Solar panels are modules built with a collection of solar cells and are used for the production of DC voltage and current directly from solar energy.

Materials

Solar panels are made from cells which can be manufactured from several types of materials. These materials are generally group IV elements on the periodic table.  

Silicon

Silicon is the second most abundant element in the Earth's crust and it is therefore much cheaper than other semiconductor materials. Since it links well with the energy of visible sunlight it is the dominant material used for solar cells.

 Gallium arsenide 

Silicon Solar Cells  

There are three basic types of silicon panels: mono-crystalline cells, polycrystalline cells, and amorphous cells. Crystalline silicon is the most common material for commercial applications. It has a well-known standard process because silicon is abundant. However, it requires expensive, highly pure silicon and competes with electronics industry for silicon supply.     

A mono-crystalline cell is the most efficient, but also the most costly photovoltaic cell. 

Panel Type

Solar panels are available in off-grid or on-grid configurations. 

Solar Panel Connectors

There are several types of connectors that are specifically designed for solar panels.     

Encapsulant

An encapsulant is a material used to encase another material. Encapsulation is the method in which PV cells are protected from the environment. This is typically laminated between a glass superstrate and substrate. Encapsulation is the most important part of the module manufacturing process. It keeps out moisture and contaminants that cause PV modules to fail prematurely. They are in fact the "glue" between the front or/and back sheet of the PV cell. Typical materials include: special resins [i.e., DuPont Elvax EVA (Ethilene Vinyl Acetate)], polyvinyl butyral, ionomers, thermoplastic urethane (TPU), polydimethylsiloxane (silcone rubber), etc.

• Ethylene tetrafluoroethylene (ETFE) is a high-corrosion resistant plastic.
• Ethyl Vinyl Acetate (EVA) is a common encapsulant for c-Si modules.
• Polyvinyl Butyral (PVB) is an encapsulant normally used in thin-film modules.
• Thermoplastic is an encapsulant mainly used in thin-film modules.

Specifications

There are several important performance specifications that should be considered when selecting solar panels.   

Power - The output power of the solar cell, also known as solar power, is the conversion of sunlight into electricity, either directly using photovoltaics or indirectly using concentrated solar power.

Efficiency - The efficiency of the solar cell. The solar cell efficiency is the ratio of the elctrical output of a solar cell to incident energy in the form of sunlight.

Open circuit voltage - The open circuit voltage is maximum voltage of the cell when the device is under infinite load, or in an open-circuit situation.

Short circuit current - The short circuit current is the maximum current when the cell is under zero load.

Peak voltage - The maximum voltage produced by the panel or cell.

Peak current - The maximum current produced by the panel or cell.

In order to design a photovoltaic system there are several steps that must be considered. The total load current and operational time should be determined and then system losses can be added. Load refers to all the devices in the system that consume electrical power. Additional design rules include determining the solar irradiation in daily equivalent sun hours, the total solar array current requirements, optimum module arrangement for the solar array, and battery size for recommended reserve time. More information can be found at How to Select Photovoltaic Cells and Panels Information.

Applications

Photovoltaic power is reliable, creates no pollution, and can be quickly installed. A photovoltaic cell manufacturer or a solar cell manufacturer can produce this type of cell for many applications, ranging from calculators to satellites to telephones and vehicles. The expected lifetime for photovoltaic cells can be up to 40 years. The time to recoup the cost of a solar panel averages five years, but can range between one to thirty years depending on the type of solar panel and its larger photovoltaic system. 

Standards

There are several standards which solar panels must adhere to ensure proper design and functionality.

AIAA S-112—This document establishes qualification and quality requirements for single crystal, silicon and gallium arsenide in single, dual and triple junction solar cells for space solar panel applications. It also defines requirements for solar panel manufacturer quality systems and for qualification and characterization of solar panels. Requirements for acceptance testing of panels are not defined in the current version of this document.

ISO DIS 11221—Space System - Space solar panels. Spacecraft charging induced electrostatic discharging test materials.

Resources

Solar-Grid-Tie or Off-Grid

Image credit:

Cannon Water Technologies Inc.