How Do Polysilicon Panels Support Sustainability | Materials Production, Recycling

Polycrystalline silicon panel production energy consumption is lower than single crystal by 20%.

After through thermal dissociation and physical crush operation, its glass, aluminum material, and silicon material's comprehensive recovery rate is as high as 95%, waste modules can directly re-melt manufacture new material, realize true green closed loop.

Materials Production

Dig sand extract refine

Production source head needs purity reach 99.5% quartz sand ore. The smelting plant takes quartz sand and, according to a 2 to 1 proportion, mixes carbon material and sends it into an electric arc furnace. The furnace inside temperature needs continuous pull rise to 1900 to 2000 degrees Celsius range, urging silicon dioxide complete chemical reduction.

Every produces 1 ton of purity at 98.5% to 99% metallurgical grade silicon, and consumes 10,000 to 12,000 degrees of electric energy. Liquid state silicon at 1800 degrees Celsius was drawn from the flow out furnace, injected into a thickness of 20 centimeters' mold inside a natural cool 24 hours. Cool after's block shape silicon was sent into a heavy type crush machine, ground into diameter 10 millimeters to 100 millimeters' irregular broken blocks.

· The whole primary smelting cycle's finished product conversion rate maintains at 85% up and down fluctuate.

· Metallurgical grade silicon's single ton manufacture total cost roughly controlled at 2000 to 2500 dollars.

· Ore raw material to primary silicon's weight attenuation rate roughly is 55%.

Gasify wash silicon

Metallurgical grade silicon broken block in 300 degrees Celsius and 30 standard atmospheric pressures' fluidized bed reactor inside with hydrogen chloride gas mix, generate boiling point only being 31.8 degrees Celsius' trichlorosilane gas. 20 to 30 meters high's fractionation tower using every day 24 hours' frequency carry out continuous precise distillation, take boron, phosphorus impurity's concentration compress to billionth one (ppb) level. Purify after high purity gas enters the Siemens reaction furnace, the furnace inside has a U-type silicon core serving as the deposit base bottom.

· Current heat makes silicon core temperature stable at 1,100 to 1,150 degrees Celsius.

· Gas phase deposit process continuous 70 to 120 hours without break flow.

· Final grow's polycrystalline silicon rod diameter reaches 15 to 20 centimeters, single root weight upper limit is 100 kilograms.

Material purity from this leap rises to 99.9999% (6N level). Purify link's electric power consumption roughly occupies 40% of the total budget. Every kilogram of polycrystalline silicon needs to consume electricity 40 to 50 degrees, production cost unit price roughly at every kilogram 15 dollars fluctuate, month produce amount 500 tons' factory every month needs to pay about 1.5 million dollars electricity fee.

Melt water cast ingot

Purify after's silicon rod was physically crushed into 5 to 10 centimeters' broken blocks, in concentration being 5% hydrofluoric acid solution inside soak wash 30 minutes in order to remove surface oxide. Wash clean's silicon material into a high purity quartz crucible, push into a vacuum induction furnace. Furnace cavity heats up to 1414 degrees Celsius above, usually maintained at 1500 degrees Celsius to carry out full melt. Single standard size's crucible load capacity is 800 to 1,200 kilograms between. The directional solidification crystal growth stage needs to consume 40 to 50 hours.

· Bottom part to top part's temperature gradient strictly controlled at every minute drop 1 to 2 degrees Celsius.

· Melt state under's residual impurity follows liquid state silicon float up to top part 2 to 3 centimeters' region.

· Cool form shape after, mechanical saw cut remove top part and bottom part each 5%'s volume in order to guarantee purity consistency.

Finished product polycrystalline silicon square ingot size is usually 1 meter multiplied by 1 meter, height at 40 to 50 centimeters, internal crystal grain size is distributed in the 1 millimeter to 10 millimeter range. The whole cast ingot cycle takes 60 to 70 hours, a single furnace run consumes electricity about 4,000 degrees, and equipment depreciation fees share to every kilogram of silicon material about 1.5 dollars.

Cut thin piece

Polycrystalline silicon square ingot first was cut edge machine trim to 156.75 millimeters multiply 156.75 millimeters' standard silicon block. Diamond wire cut machine internal arrangement has net shape array's cut wire, wire body diameter is only 55 to 65 micrometers, run wire speed reaches every second 15 to 25 meters. Cut wire tension keep at 20 to 30 Newtons between, prevent break wire. Cool liquid using every minute 50 liters' flow rate continuous spray, maintain 25 degrees Celsius' working temperature.

· Cut loss rate at 30% to 35% between fluctuate, represent become silicon powder waste material's weight ratio.

· One section 50 centimeters long's silicon block consumes time 6 to 8 hours and can cut out about 3000 pieces of single crystal thin piece.

· Single piece thickness parameter fixed at 160 to 180 micrometers, total thickness deviation (TTV) was limited at 15 micrometers within.

The single month throughput amount of the cut machine is 400 to 500 pieces of silicon block, and the equipment full load run rate needs to keep at 95% above. Good product rate bottom line require reach 97.5%, process process inside's physical break piece rate needs strictly controlled at 1.5% to 2.5%'s error range within. Single piece silicon wafer's manufacture process fee roughly is 0.15 to 0.20 dollars.

Plate film print wire

Silicon wafer enter temperature being 80 degrees Celsius, concentration being 10% potassium hydroxide alkaline solution inside corrode 10 minutes, surface height being 2 to 5 micrometers' random pyramid textured surface, surface physical reflectivity from initial's 30% drop to 10%. Following send into quartz tube diffusion furnace, at 850 degrees Celsius' high temperature under pass into phosphorus source gas bake 45 minutes, form depth 0.3 to 0.5 micrometers' PN junction, square resistance indicator reach 90 to 110 ohms/square.

· Plasma enhanced chemical vapor deposition (PECVD) equipment at 400 degrees Celsius and 1 Torr pressure under work.

· Silicon wafer surface evenly deposits 75 to 80 nanometers thick silicon nitride anti-reflection film.

· Light ray reflectivity further compressed to 1.5% lowest value.

Screen print machine takes high conductance electricity rate's silver paste coat spread on silicon wafer front surface, single piece consumes silver amount controlled at 80 to 100 milligrams, print out's thin grid line width is 30 to 40 micrometers, height reaches 15 micrometers. Mesh belt type sintering furnace at 800 degrees Celsius under towards silicon wafer carry out 3 to 5 seconds' instant high temperature heat. Finished product photovoltaic cell piece's test parameter inside, fill factor reach 78% to 81%, open circuit voltage measure at 0.63 to 0.65 volts, photoelectric conversion efficiency average value fixed at 17.5% to 18.5%.

Recycling

Pull away old board

Photovoltaic power station first batch install's equipment use life has already broken through 25 years, module's power generation power widely attenuated to initial rated power's 75% to 80% range. Scrap recycle network's single-time logistics transport radius usually delineate at 400 to 500 kilometers range within.

Standard load weight 20 tons' heavy type truck single trip full load transport about 1000 pieces single piece weight at 18 to 22 kilograms' polycrystalline silicon panel. Unload goods area equipment's infrared ray scanner using every minute 40 pieces' speed read back plate on's barcode, record use years limit, size specification and material batch. Panel following send into test bench, apply 1000 volts' direct current voltage test leakage current indicator.

Physical break rate exceeds 40% panel enters deep disassemble line, surface glass intact and fill factor maintains at 65% above's module flow towards second-hand trade market. Single body recycle treatment fee usually accounts for every piece 15 to 20 dollars, including transport, sorting, and storage costs. The factory storage area maintains a constant temperature of 25 degrees Celsius and 50% relative humidity, prevents suffering damp short circuits, and single month material flow turn amount reaches 3,000 to 4,000 tons.

Disassemble parts

Send into automatic flow line's panel first pass through pneumatic disassemble frame machine. Hydraulic chuck at four corners simultaneously apply 1500 Newtons' horizontal pull force, consume time 8 to 10 seconds to take anodic oxidation aluminum border frame complete peel off. Single piece panel disassemble out 2.5 to 3 kilograms' waste aluminum, produce about 0.5% metal deformation loss. Junction box by high frequency mechanical scissors cut break, peel off internal contain 95% high purity copper's tin plated copper solder ribbon, every piece of board collects about 0.15 kilograms.

Peel off border frame after's no frame laminate piece send into roller press crush machine, equipment rotate speed set at every minute 120 revolutions, roller gap controlled at 4.5 millimeters. Physical roll press takes most outer layer's 3.2 millimeters thickness tempered glass peel fall, vibrate screen machine frequency maintain at 50 Hertz, take broken glass's particle diameter screen distribute at 2 to 4 millimeters between. High pressure wind machine using every second 25 meters' wind speed blow away glass powder, separate out's glass broken piece weight occupies original material total weight as high as 70%.

Bake, melt, remove glue

Remove the over glass and border frame's remain sandwich structure contains silicon wafer, ethylene-vinyl acetate copolymer (EVA) encapsulate adhesive film as well as polyester back plate. Conveyor belt using every minute 0.5 meters' speed rate to take sandwich pieces into continuous type pyrolysis furnace. Furnace cavity internal divided into three temperature zones, temperature gradient respectively set at 300, 450 and 550 degrees Celsius. In order to prevent material burn, the cavity body internal passes into purity 99%'s nitrogen gas, and oxygen gas concentration is forced to press at 1.5%'s lower limit below.

Pyrolysis cycle continuous 45 to 60 minutes, solid state EVA and back plate receive heat volatilize become hydrocarbon gas. Exhaust out's tail gas temperature as high as 400 degrees Celsius, immediately sent into an alkaline liquid spray tower for rapid cooling treatment. Spray system circulate inject pH value maintain at 9.5 to 10.5's sodium hydroxide solution, gas flow speed is every hour 1000 cubic meters, take acid by-product's neutralize rate pull rise to 99.2%. Pyrolysis after's solid residue weight drops past about 10% to 12%, obtain silicon wafer and metal net wire's mixture.

Soak acid extract silver

The first pass process injects a concentration of 25% to 30% nitric acid solution, and the stir machine uses every minute 80 revolutions' speed. Solution temperature heat and constant at 60 degrees Celsius, soak reaction time accurately controlled at 90 minutes. Solid state silver complete oxidize dissolve generate silver nitrate liquid, silver's leach out rate at 92% to 95% range fluctuates.

The filter machine uses a 0.5 micrometer diameter polytetrafluoroethylene filter membrane to separate solid liquid, collect the arriving filter liquid inside, and add it to a 15% sodium chloride solution, generating white color silver chloride precipitate. Precipitate matter is sent into a high-temperature melt smelt furnace, and under 1,050 degrees Celsius, purity reaches 99.9% silver original block.

Every process 1 ton of scrap old panel produces out 15 to 20 grams of silver. Remain's solid state silicon wafer surface still attaches silicon nitride anti-reflection film, take it transfer to a polypropylene tank inside, inject a 5% hydrofluoric acid soak wash 10 to 15 minutes. Clear water carry out three times rinse wash after, centrifuge machine using every minute 3000 revolutions' rotate speed spin dry water moisture. Recycle's polycrystalline silicon wafer broken piece purity returned to 98.5% above, can serve as metallurgical grade raw material using every kilogram 1.5 to 2.0 dollars' price re-flow back melt cast supply chain.