Mark Roemer Oakland image of solar panels on the top of a house.

How Efficient Are Solar Panels for Homes?

I, Mark Roemer Oakland, believe that there are certain factors that you should consider before choosing solar panels for your home. Many people only look at solar panel efficiency since it is a term heavily promoted by manufacturers. And, although good solar panel efficiency is important, you should also check other factors such as the power rating of the solar panel, the lifespan of the individual solar cells, the cost, and even the aesthetics.

Now, if you have no idea what solar panel efficiency means and how it affects the products, don’t worry. We will discuss what solar panel efficiency means, how it is affected by various factors, and how to choose good solar panels for your home.

What is solar panel efficiency?

Only a limited amount of the sunlight that hits a solar panel is absorbed by it and converted into electricity. Solar panel efficiency rating is the amount of sunlight that is actually absorbed by the solar panel.

For instance, a solar panel with an efficiency rating of 17% would absorb 17% of the solar energy hitting the panel and convert it into electricity. Thus, it is better to select solar panels with a higher efficiency rating, although the cost also rises with a higher efficiency rating.

According to the National Renewable Energy Laboratory (NREL), modern solar panels have an efficiency rating between 16-22% with 19.2% being the average. Premium solar panels have an efficiency rating of over 20% and are much more expensive.

How is solar panel efficiency calculated?

Generally, the efficiency of solar panels is determined by testing them in labs under Standard Test Conditions (STC) where it is assumed they will receive irradiance levels of 1,000 watts of sunlight per square meter.

The formula for calculating solar panel efficiency is as follows:

Efficiency = [Power output of panel / (Area of panel x solar irradiance)] x 100

The factors that affect solar panel efficiency ratings

The efficiency of solar panels is primarily affected by their construction and the materials used to build them. Let’s take a look at the most important factors that affect solar panel efficiency rating below:

1. Solar cell type – The type of solar cells used to build the solar panel greatly affects its efficiency since these are the parts that absorb the sunlight and convert it into electricity.

Generally, there are three main types of silicone solar cells available in the market today. These include — polycrystalline, monocrystalline, and thin-film solar cells.

For home solar panels, you only need to learn about monocrystalline panels since they are the most popular high-efficiency solar panels that you can purchase. Now, let’s take a look at the most common monocrystalline silicon cell types below:

  • PERC solar cells – Passivated emitter and rear contact cells (PERC) solar cells have a reflective back layer that reflects the light passed through the cell back into it. As a result, it offers a boost of about 1% to the overall efficiency of the solar panel.
  • Half-cut or split cells – Split-cell or half-cut technology incorporates the use of high-precision lasers that cut the solar cells in half. This reduces the heat and resistance of the cells and increases overall efficiency.
  • HJT solar cells – Heterojunction with intrinsic thin layer cells are similar to traditional monocrystalline solar cells with one difference. These are sandwiched between layers of different types of silicon, each of which absorbs different wavelengths of light. This helps to improve overall power production.

2. Busbars and wiring – The efficiency of solar panels is also affected by how they are wired together. Generally, these include aluminum or copper wires that conduct electricity and facilitate the flow of electricity from the solar cell to the solar inverter.

To improve the efficiency of solar panels, many manufacturers have opted to utilize multiple ultra-thin busbars instead of a few, thicker busbars. This is known as multi-busbar technology. Thinner busbars allow it to absorb more sunlight by reducing the amount of shading on the solar cells.

3. Backing – Generally, black backing allows solar panels to look sleeker since it blends seamlessly with the color of the solar cells. That is why it is also a popular choice among homeowners. However, since black backing produces more heat, they are less efficient than solar panels that feature white backing.

How environmental conditions affect the efficiency of solar panels

The efficiency rating of solar panels is tested under specific lab conditions. Unfortunately, these ideal conditions are not present in the real world. As a result, the actual efficiency of the solar panels installed on your roof will depend on the environmental conditions in your region. Let’s take a look at those below:

1. Temperature, weather, and shading – Solar panels don’t perform well in hot weather since high temperature reduces their energy efficiency. They provide the best results under cold and sunny conditions.

However, cloudy weather and shading due to tree branches, roofs, and more can also dramatically reduce their efficiency.

2. Snow, ice, and hail – Generally, normal snowy weather doesn’t affect efficiency as long as there is still sunlight. However, the efficiency of the panel can drop by a full 100% if it accumulates up to 5 cm of snow. This usually happens if the panel is not tilted appropriately.

And, if there is no silicone coating on the panel, it can accumulate ice on the surface of the cells which can reduce the efficiency by 25-100%. Extreme hail can damage solar panels if they are not protected.

3. Wind – An increase in wind velocity can slightly decrease efficiency. However, cool winds can decrease the temperature of the panel by 1 degree which can improve efficiency by 0.5%.


I, Mark Roemer Oakland, suggest you choose highly efficient solar panels if you have limited roof space where you need every single solar panel to produce as much power as possible. However, it is more beneficial to choose a solar panel with a higher power rating than which is more efficient since it would allow you to save more money while offering you better energy output.