Minerals for Solar Energy — Silicon, Silver, Copper, Tellurium, Gallium & the Polysilicon Supply Chain

Solar Energy’s Mineral Profile

Solar photovoltaic energy has become the fastest-growing source of new electricity generation capacity in the world. Global solar PV installations exceeded 400 GW in 2023 and are projected to reach 500 to 700 GW annually by 2030 under various IEA scenarios. This deployment scale makes solar PV a major and growing source of mineral demand, though the mineral profile of solar differs significantly from batteries and wind turbines.

The dominant solar PV technology—crystalline silicon (c-Si), which accounts for over 95 percent of the global market—relies on a specific set of materials: high-purity polysilicon for the solar cells, silver for cell metallization contacts, copper for wiring and inverters, aluminium for frames and mounting structures, glass for the front cover, and various polymers for encapsulation and backsheet. Thin-film solar technologies (cadmium telluride, CIGS) use different material sets including tellurium, cadmium, gallium, indium, and selenium, but represent less than 5 percent of global production.

The mineral intensity of solar PV is approximately 7 tonnes per megawatt of installed capacity, lower than wind turbines (10 to 15 tonnes per MW) but deployed at greater scale. The cumulative mineral demand from solar deployment is therefore comparable to or exceeds that of wind, and the specific materials involved—particularly polysilicon and silver—face their own supply concentration and constraint challenges.

Polysilicon: The Core Material

Polysilicon—ultra-pure silicon with a purity of 99.9999 percent or higher (six-nines purity for solar, nine-nines for semiconductors)—is the fundamental raw material for crystalline silicon solar cells. Each gigawatt of solar PV capacity requires approximately 2,500 to 3,500 tonnes of polysilicon, depending on cell technology and wafer thickness. Global polysilicon production in 2023 was approximately 1.5 million tonnes, with solar accounting for over 95 percent of consumption.

The polysilicon supply chain is among the most geographically concentrated of any major industrial material. China produces approximately 80 to 85 percent of global polysilicon, with the majority concentrated in four provinces: Xinjiang, Inner Mongolia, Sichuan, and Yunnan. The Xinjiang concentration has been particularly controversial due to allegations of forced labour in the region's industrial operations, leading the United States to enact the Uyghur Forced Labor Prevention Act, which creates a rebuttable presumption that goods produced in Xinjiang are produced with forced labour and bars their import.

The polysilicon production process is energy-intensive, requiring approximately 60 to 80 kWh of electricity per kilogram through the dominant Siemens chemical vapour deposition process. Chinese producers in Xinjiang and Inner Mongolia have achieved cost leadership partly through access to low-cost coal-fired electricity, creating a carbon intensity paradox: the solar panels designed to decarbonise electricity generation are manufactured using coal-intensive processes.

Non-Chinese polysilicon producers include Wacker Chemie (Germany), OCI (South Korea), REC Silicon and Hemlock Semiconductor (United States), and Tokuyama (Japan). These producers collectively account for less than 20 percent of global output and operate at significantly higher cost than Chinese competitors. US tariff and trade enforcement actions have created a partially protected market for non-Chinese polysilicon in American solar manufacturing, but global market economics remain dominated by Chinese cost leadership.

Silver for Cell Metallization

Silver is used in solar cells for the fine conductive grid lines (fingers and busbars) that collect and transmit the electric current generated by the photovoltaic effect. These metallization contacts must be highly conductive and precisely applied, and silver's unmatched electrical conductivity makes it the material of choice. Each solar cell uses a small quantity of silver—approximately 10 to 20 milligrams for a standard PERC cell—but multiplied across billions of cells manufactured annually, the aggregate demand is enormous.

The solar industry consumed approximately 6,000 to 7,000 tonnes of silver in 2023, making it the single largest industrial consumer of silver, surpassing electronics, brazing alloys, and photographic applications. This represents approximately 25 percent of total annual silver mine production of approximately 26,000 tonnes. Solar silver demand is projected to reach 8,000 to 10,000 tonnes by 2027 and could exceed 12,000 tonnes by 2030 under aggressive deployment scenarios.

A critical dynamic is the impact of new cell technologies on silver intensity. The transition from PERC (Passivated Emitter and Rear Contact) cells to TOPCon (Tunnel Oxide Passivated Contact) and heterojunction (HJT) cells improves solar cell efficiency but increases silver consumption per cell. TOPCon cells use approximately 50 percent more silver than PERC, and HJT cells use roughly double the silver of PERC. If the industry transitions rapidly to these higher-efficiency architectures, silver demand could exceed supply growth, potentially driving silver prices higher and incentivising the development of copper-based metallization alternatives.

Copper plating is being developed as a silver substitute for cell metallization, and several manufacturers have announced pilot production using copper-plated contacts. However, copper metallization requires additional barrier layers to prevent copper diffusion into the silicon, adding manufacturing complexity. Commercial-scale copper metallization is expected to emerge in the 2027 to 2030 timeframe but is unlikely to fully displace silver before the mid-2030s.

Copper in Solar Systems

Copper is the primary wiring and interconnection material in solar PV systems, used in cell interconnections (ribbon wire), module junction boxes, DC cabling between modules, AC cabling from inverters to the grid, inverters themselves, and transformers and switchgear at the point of grid connection. A typical utility-scale solar installation requires approximately 2 to 5 tonnes of copper per megawatt, with the majority consumed in the balance-of-system (BOS) components rather than in the solar panels themselves.

At an average of 3.5 tonnes of copper per megawatt and projected annual installations of 500 to 700 GW by 2030, solar-related copper demand could reach 1.7 to 2.5 million tonnes per year—approximately 7 to 10 percent of current global copper consumption. This demand sits alongside EV, wind, grid, and data centre copper requirements, contributing to the aggregate copper demand surge that threatens to create structural supply deficits.

Aluminium is used extensively in solar mounting structures and panel frames but does not substitute for copper in electrical applications where conductivity is critical. The solar industry's copper demand is therefore relatively price-inelastic: copper cannot be easily replaced without compromising system efficiency and safety.

Thin-Film Materials

Thin-film solar technologies use alternative semiconductor materials deposited as thin layers on glass or flexible substrates. While they represent less than 5 percent of global production, their specialised mineral requirements are strategically significant.

Cadmium Telluride (CdTe)

CdTe thin-film modules, manufactured primarily by First Solar (the only major Western solar manufacturer), use cadmium and tellurium as the semiconductor absorber layer. Tellurium is one of the rarest elements in the Earth's crust, produced primarily as a byproduct of copper refining. Global tellurium production is approximately 500 to 600 tonnes per year, and First Solar alone consumes a significant fraction of this supply. Scaling CdTe production beyond current levels is constrained by tellurium availability, though tellurium recovery from copper anode slimes could be improved.

CIGS (Copper Indium Gallium Selenide)

CIGS thin-film cells use a semiconductor layer of copper, indium, gallium, and selenium. Indium and gallium are both relatively scarce and produced primarily as byproducts of zinc and aluminium smelting, respectively. Gallium has gained particular strategic prominence since China imposed export restrictions on gallium and germanium in 2023, citing national security. China produces approximately 80 percent of global gallium, and the export controls sent a clear signal about Beijing's willingness to use mineral supply as a geopolitical lever.

Perovskite (Emerging)

Perovskite solar cells, a rapidly advancing technology, use lead halide perovskite compounds as the absorber material. Perovskites can be manufactured from abundant materials (lead, iodine, methylammonium) and deposited using low-cost printing or coating processes. If perovskite or perovskite-silicon tandem cells achieve commercial scale, they could reduce the solar industry's dependence on silver and potentially on high-purity polysilicon, fundamentally altering the mineral demand profile of solar energy. However, long-term stability and lead toxicity concerns remain significant commercialisation barriers.

Supply Chain Concentration

The solar mineral supply chain exhibits extreme geographic concentration that mirrors—and in some respects exceeds—the concentration seen in battery mineral processing. China's dominance extends across every major stage of the crystalline silicon solar supply chain.

The wafer stage is the most concentrated: over 95 percent of the world's silicon wafers for solar cells are produced in China. Even when modules are "assembled" in Southeast Asia (Vietnam, Malaysia, Thailand, Cambodia) to avoid US tariffs on Chinese-origin solar products, the wafers and cells typically originate from Chinese factories. The resulting supply chain dependency is so complete that a disruption to Chinese solar manufacturing—whether from trade sanctions, energy shortages, or natural disaster—would have immediate global consequences for solar deployment.

Demand Projections

The most constrained material is silver, where solar demand growth is projected to consume an increasing share of global mine production. If solar deployment reaches 700 GW annually and TOPCon/HJT cells become dominant, silver demand from solar alone could consume 40 to 50 percent of global silver mine production—a level that would likely trigger significant price increases and accelerate the development of copper metallization alternatives.

Strategic Implications

Solar energy's mineral requirements have limited direct implications for the Lobito Corridor, as the primary solar materials—polysilicon, silver, aluminium—are not produced in the corridor's mineral hinterland. However, the indirect implications are significant. Solar deployment is a major driver of copper demand, and Copperbelt copper produced along the corridor serves the global copper market that feeds solar installation worldwide. Every solar farm wired with copper represents demand for the metal that the corridor transports.

The broader lesson from solar's mineral supply chain is the risk of concentrated dependency. China's dominance of the solar supply chain serves as a cautionary example for the battery mineral supply chain: if processing and manufacturing capacity is allowed to concentrate in a single country, the resulting dependency creates strategic vulnerabilities that are extremely difficult to unwind. The processing gap in battery materials exists precisely because the solar playbook—in which Chinese industrial policy captured dominant market share while Western nations failed to invest in manufacturing—was repeated in batteries.

For policymakers and investors focused on the energy transition mineral supply chain, the solar experience underscores the urgency of building diversified processing capacity for battery materials before the same concentration pattern becomes irreversible. The window for action is narrow, and the Lobito Corridor represents one of the most tangible opportunities to build a non-Chinese supply chain pathway for the minerals that power the energy transition.