After reading this you probably know more about solar panels than your installer.
THE CRYSTALLINE SOLAR-PANEL
Through research, innovation and billions of dollars of investment over the last decades the solar panel as we know it today has reached a level of development that makes it affordable for the average household and makes it possible for us to draw our daily energy need. The last generation solar panel has become so durable that it can produce energy for forty years at a cost of about 5 cents per watt. In comparison, at the dawn of the ‘solar revolution’ in the late 1970’s, the price for that same ‘crystalline silicon watt’ was about $75.
Production of solar panels and solar cells
What we call a solar panel is actually a ‘module’. A module contains a series of soldered rows of solar cells.
A solar cell is made from silicon which is made from pure quartz. The silicon is heated till it melts and a minimum of Boron is added to give it electrically conductive properties. Thin slices are cut from the material after it has cooled down and hardened.
These slices are then treated in a phosphor bath before the top side receives an anti-reflective coating. Then contacts are attached to the top side (positive) and an aluminized conductive material is applied to the bottom side (negative). The cells are arranged in a row, soldered together and then laminated to protect them from the elements and slow down aging. The cells are further protected with a layer of glass and fitted in a plastic or aluminum frame.
The description of this production process is a brief summary of what is actually a meticulous process subject to stringent regulations over which inspectors keep a watchful eye all over the world. Still faults can occur in production batches and these faults can result in a reduced energy output after a panel has been in use for only a few years. That is why it is important to invest in panels that come with a warranty certificate but also to make sure that the manufacturer and or the importer honor the warranty.
It is true that with many brands, usually relatively unknown brands, the question of honoring warranty is a grey area. Especially when many of these smaller brands are going out of business and disappear and importers and installers can not always be traced. A reputable installer will therefore prefer to work with a reputable brand and deserves you preference.
Monocrystalline
The dark blue or nearly black panel is usually a monocrystalline panel. The crystals in this panel are of high purity which is achieved during production when the single crystal is slowly grown. A high purity ensures a better absorption of sunlight.
Polycrystalline
The blue panel that can often be seen on roofs is usually a polycrystalline panel. Less pure than the monocrystalline variant it is recognizable by the blotched appearance of the surface. In this case the single crystal is not grown but molten silicon is poured into a mold. A process that is quicker and cheaper.
Often the preference goes out to a monocrystalline panel because its cells of are made from purer silicon. However, the current generation of polycrystalline panels from reputable manufacturers are no longer inferior to their monocrystalline variant and this due to advances in their production process.
Note: a solar panel comes with it’s own certificate in which the manufacturer mentions the average output.
Determining the output
When starting to investigate solar energy systems you will encounter terminology like ‘250Wp’ or ‘275Wp’. Wp stands for Watt Peak. One Wp is the unit used to describe the average generating capacity of a solar cell or module tested according a standard procedure. It is an average capacity because many factors like irradiance, air pressure and temperature have their influence during use. In a so called flash-test these factors are measured and compiled after which the module is classified according to it’s capacity category then serialized and a corresponding certificate is created.
After production of a batch of modules has finished the manufacturers classify the entire batch according to an average capacity. A batch of modules that yields an average value of 265 Wp, but not lower than 250Wp, will often receive the designation 250 Wp on to which the manufacturer will specify a deviation of, for instance, +3%. This tolerance means that the modules could produce up to 3% more energy than the figure mentioned on the certificate. Some manufacturers go as high as +5%. It’s better to ignore quotes that propose modules with a – tolerance. Another indicator of outdated technology is if the module only has 2 conductors, also called busbars, per solar cell. Busbars are the metal-colored lines that interconnect the cells and they transport the energy that is generated.
Attention points
At least three busbars per cell
At least a tolerance of +3%
Note: when a system proposal or quote is attractively priced the reason might be that you are being offered an older and maybe outdated technology. Request the datasheets for the modules that are being proposed.
The thin film solar panel
At the moment this type of panel is not yet widely used for noncommercial purposes. The main reason being the rapid decrease of efficiency in comparison to the crystalline panel. The thin film panel is made up of ultra thin solar cells, also called amorphous or flexible cells, and best known from portable calculators.
The thickness of the solar cell, a mere 1 micrometer or 0.039 mils (0.001 mm), gives the thin film panel it’s name.
In comparison: a crystalline cell measures 350 micrometer in thickness. The production process is different as well. A mix of semiconductors is sprayed on to a substrate. This extremely thin layer is flexible but is enough to absorb sunlight. The semiconductors used in this process are not always the same and depending on which one was used the thin film will receive a suffix to it’s name. The three most common semiconductors are:
• – Amorphous silicon (a-Si)
• – Cadmium telluride (CdTe)
• – Copper, Indium, Gallium Deselenide (CIGS)
Up until recently thin film panels were produced using a-Si solar cells. These cells have the annoying trait to age quickly when directly exposed to sunlight. Despite the production process being cheaper in comparison to crystalline cells this makes them less interesting for use on a roof. The remaining two, CdTe and CIGS, are relatively new. Especially CIGS-technology seems very promising. The use of Gallium slows down the aging of the solar cell and ensures a more efficient energy management. Pure Gallium does not occur in nature but is amply present all over the world. In small quantities it is present in bauxite, aluminum, coal and even in the human body. This makes Gallium quite precious and expensive.
Currently there are crystalline panels being offered that are Gallium panels. The manufacturer adds a hint of Gallium to the conductors and claims that the efficiency is increased. Independent test results that could verify these claims are not yet available. Because of the precious Gallium these panels are more expensive.
Tinted solar panels
Sometimes the color of solar panels is a reason for people not to buy them. On many roofs the blue color stands out and some find that ugly, others do not mind. In other instances the building code simply does not allow such a color on a roof. In America the rules and regulations are often quite stringent and such an exclusion is often found.
Transparent modules
If you have visited the new railway station in Rotterdam then you have probably seen them: transparent solar panels. I can vividly remember the first time I saw the immense roof of the platform hall made up of transparent solar modules. I was instantly enchanted and could not stop myself from tweeting a picture.
But transparent solar modules are less exotic than we would expect. During production less cells are incorporated leaving more room between them. The absence of a backing layer leaves the panel largely transparent and the cells they contain seem to float.
Less solar cells off course mean less capacity in comparison to a standard solar panel of the same size. Therefore the choice to use transparent solar panels is mainly made from an esthetic point of view.
MODULE DATASHEET
Every solar panel has it’s own datasheet. I like to call it a panel passport. Amongst other things the datasheet will state which standards the panel meets, which is the maximum capacity it can deliver and which warranties apply. It has proven to be difficult for many people to get a good understanding of the many abbreviations and descriptions. What follows is a summary of commonly found descriptions on a datasheet.
High Module Efficiency: Maximum capacity of the panel measured per square meter as per STC (Standard Test Conditions). In short this means that the maximum capacity can be achieved according to the specifications of the STS on the 41st parallel north or otherwise said, at the level of New York, California, Nebraska, Illinois, Ohio, Barcelona, Rome and Istanbul.
Positive Power Tolerance: The amount the capacity can deviate from the stated value, expressed as a perecntage. Usually +3% or +5%. Never a negative value.
Robust frame to up 4.500 Pa load: Indicates the force per area the panel can withstand. Indicates the resistance to weather conditions like snow, storm and hale.
Outstanding Performance at Low Irradiance: Indicates that the panel performs above average in low sunlight conditions.
High Energy Yield at Low NOCT (Nominal Operating Cell Temperature): Modules are tested in more ideal conditions than the ones they will eventually be used in. With this description the manufacturer wants to make clear that the panel will perform well in less ideal circumstances.
EL Screening (Electro Luminescence): During manufacturing the cells are tested for defects before laminating.
Current Binning: With this technique any minute interruptions within the electrical circuit of the cell, which could interfere with the current, are removed.
Accredited Salt Mist / Ammonia Resistance: Indicates resistance to a coastal/marine environment.
25 Years World Wide Coverage: Manufacturer’s warranty for 25 years.
100% Warranty Term Coverage: The manufacturer is entirely responsible for the mentioned coverage during the warranty period.
Providing Third Party Bankruptcy Rights: In case of bankruptcy of the seller the customer will be covered by the manufacturer’s warranty.
Non-Cancellable: The warranty cannot be revoked unilaterally.
Insured by Two World top Insurance Companies: The manufacturer has deposited the warranty with two major worldwide insurance companies. If the company would go out of business these insurances will remain active.
IEC – 61215: Satisfies the International Electrotechnical Commission standard regarding aging by weather conditions.
IEC – 61730: Satisfies the International Electrotechnical Commission standard regarding safety.
IEC – 61701: Satisfies the International Electrotechnical Commission regarding corrosion in marine environment. UL 1703: Underwriters Laboratories standard regarding absorption of light intensity.
ISO 9001: Standar by the International Organisation for Standardization regarding quality management in organisations.
Cell Type: Indicates monocrystralline or polycrystalline cells. The amount of busbars is also mentioned.
Cell Arrangement: Number of cells in a module including the specific arrangement.
Dimensions: The module’s hight, width and depth.
Weight: The total weight of the module.
Front Cover: Thickness and type of glass cover.
Frame Material: Specifies the material the frame of the module is made of.
J-Box: The type of junctionbox at the back of the panel.
Graph I-V Curves: The current/voltage ratio.
ISO/TS 16949: A type of quality management certification.
ISO 14001: Indication that the product satisfies environmental standards.
QC080000 HSPM: Indication that the product satisfies standards regarding use and disposal of hazardous substances.
OHSAS 18001: Meets British operational health and safety standards.
Pmax: Maximum nominal power.
Vmp: Voltage at maximum power.
Imp: Amperage at maximum output.
Short circuit current: The maximum current expressed in amperes.
Module efficiency: The power output that is converted from absorbed sunlight.
Operating temperature: Temperature range in which good working order is guaranteed.
Maximum system voltage: Maximum voltage load in configuration with the transformer.
Maximum series fuse rating: Maximum load of the panel in ampere.
Application Classification: Indicates the class of panel. Summary of qualities and certification.
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Arjan Eikelenboom – @mrsunshinenet –
