Solar PV Module with High-Efficiency:

What is the High Efficiency Solar PV Module?

As we know a solar PV module is a Photovoltaic (PV) module, also known as a solar panel, is a solid-state device that converts sunlight into electricity.

Here, we consider 19.5-20% efficiency as high-efficiency solar PV modules, but efficiencies up to 24% are also feasible nowadays.

High-Efficiency Solar PV Module has the following characteristics:

Minimum module efficiency of 19.50% with a Temperature coefficient of Pmax better than -0.30% per degree Celsius

or

Minimum module efficiency of 20% with a Temperature coefficient of Pmax equal to or better than – 0.40% per degree Celsius

Here solar panels are 19.5% efficient, which means that 19.5% of the energy in that sunlight reaching the solar panel gets turned into electrical energy.

Let us see what is the Pmax and Temperature coefficient of Pmax is

Pmax-Maximum Power at Standard Test Conditions:

Pmax is used as the main parameter in manufacturing High-Efficiency Solar PV Modules.

• Pmax = Maximum Power at Standard Test Conditions (STC), i.e. Irradiance 1000 W/m², cell temperature 25°C, air mass (AM)= 1.5;

Temperature coefficient of Pmax:

Module’s temperature coefficient of Pmax refers to the percentage change in Pmax per degree Celsius rise in temperature.

Solar PV Module Efficiency Calculation:

Solar panel efficiency is calculated by dividing the module power rating (Pmax) by the area (m2) at Standard Test Conditions   STC (1000W/m2).

% Solar PV Module Efficiency = Pmax/ (Area x 1000 W/m²) x100

Hence from the above formula, we came to know that

The two factors determine solar panel efficiency:

1. The photovoltaic (PV) cell efficiency, based on the solar cell design and silicon type, and
2. The total panel area is based on the cell layout, configuration, and panel size.

Stages Involved in Manufacturing High-Efficiency Solar PV Module:

Stage-1:

Manufacturing of Polysilicon or Monocrystalline

Solar panels installed today are made of either Monocrystalline or Polycrystalline types.

Manufacturing a Polysilicon or Monocrystalline from Metallurgical grade silicon (MG-Si), which is made from silica, is used in the production of solar panels. 

Monocrystalline silicon panels are made from a single silicon ingot sliced into thin wafers, and are the most efficient, at 17% to 22%. 

Polycrystalline silicon is a multi-crystalline form of silicon with high purity and is used to make solar photovoltaic cells at a cheaper price.

Polycrystalline silicon panels generally range from 15% to 17%. 

Monocrystalline solar cells are more efficient than polycrystalline cells.

Stage-2:

Manufacturing of Ingots-Wafers from Stage-1 Polysilicon or Monocrystalline Silicon

Growing an ingot and using it to make wafers are the processes involved in this stage.

Growing an ingot:

It is the first step in the silicon wafer manufacturing process. To grow a silicon ingot, the first procedure is to heat the silicon to 1420°C, which is above the melting point of the silicon. 

Most single-crystal silicon wafers are grown through the CZ method, while the rest are grown through the FZ method. 

• Float Zone (FZ) Method: Silicon is melted by induction heating. The float zone (FZ) method is a technique, for growing crystals and alloys without a crucible. It uses a high-purity polycrystalline rod and a monocrystalline seed crystal to create a single crystal. 

• CZ Method: A magnetic field is applied to the melted silicon. The Czochralski (CZ) method is a crystal growth technology that starts with the insertion of a small seed crystal into a melt-in crucible, pulling the seed upwards to obtain a single crystal.

Manufacturing Wafers:

• Slicing: 

The circumference of the Monocrystalline ingot is ground down to a uniform diameter. The ingot is then sliced into thin wafers using a wire saw

• Lapping:

The sliced wafers are lapped to remove saw marks and surface defects

• Polishing:

The wafers are polished in a clean room to create a highly reflective, scratch-free surface

 Stage-3:

Manufacturing of Solar cells from Stage-2 Wafers

Silicon wafers are then fabricated into photovoltaic cells. The first step is chemical texturing of the wafer surface, which removes saw damage and, increases how much light gets into the wafer when exposed to sunlight.  

Most cell types require the wafer to be exposed to a gas containing an electrically active dopant, and coating the surface of the wafer with layers that improve the performance of the cell.

Screen printing silver metallization for electrical contacts as shown in the above figure is also very common among cell types.

 Stage-4:

Manufacturing of PV Modules from Stage-3 Solar Cells

Copper ribbons plated with solder connect the silver busbars on the front surface of one cell to the rear surface of an adjacent cell in a process known as tabbing and stringing.

The interconnected set of cells is arranged face-down on a sheet of glass covered with a sheet of polymer (EVA- ETHYL VINYL ACETATE) encapsulant. A second sheet of encapsulant is placed on top of the face-down cells, followed by a tough polymer back sheet or another piece of glass.

The whole stack of materials is laminated in an oven to make the module waterproof then fitted with an aluminum frame, edge sealant, and a junction box in which the ribbons are connected to diodes that prevent any backward flow of electricity.

Electrical cables from the junction box convey the current produced by the module to an adjacent module or the system’s power electronics.

The negative contact of one solar cell is connected to the positive contact of the next cell.