Solar Technologies for Net-Zero and Low-Carbon Energy Systems: A Comparative Overview

1. Introduction

Solar energy offers a sustainable path toward net-zero emissions, with the Earth receiving over 120 petawatts of solar energy daily—enough to meet global energy demands for over two decades from just one day’s solar input. As governments, industries, and communities transition toward low-carbon energy systems, solar-based technologies have emerged as essential solutions due to their scalability, modularity, and compatibility with other renewable and conventional power systems. This paper presents a comparative overview of key solar energy technologies, categorizing them into two main classes: Photovoltaic (PV) systems and solar thermal power (Concentrated Solar Power – CSP) systems. Each technology is evaluated based on its efficiency, environmental footprint, system design, and cost implications in the context of supporting net-zero and low-carbon goals. To help interpret the stage of development and commercial viability of each solar technology, we apply the Technology Readiness Level (TRL) scale. TRL is a standard metric that indicates the maturity of a technology on a scale from 1 (basic research) to 9 (fully commercialized and deployed systems). Some recent studies extend this to TRL 10 to indicate widespread adoption and refinement. A higher TRL reflects a greater degree of real-world deployment and reliability. Throughout the paper, TRL values are noted in parentheses for each technology to guide readers in understanding its current status in the innovation-to-market pipeline.

2. Photovoltaic (PV) Technologies

2.1 Crystalline Silicon (C-Si) – TRL 10

C-Si is the most mature and widely used PV technology, representing over 95% of the market. It is based on p–n junction semiconductors and achieves efficiencies up to 22–27%. C-Si is highly reliable and suitable for both grid-connected and standalone systems. Although it involves energy-intensive manufacturing and generates hazardous waste, recycling practices and cost reductions have improved its sustainability and affordability.

2.2 Multijunction – TRL 9

These PV cells use multiple semiconductor layers with different bandgaps, achieving record efficiencies of up to 47%. They are primarily used in space applications and concentrated solar systems due to their high power-to-weight ratio and high cost. Despite excellent performance, their complex manufacturing process limits mainstream adoption.

2.3 Floating Solar PV – TRL 8

Floating PV systems are installed on water bodies, offering higher efficiency due to cooling effects and saving land space. However, they incur 30% higher costs than land-based systems and pose challenges like water-based corrosion and anchoring impacts on aquatic ecosystems. Despite these, their dual use of space and water conservation benefits make them promising.

2.4 Cadmium Telluride (CdTe) – TRL 6

CdTe thin-film cells are low-cost and efficient (lab: 22.1%, commercial: 18%), used mainly in utility-scale installations. The presence of cadmium, a toxic metal, poses environmental challenges, requiring stringent recycling and disposal protocols. CdTe cells offer advantages in large-scale, low-GHG operations.

2.5 Copper Indium Gallium Diselenide (CIGS) – TRL 6

CIGS thin-film cells offer efficiencies up to 22% and better performance under low light and shading. They use non-toxic materials, making them more sustainable than CdTe. Flexible, lightweight, and suitable for building integration, their main drawbacks are complex manufacturing and high initial costs.

2.6 Organic PV – TRL 6

Organic solar cells use carbon-based compounds and are cost-effective, lightweight, and highly flexible. Despite sustainability advantages and printable manufacturing, they have lower efficiencies (11–17%) and shorter lifespans, making them ideal for small-scale or niche applications.

2.7 Perovskite – TRL 4

Still in the R&D phase, perovskite PVs show promise with efficiencies up to 25% and low production costs. However, issues with stability, degradation, and potential lead toxicity hinder commercialization. Tandem perovskite–silicon cells show record efficiencies nearing 30%, offering potential for next-generation PV systems.

3. Solar Thermal Technologies

3.1 Solar Thermal Tower – TRL 9

These systems use heliostats to focus sunlight onto a central tower to heat molten salts or fluids, driving turbines for power generation. With efficiencies of 30–40% and integrated thermal storage, they offer dispatchable power. However, high capital costs, land, and water use limit scalability.

3.2 Parabolic Trough – TRL 9

A mature CSP technology, parabolic troughs use curved mirrors to heat a fluid in a receiver pipe. They are effective in CHP applications and reach 11–16% efficiency. Although widespread in the United States, their deployment is challenged by high costs and moderate output.

3.3 Parabolic Dish – TRL 9

This system focuses sunlight onto a single receiver using dish mirrors and can achieve high temperatures (up to 750°C). Though highly efficient and suitable for off-grid or remote use, commercial adoption remains limited due to high capital costs and complexity.

3.4 Linear Fresnel Reflector (LFR) – TRL 8

LFR systems use flat mirrors to reflect sunlight onto an elevated receiver. These are modular, cost-effective alternatives to troughs, with solar-to-power efficiencies of about 13%. Despite being land-intensive and less efficient, they offer promise in industrial heat and desalination.

4. Discussion

The choice of solar technology depends on location, scale, application, and budget. Crystalline silicon remains dominant due to its reliability and cost reductions. Advanced technologies like multijunction, perovskite, and floating PVs show promise for specialized applications and future scalability. Solar thermal systems offer dispatchable power but are capital intensive. Integration with storage systems and hybrid configurations (e.g., solar-hydrogen, PVT systems) enhances energy reliability and supports net-zero goals.

5. Conclusion

Solar energy technologies are central to achieving net-zero emissions. While PV systems lead in terms of global adoption, CSP systems complement them by offering dispatchable power. Advancements in materials, system integration, and cost reductions are critical to scaling these technologies. A diversified solar portfolio combining mature and emerging technologies will be essential to meet global climate targets and energy demands.

6. References

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