The following is the estimated consumption of various appliances and devices. Check your appliances for the specific watt consumption. To get the watt hour usage per day, multiply the watts on the table by the number of hours you use the device. There are some things you need to keep in mind when computing total. There are two methods to find out. The first is to use add the total watts of every appliance you use. You can use the charts above as a guide but you should always check the specs on each appliance to be sure. The second way is easier. Look at your monthly bill and how. No, batteries are not required to reach 3000W output. Where the batteries are needed is to store the excess power produced by the solar panels. The battery's reserve power. The average solar panel is 250W. 250 x 12 = 3000, so you need 12 panels, right? Actually you will need 15 solar panels to run a 3000W system.Here's why. Solar panel ratings are based on peak output. So when a panel is rated at 250 watts, that is peak performance. But. Inverters come in various sizes, but the basic rule is it should be at least equal to your system's DC rating. inverter size is measured in watts so it's easy to compare the two. In a 3000W solar system you need at least a 3000W inverter. However, inverters are not 100%.