Cassandra has moved. Ugo Bardi publishes now on a new site called "The Seneca Effect."

Sunday, September 24, 2017

We’ll always have the Sun: solar energy and the future of humankind

Above, Rick (Humphrey Bogart) speaks to Ilsa (Ingrid Bergman) in the movie “Casablanca” (1942). Here, the sentence has been a little changed. In the film, the phrase refers to “Paris”, not “The Sun”. But in the debate on the future of civilization, there is only one certainty: we’ll always have the sun.

This post was originally published on Aug 15, 2017 by INSURGE INTELLIGENCE, a crowdfunded investigative journalism project for people and planet. Support us to keep digging where others fear to tread.

In this eight 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 devicewhat 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.

Ugo Bardi is Professor of Physical Chemistry at the University of Florence, Italy. His research interests encompass resource depletion, system dynamics modeling, climate science and renewable energy. He is a member of the scientific committee of ASPO (Association for the Study of Peak Oil) and blogs in English on these topics at “Cassandra’s Legacy”. He is the author of the Club of Rome report, Extracted: How the Quest for Global Mining Wealth is Plundering the Planet (Chelsea Green, 2014) and The Limits to Growth Revisited (Springer, 2011) and "The Seneca Effect" (Springer 2017).


  1. If solving our energy predicament simply allows us to then continue our growth at all costs, then it is merely facilitating the ongoing destruction of the environment by our hand.

  2. And no matter what one writes, there will always be someone who misunderstands it completely

  3. Regarding insight 2.

    Will it be possible to feed 7 or 8 billion without the use of fossil fuels? Seems to me rather impossible. Most countries need to import huge amounts of food for example.

    1. Does this not imply a collapse? Or will population gradually decrease. Hard to imagine!

  4. This has said nothing about the real world. Do we want aluminum or glass or copper or many other materials. How will we meet the requirements for those and many other important components.

    There are multiple questions that a realistic assessment of the future of these devices requires. Each of these questions, asks about the future of “renewable” devices.

    As stated above with charts and videos available, at present solar and wind energy collecting devices including their auxiliary components and the majority of tools and toys in our techonogical environment are extension of the fossil fuel supply system and the global industrial infrastructure.

    First and foremost:
    What do we need the energy for?
    Not, why or what do we want this electricity for.
    This must be one of the mantras for survival now and tomorrow.

    When it comes time to replace these devices:
    Where will the energy and resources come from?

    To replace components of these systems:
    Where will the energy and resources come from?

    As we need to manufacture the tools and toys we want the electricity for:
    Where will the energy and resources come from?

    Will we sequester/store the energy to provide for these future needs?
    How will we do that?
    Will dedicated devices be built simply to facilitate replacement?

    Who will manage these dedicated devices?

    What will stop society from using this sequestered energy?

    Will the need to protect this sequestered energy create an even more constrained and draconian social environment?

    How will this electricity be equally shared globally compared to the present unequal energy availability?

    How will we mine and transport all these raw resources:
    the basic material for fabrication, the actual devices, the various auxiliary equipment, the tools and the toys?

  5. Many materials used in our industrial world require energy from mining to manufacturing for processing and transportation. The energy for some of these products is in the form of high temperatures – 2000° F (nearly 1100°C).
    These processes run 24/7 365 days.

    There are proposals that solar and wind energy collecting devices can provide the energy to maintain the industrial world. To look at this possibility, solar electric panels, wind turbines and concentrated solar installations in the form of parabolic trough collectors (PTC) have been assessed.

    The energy requirements in 2010 for the following essential components of our industrial world are provided: steel, aluminum, chromium, copper, manganese, cement and glass. This energy would be mining, processing and transporting to name some. Other important components of the industrialized world such as nickel and cobalt are not considered because they are part of the high temperature processing of other ore metals.

    The kWh output and area required for installations of solar electric panels, wind turbines and PTC has been researched. This then is divided into the energy (exajoules converted to kWh) required for global production of each material in 2010.
    121,214.45 Square Miles of Solar Electric Collectors
    257,472 square miles and 2,807,276 Wind Turbines
    77183.4 square miles of PTCs
    There are many other critical components of our global industrialized world that require industrial heat (lead, silver, tin, food processing) that are right at the top heating limit of solar devices. They must also be included in an all “renewable” future. If only half of important materials were provided, what would our world be like?


    See maps, images and calculations at:

    1. What is the problem? If you have high EROEI, you can have enough energy for whatever industrial needs you can list. And with electric power you can have industrial temperatures as high as you want.

  6. No item of this list is a problem if the technology has an EROEI much larger than 1. And this is the case for PV and wind.

  7. I admire both of you gentlemen immensely but I have to comment you need to read John Weber's blog in detail rather than flip him off with the EROEI response. John Weber for decades was totally into renewable energy until he did his homework. Meanwhile I am waiting for one of "the treasures" of the U.S. to build his solar furnace for replacing fossil fuel furnaces to carry the renewable movement for future (so far no word in three years).

  8. I read John Weber's blog and I am not flipping him off. Really, what you need to know about an energy is the EROEI. Then, the rest are details.

    1. You also need to know when the Energy Invested happens and how great an investment is required. If, as in the case of renewables, the energy invested is all up front and due to climate change risk a large additional energy investment cannot come from fossil fuels, then even if the EROEI is good, one cannot afford to make the investment.

      Considering the "details" of the massive infrastructure changes that would be required to run our industrial civilization on renewable electricity (transportation, space heat, industrial process heat, grid expansion etc.), don't you think that it is too risky to power those changes with additional fossil fuels? Or perhaps you think we can free up enough carbon through affluence reduction to replace all of our fossil energy production and consumption infrastructure?

  9. "Will it be possible to feed 7 or 8 billion without the use of fossil fuels?"

    Of course.

    The key word is "possible". Will homo sapiens transition to a world where 8 billion are fed without the use of fossil fuels without first experiencing a collapse of industrial civilization and population levels? Highly unlikely.

    Imagining a scenario that feeds 8 billion people utilizing the remaining resources of the planet and current technologies is easy. However the societal barriers to arriving there are nearly insurmountable and the roadmap is invisible. And it remains to be seen how much of what we call human would still exist in the brave new technosphere.

    Here is one scenario.

    1- China is the only country actively working to develop the next generation of nuclear reactors. Even Bill Gates has moved his pet reactor project there. ( Of the four leading designs at least one (the liquid fluoride thorium reactor: has an operating prototype track record and the potential to provide the base energy requirements for an advanced technological society at a cost less than that of current fossil fuels.

    2- Given a reliable base load nuclear power like LFTR or one of the other candidates and smart grid switching, renewables with current technological sophistication could provide at least 50% of the total energy requirements for a population of 8 billion. The EROI of a LFTR/renewable energy system should be substantially superior to that of our current fossil fuel system as it enters its dotage. The synergy between an extremely high energy density power source and a dispersed system designed to collect low density solar energy would improve the system stability.

    3- Agriculture as it is currently practiced in the US is an industrialized system that uses fossil fuel energy in fertilization, cultivation, harvest, and transportation to capture solar energy and multiply it into profits.

    Given cheap electrical power and adequate capital, biodynamic aquaponics systems are far more efficient at producing both plant matter and protein than the most advanced land farms. A common suburban lot has enough surface area to produce all the biomass and fish protein required for a family of three while using only 1/10 the water. (the family would have to forgo their crab grass though) If the majority of food were produced with this technology the natural world could conceivably be allowed to begin rebuilding itself.

  10. This article refers to Australia,but the points made are relevant more generally. If the link doesn't work,go to

  11. One additional energy use that will come up: reconcentrate the raw materials we dug out and let diffuse into the environment. We create a lot of entropy there, and to reverse this process, we need a lot of exergy.
    One day, governments will invent an entropy-increase-tax, that will reflect this fact. For the time beeing, nobody is wasting a thought about it.

  12. State of affairs: A friend of mine has daughters, who have to do some internship, and one did it in Cameroun in a charity institution, the other in Windhoek in a Waldorf school. I asked him, if he considered to pay the (small) climate offset for the large emissions caused by the flights. He looked at me as if I had asked him to stick his legs into boiling oil.

  13. Sorry, EROI is not all you need to know about energy. The most important thing to know about energy is what useful work it facilitates. X joules of energy in the form of a highly focused laser scalpel that was able to surgically remove individual cancer cells without harming their neighbors is not the same as x joules of energy in the form of bunker fuel suitable only for powering the engines of a container ship. Do you think for a minute that a negative EROI for the pure form of energy used by the hypothetical laser scalpel would prevent its use?

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

    Sorry, but that is a question for engineers and scientists. The answer is probably "yes", but that is irrelevant.

    The real question is rather: "Can we change society so that all stakeholders accept the lower lifestyles involved in getting rid of fossil fuels - without first having a collapse?"

    I believe the answer is "No". Those on top will always want newer and better gadgets. And being on top, they will find a way to get what they want, at the expense of everybody else. That is the point of being at the top of a hierarchy: you get your way.

    The system will deteriorate until it collapses. And then, of course, "we'll always have the sun".

    The switch to other energy sources is not a technical one, it is a sociological and political one.

    Just read a random newspaper and you'll realize that the challenge is hopeless.

    1. I agree. While technically feasible, the sacrifices required at every level of society from the political classes on down will be too much. Not only would it require a severe reduction in per capita energy use, but also a complete re-working of every fossil fuel dependent system on the planet. I appreciate the optimism in Dr. Bardi's article but it seems to fly in the face of the Seneca Cliff argument. I believe we continue on our trajectory of denial for many and complacency for most until it all unravels. The financial system will break first, and then access to affordable energy, and finally society. On the bright side, the collapse will not be evenly distributed across the planet and there will be areas that will come up with surprisingly effective adjustments and adaptations. If you're a member of the !Kung living in the Kalahari desert you might not even notice.

  15. One of the key benefits of fossil fuel (and nuclear) is not the energy density, but the implicit energy storage capacity. A lump of coal or barrel of oil can store energy more or less indefinitely and is represents a relatively simple energy vector. Ugo is right that the sun is the primary source - fossil fuels are just a very long term storage of solar energy, albeit a one-time-use method. As Ugo points out (in the comments too), the challenge for high renewable penetration is not the amount of energy or the distributed nature or cost or upfront investment (although these are not trivial). The principle barriers to phasing out fossil fuels are storage and dispatchability. And before someone starts talking about great new horizons in battery tech, be aware that there is nothing even on the horizon that will come close to the very large scale storage necessary.
    The bottom line is that, for me, the most important insight from Ugo's article is that we must imagine an alternative to the assumption that "an industrial civilization can’t survive without having energy “on demand”, that is available 100% of the time, always at the same price. "


    1. What tends to gets left out of discussion is that benefits of industrial civilisation are very badly distributed - inevitably so, given the history. It might even be the case that a world majority of persons suffer serious downsides with dubious net benefits. Perhaps we need to elaborate the details more carefully?

      The current business model has extravagantly burned roughly the first half of economically available fossil fuel. At this rate of profligate consumption Ugo's Seneca Cliff seems a real risk. It is sad also that such a temporary bonanza has additionally created enormous long term climate risks and is trashing a lot of ecologically important biodiversity. Could we more affluent cogs in the industrial machinery take some responsibility and do better in the second half?


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


    This is indeed the crux of the predicament however nearly everyone including you Ugo are WAY too optimistic in presenting your version of the answer and this is where it all fails. Were you to be honest/realistic in your proposed solutions the vast majority of humanity would find that future unbearable to even contemplate. The future is all about less and everyone wants more.

  17. Jef said ". The future is all about less and everyone wants more. "

    absolutely true.

    But what can I do, here and now?

    Not very much, but I think I should try to do everything I can. On a very, very local level, with the very small things I have.

    Be very practical, flexible, like a fox.

    Foxes have hard lives and no future guaranteed. But they never make a wrong move.

  18. in the era that preceded agriculture, humankind behaved as all other biological species: We took our sustenance from the surrounding environment as we needed it.

    If it was plentiful, we thrived, if it was in short supply, we ate each other, starved, and quite often died.. We enjoyed the advantages of fire and primitive weapons, but in all other respects, we were just another higher primate.

    Then a clever nomad had the idea of enclosing land and growing food, instead of chasing it. We started the myth that the Earth was private property, and our life pattern changed forever.
    because when you enclose land, you must pay people to look after it, defend it, pray over it, and acquire more of it to satisfy your growing tribe.

    in other words you create employment separate from energy (food) production.

    and when you create employment, it becomes an ever expanding monster that demands constant feeding.
    but you cannot have employment without energy consumption, so your energy availability must increase at an infinite rate, in lockstep withe population that increases and demands to be employed.

    it requires only a short leap of imagination to see where we are right now, 7.5 bn people mostly supported by energy-consuming employment. To simplify that, the sustain themselves by consuming and processing and marketing “STUFF”.

    Think about that for a moment.

    Without indespensable components of oil coal and gas, Your home, your job, your transport, your food, your healthcare (I could go on) would cease to be. They are the means by which they become a tangible, commercial concept. Our ‘employed’ existence in a viable commercial infrastructure depends on making and selling those millions of diverse objects, and we must consume fuel to do it. There is no other way.The slightest downturn in employment brings catastrophic civil disorder.

    Yet we read that we can sustain our current lifestyle using electricity alone (100% renewables).
    Can someone explain how we will all be employed, given the above reality that I have set out? Because if we are not employed, history is very clear on what happens next

    This explains the problem in more detail:

    We've screwed ourselves with fossil fuels, but to expect solar panels to deliver a cornucopian future is a stretch the expertise of the wish-fairy beyond any known limit.

    I could be wrong of course

  19. In his blog, Kris de Decker has an interesting essay on the "how" of such an economy:

    His essay is obviously short on numbers and specifics, but then, precision should not be allowed to be the enemy of accuracy… or relevance.

    1. Ugo Bardi plus Kris de Decker, why not?

    2. That has opened a door I did not know was there.
      K de D works with

      Terrific paintings in the K de K article btw.
      For background history and geography see Bunker & Ciccantell 'Globalization and the Race for Resources'. Additionally, the articles in ‘Rethinking Environmental History’, Ed. Alf Hornborg, (2007) give an intro to the relationship between bulk trade, agriculture (and later modern agriculture) and urbanisation, and Capital. Earlier historical development (see Holland again) pre-dated industrial expansion and enabled it. My favourite article though in the Hornborg collection is the failed first Swedish industrialisation based on wood biomass; ‘Food, war and crisis in the 17thC Swedish Empire’, (Janken Myrdal).

  20. Dear Prof Bardi,
    here you are in contradiction to un report: 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.
    The un report says:
    Während die Stromerzeugung aus erneuerbaren
    Quellen rasch ansteigt, gibt es im Wärme- und
    Verkehrssektor keine vergleichbaren Fortschritte
    Der Anteil der erneuerbaren Energien am weltweiten Energieendverbrauch
    ist zwischen 2010 und 2014 nur leicht von 17,5 Prozent auf
    18,3 Prozent gestiegen. Dank technologischer Fortschritte und sinkender
    Kosten hat sich jedoch die Erzeugung von Wind- und Sonnenenergie im
    selben Zeitraum mehr als verdoppelt. Der Zuwachs bei den erneuerbaren
    Energien ging hauptsächlich auf den Elektrizitätssektor zurück, und der
    Anteil der erneuerbaren Energien an der Stromerzeugung stieg folglich
    von 19,6 Prozent im Jahr 2010 auf 22,3 Prozent im Jahr 2014.
    link for german version:
    greatings from aribert peters

    1. Argh.... you force me to learn German! But, if I understand correctly, when it says "zwischen 2010 und 2014 nur leicht von 17,5 Prozent auf 18,3 Prozent gestiegen" it means RELATIVE INCREASE, not global production fraction. Am I right?

    2. No wait.... that's wrong. Sorry for my bad German. I think what they mean is the TOTAL renewable energy share, which includes hydroelectric. I gave the values for solar and wind only. So, both sets of values are correct, once related to what they are meant to describe.

      Anyway, who had this silly idea of building a tower in Babel?

    3. It was my fault not to provide the link to the english paper, the report is in many aspects remarkable, here comes the link



Ugo Bardi is a member of the Club of Rome, faculty member of the University of Florence, and the author of "Extracted" (Chelsea Green 2014), "The Seneca Effect" (Springer 2017), and Before the Collapse (Springer 2019)