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In this eighth contribution to the INSURGE symposium, ‘Pathways to the Post-Carbon Economy’, Ugo Bardi, Professor of Physical Chemistry at the University of Florence, Italy, reflects on the importance of transitioning away from fossil fuels and how it, inevitably, means we should engage with some form of renewable energy.

But, he points out, while such a transition requires us to recall the fundamental role of the Sun as the primary energy source for all our activities, it also means we will have to re-think and re-do civilization-as-we-know-it. Whatever happens, much of what we have taken for granted in our consumer-centric societies today will be increasingly meaningless in the post-carbon future.

What we do know, concludes Bardi, is that we will always have the Sun: the question remains — what will we, and can we, do with it?


As it becomes clear that we must get rid of fossil fuels before they get rid of us, a question is being asked over and over:

“Can renewables replace fossil fuels?”

Some people have been sufficiently impressed by the rapid decline of the price of renewable energy that their answer is not only, “yes,” but that switching to renewables will be fast and painless. It will come simply as the result of the free market mechanisms, at most aided by a little magic called “carbon tax”. Then, economic growth will continue unabashed in the best of worlds.

Others take the opposite position. Noting that renewables require large investments in the energy infrastructure, that they don’t easily produce liquid fuels, that they can’t support energy “on demand,” and more, they conclude that renewables are useless; an illusion, if not an outright scam.

This viewpoint is further split in two views. One seems to welcome the collapse of an energy-starved economic system and the associated return to the Middle Ages, or even to extinction. The other simply sees fossil fuels as a good thing to be kept and subsidised. After all, CO2 is food for plants, isn’t it?

The debate is raging and, as usual in debates, rational arguments seem to have little weight in them, and we could go on forever debating arcane technological details.

But I would rather point out that maybe all this discussion is based on a wrong question.

Axiom 1: Asking if renewable energy can replace fossil energy implies that the only possible civilization is our civilization as it is nowadays, including SUVs parked on every driveway and vacation trips to Hawaii by plane for everyone.

But keeping these incredibly expensive wastes of energy will obviously be impossible in the future, even imagining that we were able to stay with fossil fuels for another century or even more.

We are hitting so many physical limits on this planet that the question is a completely different one. I could frame it as this:

“How can renewable energy help us in getting rid of fossil fuels, while maintaining at least a minimum indispensable supply of energy to society?”

Seen in these terms, are renewables a help or a hindrance? I would say that they are not only a help, but a big help and a great hope. To explain this point, I think we need another little reframing.

Rather than speaking of “renewables”, I would use the term “solar energy.”

This term includes technologies which directly exploit sunlight, such as photovoltaics, and those which do that indirectly, such as wind turbines (this definition doesn’t include geothermal, but it is a detail).

Once we frame the question in this way, we see the following:

Axiom 2: Solar energy has been used by humans for a long, long time. Agriculture is the most ancient technology directly using sunlight, while windmills and watermills are indirect methods of exploiting sunlight, used for millennia in the past. What we have been doing recently consists of developing more efficient ways to do exactly what we have been doing in our remote past.

Photovoltaic energy is a sophisticated way to duplicate in a solid-state device what biological photosynthesis does in the leaves of plants. The modern wind turbines are upgraded versions of the old windmills. The same is true for hydroelectric plants, today more efficient than in the past, but still basically the same.

The real oddball in the panorama is fossil energy; something that has been around in a massive form for just a couple of centuries and that will disappear in a century or less, no matter what dreams of energy dominance may be popular in Washington D.C.

This said, we could examine the arguments against solar energy that pervade the debate. For instance, that modern solar energy technologies are not really renewable because they cannot produce enough energy to replace themselves after their lifetime is over. Or that their energy yield is so low as to make them useless. Or that they need rare minerals that will soon run out. Or that an industrial civilization can’t survive without having energy “on demand”, that is available 100% of the time, always at the same price. And many others.

Here, in part we are dealing with people who can’t conceive a world different than the one they are used to. In part, we are dealing with objective difficulties which, however, may have some technological solutions.

As an example, consider the common objection of the low energy yield of solar energy. It is often expressed in terms of “EROI”( (energy return on investment) a concept made popular by professor Charles Hall.

It is said that the EROI of solar energy is very low in comparison to that of fossil fuels and that for this reason solar energy is useless. But this is just wrong.

Let me ask you a question: what was the EROI of fossil fuels at the time of the Apollo program that sent men to the moon? Was it an order of magnitude larger than that of solar energy, as it is sometimes said? No, it was around 20–30, about the same EROI that we have today for wind turbines and not much larger than that of photovoltaics.

Surely, then, these values are not so small as to make solar energy useless.

As another example, it is easy to find on the web that solar cells need expensive and rare elements. Once again, this is not the whole truth, as solar cells can be made using only materials that are common in the earth’s crust, mainly silicon, aluminum and oxygen.

We could spend a lot of time in this discussion, but the point that I would like to make here is this:

Insight: All these objections have been unable to disprove that solar energy today is a set of robust and economically viable technologies.

The most advanced ones (solar and wind) account for a significant, although still small, fraction of the world’s energy mix, about 6% of the global electric power production and around 1.6% of the total energy consumption.

Can they grow to 100% without the world’s economy collapsing and without climate going over the “tipping point”? They could, according to a study carried out by Sgouridis, Csala, and myself.

We used the term “Sower’s Strategy” for a concept analogous to what ancient farmers did, saving some of their current harvest for the future harvest.

Insight 2: We found that it is possible to move to a fully solar-powered society without collapsing and without wrecking the climate system, if we are willing to use the same strategy: that is, investing in solar energy a sufficiently large fraction of the energy produced today.

Will we follow the wisdom of our ancestors and save enough of our current energy harvest for our future?

Or will we waste our remaining resources in the desperate attempt to keep using fossil fuels, even putting our trust in untested and potentially counterproductive technologies such as carbon capture and sequestration? To say nothing about the risks and the uncertainties involved with a possible return to nuclear energy.

As usual, it is impossible to say what the future has in store for us, but there remains a certainty: we’ll always have the sun.