This article will cover the most efficient solar cell technologies recorded in standard test conditions and the most efficient panels available in the market. The article will be constantly revised through the year to include the most up to date information.
A Few Points on Solar Cell Efficiency
Lab efficiency is always higher than true efficiency as tests are carried out in standard conditions. The test conditions correspond to a fixed irradiance of 1000 W/m2 at a temperature of 25 °C.
The amount of solar irradiation falling over a meter square surface just outside the atmosphere is approximately 1357 Watt/m2. This uninterrupted solar radiation is also referred to as AM0 Spectrum. The amount of solar energy is lowered as it reaches the ground or sea-level because of atmospheric attenuation. If the sun is at the zenith, then rays of light have to penetrate the least amount of atmosphere. The spectrum of solar radiation reaching the earth’s sea level in this case is called AM1. However this condition is rarely achieved in real life. Even when it is, it is for a short duration in regions that are not very populated (equatorial belt).
On a clear summer day (when solar declination is low), it is possible to get around 1000 Watts /meter square falling on a horizontal (flat surface) on the ground. For majority of the population centres the AM1.5 spectrum is a reasonable standard to measure solar performance . The AM1.5 corresponds to the spectrum of solar energy is not directly above (the Zenith) but in which the sun is slightly slanted (48.2 ° from Zenith).
Another reason why lab efficiencies are higher is because the temperature of the cell surface is controlled at 25 °C, whereas in real conditions, cell temperature can rise (depending upon ambient temperature). The efficiency of the solar PV panel drops because of temperature rise.
There is a general thumb-rule in electrical engineering which suggests that for every 10 °C rise in temperature, the ohmic resistance in the circuit doubles. This rise in resistance also inhibits the flow of charge carriers in PV circuits.
It should be understood that high efficiency does not necessarily equate to a huge monetary benefit. In fact, if the available space for installation is not an issue, then lower efficiency of panels can be off-set by using more of them. It is only when the space available for PV panels is limited, such as in satellites or small roof spaces, then efficiency of the panel does come into play. Furthermore, some panels respond better to poor light conditions compared to others. For example, thin film panels retain their efficiency close to maximum efficiency even in poor lighting conditions. Regions on earth that have more diffuse radiation than direct radiation (such as UK) can therefore consider panels of this technology (thin-film), to get a more consistent output. Although Thin-film panels may have a lower efficiency to begin with, but their output can exceed that of mono-crystalline or poly-crystalline (rated higher in efficiency) in diffuse conditions.
There is also the issue of availability. Most high-efficiency panels are snapped up by OECD countries. Because of the high affordability, these countries can afford to pay the premium that comes with top rated panels. Most panels available in the developing world tend to be cheap poly-crystalline panels, whose efficiency is lower than their mono-crystalline counterpart because of interface resistance. They are nonetheless cheap and therefore more affordable for the less affluent.
When designing a PV system, the Return on Investment should be the main criterion for selection of panels not the efficiency.
The national Renewable Energy Lab frequently publishes a chart on which solar cell efficiencies improvements in the last century has been recorded. It is a matter of great prestige for solar cell manufacturers to feature on the chart. Similarly, the bi-annual journal “Progress in Photo-Voltaics” is also a useful resource to check for the latest development in this technology.
List of Cell Lab Efficiency Values
The list for most efficient solar cells in 2017 by technology is as follows:
|Multi Crystal Silicon||21.30%|
|Single Crystal Silicon||27.50%|
|Multi-junction (Non Concentrator)||38.80%|
The values in the above list that are in bold fonts are the ones that have changed since February 2016. The rise of Pervoskite cells has sparked curiosity among several researchers and captured the interest of several investors. Nonetheless because of its abundance, omnipresence and huge refinement infra structure, silicon PV cells will remain the king in the near future. Organic solar cells have also shown tremendous promise because of their ease of manufacture, which is similar to polythene bags.
List of Most Efficient Solar Panels in the Market
The list for most efficient solar panels available in the market is as follows.
|Panasonic||Silicon Hetro-structure (HIT)||N240||19.00%|
|Kaneka||Thin Film Hybrid||U-EA120||9.80%|
|First Solar||Thin Film CdTe||FS-4105A||16.80%|
|Spectrolab||Multijunction||NeXt Triple Junction||29.50%|
|Alta Devices||Multijunction||Ga-As (Gen 4)||25.00%|
Note that all the cell efficiencies tested in lab are more than the corresponding panel efficiencies available in the market. First Solar for instance has a lab record of 22.1% Cd-Te thin film cells, however their panel available in the market is only 16.8% efficiency. One reason for this the extra bits that are needed to be added on when converting cells to a panels. These are mainly structural support components and charge carriers. The more important thing to take away is that First Solar panels have out performed similar nameplate capacity power plants by almost 10%. This is because of their better response to shading and hot weather.
The Future of Solar Cell Efficiency
It is anticipated that in 2017 and in the years to follow, Graphene will play a major role in raising the panel efficiency. This is because the charge collecting wire mesh that lies on top of the PV panel (busbars, fingers, inter-connectors) blocks some amount of radiation falling on the silicon P-N chip. With smaller Graphene charge carriers, much less area will be blocked and that will improve the overall solar cell efficiency. It is also well known that solar panel efficiency degrades with rising temperatures. Research is being carried out for cooling systems that would not only improve the efficiency but also the life of the panel, by keeping the temperatures well below the maximum operable temperature.
For starting your own solar energy business, a great online course is available and can be accessed from the following link.
Video of the most efficient cells in the lab and most efficient panels in the market is copied below.
Please feel free to share this article and spread the word. Social media sharing buttons are present below.