Which types of solar panel degradation exist?

Types of degradation

Which types of solar panel degradation exist?

Degradation of solar panels results in efficiency losses. Next to Potential Induced Degradation, several other types of solar panel degradation exist.

A. HOT SPOT

A local increase of the resistor mainly occurs due to cracks in the solar cell. Therefore the total current of the cells in series will be limited. A discharge of power in the form of heat originates in the broken cell. Because of this, strong heating cells can become inactive.

Fig 1
Fig. 1: hot spot with infrared camera and physical image of the panel

B. SNAIL TRAILS

Solar panels sometimes have to deal with figurative ‘snail trails’, which are understood as linear discolorations on parts of the solar cell surface. Snail trails may result in ‘hot spots’ (see A.) and lead to efficiency losses.

More information abuot snail trails is to be found here.

Fig 2bis
Fig. 2: solar panel with snail trail

C. SHORT-CIRCUITING BETWEEN CELLS

Short-circuit can be caused by bad connections between the cells. This problem is common for thin film solar panels, which have the front and back side connections located very close to each other.

Fig 3
Fig. 3: short-circuiting between cell

D. INTERRUPTION OF/OR BETWEEN CELLS

Interruption can be the result of fragile cells, or damage caused by all sorts of things. Interruptions can also occur between cells. Redundancy contacts and bush bars are used to make sure that the cell, or a part of it still continues to operate.

An interruption can be caused by expansion by high temperature, hailstones and damage through production and assembly.

Fig4
Fig. 4: micro crack

E. DEGRADATION OF THE CONNECTION BETWEEN THE PANELS

Defects on the connections between solar panels come into existence at the wiring, connectors of the junction box. Because of weathering the protection of these components degrades.

Cables are not always stripped in the right length of insulation, through which the metal is exposed at weathering. As a result, contacts can be oxidized, with the result they are less good electrical conductivity.

Fig5
Fig. 5: oxidized cable

F. RESISTORS

When the equivalent circuit diagram of a solar cell is proposed, it will be seen that it is composed of a shunt resistor (Rshunt) and a series resistor (Rserie).
Fig6
Fig. 6: equivalent scheme from a PV-cell

The shunt resistor illustrates the intern leaks. In the first instance the short-circuit current will lightly increase, but when the load increases, this current will decrease. As a result, the diode is at a lower voltage in the guiding. The output voltage is equal to the voltage across the diode. This results in loss of power at the output of the cell.

The series resistor illustrates the losses at the contacts, the resistance of the conductors, semiconductor,… In ideal situation is this as low as possible. If this resistance rises, the diode will become more conductive. This results primarily to an increase of the voltage and a slightly decrease of the current. If more power is delivered, the output current drops sharply. The voltage drops now, thus less power is supplied.

G. DELAMINATION

Delamination is a visible form of degradation. Solar panels are laminated in order to protect them against ingress of humidity and/or oxygen. When imperfections or damage to the lamination occurs, there is less protection against these external factors. Delamination is enhanced at higher temperatures.

Fig. 7
Fig. 7: delamination of solar panels

H. BROWNING

When solar cell browning occurs, the temperature in the cells is much too high. This is due to interruptions, so that the cell becomes a resistor and the currents run high. These currents provide a lot of heat, which in turn provides the browning process.

Fig8
Fig. 8: solar cell with browning

I. LID

Light Induced Degradation occurs during the first few hours when the solar panel is in use. The solar panel is being degraded by its first contact with the sunlight and ultraviolet rays.

A second form of LID is obsolescence from the solar cells. This process occurs gradually and applies to each solar panel. After all, they can’t operate eternally on the maximum conversion efficiency.

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