XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3261
reviews the current recycling technologies for silicon solar
modules, analyzes major technical barriers in silicon module
recycling, and summarizes significant progress in achieving
a 90–95 wt% circularity for silicon modules. A 100 wt%
circularity, while desirable, is not feasible. This is because
the polymers in silicon modules, including the encapsulant
ethylene vinyl acetate and the back sheet polyvinyl fluoride,
are difficult to recycle with our current knowledge.
CURRENT RECYCLING TECHNOLOGIES
Most end-of-life silicon modules end up in landfills today.
Even for those modules which go through today’s recycling
processes, they are often only 10–15 wt% circular. That is,
only the aluminum (Al) frame and sometimes the copper
(Cu) wires in the junction box are recovered which can be
remelted for new frames and wires. The remaining 85–90
wt% of the materials are either landfilled or sometimes
downcycled to concrete aggregate.
The technology underlying today’s recycling processes
employs all physical methods for material separation. As
shown in Figure 1, the first step in silicon module recycling
is to cut off the junction box (Figure 1(a)). Once the plas-
tic casing is crushed and the plastic sheath is removed, the
copper wires can be recovered from the junction box. The
next step is to strip off the aluminum frame (Figure 1(b)).
There is a silicone sealant attached to the aluminum frame.
It needs to be removed before remelting the aluminum. The
next steps should be removal of the back sheet and separa-
tion of silicon solar cells from glass, but most recyclers do
not know how to proceed, so they stop after copper wires
and aluminum frame, leading to about $2.50/module in
revenue:
• ~$2/module for aluminum
• ~$0.60/module for copper
The remaining module in Figure 1(c) is 90 wt% glass.
Today most recyclers crush it, but no glass recyclers want
the crushed module for two reasons. First, the polyvinyl
fluoride back sheet is still attached to the glass. When they
remelt the crushed module for new glass products, the back
sheet would release a fluorine exhaust. Second, the silicon
cells still attached to the glass would never melt (the melt-
ing point of silicon is 1420°C), resulting in new glass prod-
ucts dotted with silicon particles.
The most advanced module disassembly technology
today is the hot-knife method (NPC Inc., 2023a). The
tool is commercially available. It first removes the junction
box and aluminum frame as shown in Figs. 1(a) and 1(b),
then leaves alone the back sheet (Figure 1(c)), and finally
separates the silicon cells from glass by slicing a steel blade
through the encapsulant between silicon cells and glass. To
soften the encapsulant for easier cutting, the steel blade is
heated to about 300°C. Figure 2 shows the separated silicon
cell sheets and glass sheets by the NPC tool.
The separated glass sheets in Figure 2(b) contain only
residual encapsulant without any back sheet. When they
are remelted for new glass products, the residual encapsu-
lant, ethylene vinyl acetate, releases only carbon dioxide
(CO2) and water vapor (H2O). It is also possible to pro-
duce new solar glass sheets from the separated glass sheets,
which would make the glass completely circular and gener-
ate more value than regular glass products. The key for new
solar glass sheets is to keep the iron content in the glass
below 100 ppm, even with potential contamination from
the recycling process. If the glass is recovered as solar glass,
the total revenue reaches about $4/module:
• ~$2/module for aluminum
• ~$0.60/module for copper
• ~$1.30/module for glass
Figure 1. Mechanical disassembly of silicon modules: (a) removal of junction box, (b) removal of aluminum frame (c) removal
of back sheet, and (d) separation of silicon cells from glass
reviews the current recycling technologies for silicon solar
modules, analyzes major technical barriers in silicon module
recycling, and summarizes significant progress in achieving
a 90–95 wt% circularity for silicon modules. A 100 wt%
circularity, while desirable, is not feasible. This is because
the polymers in silicon modules, including the encapsulant
ethylene vinyl acetate and the back sheet polyvinyl fluoride,
are difficult to recycle with our current knowledge.
CURRENT RECYCLING TECHNOLOGIES
Most end-of-life silicon modules end up in landfills today.
Even for those modules which go through today’s recycling
processes, they are often only 10–15 wt% circular. That is,
only the aluminum (Al) frame and sometimes the copper
(Cu) wires in the junction box are recovered which can be
remelted for new frames and wires. The remaining 85–90
wt% of the materials are either landfilled or sometimes
downcycled to concrete aggregate.
The technology underlying today’s recycling processes
employs all physical methods for material separation. As
shown in Figure 1, the first step in silicon module recycling
is to cut off the junction box (Figure 1(a)). Once the plas-
tic casing is crushed and the plastic sheath is removed, the
copper wires can be recovered from the junction box. The
next step is to strip off the aluminum frame (Figure 1(b)).
There is a silicone sealant attached to the aluminum frame.
It needs to be removed before remelting the aluminum. The
next steps should be removal of the back sheet and separa-
tion of silicon solar cells from glass, but most recyclers do
not know how to proceed, so they stop after copper wires
and aluminum frame, leading to about $2.50/module in
revenue:
• ~$2/module for aluminum
• ~$0.60/module for copper
The remaining module in Figure 1(c) is 90 wt% glass.
Today most recyclers crush it, but no glass recyclers want
the crushed module for two reasons. First, the polyvinyl
fluoride back sheet is still attached to the glass. When they
remelt the crushed module for new glass products, the back
sheet would release a fluorine exhaust. Second, the silicon
cells still attached to the glass would never melt (the melt-
ing point of silicon is 1420°C), resulting in new glass prod-
ucts dotted with silicon particles.
The most advanced module disassembly technology
today is the hot-knife method (NPC Inc., 2023a). The
tool is commercially available. It first removes the junction
box and aluminum frame as shown in Figs. 1(a) and 1(b),
then leaves alone the back sheet (Figure 1(c)), and finally
separates the silicon cells from glass by slicing a steel blade
through the encapsulant between silicon cells and glass. To
soften the encapsulant for easier cutting, the steel blade is
heated to about 300°C. Figure 2 shows the separated silicon
cell sheets and glass sheets by the NPC tool.
The separated glass sheets in Figure 2(b) contain only
residual encapsulant without any back sheet. When they
are remelted for new glass products, the residual encapsu-
lant, ethylene vinyl acetate, releases only carbon dioxide
(CO2) and water vapor (H2O). It is also possible to pro-
duce new solar glass sheets from the separated glass sheets,
which would make the glass completely circular and gener-
ate more value than regular glass products. The key for new
solar glass sheets is to keep the iron content in the glass
below 100 ppm, even with potential contamination from
the recycling process. If the glass is recovered as solar glass,
the total revenue reaches about $4/module:
• ~$2/module for aluminum
• ~$0.60/module for copper
• ~$1.30/module for glass
Figure 1. Mechanical disassembly of silicon modules: (a) removal of junction box, (b) removal of aluminum frame (c) removal
of back sheet, and (d) separation of silicon cells from glass