Multijunction Solar Panels

In 1983, solar was first recorded as supplying electricity for global usage and yielded less than 1 Terawatt Hour [1]. Exactly 40 years later in 2023, 4264 TWh was supplied, but met just 2.33% of total energy needs. While any is arguably better than none, many individuals and manufacturers have realized renewables at low respective production (to fossil fuel output) are not enough to stabilize the environment. To mitigate this, decades of efficiency studies, refinement, and integration have occurred with promising results.

Although general design has remained quite similar with components (from outermost to innermost) including glass, an encapsulant, solar cells, (more encapsulant), back-sheet, junction box, and mounting brackets, semiconductors have undergone significant development.

Currently, monocrystalline and polycrystalline panels are available for consumer purchase and average 22% conversion efficiency, but both have drawbacks [2]. As their names suggest, monocrystalline contains one piece of silicon per wafer while polycrystalline is comprised of many fragments melted together [3]. By using just one crystal, its composition is pure, yielding greater absorption and electron flow (output), but higher manufacturing costs. Concurrently, several crystals fused together are less conducive but can reduce waste materials (otherwise discarded silicon) and sit at a lower cost. Despite their contrasting qualities, both suffer from high back-sheet absorption due to wavelengths of light penetrating through the single-layer wafers.

While often confused with polycrystalline, multijunction (or tandem) cells are commonly comprised of many semiconductors vertically stacked between the outermost glass and furthermost panel [2]. Such conductors are made from gallium indium phosphide, indium gallium arsenide, and germanium which each absorb a unique wavelength range. When used together, their net absorption becomes substantially more effective (reducing the amount which reaches the back-sheet), and rivals some of the most developed resources (fossil fuels).

Although manufacturers have yet to reach a design consensus feasible for the consumer market, recent multijunction prototypes with 4 layers are nearing a calculated maximum of 45% conversion efficiency [2]. Additionally, a 70% energy return is projected at 5 to 6* vertical cells, but physical units aren’t yet possible to construct due to material science limitations.

As it stands, multijunction layering is an extremely new technology still early in its research and development. Despite this, it already shows significant signs of promise for future energy production and consumer availability at double the average efficiency as well as declining cost.

*Note that as sunlight only occurs in a set wavelength range, any number of layers beyond the quantity it takes to cover that will be redundant. (Therefore, vertical stacking is limited to a finite value). Once reached, improvements can continue to be made by refining individual wafer conductivity, efficiency, materials, and ease of manufacturing/installation.

 [1]  H. Ritchie, P. Rosado, and M. Roser. “Energy Production and Consumption.” https://ourworldindata.org/energy-production-consumption (accessed January 23, 2025).

[2]  J. Marsh. “Multi-junction solar cells: What you need to know.” https://www.energysage.com/solar/solar-photovoltaic-cells/multijunction-solar-cells/ (accessed January 23, 2025).

 [3]  J. Marsh. “Monocrystalline vs. Polycrystalline solar panels.” https://www.energysage.com/solar/monocrystalline-vs-polycrystalline-solar/ (accessed January 23, 2025).

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