A sunrise metal: Tellurium in solar panels

By Amen Seo

Earlier this year, we saw skies clearer than ever seen by our generation, as blankets of smog dissolved as an inadvertent side effect of efforts to contain Covid-19. On our respective screens, we marvelled at before and after photos of cities all over the world, pondering just how reversible the ills of human impact on the environment might be and yet seem to be economic impossibilities to fix in the absence of a brute force of lockdown.

In the meantime, another side effect: the unobstructed skies boosted the productivity of photovoltaic power stations, which turn sunlight into electricity.

In the UK, the simultaneous fall in electricity demand meant that coal and gas fired stations were taken offline for a record 67 days. On 20 April 2020, UK’s solar generation peaked at 9.7 GW, making up almost 30% of electricity supply (usually <4%). This is particularly notable, because the UK’s reputation for precipitous weather makes solar power an unlikely candidate to lead the way in the transition to renewable energy compared with wind power. With the global acceleration of solar power projects coming online in the next few years, and many countries set to triple their solar capacity in the next few years, solar energy has come of age.

Global solar power generation is ramping up at an unprecedented scale in the next decade

This meant that while many commodities markets took a deep plunge between February 2020 and August 2020, the price of Tellurium rose by around 30%, driven by increasing demand for thin-film Cadmium-Telluride photovoltaic (PV) cells. CdTe PV cells are the second most common photovoltaic technology in the world after crystalline silicon, representing 5% of the solar PV market, and are the most commercially successful thin film solar cells.

Currently, CdTe PV cells consume around 40% of the global production of Tellurium metal (400mt pa approx.), and some predict that the Tellurium market will grow by 15% in the next 4 years, driven primarily by growth in this sector.

CdTe PV – how it works

CdTe photovoltaics is a PV technology that uses CdTe in a thin semiconductor layer which absorbs and converts sunlight into electricity. The CdTe film acts as the photoconversion layer, which absorbs visible light. The CdTe, CdS and TCO (transparent conductive oxide) layers then form an electric field that converts this light into current and voltage.

CdTe thin film solar cells have achieved 22% efficiency in the lab, and around 18% in commercial panels.

Cadmium telluride photovoltaic cell structure. Image by Alfred Hicks/NREL

CdTe PV cells vs. silicon-based PV cells

CdTe thin-film solar cells are a lower cost alternative to conventional silicon-based PV cells, and have the smallest carbon footprint, lowest water use and shortest energy payback time (less than a year) of any current PV technology on a lifecycle basis.

Ongoing developments in technology are expected to continue to cut production costs of CdTe PV panels further. For example, a research team from Washington State University (Al-Hamdi et al., 2020) recently revealed that a scalable high-pressure manufacturing process can be used to synthesise CdTe crystals in a more cost-effective way, producing CdTe PV panels which are 45% cheaper than current industry standards.

Cost-competitiveness: Solar PV overtakes fossil fuels

In the wider solar PV sector, the average cost per watt of solar energy produced has tumbled dramatically, falling 82% in the last decade (IRENA), in line with Swanson’s law: the price of solar PV modules decreases by about 20% for every doubling in global solar capacity. This trend applies to many different technologies as they scale up, and the cost of solar is projected to continue downwards.

By 2021, globally, there will be up to 1200 GW of existing coal capacity that will cost more to operate than it would to install new solar PV capacity. Finally, solar’s replacement of fossil fuels will result in economic savings, a pivotal moment in renewable energy.

IRENA estimates that replacing the costliest 500 gigawatts of coal capacity with solar and wind would cut annual system costs by up to USD $23 billion per year and yield a stimulus worth USD $940 billion (1% of global GDP), and reduce annual carbon dioxide (CO2) emissions by around 1.8 gigatonnes (5% of last year’s global total).

While there are risks that the economic fallout from a global contraction in GDP may temporarily slow the overall momentum of the renewable energy sector, we think that the robust economic case for solar energy will entail huge growth opportunities over the long term, driving demand for minor metals like Tellurium.