What Factors Determine Solar Panel Efficiency?

Solar panel efficiency, or conversion rate, refers to how much of the incoming solar energy is converted into electrical power. Typically, the efficiency of commercial solar panels operates in the range 11-15%.

What are the most efficient solar panels? The most efficient solar cell to this date is based on a multi-junction concentrator and converts 44.0% of incoming solar energy into electricity. The highest performing solar panels on the U.S. market today is SunPower SPR-327NE-WHT-D with a module efficiency of 20.1%.

SunPower SPR-343J-WHT-D and SPR-343NJ-WHT-D have been confirmed at 21.0%, but these are currently not in production.

Update June, 2013: Newly released SunPower X21-345 operates at record-breaking 21.5%.

The efficiency of solar panels is influenced by a whole host of variables. The following are the most important ones:

Solar Panel Type

  • Monocrystalline solar panels are based on the highest-purity silicon available. This makes them the most efficient solar panel type available for homeowners.
  • Solar panels based on polycrystalline silicon are usually not quite as efficient as monocrystalline, but there is not that much of a difference.
  • Today`s thin-film solar panels are relatively inefficient, but they also cost less. Thin-film solar panels take up a lot more space than mono- or polycrystalline solar panels, which is why they are unsuited for most households.
The efficiency of individual solar cells (not entire solar panels/modules) is typically higher. For a complete overview over the development of the different types of solar panels over the years check out Best Research-Cell Efficiencies (NREL).



Shade will obviously affect the output of solar panels. Depending on your setup, a little shade can even bring down an entire solar system. Micro-inverters offer a possible solution to shading issues.

Professional solar panel installers will do a thorough analysis of shading in your specific situation.


For best efficiency, solar panels should be positioned to maximize the input of sunlight. This means that solar panels should be faced south in the U.S.

Solar trackers were invented in order to adjust the orientation of solar panels to follow the sun`s trajectory throughout the day. For most homeowners, solar trackers do not pass a cost-benefit analysis – they are simply too expensive.

The pitch of your roof can be altered with racks. In many cases this will allow your solar panels to stay longer in the sun.


Temperature is not something you have to consider unless you live in very hot areas (e.g. San Antonio and Phoenix in the U.S.). As the temperatures increase, the efficiency of solar panels usually decreases a little bit.

Professional installers will make sure that the solar panels are positioned to receive sufficient amounts of airflow. This induces natural cooling, which help keep the efficiency rates up.


The efficiency of solar panels does degrade a little bit over time. The general rule of thumb is that the power output drops by 0.5% every year.[3] Solar panel manufacturers often offer a warranty that guarantees the power output stays above 80% after 25 years.


A solar system generally requires very little maintenance – especially if the system is grid-tied. However, cleaning the solar panels on a regular basis is recommended. Dust and dirt will affect the efficiency of solar panels if not taken care of.

In most places, wiping off the dust with soapy water is sufficient. In some places, the rainfall will do the job for you. Use cleaning services if you`re too anxious to get up on the roof.

How often should I clean my solar panels? Unfortunately, there is no single answer for this question. Best practices would be to monitor the power output of the solar panels to get an idea of how often cleaning them is necessary.

How Important is Solar Panel Efficiency?

Efficiency ratings of solar panels are only one of many different factors that have to be taken into account when considering going solar.

Consider this: Solar panels with conversion rates of 8% will need twice the area as solar panels with conversion rates of 16%. This is why most homeowners end up choosing mono- or poly-crystalline solar panels – these have great efficiency rates and are also space-efficient.

Is there anything I can do to make sure my solar panels perform the way they should? This is where solar panel monitoring comes in.

Comments - 1

John Fergus

I am trying to find out the cost of SPR-343NJ-WHT-D per watt in Australia. Or the price of SPR-327NE-WHT-D per watt in Australia. Do you know of this information, or can you direct me to it?

August 24, 2013 6:19 am Reply

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