How Do Solar Panels Work

In order to truly understand how solar technology works without creating any carbon emissions post-production, we've created this page to teach you the basic ins and outs of what solar panels are all about. As mentioned on our home page, solar panels are among the most common technologies used to convert solar power into electricity. This section is designed to explain how they work, their make-up, the different types of technologies used, and what to expect in terms of selection when you're looking to purchase one.

Basic make-up:

Solar panels are different from solar thermal collectors, the other common solar technology, in that they convert solar energy into electricity, whereas thermal collectors convert solar energy into usable heat energy. Solar energy is collected and then converted to electricity by photovoltaic technology, specifically solar/photovoltaic cells. (Photovoltaic cells convert energy from light into electricity, and solar cells specifically convert solar energy into electricity). Solar panels are made up of an installation of photovoltaic modules, also called a photovoltaic array. These modules contain several layers of photovoltaic cells connected electronically and packaged into a module. The units are commonly framed in aluminum or other metals, plastic or fiberglass and encased in glass. When several modules are mechanically fastened together, wired, and designed to be an installable unit, they then get the name of solar panel.

"These solar powered installations also generally require an inverter, batteries (for off-grid use, mainly away from city centers), and interconnected wiring."

Crystalline silicon and gallium arsenide are two examples of common materials used to produce solar cells. Gallium arsenide crystals are grown especially for photovoltaic use, and are therefore more expensive and in more limited supply, while silicon crystals are available in less-expensive mass quantity, often cast into a shape that is easy to handle - called an ingot. Silicon crystals are used extensively in the production of several micro-electronic technologies. While crystalline silicon does have lower sunlight-to electricity conversion efficiency, it's lower cost makes it a popular component.

On the Production Line

During process of production of solar cells, crystalline silicon ingots are sliced into wafer-thin disks and polished to do away with any rough edges caused by the slicing. Then, one or more doping agents are added, in order to alter and/or enhance the optical/electrical properties of the cell. Afterwards metallic conductors are planted onto the surface of each cell. The conductors generally have a thin grid on the side facing the sun and a flat sheet on the other. After the solar cells are created and fused with conductors, they are then constructed into solar panels, as previously explained, by encasing and protecting the cells in glass, and cementing the materials onto a rigid or flexible substrate.

After constructing the panel, electrical connections are then prepared in series or wired in parallel to achieve the required voltage of electricity and/or source capability. However in order for the electrical connections to work, the cement/encapsulant and the substrate layer must both be thermally conductive. Because solar cells heat up from absorbing infrared energy, and not all of that energy is converted into electricity, it must be released into the air surrounding the panel.

"If the cells overheat, their efficiency decreases, so it's advantageous to ensure that conductive materials are present when they should be."

Categorizing Solar Panels

Solar panels are categorized into different types based on the type of material their solar cells are made up of and also to an extent how they are designed. There is also different packaging for different types which is required in order to protect the cells from environmental damage. There are three basic module types- Crystalline Silicon modules, rigid thin-film modules, and flexible thin-film modules. Generally solar panels will fall into some variation of these categories.

Crystalline Silicon modules

Crystalline Silicon modules are the most common design of solar panels today. They contain 72 photovoltaic cells that are linked through the use of conductive ribbons and divided into three 'strings' of solar cells. These strings are encased using a polymeric encapsulant between solar glass in the front, and a strong and flexible polymer backsheet. To ensure everything stays in place and sticks together, the encapsulant is melted and cross-linked in a vacuum laminator. Also, the strings of photovoltaic cells are electrically terminated into a junction box generally glued onto the module's back. Afterwards, a frame typically made of aluminium is fitted around the module's edges. Although crystalline models usually have a conversion rate of only about 10-12 %, they are also cheaper to produce because of the ever-ready supply of silicon - it's also virtually harmless to the environment, which is likely what makes them a popular type of solar panel for manufacturers.

Rigid Thin film modules

Rigid thin film modules are another, slightly less common type of solar panel, in which the solar cell is produced directly onto a glass substrate or superstrate (layer), and the electrical connections are created while the solar cell is in place. The substrate or superstrate is laminated with an encapsulant to a front or back sheet, as in crystalline silicon modules; however these modules use different materials and production techniques in their creation of solar cells. The primary solar/photovoltaic cell technologies used in the production or rigid thin film modules are: CdTe or cadmium telluride ? an efficient light absorbing material, different in that it is easier to deposit and more suitable for large-scale production. Despite the fact that cadmium is a heavy metal, in CdTe-based cells the release of cadmium into the atmosphere is actually lower than with silicon-based cells and other thin-film solar cell technologies; Amorphous silicon - which is also an efficient light absorbing material, amorphous silicon is also popular in large-scale production of solar panels; Micromorphous silicon - which is less efficient for large scale production than it's amorphous counterpart; and CIGS (Copper Indium Gallium Selenide) - another semiconductor material used to produce solar cells, these cells have so far reached an efficiency of almost 20% (there are also several different variations of this type of cell, some which include the use of sulphide as another additive).

Flexible thin film modules

Flexible thin film cells are the third basic type of solar panel technology. They are designed somewhat similarly to the other modules, except that they deposit the photoactive layer and other necessary layers (of encapsulant, solar cells, etc) on a flexible substrate. If the substrate is an insulator (e.g. polyester or polyimide film) then monolithic integration (the use of an integrated circuit, formed in a single chip) can be used in the system's set up, however if the substrate or backing of the solar panel is a conductor, then monolithic integration cannot be used, and another technique for electrical connection must be used instead. The cells are packaged into a panel unit by laminating the layers to a transparent clear fluoropolymer on the front side and a polymer made of material suitable for bonding to the last substrate on the back. However, the only commercially available panel in mass quantities in a flexible thin film module is an amorphous silicon triple junction from Unisolar.

Efficiency

The efficiency of solar panels depends largely on its construction and the materials that make up its solar cells. Theoretically, a solar panel can collect a range of frequencies of light and can produce electricity from them; however photovoltaic technology has yet to collect energy from the entire solar spectrum of light. Unfortunately much of available incident sunlight energy is wasted during the use of solar panels. However, the panels do become more efficient when illuminated by monochromatic light. Also, some of the more technologically sophisticated multi-spectrum photovoltaic arrays have various solar cells that are tuned to different light frequency ranges. Although these advanced panels can raise the effectiveness of the solar panels conversion rate by several times, it is also still much more pricey to manufacture.

"Presently a typical photovoltaic module converts about 15% of sunlight into electricity."

However there are solar panels out there that have a much higher rate of conversion, like the afore-mentioned multi-spectrum arrays. Until recently, a Stirling solar system had the record for efficiency in converting energy from the sun into electricity with a conversion rate of 30% at 1,000 watts per square meter. However, systems that harness such a high level of concentrated sunlight unfortunately generate little to no electricity when conditions are overcast. This is due to the fact that they incorporate a solar tracker which aims the panel directly at the sun, and if the sun is hidden behind clouds, the technology ceases to function. Also, the previous record of 30 per cent has now been broken by a panel developed by a consortium led by the University of Delaware, which had a conversion efficiency of just over 40 per cent. This may seem low, but during the 1990's conversion rates were 30% lower than they are today, so definite progress has been made, and will continue as the technology develops, and production costs are lowered through more efficient techniques.