Before we get into the system sizing process, consider the following: 1. Sun Hours Some parts of the country get more exposure to the sun than others. You'll need to know how many sun hours you get in your location -- a measure of the duration and intensity sunlight in your. There are three key factors to consider when sizing an off-grid system: 1. Peak power demand 2. Daily kWh usage 3. Nightly kWh usage. What are the electrical loads that you will need to run? Will they all run at the same time, or can you rotate the loads? Your peak power demandis your total wattage usage when you are. In the daytime, the power you use comes straight from your solar panels. When the sun goes down and panels are no longer generating power, the battery bank takes over and your. Using the load evaluation worksheet you filled out, multiply the appliance wattage by the number of hours it will be in use each day. As an example, if you run a 1,500-watt dishwasher for 30 minutes each day: 1,500 watts x 0.5 hours = 750 watt-hours (Wh) Remember to.