Solar panel efficiency is usually termed solar module efficiency and for a mono crystalline or poly crystalline solar panel should be somewhere in the range of 12% to 19% efficiency; thin film solar panel efficiency currently sits at around the 10% mark.

What Does Solar Panel Efficiency Mean?

Solar panel efficiency - is it something worth worrying about?

Solar Panels or solar modules are tested in laboratories to an industry standard called Standard Test Conditions, or STC. As solar panels produce different amounts of power depending on the conditions that they are operating under a standardised set of conditions was required to give an accurate measurement between different solar panels, hence the introduction of the STC. STC, or Standard Test Conditions is set at 1000 Watts of irradiance per metre2, an ambient temperature of 25 oC and an Atmospheric Mass (AM) of 1.5. These conditions are an industry standard, but please be aware that they are NOT standard conditions in the real world! The amount of irradiance per metre2 and the ambient and cell temperatures vary greatly every day, which all affects the power produced by your solar panels.

What this all means is that the rating of a solar panel is at these standard test conditions, so a 250W rated REC solar panel should be producing 250W of power out of the box at STC. If 1000 Watts of power is falling on the panel per metre 2 and the solar panel outputs 250W of power from its area (which is an area of 1.65m2) it would be converting 15.1% of the power falling onto it into DC electricity. This 15.1% is the solar panel efficiency.

What is Solar or Photovoltaic Cell Efficiency?

As a solar panel or module has a rated efficiency so do the cells inside the solar panel. The Solar Photovoltaic cell efficiency is always higher than the overall solar panel efficiency as when the cells are installed in a solar panel they are subjected to some extra losses. These losses come from 3 main issues:
1. Series loss from connections between solar cells
2. The physical layout of the solar panel and framing
3. Optical losses from being encapsulated inside glass

So Does Solar Panel Efficiency Matter?

Solar Panel Efficiency is important, but not as important as you may think. Because solar panel efficiency is a product of the power being generated per m2 all it means is that a less efficient solar panel will take a slightly larger space than a more efficient solar panel. Of course if space is of an absolute premium then the more efficient solar panels will be your best choice. Currently the most efficient solar panels around that are readily available are Sunpower 327W solar panels with a solar panel efficiency of 20%, but the price of these solar panels at nearly double a high quality 250W REC solar panel with an efficiency of 15.1% makes them an unrealistic option unless it is imperative to get as much power as possible out of a minimal space.

When choosing a solar panel efficiency is not usually the most important factor to take into consideration, however there are very important factors to take into account, check out the following articles to learn more about which solar panel is best for you: