Solar Panel Efficiency


You may have come across the term “efficiency” while buying solar panels or while reading about solar panels. It seems like it is the only specification of solar panels you need to check out. But it is not. Yes, you are reading it right, solar panel efficiency is not the only important factor that determines its quality. In fact, it is one of the important specs.

solar panel efficiency

But, what is solar panel efficiency? What does it denote? Can there be panels without efficiency? How does environmental conditions affect efficiency? and if so, by how much? We will answer all your questions in this post.

What is Solar Panel Efficiency?

Solar panel efficiency is the measure of how much of solar energy a solar panel can convert into usable electricity under given conditions.

This is a very simple concept. Let me give you an example to understand it clearly. Suppose you have a solar panel mounted on your roof with 16 percent efficiency marked on its back side. This means that the solar panel you have can transform 16 percent of sun’s energy or sun rays falling on it into electricity that can be used by you.

Do remember that, all these measurements are only under certain laboratory conditions. These conditions are called Standard Test Conditions (STC). In reality, it is mostly lower than the one marked on the solar panel’s backside.

Solar Panel Efficiency Value

Most of the solar panels available today in the market have solar panel efficiency between 15 percent and 18 percent. This include both polycrystalline and monocrystalline solar panels widely available. It is important to consider here that, the solar panel efficiency of monocrystalline solar panels is slightly higher than polycrystalline solar panels.

For the geeks out there, the best efficiency ever achieved by a solar cell is 46 percent. This is achieved by a multi-junction concentrator solar cell. This is a world record as well. Please note that, this efficiency is for solar cell and not the solar panel which may consist of many solar cells.

Factors affecting Solar Panel Efficiency

Your solar panels can get affected by many factors. These can be environmental, that is, the ambient atmosphere in which the solar panels are installed, and the way in which your solar panels are installed.

Environmental Factors

Environment highly affects the efficiency of solar panels and therefore, determines the output you’ll get from the panels. This is the reason for the fluctuation you may have seen in the output of the solar panels.

Some of the environment conditions, that affect efficiency are as follows.


Any change in temperature from that of the Standard Test Conditions (STC) will change the efficiency of solar panels.

Generally, the STC temperature is 25 degree Celsius or 77 degree Fahrenheit. Any temperature other than this will yield an efficiency different from the one mentioned in the specifications sheet of your solar panel. Though remember that, temperature is not the only factor that affects efficiency and final efficiency at any given moment depends on several factors.

The rise in temperature decreases the efficiency of solar panels. You may have noticed that in the peak summer months the output of your panels is unexpectedly lower than what it was a few months back. This is because of the reduced efficiency because of high temperature.

Dust and Dirt

The dust and dirt, which includes soiling, bird droppings, accumulation of various things etc. on the surface of panels result in decrease in solar panel efficiency.

Solar panel transforms the sunlight falling on it into the electricity to be used by you. If there is dust or any kind of dirt on the solar panels, sunlight can’t reach the solar cells and this results in less output. This decreases solar panel efficiency.

Design Factors

On the basis of design, there can be several factors that can affect the efficiency of solar panel. Research is being carried out throughout the world to increase the efficiency of solar panels.

Some design factors that affect solar panel efficiency are as follows.

Type of Solar Panel

I have already pointed out that monocrystalline solar panels are more efficient than polycrystalline solar panels.

But these two are not the only types of solar panels. There are only the ones currently being mostly widely used throughout the world. There are innumerable types of solar cells under research and all have different efficiency and it’s characteristics.


You will get the best efficiency of solar panels, when you align the panels facing exactly and directly towards the Sun.

Now, Sun changes it’s position throughout the day and goes from east to west over south or north depending on the earth’s hemisphere you are in.

So, solar trackers or sun tracking system can be used. But, these are very expensive and Return on Investment (ROI) becomes too high to be preferred in rooftop installations. So, as of now, they are only being used in utility scale installations.

So, currently, the best way is to install solar panels facing south if you’re in the Northern Hemisphere (For Example, India) and facing north if you’re in the Southern Hemisphere (For Example, Australia).

In addition to direction, angle of orientation is also important which depends on the latitude of the place of installation.


The efficiency of solar panels degrades a little over time. The general rule of thumb is that the power output drops by 0.5% every year. 

Nevertheless, you get module warranty of 25 years, which generally means that the efficiency of solar panels will not decrease below 80 percent.

Importance of Solar Panel Efficiency

Solar panel efficiency is not the only factor to look for while buying solar panels, but it is definitely one of the most important specification to be considered while buying a solar panel.

You may choose a high efficiency solar panel, if you have small roof space and you want to utilize it in the best manner. High efficiency solar panels might be expensive, but they will definitely give you more power in less space.

Similarly, you may not want the most efficient and expensive solar panels if you enough space for the power you require.


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