It is the amount of energy intake, equivalent to running a 1,000-watt appliance for 1 hour. Today, a typical home solar panel falls in the range of 350–450 watts per panel. The biggest the rated wattage of a solar panel, the more kWh. . This in-depth guide breaks down the numbers, the factors that influence output, and how to calculate what you can expect. Solar panels degrade slowly, losing about 0. 5% output per year, and often last 25–30 years or more. Simple, fast, and accurate! Ever look at your electricity bill and feel a mix of confusion and dread? You're not alone.