What are the Applications of Solar Fuels?

By Owais AliReviewed by Lexie CornerAug 20 2024

Solar fuels are synthetic fuels produced from water and carbon dioxide using solar energy, offering a sustainable alternative to fossil fuels. This article highlights their diverse applications in modern energy systems and their potential to transform our approach to clean, renewable energy.

Image Credit: IM Imagery/Shutterstock.com

Introduction to Solar Fuels

While solar energy research has primarily focused on electricity generation, which accounts for only about one-third of global primary energy consumption, it can also be converted into liquid fuels, which dominate global energy use.

Solar fuels offer a sustainable, storable, and portable energy source that could diversify fuel supplies and improve the sustainability of our energy. Their ability to be stored long-term and transported easily could significantly improve the reliability and flexibility of the electric grid.¹

How Solar Fuels Are Produced?

Solar fuels can be produced through several methods, each with distinct processes and benefits:

1. Photo-electrochemistry: This method splits water into hydrogen and oxygen using three main techniques: photocatalytic (PC), which directly uses light to drive the reaction; photoelectrochemical (PEC), which integrates light absorption and electrochemical processes; and photovoltaic-electrolysis (PV-EC), where sunlight is first converted into electricity to power the electrolysis process.
2. Thermochemistry: It is a straightforward method with two main approaches: the Two-Step and Multistep methods. The Two-Step method involves heating a catalyst to release oxygen and cooling it to react with CO₂ or H₂O to produce CO or H₂. In contrast, the Multistep method requires lower temperatures but involves more complex procedures and yields corrosive intermediates.
3. Photo-thermal co-catalysis: This technique utilizes three mechanisms—electron-hole excitation, photon-to-phonon conversion, and plasmon activation—to drive solar fuel production. This approach combines the benefits of both photochemical and thermal processes to enhance fuel production efficiency. It often involves using plasmonic materials or heavily doped semiconductors to capture a broader solar energy spectrum.²

Key Applications in Different Sectors

Transportation: Driving Towards a Cleaner Future

The transportation sector benefits significantly from adopting solar fuels, particularly in reducing vehicle carbon emissions. For instance, hydrogen fuel cell vehicles provide long driving ranges of around 400 miles per fill-up and faster refueling than electric and some gasoline vehicles.³

The University of British Columbia's Smart Hydrogen Energy District (SHED) is a prime example of solar fuel integration in transportation infrastructure. This $23 million initiative leverages solar power to produce hydrogen for fueling stations and charge electric vehicles, showcasing hydrogen's potential to reduce transportation emissions and support heavy-duty vehicles.⁴

Power Generation: Overcoming Intermittency Challenges

Another key application of solar fuels is in addressing the intermittency of wind and solar power on the electric grid.

In this approach, known as "power to gas," excess electricity from solar and wind produces hydrogen via electrolysis, which splits water into hydrogen and oxygen. The hydrogen is then stored and injected into natural gas pipelines. When renewable energy is unavailable, the stored hydrogen can be converted back into electricity using conventional natural gas power plants.

Currently being explored in Germany, this method offers a pathway to leverage existing gas infrastructure for a cleaner energy transition, potentially minimizing the need for expensive new transmission lines.³

Industrial Processes: Cleaner Manufacturing and Chemical Production

Solar fuels play a significant role in industrial applications by replacing fossil fuels in high-temperature processes like steelmaking and serving as a crucial feedstock for producing ammonia and other chemicals. This supports the decarbonization of these sectors.

Several companies are pioneering the use of solar energy to produce green ammonia, offering a cleaner alternative to traditional methods that rely on fossil fuels. The Kenya Nut Company is set to become the first farm to produce fossil fuel-free fertilizer using solar power to extract hydrogen from water, creating sustainable "green ammonia."⁵

In the U.S., Starfire Energy is developing an ammonia plant that adapts to fluctuating renewable energy sources, using electrolyzers to extract hydrogen from water. Similarly, Iceland's Atmonia is focusing on compact, portable plants to produce green ammonia, supporting both fertilizer production and as a sustainable fuel alternative.⁶

Residential Use: Powering and Heating Homes

Natural gas, mainly methane, is widely used for heating and cooking in homes and is the second most significant anthropogenic greenhouse gas (GHG) after CO₂, contributing about 16 % of global emissions.

One approach being explored is blending solar-generated hydrogen into existing natural gas networks. The UK, for example, aims to start transitioning to hydrogen heating within the next decade, with trials exploring blends of up to 20 % hydrogen by 2026. This strategy could significantly reduce emissions from residential energy use while utilizing existing infrastructure.⁷

Benefits of Using Solar Fuels over Fossil Fuels

Solar fuels offer several advantages over traditional fossil fuels. They are compatible with existing infrastructure, including engines and refineries, and are expected to be cost-competitive by 2033, targeting production costs of EUR/CHF/USD 1 per liter.

Solar fuel technology can produce a range of fuels, such as jet fuel, gasoline, and diesel, and is scalable to meet global demand due to solar energy's abundance.

Environmentally, they emit less CO₂ and harmful gases than conventional fuels and have a high energy density that facilitates storage and transport. Solar fuels can also be produced globally, reducing dependency on fossil resources and supporting a circular carbon economy by releasing only as much CO₂ as was used in their production.^3,8

Recent Research and Developments

World's First Industrial Solar Fuel Plant

In June 2024, Synhelion inaugurated DAWN in Jülich, the world's first industrial-scale plant for producing synthetic fuels using solar energy, marking a major step in scaling up solar fuel technology for transportation, particularly in the aviation industry.

It features a 20-meter-high solar tower equipped with a solar receiver, thermochemical reactor, and thermal energy storage and is set to produce several thousand liters of synthetic crude oil annually starting in 2024. This oil will be refined into solar kerosene, gasoline, and diesel, which are fully compatible with existing fuel infrastructure.

The large-scale use of sustainable aviation fuels is one of the most important measures to achieve the CO₂ targets in aviation. The inauguration of DAWN marks a milestone in this process. As strategic partners of Synhelion, Lufthansa Group and SWISS, as investor are proud to support the market introduction of solar fuels and congratulate Synhelion on this extraordinary achievement.

Heike Birlenbach, CEO of Swiss International Air Lines⁹

Solar-Powered 'Artificial Leaves' Convert GHG into Clean Fuels 

The University of Cambridge researchers developed a solar-powered technology, 'artificial leaves,' that converts carbon dioxide and water into liquid fuels, such as ethanol and propanol, which can be directly used in car engines. Inspired by photosynthesis, this technology uses a copper and palladium-based catalyst to produce high-energy-density emission-free fuels in a single step.

Although the technology is still at the laboratory scale, it represents a significant step forward in creating sustainable, carbon-neutral fuels.¹⁰

Normally, when you try to convert CO₂ into another chemical product using an artificial leaf device, you almost always get carbon monoxide or syngas, but here, we've been able to produce a practical liquid fuel just using the power of the Sun. It's an exciting advance that opens up whole new avenues in our work.

Dr. Motiar Rahaman, first author of the study

Conclusion

Solar fuels have diverse applications across transportation, power generation, industrial processes, and residential use. They offer a promising path toward sustainable energy systems that can significantly reduce our dependence on fossil fuels.

However, continued research and development are crucial to overcoming remaining challenges, such as cost competitiveness and the need for innovative materials and system designs, to unlock the full potential of solar fuels for a cleaner energy future.¹¹

More from AZoOptics: Spectroscopy: A Key Tool for Climate Change

References And Further Reading

1. U.S. Department of Energy. (2024). DOE Explains...Solar Fuels. [Online] U.S. Department of Energy. Available at: https://www.energy.gov/science/doe-explainssolar-fuels
2. Fu, Y., Wang, Y., Huang, J., Lu, K., Liu, M. (2024). Solar fuel production through concentrating light irradiation. Green Energy & Environment. doi.org/10.1016/j.gee.2024.01.001
3. Cho, R. (2016). Turning Sunlight into Fuel. [Online] The Columbia Climate School. Available at: https://news.climate.columbia.edu/2016/08/24/turning-sunlight-into-fuel/
4. Crawford, T. (2024). Renewable energy hub: Hydro, solar, hydrogen in one place. [Online] Times Colonist. Available at: https://www.timescolonist.com/business/ubc-23m-energy-hub-combines-hydro-solar-hydrogen-9090761
5. Edmond, C. (2023). From fuel to fertilizer, how green ammonia could help curb emissions. [Online] World Economic Forum. Available at: https://www.weforum.org/agenda/2023/11/green-ammonia-climate-change-energy-transition/
6. Baraniuk, C. (2024). Why firms are racing to produce green ammonia. [Online] BBC News. Available at: https://www.bbc.com/news/business-68230697
7. National Grid. (2024). Heating our homes with hydrogen. [Online] National Grid. Available at: https://www.nationalgrid.com/stories/energy-explained/heating-our-homes-hydrogen
8. Synhelion. (2024). The clean alternative to fossil fuels. [Online] Synhelion. Available at: https://synhelion.com/solar-fuels-and-plants/solar-fuels
9. Synhelion. (2024). Synhelion inaugurates DAWN – the world's first industrial plant for the production of solar fuels. [Online]. Synhelion. Available at: https://synhelion.com/news/synhelion-inaugurates-dawn
10. Rahaman, M., et al. (2023). Solar-driven liquid multi-carbon fuel production using a standalone perovskite–BiVO₄ artificial leaf. Nat Energy. doi.org/10.1038/s41560-023-01262-3
11. Caltech. (2024). Solar Fuels. [Online] Caltech. Available at: http://nsl.caltech.edu/home/solar-fuels/

Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.