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How to Size a Solar System: Step-by-Step

1. Calculate your kWh usage

  1. Gather Usage Data: Collect your kilowatt-hours (kWh) usage data from your electric bills covering a full 12-month period. This comprehensive data allows you to observe usage patterns throughout the year, including peaks and troughs associated with seasonal variations, notably increased consumption during summer and winter due to heightened reliance on air conditioning and heating systems.

  2. Calculate Average Monthly Consumption: Determine your average monthly kWh consumption by summing up the kWh usage for the entire year and dividing by 12. This calculation provides a baseline understanding of your typical energy consumption on a monthly basis.

  3. Estimate Daily Usage: Estimate your daily kWh usage by dividing your average monthly consumption by 30, reflecting variations in daily energy needs. This figure is useful for understanding your daily energy demands, helping to size your solar system appropriately.


Here is an example of what you should be looking for on your electric bill: 

Electric Bill Example

Now if you don't have an electric bill you can always take a look at this home appliances chart to figure out the amount of power you are using manually. 

2. Look Up Your Peak Sun Hours

Average peak sun hours are influenced by your geographical location and climate conditions. To optimize solar power usage:

  1. Consult a sun hours chart to ascertain daily peak sunlight hours.

  2. Record the daily peak sun hour average of the nearest city to gauge your solar potential.

Peak Sun Hours Map

3. Calculate the Size of Your Solar System

  1. Divide your daily kWh energy requirement by average sun hours to find kW output.

  2. Divide kW output by panel efficiency for the estimated number of solar panels.

For example, with 33 kWh daily and 6 peak sunlight hours:

(33 kWh ÷ 6.1 sun hours) x 1.15 efficiency = 6.2 kW DC system size.

Multiply by 1000 to convert kW to watts:

6.2 kW x 1000 = 6200 watts of solar panels needed.

You can also use our calculator here: