Getting a complete list of electrical appliances, devices and components you'll use in your RV is the most critical part of sizing the electrical system. Underestimate it and you may run out of power. Overestimate and you'll probably spend more money and make your setup more complex than necessary. Work through your typical day,. The aim of the calculation to size your camper electrical setup so you have enough power every day. With this in mind, it's important to consider your most heavy usage day. Maybe you intend to live in your camper during the winter. Your heating will run for longer and probably your ventilation fan too (it's the best way to stop. The watts of most devices can be found either printed on the device, in the operating manual or the manufacturer's website online. Sometimes, products list the power usage in current (i.e. amps). In this case, use the wattage calculator at the top of the solar calculator above to convert the current and volts to watts. The way the power is stated o.