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Is solar panel efficiency important?

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There is lots of talk about how efficient different solar panels are. Does efficiency really matter and if so, when does efficiency matter?

Solar panel efficiency is a measure of how much of the sun’s light hitting a certain surface area is converted into usable electricity. This is measured in a Lab under standard test conditions(STC). Based on a temperature of 25ºC, 1000W/m2 of light, with an air mass of 1.5(imitating the atmosphere).

When does solar panel efficiency matter?

Solar Panel Efficiency

As solar panel efficiency is related to how much power you can produce for a certain area. The main situation solar panel efficiency matters is when the installation location has limited space.

For example if you want a 6kW solar system and you can only fit 15 panels on. Then you would use 415W SunPower Performance 6(6.2kW) over 395W SunPower Performance 6(5.9kW) as they are slightly more efficient and will produce more power per m2.

Higher efficiency solar panels generally cost more. If cost is a factor then lower efficiency panels may do the job just fine. What matters is the total combined wattage of panels.

What matters more than solar panel efficiency?

Many things matter much more than solar panel efficiency.

Quality of panels:

It’s important to use a panel from a quality manufacturer. A quality manufacturer has robust quality checks on their production line. The higher quality the panel, the less chance of failure during its life. High quality panels will last longer.

Solar array design:

It is important that a solar system is designed by an experienced designer. The design of a system can make a huge difference to the system performance. A good quality design will take into account shading, compatibility of panel strings with inverter, aspect of panels, angle of panels and overall suitability to the end customer.

There is no point in having higher efficiency panels if the solar system is designed in a way that they are unable to perform. At Wanaka Solar, we have a team of experienced designers and installers that will make sure all components of the system will perform like they should.

Solar panel Warranty:

A good panel warranty matters. Panels come with two warranties, performance and product warranty. The performance warranty states the panel will produce a percentage of its original power output at the end of a time period, usually 25 years. The product warranty protects against failure and defects.

The product warranty is the most important one. Be careful as many suppliers try to sell the performance warranty if the panel has a short product warranty.

At Wanaka Solar we use SunPower as they have a 25 year product and performance warranty. This gives peace of mind as you know your system will be working way into the future. 

A clean solar array:

Keeping your panels free of debris and dirt will ensure your panels regardless of the efficiency will be able to perform at their best. A good solar design should position the panels in a way that general dust and dirt will be cleaned off by the rain.

Leaves can be blown off the array with a leaf blower and bird excrement can be cleaned off with water and a soft brush or cloth.

The power temperature coefficient of the solar panel:

As mentioned above, solar panels efficiency is derived from a test in a lab. This STC test is done at 25ºC.

Often the temperature of the solar panel in real world conditions is much higher than 25ºC. As a panel increases in temperature the performance will reduce. This is measured in %/ºC, for every ºC increase the panel will reduce its power by a certain percentage.

SunPower Performance 6 have a very low temperature coefficient of 0.34%/ºC, to ensure high performance of the system throughout the hot summer months.


Efficiency of various solar technologies

There are lots of different solar technologies with varying degrees of efficiency. The main technology current used is silicon cells. There are some hopeful emerging technologies which could reduce the cost of solar, but they are yet to be able to be put into production.

Currently the highest efficiency solar cell is 47.1% efficient, recorded in 2019 in the NREL lab. This is a multijunction solar cell, which uses a number of solar technologies in a sandwich like structure, to take advantage of more areas of the light spectrum.

How amazing is it that we are able to convert about half of the light that hits a surface into electricity!


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