PV Performance: Systems
Reliability of photovoltaic (PV) arrays is an important factor in the cost of systems and in consumers accepting this technology. The PV cell itself is considered a "solid-state" device with no moving parts, and therefore, it is highly reliable and long-lived. Therefore, reliability of PV usually focuses not on cells, but on modules and systems.
One way to measure reliability is the rate of failure of particular parts. The failure of solar cells mostly involves cell cracking, interconnect failures (resulting in open circuits or short circuits), and increased contact resistance. Module-level failures include glass breakage, electrical insulation breakdown, and various types of encapsulant failures (e.g., delamination).
Fault-tolerant circuit design involves using various redundant features in the circuit to control the effect of partial failure on overall module yield and array power degradation. Degradation can be controlled by dividing the modules into a number of parallel solar cell networks called branch circuits. This type of design can also improve module losses due to broken cells and other circuit failures. Bypass diodes or other corrective measures can mitigate the effects of local cell hot-spots. Replacement of the entire module is a final option in dealing with PV array failures. However, today's component failure rates are low enough that, with multiple-cell interconnects, series/paralleling, and bypass diodes, it is possible to achieve high levels of reliability.