Understanding the Numbers

There are a lot of different numbers, statistics, and ratings that come with understanding your solar panel system. If you are confused and want to learn more, keep reading!

Power Output 

Solar panels come with a specified number of watts. For example, you might see a “Solaria PowerX 400” panel or a “REC 370” panel. These numbers indicate power output of one solar cell. A 400 watt panel can produce 400 watts of power in one hour of full sunlight exposure. Often, solar panel systems will be described by their total wattage, which is simply the sum of the wattage of all the individual solar panels. Solar panel systems for your home can range anywhere from 5 kW to 30 kW, or even more. Keep in mind that 1000 watts is equivalent to one kilowatt. 

So, the total wattage of your solar panel system describes how much power it can produce at any given time. However, to determine how much electricity your home will receive, we have to think about the energy output of your solar panels. This is measured in kilowatt hours (kWh). Typically, residential panel systems produce between 20 and 40 kWh per day. To calculate energy output for your panels, multiply the following:

  1. The total system size
  2. Your solar panel’s efficiency percentage 
  3. Number of hours of sunlight 

For example, here is the calculation for a 20 kW system with a 20% efficiency rating, receiving 12 hours of full sun. 

15 x 0.2 x 12 = 36 kWh.

Keep in mind that this is an estimate, and that actual energy output depends on location, time of year, shading, and other factors. However, this formula is a good guideline to use. 

So, now that we can determine the energy output of your solar panel system, what does that actually mean for your home?

According to the Energy Information Agency (EIA), households in the United States consume around 29 kWh of electricity per day, on average. Again, actual system output depends on a variety of factors, but given the math above we can see that  solar panels have the potential to take a big dent out of, or potentially eliminate, your energy bill.


As we mentioned, a significant factor in calculating a solar panel’s electricity potential is the efficiency factor. Polycrystalline panels tend to be 17% efficient, while monocrystalline panels are above 22%. 

What does efficiency mean?

Efficiency describes how much wattage a solar panel produces given how much sunlight it receives. So, these statistics mean that solar panels tend to translate about ⅕ of the energy they receive from the sun into electricity. This may seem like a low percentage – but remember that the only input solar panels take is the sun, and they produce no emissions! Since it doesn’t cost any more to you to increase the input to your system, the efficiency statistics matter less. Additionally, as we saw above, even a solar panel system with a 20% efficiency rating still produces a significant amount of energy for your home! 

Temperature coefficient

A more “nitty gritty” factor to consider when purchasing solar panels is the temperature coefficient. Solar panels have an optimal temperature of around 77 degrees Fahrenheit, and after this point they begin to lose efficiency. The temperature coefficient describes the rate at which this efficiency declines. The temperature coefficient could be a value such as -0.20%. This means that with an increase in temperature of 10 degrees, your solar panels will be 2% less productive. Most of the time, this effect is negligible. Temperatures would have to be pretty high for solar panels to lose any significant amount of productivity.

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