Solar Panels – A Brief Overview

A SHORT HISTORY OF SOLAR PANELS

Solar panels got their start further back in history than most of us know. Becquerel discovered the photovoltaic effect in 1839.  Becquerel’s discovery then led to the invention in 1883 by Charles Fritts of the first genuine solar cell which was formed by coating sheets of selenium with a thin layer of gold. And from this humble beginning would arise the device we know today as the solar panel.

Russel Ohl, an American inventor on the payroll of Bell Laboratories, patented a light sensitive device 1941. Ohl’s invention led to the production of the first solar panel in 1954 by the same company. Solar panels found their first mainstream use in space satellites.

In 1955 – Western Electric licences commercial solar cell technologies. And Hoffman Electronics-Semiconductor Division creates a 2 % efficient commercial solar cell for $25/cell or $1,785/ watt. Things got better from there with efficiencies and price drops.

For most people, the first solar panel in their life was probably embedded in their new calculator – circa the 1970s!

How Do Solar Cells Work

Solar modules use light energy (photons) from the sun to generate electricity through the photovoltaic effect. Most solar modules are rigid, but semi-flexible ones are available, based on thin-film cells. These early solar modules were first used in space in 1958.

The cells must be connected electrically to one another and to the rest of the system. Externally, popular terrestrial usage photovoltaic modules use MC3 (older) or MC4 connectors to facilitate easy weatherproof connections to the rest of the system.

Bypass diodes may be incorporated or used externally, in case of partial module shading, to maximize the output of module sections still illuminated.
Some recent solar module designs include concentrators in which light is focused by lenses or mirrors onto an array of smaller cells. This enables the use of cells with a high cost per unit area (such as gallium arsenide) in a cost-effective way.

Solar Cell Efficiency

Much of the incident sunlight energy is wasted by solar modules, and they can give far higher efficiencies if illuminated with monochromatic light. Scientists from Spectrolab, a subsidiary of Boeing, have reported development of multijunction solar cells with an efficiency of more than 40 %, a new world record for solar photovoltaic cells. The Spectrolab scientists also predict that concentrator solar cells could achieve efficiencies of more than 45 % or even 50 % in the future, with theoretical efficiencies being about 58 % in cells with more than three junctions.

Other basic factors that affect the amount of power a solar panel will produce–

Irradiance – how much solar energy reaches the earth or a specific area. Usually measured on watts/sq meters

Insolation – When it is perpendicular, Insolation– how much solar energy reaches each spot on the earth affected by angle and strongest

Heat – When the temperature rises the solar cells become less efficient, heat– and how this can lower the amount of power produced–

Solar Panel and Solar Cell Definitions

Solar Cell: Semiconductor device that converts sunlight into direct current (DC) electricity
Module: PV modules consist of PV cell circuits sealed in an environmentally protective laminate and are the fundamental building block of PV systems
Solar Panel: Includes one or more PV modules assembled as a pre-wired, field-installable unit
Array: A PV array is the complete power-generating unit, consisting of any number of PV modules and panels
The primary component of a solar panel is the solar cells, or photovoltaic cell. This is the key component that converts sunlight into electricity.
At the present time about 80 % of all solar panels are made from crystalline silicon (i.e., monocrystalline, polycrystalline, amorphous silicon, or hybrids) solar cells. Typically the solar cells are laid out in a grid pattern– with perhaps as many as 72 different solar cells.

The other 20 % consist primarily of solar cells made mostly from Cadmium Telluride and a small but growing amount from CIGS. The appeal of these types of cells is their low cost resulting from the fact they can be made in large single sheets.

There is a lot of research going on in the industry to develop more efficient and lower cost solar panels. Click on Solar Research to learn about some of these developments.

The solar panels, after usually after being hermetically sealed to protect them are covered in a non-reflective glass to protect the solar cells from environmental damage and placed into a rigid frame.
Typically, the frame is designed to prevent it from deforming due to freezing weather or strong winds. The frame will usually include a drainage hole to help prevent water buildup on the panels, which can reduce output.
The back of the panel is also sealed to prevent damage. This is typically where the junction box is located.

Purchasing A Solar Panel System

The amount of power solar panels produce is influenced by the amount of sunlight falling on your specific location per year, the efficiency of the underlying solar cell technology, the materials and technology used in making the solar panel, keeping your panels clean, and the amount of time the solar panel has been in use.

When purchasing solar panels, it is therefore wise to look beyond size and look at the dollars/watt ratio. As solar project developers in Europe – we look more at the estimated kWh produced over the life of the solar panel … and calculate what our net return on investment will be.

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