Page 20 - Issue 4 2023

TECHNICAL

disconnected and inverters turned off,
the panels will continue to generate
electricity as long as the sun is shining.
Most rapid shutdown rules require
disconnection to occur at module
level, and MLPEs or micro-inverters
achieve this by reducing the panel’s
output to a very low voltage.

Module level monitoring
Figure 2: Microinverter installation (Solarworld) Some optimisers are capable of
performing module level monitoring,
Micro-inverters also address the problems usually associated with a solar system where current, voltage and power
facing different directions or being shaded over for part of the day by trees or levels are measured and stored. This
buildings, by ensuring that all of the energy is harvested. facility is useful for very large panels
Micro-inverters convert the DC from the panel to AC for transmission across the and can give an indication of failure or
rooftop at a relatively low voltage (240 V). degradation at panel level.

Optimisers Smart inverter developments
In a string of PV panels, shading or other problems with a panel would generally Smart inverters incorporate functions
reduce the output voltage of the panel thus affecting the string voltage. An optimiser, that improve the safety, operation
consisting of an MPPT and a DC/DC converter attached to each panel, adjusts and maintenance of the solar PV
the output voltage of the panel to maintain the string voltage at the input to the installation.
inverter, while generating power at its maximum point under reduced conditions.
Optimisers can be installed on every panel or only to selected panels, depending DC arc flash protection, arc fault
on the operating conditions of the string. The MPPT sets the operating point of the circuit breaker and rapid shutdown.
panel, while the DC/DC converter maintains the output voltage at that required by Long strings of PV modules can reach
the string inverter. voltages in excess of 1000 VDC, and
Optimisers may be added externally or be integrated by the panel manufacturer. batteries connected to the PV system
Smart panels are standard panels with an integrated optimiser pre-installed at the can provide the current required to
back of the panel. When using optimisers, the panels are connected in series and the support a DC arc. Most fires in PV
string is connected to the inverter. modules are caused by DC arcing.
Where PV modules’ contact points
Rapid shutdown disconnectors have a poor connection, conductors
In the case of an emergency, such as arc flash or fire, the PV panel must be are damp, or insulation is damaged,
de-energised quickly. Although the electricity supplied to the inverter can be high voltage arcs can occur. The arc
characteristic is related to many
factors such as line length and current,
and precise arc detection is difficult.
Rapid shutdown can be used both
to control the formation of arcs and
to place the output at a safe level.
PV rapid shutdown systems (PVRSS)
reduce the voltage appearing at the
output of the system to a safe value.
Internal wiring and interconnections
are usually inaccessible.

Potential induced degradation
counteraction
PID can result in a loss of capacity in
excess of 30%, as well as other faults
Figure 3: Block diagram of PV optimiser. in the module, and has become an

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