Abstract:
Potential Induced Degradation (PID) causes significant module degradation leading to
decreased power output in photovoltaic (PV) power plants. Many PV power plants are
constructed using transformerless inverters and may be susceptible to issues associated
with the galvanic connection between the PV configuration and the power grid. This
increases the likelihood of a leakage current between the PV system`s active circuit and
the ground. The resulting electric field causes sodium (Na+) ions to drift to the cell and
some at a certain concentration may diffuse into the PN junction creating shunting paths.
The PID detection tools employed in this work are maximum power measurements,
comparison of open circuit voltage (Voc) at low irradiance (200 W.m-2
) and high
irradiance (1000 W.m-2
) and Electroluminescence (EL) imaging at 10% of Short-circuit
current (Isc). These techniques are used to assess the degree of PID and to monitor the
module recovery. This work explores two recovery methods for PID affected modules,
forced recovery and natural recovery. Forced recovery involves reverse biasing the
module terminals for a few hours while natural recovery, modules are left unbiased for
several months. This yields a maximum power recovery of approximately 95% and 94%
for forced and natural recovery respectively. These techniques are used to assess the
degree of PID and to monitor recovery. This paper demonstrates that PID recovery on
modules depends on two mechanisms, viz. drift or diffusion, or combined.
