Solar panels producing 30-50% below expected output usually indicates dirt buildup, partial shade, or temperature effects—not panel failure. A 100W panel rated for 100W at 77°F will only produce 70-80W on a 95°F day, and that's normal. 8% annually: Quality solar panels naturally lose efficiency over time, so a system producing 10,000 kWh in year one should generate around 9,950 kWh in year two – this gradual decline is expected and warranty-covered. Soiling is the #1 culprit: Dirt. Solar panels are meant to quietly do their work turn sunlight into savings. Anything that reduces the amount of light reaching the panel—or interferes.