A simple guide to solar fuels 1 – Turning sunlight into a fuel

Turning sunlight into a liquid fuel that is an abundant, sustainable, storable, and portable source of energy might sound like the fantasy machinations of a sci-fi novel. However, the reality is possibly even more exciting: energy in that sunlight can be sued to convert COand methane, potent greenhouse gasses, into high-value products for the production of fertilizers, plastics or even pharmaceuticals.

In this series of blog posts we will find out how this is possible, how scientists are on a quest to find the “perfect material” for the production of solar fuels, and how the research community is trying to produce hydrogen, using sunlight, sufficiently cheaply that it will pave the way for solar hydrogen to be included in the future energy mix.

In our first post we find out how solar fuels have the potential to produce clean green hydrogen.

By Dr Miriam Regue and Dr Minsu Park, Research Associates in the Department of Chemical Engineering.

“Climate change is one of the biggest threats that we are facing today” – is a phrase we have probably heard countless times at this stage. It may have lost some of their shock factor with repetition, or have made some of us too disheartened by their meaning that we choose to ignore it, but its message gets more urgent year by year.

As most of us already know, human-made CO2 emissions are one the main triggers of climate change, contributing directly to global warming. However, the evidence for just how rapid and irreversible this change is happening is stark. Over the last 20 years alone, the concentration of CO2 in the atmosphere has increased sharply, reaching a record value of 416 ppm of atmospheric CO2 (June 2020), a ⁓13 % increase since 2000 [1]. That is according to the Mauna Launa Observatory in Hawaii, the institution with the longest record of direct CO2 measurements in the atmosphere. Indeed these concentrations are almost double the amount of atmospheric CO2 that has ever been on Earth at any time over the past 400,000 years. Data shows that this continuous rise in CO2 is directly related to the combustion of fossil fuels such as oil, natural gas or coal that, unfortunately, our society still widely uses on a daily basis. Failing to reduce our reliance on fossil fuels to heat our homes, power our transport systems, and produce our goods, will cause unprecedented change, and damage, to both our way of life and the natural world alike.

Monthly mean carbon dioxide measured at Mauna Loa Observatory, Hawaii, from March 1958 to the present. Imager courtesy of the National Oceanic and Atmospheric Administration

The sharp increase in CO2 over the last 20 years clearly shows that scientists, engineers and policy makers must work together, and quickly, to ensure that the energy we produce and the products that we make are not as a result of releasing CO2 into the atmosphere. Indeed scientists and engineers are currently devoting considerable efforts to find efficient and scalable approaches for the production of alternative clean fuels. One revolutionary and promising alternative to conventional fossil fuels are what are known as Solar Fuels. As the name might suggest, these are fuels produced by capturing the abundant solar energy that reaches the Earth’s surface. But as our title asks, how can we turn sunlight into a fuel?

Energy production via solar fuels could recreate the starting chemicals, forming a closed cycle that minimises unwanted by-products. Image courtesy of the U.S. Department of Energy Office of Science

Certain materials can absorb the energy from sunlight and transform it into another form of energy, including electric current – the same principle used in a solar panel. The electric current generated can then be used to split water (H2O) into its components, hydrogen (H2) and oxygen (O2). Currently, the main industrial method for mass hydrogen production is done using a process known as steam methane reforming – which emits CO2. But hydrogen gas produced from solar energy is emission free and among the most promising solar fuels currently being investigated. One huge potential application of solar hydrogen is as an emission free fuel to power the hydrogen vehicles of the future! 

In fact, the European Union has recently released a green hydrogen strategy as part of the European Green Deal in which it aims to deploy green hydrogen at a large scale to ensure decarbonization of industries, transport, buildings and power by 2030. Therefore, it is now the perfect time to boost the potential of solar hydrogen to ensure it can be part of such a fascinating but challenging transition to a fossil-free economy.

In the next blog we will discover that in spite of the great promise and potential of solar fuels, they are still far from being commercialised.


  1. NASA, relentless rise carbon dioxide. https://climate.nasa.gov/climate_resources/24/graphic-the-relentless-rise-of-carbon-dioxide/

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