Solar Lattice

FailureMode

Hot cell

ID
fm:hot-cell
IRI
https://solarlattice.org/kb/fm/hot-cell
Status
active

A hot cell is a solar cell that heats up evenly over its whole area because current mismatch, from shading or cell cracks, pushes it into reverse bias and makes it dissipate power. It is mainly seen in monocrystalline cells, while the classic hot spot is a localised point of heating mostly found in multicrystalline cells. Infrared thermography shows the affected cell as uniformly warmer than its neighbours. A single hot cell usually costs little power, but the heat can lead to discolouration, delamination, interconnection failures, cell cracks, backsheet deformation, glass breakage and loss of insulation. Bypass diodes limit the power a shaded cell can dissipate, but they do not remove the hot cell risk. Preventive measures include binning cells by current, screening cells for low shunt resistance, using shade-resistant module designs and putting fewer cells on each bypass diode.

<!-- review notes

Claims

caused_by

c1 drafted · lead Cell current mismatch

c2 drafted · lead Cell reverse bias

The underperforming cell is driven into reverse bias and dissipates power as heat.

c3 drafted · lead Partial shading

c4 drafted · lead Cell Cracks

affects

c5 drafted · lead Solar cell

c6 drafted · lead Backsheet

Very high cell temperatures can cause backsheet bubbles and deformation.

c7 drafted · lead Encapsulant

Polymeric materials can discolour, delaminate or embrittle at high temperature.

review note: support check: partial - Polymeric materials discolour, delaminate and embrittle above 150°C, but encapsulant is not named explicitly.

presents_as

c8 drafted · lead Uniformly heated cell

Temperature rises evenly over the whole cell area, not at one point.

detected_by

c9 drafted · lead Infrared thermography

IR thermography of aged field modules revealed hot cells.

distinguished_from

c10 drafted · lead Module Hotspot from Cell Damage — told apart by Infrared thermography

A hot spot is localised heating from local junction breakdown, mainly in multicrystalline cells; a hot cell heats evenly over the whole cell area and is linked to monocrystalline cells.

review note: support check: partial - The hot spot/hot cell distinction is stated (localised vs homogeneous, multi vs mono), but the passages don't say IR thermography is used to tell them apart.

leads_to

c11 drafted · lead Discoloration

c12 drafted · lead Cell Interconnection Failure

Solder joints can fail if the cell temperature exceeds the solder melting point.

c13 drafted · lead Cell Cracks

c14 drafted · lead Delamination

c15 drafted · lead Loss of electrical insulation

c16 drafted · lead Backsheet bubbling and deformation

c17 drafted · lead Glass Breakage

c18 drafted · lead Junction Box Failure

In extreme cases the junction box may detach.

mitigated_by

c19 drafted · lead Cell current binning

c20 drafted · lead Cell shunt resistance screening

c21 drafted · lead Bypass diode integration

Bypass diodes cap the dissipated power but do not eliminate hot cell effects.

c22 drafted · lead Shade-resistant module design

Examples include half-cell, shingled and per-cell diode modules.

review note: support check: partial - Shade-resistant modules (half-cell, shingled, per-cell diodes) are offered, but the text doesn't explicitly say they mitigate hot cells, and notes shade resistance is poorly defined.

c23 drafted · lead Shorter bypass diode substrings

Fewer cells per bypass diode lowers the reverse voltage and hot cell temperature.

temperature_rise

c24 drafted · lead ≤ 25 DEG_C

Conditions: IBC half-cell module in an indoor hot-spot test at 55°C module temperature; hot cell temperature relative to module temperature

Referenced by

Data