WHAT YOU NEED TO KNOW BEFORE BUYING SOLAR PANELS
Categories: Solar Power
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.
The dark blue or nearly black panel is usually a mono-crystalline 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.
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 radiation, 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.
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)