Behind the Science: The Sun-Powered Civilization

Behind the Science: The Sun-Powered Civilization

Author: Anne Deveson, Nicola Armaroli

Dr. Anne Deveson, Deputy Editor of Chemistry – A European Journal, talks to Professor Nicola Armaroli from the National Research Council (CNR) in Bologna, Italy, about his recent review article on the current status and future perspectives of solar electricity and solar fuels. The paper was published in collaboration with Professor Vincenzo Balzani, University of Bologna, in Chemistry – A European Journal.

What is the most significant concept described in the article?

Over the past 70 years, part of mankind has enjoyed a unique period in history, shaping the so-called “modern civilization”. This occurred quite rapidly through the exploitation of finite energy resources – fossil fuels – which provided amounts of energy tens of times greater than those required to extract them. Technically speaking, fossil fuels are characterized by a very high energy return on investment (EROI).

This bonanza grew during a period of material abundance, which created the illusion that Earth is an unlimited deposit of natural resources, such as fuels, metals, freshwater, and biomass. Now the fossil-fuel age is close to its final stages and we are moving into a rather different territory: the sun-powered civilization.

This will be based on an unlimited primary source, solar photons, which, however, must be exploited by technologies characterized by relatively low EROIs. Natural resources needed to convert sunlight into usable energy forms such as heat, electricity, and fuels are limited. The competition to acquire these resources will be increasingly strong. Ultimately, we could finally reach the physical and energy limits of conventional economic growth.

Did this work pose any ethical questions?

Definitely. In the paper we analyze the per capita energy consumption of over 30 countries and demonstrate that being a prosperous industrialized country does not mean you have to reach the irrational energy habits of top energy consumers. Moreover, the energy transition to renewables will cause an unprecedented pressure on natural resources, particularly some metals. Therefore, decreased energy consumption in the wealthiest countries and international agreements on the fair exploitation of mineral resources will be essential steps to guarantee widespread access to energy and acceptable social stability at the global level.

The energy transition is bringing tremendous challenges not only at the scientific and technological level, but also at the ethical level.

What prompted you to look at this rather broad topic?

Often, scientists are primarily focused on their own research projects and ideas, without observing the big picture. We have thus decided to combine the discussion on solar electricity and solar fuels, which are usually treated separately, within the larger context of the ongoing energy transition, analyzing constraints and opportunities. In short, we are attempting to provide a taste of the big picture, fully aware that the solar energy picture is huge and cannot be comprehensively covered in a 26-page article.

What is the level of development of solar electricity and solar fuels?

Solar electricity is a market reality. It now successfully competes with electricity generated by burning fossil fuels. It is probably the biggest technological advancement of the early 21st century. Silicon-based photovoltaics and wind turbines, which are an indirect solar technology, are the workhorses for the first wave of renewable electricity deployment on the TW scale around the globe.

In contrast, solar fuels are substantially lagging behind, in part because their development started at least two decades later. Converting photons into electricity is much easier than using them to drive redox processes to enable storage of sunlight as chemical energy, as we explain in the article.

In terms of “energy return on investment”, how do solar electricity and solar fuels compare?

There is now general consensus that photovoltaics and wind energy have EROI values between 10 and 20. This is smaller than conventional fossil fuels, but still high enough to provide acceptable levels of net energy. On the other hand, for solar fuels, a lot of research and development is still needed to make them a truly sustainable and affordable option. We must certainly foster the use of electricity as much as possible – especially in transportation – but fuels are such a convenient form of energy that we will always need them. They can be stored for an unlimited period of time and have high energy densities. That is why both solar electricity and solar fuels must be developed.

What do you consider the most exciting developments in the field?

We discuss the current status of new photovoltaic materials and concepts, such as dye-sensitized solar cells, perovskite solar cells, and luminescent solar concentrators. Presently, these approaches cannot compete with silicon photovoltaics, but, in the long term, they can provide alternatives, particularly for specific contexts such as building integration. We need sensitizers based on abundant metals, less toxic perovskites, more robust near-infrared luminescent materials. The fact that silicon is now the winner does not mean that it will forever be the only choice.

On the other hand, in the area of solar fuels, one of the biggest challenges is to promote a stronger multidisciplinary effort to the final goals, namely H2 production and CO2 reduction, involving chemists, biologists, physicists, and engineers.

What topics are you working on at the moment?

We are studying the fundamental processes that enable the conversion of solar energy into chemicals: light harvesting, energy transfer, and electron transfer. We are investigating inorganic, organic, and hybrid luminescent materials for efficient lighting devices and luminescent solar concentrators. We are also starting to work on CO2 reduction.

We have plenty of ideas and enthusiasm, which unfortunately does not find a parallel within the Italian government and its institutions to support potentially groundbreaking fundamental research. However, thanks especially to our many established international collaborations, I am confident that we will keep up steam and make progress.


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