Solar System Size for Off-Grid Living — How Much Power Do I Need?

Calculating Daily Load

To calculate your daily load, start by making a list of your major appliances and their average daily energy consumption in watt-hours (Wh). For example, a refrigerator might use 100 Wh/h, a water pump 20 Wh/h, and a TV 50 Wh/h. Next, add up the daily energy consumption of all your appliances to get your total daily load in Wh.

Sizing Your Solar System

Once you have your daily load, you can size your solar system to meet that demand. A good rule of thumb is to multiply your daily load by 1.2 to account for cloudy days and system losses. For example, if your daily load is 10 kWh, you would need a 12 kWh solar panel array to meet that demand. Be sure to also consider the efficiency of your solar panels, which can range from 15% to 20%. To calculate the size of your solar panel array, divide your total daily load by the peak sun hours (PSH) of your location. PSH is the number of hours of peak sunlight your area receives per day and can be found on a solar irradiance map.

Panel, Battery, and Inverter Sizing Worksheet

To ensure a well-designed solar system, use the following worksheet to size your panels, batteries, and inverter:

1. Calculate your daily load in Wh.
2. Multiply your daily load by 1.2 to account for system losses.
3. Divide your total daily load by the efficiency of your solar panels to get the required solar panel array size in watts (W).
4. Calculate the required battery capacity in Wh by multiplying your daily load by the number of days you want to store energy for.
5. Choose an inverter that can handle your required solar panel array size and battery capacity.