Solar Panel Efficiency
Solar panel efficiency is a measure of the amount of solar energy which falls on a panel surface and is converted into electricity. Due to the many advances in solar cell technology over recent years the average panel conversion efficiency has increased from 15% to almost 20%. This large jump in efficiency has increased the rated power output of standard size panels from 240-260W up to 300-330W.
Solar panel efficiency is determined by two main factors, the cell efficiency based on the cell design and silicon type, and the total panel efficiency based on the cell configuration and design of the panel.
Solar Cell Efficiency
The cell efficiency is determined by the silicon cell structure and base silicon material used which generally either P-type or N-type. Cell efficiency is calculated by what is known as the fill factor (FF) which is the optimum conversion efficiency of a cell at a specific temperature and conditions. The cell design also plays a big role in efficiency such as the size, number of busbars and finger layout. The higher cost IBC cells are generally the most efficient (20-22%) as they are based on high purity N-type silicon and do not suffer losses from busbar/finger shading, however more recent PERC cell technology and the latest heterojunction (HJT) cells have achieved efficiency levels similar to IBC cells.
Solar Panel Efficiency
The panel efficiency is determined by the total panel size, individual cell size, layout and design. This is based on the number and type of cells used, the busbar design, distance between the cells and interconnection of the cells. Surprisingly even the color of the panel protective backsheet can effect efficiency as a black backsheet absorbs more heat which reduces cell efficiency.
Referring to the examples in the image below; panels with IBC cells are generally the most efficient followed the half-cut and multi busbar cells, shingled cells and finally the standard 60 cell (4-5 busbar) monocrystalline cells. The common polycrystalline 60 cell panels (not shown) are generally the least efficient and cheapest panels.
Note the efficiency listed on the solar panel specification sheet and quoted by the panel manufacturer should be the solar panel efficiency, not the cell efficiency which will be higher. Learn more about the different panel designs in the solar cell technology review.
Why efficiency matters
The term efficiency is thrown around a lot but a slightly more efficient panel does not always equate to a better quality panel. Many people consider efficiency to be the most important criteria when selecting a solar panel but what matters most is the manufacturing quality which is related to real world performance, reliability, company history and warranty conditions. Read more about selecting the best quality solar panels here.
Solar panel efficiency generally does give a good indication of the long term performance especially as many high efficiency panels use very high grade silicon with improved temperature performance and lower degradation over time, some manufacturers such as LG and SunPower offer warranties with 88% or more retained power output even after 25 years of use.
Efficiency does make a big difference in the amount of roof area required. Higher efficiency panels require less area which is perfect where roof space is limited and can also allow larger capacity systems to be fitted to any roof. For example 12 x high efficiency 360W solar panels such as those from LG or SunPower with a 21% conversion efficiency will provide up to 1100W more total solar capacity than the same number of lower efficiency 270W panels.
Real world efficiency
In real world use solar panel efficiency is also dependent on a number of external factors including panel orientation, location, time of year, shading, dirt and cell temperature. A standard size 60 cell (1m x 1.6m) panel with 17-19% efficiency typically has a power rating of 290-310 Watts where as a panel with higher efficiency of the same size can produce up to 330W. The most efficient panels explained in more detail below use extremely efficient N-type IBC or Interdigitated Back Contact cells which can achieve up to 22% efficiency and generate an impressive 370 Watts.
Efficiency of different silicon solar cell types
Polycrystalline - 15 to 18%
Monocrystalline - 16.5 to 19%
Polycrystalline PERC - 17 to 19.5%
Monocrystalline PERC - 17.5 to 20%
Monocrystalline N-type - 19.5 to 20.5%
Monocrystalline N-type IBC - 20 to 22%
The most efficient solar panels
The top 3 most efficient solar panels available in 2019 use premium grade N-type IBC cells manufactured by SunPower and LG Energy, however these panels also come at a premium price. Below is a list of 12 of the most efficient and popular panels currently available.
The most efficient solar panels*
SunPower X series - 22.0%
LG energy Neon R - 21.4%
SunPower E series - 20.1%
REC N-Peak Series - 19.8%
LG energy Neon 2 - 19.6%
Qcells Q.Peak DUO G5 - 19.6%
Winaico WSP-MX series - 19.4%
JA Solar JAM60S03 - 19.2%
Phono Solar Twin plus - 19.2%
Jinko Solar Eagle 60M - 19.2%
Trina Solar Honey M plus - 19.2%
Longi Solar LR6-60PD - 19%
* Based on standard 60 (120) or 96 cell residential panels available in 2019, models and specifications may vary depending on country.
Cost Vs Efficiency
All manufacturers produce a range of panels with different efficiency ratings depending on the silicon type used and whether they incorporate PERC or other cell technologies. Very efficient panels above 20% are generally much more expensive, so if cost is a major limitation it would be better suited to locations with limited mounting space , otherwise you can pay a premium for the same power capacity which could be achieved by using 1 or 2 additional panels. However high efficiency panels using N-type cells are very high quality and will almost always outperform and outlast lower efficiency panels due to lower degradation rates, so the extra cost is usually well worth it in the long term.
Example a high efficiency 330W panel could cost around $300 while more common 285W panels typically cost closer to $180. With both made by the same manufacturer, this equates to roughly $0.60 per Watt compared to $0.90 per Watt. Although in the case the leading manufacturers such as LG, Sunpower, Winaico and REC the more expensive panels have higher performance, lower degradation rates and generally come with a longer 'manufacturers' warranty period, so it is often a very wise investment.
Panel Size Vs Efficiency
Panel size is not directly related to efficiency as the larger panels generally use more cells to achieve greater power output. The two most common size panels use either 60 or 72 cells but a few manufacturers produce 96 cell panels using smaller 5” cells. Most Australian residential installations use the standard 60 cells panels while commercial and large scale solar farms use larger 72 cell panels. In North America many residential and commercial systems use the high efficiency 96 cell panels from SunPower or Panasonic.
60 cell panel : Approx width 1.0m x length 1.65m
72 cell panel : Approx width 1.0m x length 2.0m
96 cell panel: Approx width 1.05m x length 1.60m
The new generation half-cut or split cell modules have double the amount of cells at roughly the same size. A panel with 60 cells in half-cell format is doubled to 120, and 72 cells in half-cell format is 144 cells. The half cut cell configuration is slightly more efficient as the panel voltage is still roughly the same but the current is split between the to halves.
120 cell panel : Approx width 1.0m x length 1.65m
144 cell panel : Approx width 1.0m x length 2.0m