected
  • the power requirement, 
  • the characteristics of the mounting area 
  • Aesthetic(Look) preferences, etc

On-Grid Solar System

Solar PV Modules selection

  • The Solar PV Modules are employed to capture the sun's energy and supply DC power to the system.
  • Solar panels and modules are connected together into a PV string to form a solar PV array.
  • A typical commercial solar panel measures between 2010 mm × 1007 mm × 36 mm(Length × Width × Height).
  • However, solar PV panels come in a wide range of shapes, sizes, and power outputs to suit specific applications and designs.
  • Modules may be selected on the basis of the total plant capacity and per module capacity to match the total required power capacity.
  • Solar PV panels can be usually mounted horizontally or vertically to best fit the mounting space.

Solar PV Inverter selection

  • As we know, the main function of an inverter is to convert the DC power generated by solar PV systems into AC power.
  • The converted AC power is supplied to the house holding loads or surplus power is fed to the grid.
  • Solar power inverters are sized and chosen, taking into account the power capability of each solar panel, the operating temperatures, and the number of solar panels in each string to accommodate voltages.
  • For example, for a PV plant with a DC capacity 200kWp, we need to design the inverter with an AC output capacity of 200kW.
  • On the basis of the types of inverters, a modular design may employ many small inverters as micro-inverters whilst one or two central inverters could also be chosen based on which setup achieves the optimum power output.

Solar PV Mounting Systems

  • Module mounting structures or MMS, are another essential component used in solar PV systems.
  • Roof-mounted MMS would be the most cost-effective option when retrofitting a solar PV system according to the desired outcome.
  • Most standard solar PV panels are supplied with Aluminum frames that are designed to be securely attached to prefabricated rails.
  • These rails are then used to secure the whole solar assembly to the roof.
  • Added weight on the roof, size of the roof (how many panels/how much power), and shading must be manipulated before finalizing the designs.
  • Ground Mounted is also a cost-effective solution for solar PV MMS if it possesses enough open space on the ground.
  • Ground-mounted MMS has become commercially viable nowadays to install solar PV systems.

AC and DC Isolators:

  • AC and DC Isolators are the protective devices that are used to separate faulty parts from healthy parts of a PV system for safety when carrying out installations, upgrades, and maintenance work.
  • For safety, isolators should be installed anywhere where it may be beneficial to disconnect a part of the power system for a period of time.
  • AC isolator should be provided between the main distribution board or consumer unit and the inverter(s) enabling easy disconnection of the whole PV system from the power supply.

AC & DC Combiner Boxes

  • AC combiner boxes are used on the output side of the inverter where loads are connected. 
  • These combiner boxes are used to ensure the safety of the loads and in any abnormal condition, the protective device inside the boxes either trips the system or disconnects the supply to the loads.
  • This setup is also used to safely terminate multiple strings of PV panels on the DC side i.e., before connecting to the inverter.
  • Not always necessary for smaller systems, PV combiner boxes provide the useful functions of being able to safely isolate and fuse individual PV strings and aggregate many smaller PV strings into fewer cables before connecting them to the inverter.
  • Solar Photo-Voltaic Roof Top(SPVRT) strings are connected in a junction/combiner box which also contains overcurrent protection devices and/or switch disconnectors.
  • SPVRT array and SPVRT string combiner boxes shall be at least IP 54 compliant in accordance with IEC 60529 and shall be UV resistant.
Cables & Connectors
    • Basically, there are two types of cables used in the solar PV systems-DC cables & AC cables.
    • DC cables are used on the DC side, meaning, all the cables connected from the PV plant to the input side of the inverter are DC-type cables.
    • AC cables are used on the AC side of the solar PV system, which means all the cables connected from the inverter output side to the Load side are AC-type cables.
    • Both cables are used to connect the various components and are sized and selected to perform at their best based on rated values.
    • All the cables used in the solar PV must be of standard IP ratings.
    • Cables and connectors are installed in a secure, safe area where they are unlikely to be damaged.
    • String cables connect the modules in series and to the array junction box. 
    • DC inverter cables connect the SPVRT array and DC isolator to the inverter.
    • Array cables connecting the array junction box to the SPVRT array.

Generation Meters

  • These meters are used to measure the electricity that a solar PV system generates.
  • They keep track record of the total generated power/units of the solar PV plant.
  • These meters are available for both 1-phase as well as 3-phase power networks, which must be approved by the franchises.

Remote Monitoring System

  • Most inverters are equipped with data module and communication system which sends daily energy generation.
  • This system is used for a purpose of regular monitoring of the solar PV system.
  • This is essential because we always need to check the PV system performances and the health of the plant.
  • This system can be carried out simply by most commercially available inverters, many of which can be supplied with network cards and integrated into PC and web applications.
  • Output displays of all sizes for both private and public locations where the inverter isn't accessible can also be supplied and relatively simply connected.
  • An independent energy generation and performance monitoring system can also be installed.
  • Whenever required, a residual current monitoring and earth fault alarm system shall be installed.
Lightning Protection System
  • The need for a lightning protection system shall be assessed and installed in accordance with IEC 62305-2, IEC 62305-3 or IS2309.
  • If a lightning protection system (LPS) is already installed on the building, the SPVRT system should be integrated into the LPS as appropriate in accordance with IEC 62305-3.
  • In the case where no lightning system is required on a building or in a case of a free-standing array, overvoltage protection may still be a good option to protect the array and the inverter and all parts of the installation.
Earthing & Grounding
  • Earthing is the procedure where one or more parts of an electrical system are physically connected to the ground, which is considered to have zero-volt potential.
  • Whereaswhile “Grounding” the circuit is not physically connected to ground, but its potential is zero with respect to other points.
  • The key differences are:
Earthing
  • This method protects the human being from electrocution.
  • Earthing contains zero potential.
  • The earth wire used is green in color.
  • Earthing is primarily used to avoid shocking the humans.
  • Earthing is located under the earth between the equipment body underground.
Grounding
  • This method protects the entire power system from malfunctioning.
  • Grounding does not possess any zero potential.
  • The wire used for grounding is black in color.
  • Grounding is primarily used for unbalancing when the electric system overloads.
  • It is located between the neutral, of the equipment being used, and the ground.

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