When it comes to solar panels, it is all about efficiency.  How efficiently the panel converts photons to energy.   Module efficiencies are getting better but are still far from ideal.  

Today there are numerous manufacturers of solar panels and while some manufacturers are better than others, they all have to deal with the same issue - Energy conversion.

Not to long ago, there were only three types of solar panels. Monocrystalline, Polycrystalline, Amorphous.

Today, there are new processes that are moving away from silicon based solar cells. These new types of processes allow for less expensive manufacturing cost ($1.00 to $1.50 a watt) and are much more efficient. Due to their thin film process, their use and configuration options are endless. The new thin film solar is still new to the market so we will look at what you can get today.

As stated above, there are three different panel types.
Monocrystalline, Polycrystalline, Amorphous.

Monocrystalline Silicon Panels

15-20% Efficient

Monocrystalline panels use crystalline silicon, a basic semiconductor material.
The way to identify whether a panel is Mono or Poly is simple. A Mono panel has individual cells. A Poly type panel is solid with what looks like flakes of silicon pressed together. . Monocrystalline panels are typically 15-18% efficient, meaning that for every unit of solar energy that hits the cell, the panel can convert 15-18% of this energy into electricity. These panels are usually more expensive.

Polycrystalline Silicon Panels
Polycrystalline, or multicrystalline, photovoltaics use a series of cells in place of the single large cell used in monocrystalline panels. These panels are the least expensive pv panel available today. The drawback of these panels is that they have lower efficiency rates at 12-14% efficiency.

Amorphous Silicon or Thin Film Panels
Thin-film panels are the lowest efficiency of any current photovoltaic technology at 5-10%. The primary advantage of thin-film panels lies in flexibility. Because many different substrates and disposition methods are used to produce these cells, little is known about their long term stability and it is likely to vary widely with the substrate and manufacturing process used.