Why are my panels producing less than their rated output?

It is normal for solar panels to produce less than their rated output for most of the day. Peak sun conditions occur for only a few hours each day, and even during these times your panel output will be impacted by a host of other factors. A brief explanation of how specifications are measured and the factors that influence solar production are explained below.

Where solar panel ratings come from

Solar panel ratings are based on measurements done under Standard Test Conditions (STC). This ensures that the specifications listed on different panels can be compared against each other fairly. The values included in STC are

• Irradiance: This refers to the amount of light energy reaching a given area at a point in time. For STC, this value is 1000W of solar energy per square meter
• Temperature: This value refers to the temperature of the cell itself, not to the ambient temperature of the surrounding area.
• Air mass: The air mass coefficient is a measure of how much of the Earth's atmosphere light has to travel through. The number itself refers to the angle of sun. When sun is directly overhead, the air mass value is a 1. A number high than 1 means that light has to pass through more atmosphere and becomes weaker in the process. STC has an airmass of 1.5

What factors influence solar panel performance

Standard Test Conditions are great for ensuring that different solar panels have comparable specifications. While STC ensures that all panels are measured under the same conditions, they do not accurately reflect the output of panels in a real world environment. The amount of power that your solar panels will vary greatly depending on a whole host of factors including:

• Their angle relative to the sun
• Your latitude
• The temperature of the cells
• The time of day
• The season
• The weather
• Shading
• Age

What else influences solar charging?

On top of all the factors that influence the power production of the panels, your solar charging will also be impacted by the arrangement of your array, the quality of connections and components in your system, and the type of solar controller you are using. Some of the other factors to consider include:

• Whether your panels have been connected in series, parallel, or a combination of both. More information on the best way to connect your panels can be found here.
• The type of solar controller you have installed. MPPT solar controllers are more efficient than PWM solar controllers, although the difference between the two can vary with temperature. For more information, click here.
• As with any electrical equipment, the quality of the components, cable, and fusing can have an impact on performance. Poor connections and wiring that is too small can cause poor performance. 

What if I have factored everything in and there is still something wrong?

If you have taken all of the above factors into consideration are remain convinced that your solar array is not performing properly, there several actions you can take

Double check your math

The first thing you should do is confirm the specifications of you equipment and the values of everything you are calculating. Remember that solar panels are rated in watts and that you will probably want to convert this into amps to figure out how much charge is going into your battery. Solar controllers are not 100% efficient, so you will need to factor in some power loss along the way. How you factor in panel efficiency will depend on whether you are using a PWM or MPPT solar controller. For more information, click here.

If your system is using multiple solar panels, you also need to ensure that you have factored in the impact of series or parallel panel arrangement when working out what the total should be. Depending on how you have your panels arranged, working out the total output of your panels might be more complicated than just adding together all of the wattages. For more information, click here.

If you only have a system level battery monitor, you also need to remember that your chargers will power your loads before charging the battery. For example, if your solar panels are producing 10A of current but your fridge is consuming 4A of current, then your battery monitor will only show 6A of charge flowing into the battery.

Double check your wiring

If you find a large discrepancy between your estimated charge current and the actual amount going into your battery, the next thing you should do is check all of the connections and cabling in your system. Cables that are too long or too small in diameter will negatively impact your charging ability. Loose or poorly made connections will also cause problems with your electrical system.

Double check your panels

After confirming that your system has been wired correctly with sufficient sized cable, the next step would be to test the panels themselves. This is relatively easy and can be done using only a multimeter and sunlight. Instructions on how to do this can be found here.

If you have taken all of the following steps and continue to have problems with your solar production, take photos of your solar setup and email them to support.enerdrive@dometic.com. Make sure to include the specifications of all of your panels and equipment, as well as some details regarding the environmental conditions you were testing under (temperature, weather, location, etc).