This article looks that the most efficient solar panels that have been tested in the lab and also the ones that are available in the market.
Till recently, people looking to buy solar panels did not consider the efficiency as much as they considered the price. This is because the low efficiency can be compensated by the providing extra space for the panels.
The efficiency of a solar panel is measured by dividing the amount of insolation (incident solar radiation) falling over a solar cell to the amount of electrical energy produced. A one meter square panel that is 20% efficient produces 200 watts. Similarly, a panel that is 10% efficient would produce the same amount of power (200 Watts) with a panel area of 2 meter square. Thus people would compare prices and buy the one that was cheaper unless they were limited by space.
In the UK, the maximum power allowed for a PV installation on a roof top is 4 kW. This limit is placed for houses that are on-grid and would like to utilize UK government’s “Feed-In Tariff” scheme. Very efficient PV panels would require a roof space of 19 meter square (for a 4 kW system). On the other hand, the panels easily available in the market with medium efficiency (17%) would produce the same power over an area of 23.5 meter square. As houses generally have roof space of over 30 meter square, requirement for very efficient solar panels has hardly ever arisen in the domestic market.
There is however a niche for efficient PV panels particularly in applications that are restricted by area, volume or payload (such as military or space hardware). Solar Impulse, the solar powered air-plane is another example where efficiency matters. Similarly in the case of a solar farm, more efficient cells equate to less land utilization.
There is a premium charged by the companies producing efficient solar panels and hence their price per watt is much higher. It should be mentioned that the life of a panel is almost 30 years. Therefore, even 1 % higher efficiency over the course of time could lead to several hundred extra energy units.
Solar Cell Lab Efficiency
There are various different types of technologies in solar cells. Each technology has its own upper limit or maximum theoretical efficiency. For any material the peak efficiency is governed by the Shockley -Queisser limit (33.7%).
It should be noted that this limit has been obtained using ideal band gap value of a single material. However, in practice this limit can be bypassed by using different material layers stacked on top of each other (each with a different band gap).
The following are the lab efficiencies of different cell technologies. Note that it can take up to five years for a product that has been tested in lab to be available in the market if it is deemed feasible to mass produce.
Solar “cell” efficiency is always higher compared to “panel” efficiency. This is simply because a panel has more components (tabbing wires, circuit wires, frame, glass cover etc ).
The efficiency for solar cells measured in laboratory conditions is as follows:
|Multi Crystal Silicon||21.30%|
|Single Crystal Silicon||25.00%|
|Multi-junction (Non Concentrator)||38.80%|
The efficiencies tabled above were measured by NREL (National Renewable Energy Laboratory, Colarado, USA)
Efficiency of PV panels available in the Market
The following are the most efficient solar panels available in the market
|Panasonic||Silicon Hetro-structure (HIT)||N240||19.00%|
|Kaneka||Thin Film Hybrid||U-EA120||9.80%|
|First Solar||Thin Film CdTe||FS-4105A||16.3%|
|Spectrolab||Multijunction||NeXt Triple Junction||29.50%|
Sunpower has been leading the efficiency race for almost a decade. Both Panasonic and Elon Musk’s SolarCity have made great strides in efficiency improvement and are rapidly catching up. Spectrolab’s solar panels are mostly used in space applications.
PV panels should not be just bought on the basis of their efficiency or price. There are certain aspects like performance sensitivity to temperature or diffuse radiation that should also be considered. The most efficient solar panels in the long run always prove more feasible particularly in space restricted areas. Solar radiation does not fall perpendicular to the panels for most of the times is the panels are fixed. This results in a drop in the overall output. There are solutions where panel output can also be increased by up to 30%, even when there is little allowance for tracking system.
This data has been presented to the best of author’s knowledge and is correct up to January 2016. For a great course on solar energy for starting business, click here.
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