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An unlimited supply of clean energy

  Mar 20, 2021   

Solar Energy System Components: On-Grid and Off-Grid

Solar Energy System Components

Solar energy is considered as a clean source of energy. To reduce electricity bills and promote clean electricity, solar energy proves to be a suitable option for households among all the renewable energy sources. It requires low maintenance and has a long life span with less mechanical losses (no moving parts are present).

Solar energy system is divided into two types:

  1. Off – Grid System
  2. On – Grid System

          Off – Grid System                                                               On – Grid System

type of solar energy systems

Basic components of solar power system (off-grid and on-grid) are as follows:

1.Solar panel: Solar panels are the most important part of the solar energy system; it converts solar energy into electric energy. A solar panel consists of a series of solar cells (typically made up of silicon material). The solar radiation incident on these cells is converted into DC electricity by photovoltaic effect. The output power of the solar panel is given in Watts.

Generally, with proper maintenance solar panels have a lifespan of 25 to 30 years.

Common types of solar panels are as follows:

  1. Polycrystalline solar panel – They are multi-crystalline and require generally more space. They are less efficient and cheaper compared to monocrystalline cells, and currently it is the most commonly used solar installation technology across the world.
  2. Monocrystalline solar panel – They are made up of a single silicon crystal and have a higher efficiency than polycrystalline cells. They require less area but are slightly more expensive.
  3. Thin film solar panel – They are very thin and can even be made into flexible panels. They require a comparatively higher space area and have a low efficiency 
solar panel types

Some new-generation solar panels, including those featuring perovskites, are currently at the cusp of commercial deployment.

Passivated Emitter and Rear Cell or Passivated Emitter and Rear Contact (PERC): PERC  technology is currently in use both in monocrystalline and polycrystalline solar cells. These solar cells are made out of the same conventional silicon wafer on the top side for absorbing the incident photons. The main difference between the conventional and PERC solar cell is the addition of a dielectric passivation layer on the rear side that helps in absorbing the scattered solar radiation.

This additional feature helps in converting solar light into usable electric power even under low light conditions.

converting solar light to electric power

2. Array Junction Box: The array junction box is one of the components used between the solar module and inverter.

Array junction box performs following functions:

  1. The main function of an array junction box is to electrically connect the output of various solar string wires in parallel.
  2. It consists of blocking diode on each string to protect the panel from reverse current
  3. It also  protects the system against overcurrent and overvoltages.
array junction box

3. Inverter: Inverter is known as the heart of the solar energy system. It helps in converting the produced DC (Direct current) output from the solar panel into AC (Alternating current) supply.

Most of the appliances at our home runs on AC supply, hence the inverter plays an important part in the conversion of the DC to AC. 

Inverters not only help in the conversion of power but also help in synchronizing the generated power with the appliances. This is done with the help of a conventional transformer-based or transformer less inverter.

 Inverters are classified as follows:

  1. Off -grid inverter – These inverters work independently and have no contact with the power grid system.
off grid solutions

Grid inverter– These inverters are connected to the power grid system and are the most common type of inverters used in residential applications.

on grid solutions

Grid inverters are further classified as:

String inverter: String inverters are in high demand due to their feasible cost and durable technology. In these multiple strings are connected to build a single string inverter. It comes with a drawback that if a single string gets damaged or comes under the shadow it may lead to the performance degradation of an entire inverter.

string inverter

Micro-inverter: As the name indicates this type of inverter is mostly used where space is the factor over cost (they are more costly than string type inverter), or in case of uneven shading in small solar installations. These inverters are placed on every solar panel, thus independently converting DC to AC supply. In this, even if one panel is shaded or damaged, the performance of the other panels is not affected. 

micro inverter

Central inverter: Central inverter is similar to string inverter with a high-capacity range, needing only 1 large inverter for the entire plant / section of plant. They are mostly used for large utility-scale applications.

central inverter

Hybrid inverter– Hybrid inverters are the combination of off-grid and on-grid systems. They offer a lot of flexibility for power delivery by choosing between solar power, battery backup and grid connectivity.

hybrid solutions

Solar racking and mounting (module support): Solar panels are installed either on rooftops, on ground, or as an individual pole mounted array.

Installing a solar panel in any of the above places requires proper mounting support. Mounting support not only helps in attaching the solar panel but also helps in positioning the panel at an angle that will provide maximum exposure to the solar radiation.

Mounting support is of two types:

  1. Fixed mounts– Fixed mounts are stationary and less expensive. This type of mounts cannot move with the change in angle of the sun; hence they are less efficient. 
  2. Track mounts: These mounts are flexible and rotate as per angle of the sun. The direction of the sun changes throughout the day and track mounts can follow solar radiation producing the optimum result. They are costly but more efficient as compared to a fixed mount system. Track mounts require more maintenance and are suitable for larger ground mount plants.

In rooftop systems, we usually consider only fixed mounts; the angle at which the panel is placed is optimized on the basis of the location’s latitude, allowing for as much power to be used as possible from a fixed system.

5. Cabling system: Solar cables are considered as blood vessels of the solar installation. They are responsible for the flow of electric current from the panels to the loads through the inverter.

It is important to determine the correct solar cable to ensure the system does not overheat and has sufficient current carrying capacity while keeping prices low. The size of solar cable depends on the solar panel electricity generation and the distance between the solar system and the loads.

Solar cables are classified into two types:

AC cable – These cables are used for connecting solar power inverters to the grid through other protection components, and deliver AC power from the inverter to the grid / load.

DC cable – These cables connect the panels to each other and to the inverter, and deliver the DC power generated by solar panels to the inverter. These cables are used outdoors and hence, should be insulated properly.

6. Distribution box : Distribution box or distributional panel(board) is the component of the electricity supply system. It is commonly of two types:

  1. DC Distribution Board (DCDB): DCDB is used for connecting the output power from the solar panel to the input of the inverter. Additionally, DC surge protection devices may be connected with the DC distribution box to provide against any fault in the system.
  2. AC Distribution Board (ACDB): ACDB distributes the electrical power from a solar inverter to the AC load system through an energy meter.  ACDB consists of additional protective equipment such as circuit breaker,surge protector or fuse to disconnect the solar system from the load side supply in case of any failure.
Distribution Board

Meters: For a grid-connected system, energy meters play an important role in tracking the amount of energy generated, utilized, and sold to the utility grid.

three types of meters are used in the solar energy system

Generally following three types of meters are used in the solar energy system:

  1. PV meter – PV meters are connected in series with the inverter of the solar system. These meters take into account the energy generated by the solar panel.
    1. Load meter – It is connected on the load side to note the energy consumed by different loads. 
    1. Net meter – It is connected between the grid and solar distribution panel. They are bidirectional meters. that help in monitoring the supplied and consumed power to and from the grid.

       PV and load meter are unidirectional meters and the net meter is a bi-directional meter.

8. Protection device: Due to the direct and indirect lightning and other fault conditions, components of the solar system may get damaged. To protect the solar system from these damages, protection devices such as surge arrestor, circuit breaker, grounding method and other safety devices are installed.

Off -grid connected solar:

         Off-grid system requires some other components in addition to all the essential components described above.

1. Energy storage battery: For an off-grid system or any standalone solar system, energy storage plays an important role. Energy is stored in the battery during the daytime when the solar panel generates electricity and supplies power during night time (or cloudy weather). Batteries used for solar systems undergo frequent charging and discharging, hence rechargeable batteries are used. Solar batteries help us to reduce the dependency on the utility grid, thus, saving the cost required to buy electric power from the grid.

 Types of battery

                  There are two types of batteries that are commonly used:

  • Lead acid battery – These batteries are cheaper and less efficient (80-85%) compared to lithium batteries. The depth of discharge of these batteries is 50%. Lead-acid batteries are recommended when cost is the criteria and power requirement is less. 
  • Lithium battery – Lithium batteries are costlier but they prove to be more efficient (90 to 95%) than lead-acid batteries and are maintenance-free. Depth of discharge of these batteries are 80 to 90% and are recommended for solar street lights, solar powered vehicles, mobile battery banks, etc. where there is a requirement for regular usage and deep discharge.

Depth of discharge means the actual amount of energy that can be withdrawn from the battery.

The selection of solar batteries plays an important criterion. Battery selection depends on factors such as daily usage of the load, efficiency, and lifespan of the battery.

2. Charge controllerIt is responsible for determining the adequate amount of charge to be withdrawn and supplied to the battery. It plays a vital role in improving the efficiency of the battery bank by protecting it from overcharging.

Types of charge controllers:

  1. Simple 1 or 2 Stage Controls
  2. Pulse Width Modulated (PWM)
  3. Maximum Power Point Tracking (MPPT)

Optional components:

optional components of solar energy

1. Backup generator – It is not an essential component but a good choice for places where continuous power supply is a must. Automatic generators are configured to start automatically when solar power or backup power is shut down.

The transfer switch is used for switching the power between the generator (diesel) and solar panel as per the need, either manually or can be configured to automatically switch as per the set condition.

2. Load centre – AC or DC load centre consists of a circuit breaker, fuses, and other required switches in a panel board like structure. It helps in regulating the voltage and current as per the load requirement.

The above-described optional components may be added to the system as per the design requirement.

 

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