Types & Working of Solar Panels !!!

There are so many different panels on offer, it can be hard to determine the fact from the fiction. Some companies will offer you 'high efficiency, commercial grade' solar panels, using the 'latest technology', but what does this mean?

Below we have listed the most popular types of solar panel available in Pakistan, with the benefits and drawbacks of each technology:

Types :

Monocrystalline Module
Polycrystalline Module
Amorphous or Thin Film Module

Monocrystalline Module :

Monocrystalline, as the name suggests, is constructed using one single crystal, cut from ingots. This gives the solar panel a uniform appearance across the entire module. These large single crystals are exceedingly rare, and the process of 'recrystallising' the cell is more expensive to produce.

This technology is now the most widely available in Pakistan, with the cost of producing monocrystalline cells coming down every year. They are still more expensive than polycrystalline, but can be up to 2% more efficient.

Suntech have recently made some exciting developments in monocrystalline efficiency, with the patent pending Pluto technology. Unique texturing technology, with lower reflectivity, ensures more sunlight can be absorbed throughout the day even without direct solar radiation, and thinner metal lines on the top surface reduces shading loss. Importantly, the process was developed at the University of New South Wales, and has achieved lab efficiency of 25%, and verified efficiency of approx 19%. These panels will be more expensive, but will offer far more solar electricity for less area of solar panel.

Advantages	Disadvantages
Most efficient module available	More expensive to produce
Most popular technology on market	Has more silicon - high embodied energy
Commonly available - easy to replace
Takes up small area on roof

Polycrystalline Module :

Polycrystalline (or multicrystalline) modules are composed of a number of different crystals, fused together to make a single cell (hence the term 'multi'). They have long been the most popular type of solar module, due to the lower cost in manufacturing the cells. Recently, the cost of monocrystalline has come down, making them more popular in the residential market.

As you can see in the image (left), the construction of these different crystals gives the solar panel a visible crystal grain, or a 'metal flake effect'. They are slightly cheaper to produce than Mono panels, but are also less efficient (anywhere from 0.5% to 2% less efficient depending on the manufacturer). This is because the crystal grain boundaries can trap electrons, which results in lower efficiency.

The BP Solar modules are approximately 13.5% efficient (meaning that if 100 Watts of potential solar energy strikes the panel, it will produce approximately 13.5 Watts of solar electricity).

These panels are very popular in Pakistan, and offer a good balance of value vs performance.

Advantages	Disadvantages
Cost effective to manufacture	Not as efficient as mono
Good efficiency	Has more silicon - high embodied energy
Commonly available - easy to replace
Takes up small area on roof

Amorphous or Thin Film Module :

Amorphous (or 'thin film') solar modules have recently become very popular in the Australian market. They offer better performance in higher temperatures, and have some benefits in shady locations. However, the benefits have been greatly exaggerated by some suppliers, and it is important to weigh that up against the negatives of thin film technology.

The manufacture of these panels is highly automated - silicon is sprayed onto the substrate as a gas (called 'vapour deposition'), which means that the silicon wafer is approx 1 micron thick (compared to approx 200 microns for mono and poly). This means that the panel uses less energy to produce, therefore will pay itself back from an energy point of view in a shorter time. However, it also means that the panels are far less efficient than mono or poly (approx 5-6% efficient).

The electrical connections are etched by a laser. Etching these as long horizontal cells across the panel makes these less susceptible from being blocked by shade, but it's important to recognise that there will still be a significant drop-off in performance when the panel is shaded.

Thin-film panels are significantly less efficient than crystalline panels, and a greater number is required for the same output. On average, a thin film solar array will need 2.5 times more roof area than mono or poly. This is critical if you intend to increase the size of your system later, as you may take up all of your north-facing roof for a relatively small system.

One of the biggest selling points of thin film is the performance in hotter temperatures. Unfortunately this has been misrepresented by some suppliers of thin film panels. As an example, if you live in Melbourne, and you are shown a graph that indicates the performance of thin film panels in Alice Springs, it's obvious that those panels won't provide the same advantage in a cooler climate.

Advantages	Disadvantages
Partially shade tolerant	Poor efficiency (6%)
More effective in hotter climate	Takes up more space for same output
Uses less silicon - low embodied energy	New technology - less proven reliability
No aluminium frame - low embodied energy	Less popular - harder to replace

Other Technologies :

There are many other types of technology which aren't so well known. Cadmium telluride panels have been used in a number of installations in Pakistan, and are providing a cheaper option when compared to more common technology. Due to the toxicity of cadmium telluride, there has been limited uptake of these modules within the industry. There are a number of studies underway to determine the long term effects of using this technology to produce renewable energy. Another issue is the extreme rarity of tellurium (1-5 parts per billion), which could reduce the future uptake of this technology.