The purpose of this brief is to investigate into the types of solar panel systems with a look at their theoretical maximum Energy Conversion Efficiency both in research and the top 20 manufactured commercial PV panels.
Figure 1: Reported timeline of solar cell energy conversion efficiencies since 1976 (National Renewable Energy Laboratory) (1)
Solar panel efficiency refers to the capacity of the panel to convert sunlight into electricity. “Energy conversion efficiency is measured by dividing the electrical output by the incident light power.” (1) There is a theoretical limit to the efficiency of a solar cell of “86.8% of the amount of in-coming radiation. When the in-coming radiation comes only from an area of the sky the size of the sun, the efficiency limit drops to 68.7%.”
Figure 1 shows that there has been considerable laboratory research and data available on the various configurations of photo-voltaic solar cells and their energy conversion efficiency from 1976 to date. One major advantage is that as PV module efficiency increases the amount of material or area required (system size) to maintain a specific nominal output of electricity will generally decrease.
Of course, not all types of systems and technologies are economically feasible at this time for mainstream production. The top 20 PV solar cells are listed in Figure 2 below with their accompanying measured energy efficiency.
Figure 2: Table of the top 20 most efficient solar panels on the North American Market (2)
Why Monocrystalline Si Panels are more Efficient:
Current technology has the most efficient solar PV modules composed of monocrystalline silicon. Lower efficiency panels are composed of polycrystalline silicon and are generally about 13 to 16% efficient. This lower efficiency is attributed to higher occurrences of defects in the crystal lattice which affects movement of electrons. These defects can be imperfections and impurities, as well as a result of the number of grain boundaries present in the lattice. A monocrystal by definition has only grain boundaries at the edge of the lattice. However a polycrystalline PV module is full of grain boundaries which present additional discontinuities in the crystalline lattice; impeding electron flow thus reducing conversion efficiency. (3) (4)
Other Factors that can affect Solar Panel Conversion Efficiency in Installations (5):
Direction and angle of your roof
Your roof will usually need to be South, East or West facing and angled between 10 and 60 degrees to work at its peak efficiency.
The less shade the better. Your solar panels will have a lower efficiency if they are in the shade for significant periods during the day.
Solar panel systems need to be installed a few inches above the roof in order to allow enough airflow to cool them down. Cooler northern climates also improve efficiency to partially compensate for lower intensity.
Time of year
Solar panels work well all year round but will produce more energy during summer months when the sun is out for longer. In the far northern regions the sun can be out during the summer for most of the day, conversely during the winter the sun may only be out for a few hours each day.
Size of system
Typical residential solar panel systems range from 2kW to 4kW. The bigger the system the more power you will be able to produce. For commercial and larger systems refer to a qualified consultant.