Performance Ratio (PR)
The percentage of a solar system's theoretical maximum output that is actually achieved, accounting for all real-world losses (temperature, shading, soiling, wiring, inverter). Typical: 75-85%.
Why It Matters
A declining performance ratio indicates a problem — soiling, equipment degradation, or a fault. Monitoring your PR over time helps catch issues early.
Related Topics
Related Terms
Specific Power (kWh/kWp)
The energy output per unit of installed capacity over a period (typically one year). Expressed as kWh per kWp (kilowatt-peak). A good residential system in the U.S. achieves 1,200-1,800 kWh/kWp annually.
Degradation Rate
The annual decrease in solar panel efficiency. Modern panels typically degrade 0.3-0.5% per year.
Soiling Loss
Energy production lost due to dirt, dust, pollen, bird droppings, or other debris accumulating on solar panel surfaces and blocking sunlight.