Categories: Know How

Solar panel types | Mono, Poly and thin film PV modules

2 months ago

Solar panel types | Mono, Poly and thin film PV modules. The energy needs of our planet are increasing every year by a growing world population and a greater economic activity. To reduce CO2 emissions, we have to use more alternate sources of energy, such as solar PV, wind or hydropower.

The total incident amount of photovoltaic energy exceeds the world's needs energy by more than a factor of a thousand.

Solar panel types - Mono, Poly and thin film PV modules

With goverment support in countries such as Germany and Japan. The production of photovoltaic solar energy systems is increasing by more than 30% last ten years. This resulted in production capacity of 5.5 GW PV panels in 2018. More than 90% of the solar modules produced use mono- or multi-crystalline silicon with a thickness between 200 and 300 μm.

Multi-crystalline silicon possesses the excellent semiconductor properties for use in PV cells and is also non-toxic, widely available and stable. Commercial PV systems based on crystalline silicon have efficiencies of 14 - 18%.

The strong demand for PV energy systems resulted in a declining availability of purified silicon and so in a substantial price increase of the silicon slices. The shortage of silicon and strong demand offer great potential for thin film silicon cells.

Photovoltaic cells based on thin film polycrystalline silicon are cheap alternative to the current "wafer-based" silicon PV cells. The low absorbance of light in the thin polysilicon layer is to obtain a good cell efficiency, a big challenge.

Three types solar modules, monocrystalline and polycrystalline solar and thin film. Different types of solar panels are in terms of materials, production and efficiency.

Thin film modules

For the thin film technologies, a carrier material is coated with the semiconductor material. The semiconductor material used so far is primarily amorphous silicon. Other semiconductor materials are also usable, such as cadmium telluride, CdTe, gallium arsenide, GaAs, or copper indium selenide, CuInSe2. There are also thin film modules with microcrystalline silicon.

Organic solar panels cells in which the absorber layer consists of a polymer also belong to the thin film solar panels. The production is relatively simple. They are the less expensive modules because of the elimination off the wafer production.

They evaporate the carrier with a few microns thin layer of semiconductor material. As a substrate next to glass or metal and flexible materials such as plastic in question, which widens the scope significantly.

The efficiency of thin film modules is significantly lower than poly or mono solar panels. Average efficiencies of modules available on the market are between 5 and 10%. However, significantly higher efficiencies of up to 18% could be achieved in the laboratory.

Degradation of thin-film modules are around 20 to 25% in the first 1,000 operating hours. But this is already taken into account in the manufacturer's data on efficiency.

  • Inexpensive production
  • Low acquisition costs
  • Less raw material consumption
  • Low weight
  • High yield even for diffused light
  • No efficiency losses due to heat

Thin film modules have a number of advantages despite the lower power output efficiency. Especially the high photosensitivity even with a high proportion of diffuse radiation ensures high yield even in the winter months.

At the same time, thanks to the high-temperature resistance, the current yields of thin-film modules in summer remain high. Even at temperatures above 25 ° C. More about the difference between mono and poly.

Solar panel types - Mono, Poly and thin film PV modules

Monocrystalline cells

Crystalline solar panel cells are made from the basic material silicon, in contrast to thin-film or dye cells.

For the production of monocrystalline cells, they have to meld and clean the silicon. From this melt, a rod is then drawn, which forms a uniform crystal lattice, a so-called single crystal or monocrystal. They slice these ingots into wafers. Wafers for monocrystalline PV cells are only a few micrometers thick.

The next production step involves cleaning the wafer surface by chemical treatments. Since the silicon was already doped with boron during wafer production, doping with phosphorus still has to take place for the other half of the wafer.

After wafer production, a solar cell is built with the p- and n-doped wafers. Which has a high efficiency because of the low impurities. They produce the ingots in diameters of 150, 200 and 300 mm.

Monocrystalline panels cells are easy to recognize for two reasons:

  1. Due to the uniform crystal structure, they appear uniformly dark.
  2. Moreover, they are not quite square. Because they are sawn from round ingots and thus have round corners.

Solar systems equipped with mono cells achieve significantly higher efficiency ratings than other cells. In the laboratory they archieve efficiencies more than 20% under laboratory conditions. Monocrystalline silicon solar panels performance are therefore always particularly useful if the highest efficiency possible yield on a small area. Many people appreciate the uniform look as an advantage.

Monocrystalline vs Polycrystalline solar panels

PV modules with mono cells are expensive to produce and therefore a higher price: They are significantly more expensive than other electricity producing modules. In addition, the energy-intensive production and the energy amortization of the modules with mono PV cells is worse than polycrystalline cells. Compared to thin-film cells, the efficiency in diffuse light is significantly lower.

Solar panel types - Mono, Poly and thin film PV modules

Polycrystalline PV modules

Silicon is the basic material for polycrystalline modules.

The first step in the production is the purification of the silicon. Silicon is an almost infinite raw material. However, for the production you need pure silicon.

This melting silicon will then processed. There are then various production methods.

The casting methods all have in common that the molten silicon is poured into crucibles. In order to produce the ingots, the silicon solar cell has to cool down and solidify in a certain way, namely from bottom to top. The silicon crystals grow upwards.

In the Bridgman process, the silicon gets hot with induction heating, just as in the block casting process. However, the targeted cooling takes place in the same crucible. This allows larger edge lengths of the blocks for the future polycrystalline modules.

The silicon blocks produced in this way are first sawn into columns. Then into horizontal slices (wafers). Even with polycrystalline solar cells, the doping of silicon with boron takes place even before the casting.

Solar panel types - Mono, Poly and thin film PV modules

In the case of poly modules, several crystals forming during the casting or Bridgman process, hence the name polycrystalline. The production methods described are one of the great advantages. Since they are significantly cheaper than, for example, the production of monocrystalline cells.

Therefore, the price-performance ratio of polycrystalline modules is very good. It is not without reason that the market share of these modules is well over 80%.

Poly modules have a lower efficiency than monocrystalline modules. They are also heavier than thin film modules. Polycrystalline PV modules are easily recognizable by their bright, bluish glittering surface. In contrast to some thin-film modules, there is no possibility to adapt them to the own design in the color.