If someone refers to renewables, the listener will smile easily, talking about fossils is harder. Companies have also started selling that green is good. There is an increasing consensus among experts in many areas on the need to make a transition from the energy model, including by the peak of oil or by climate change. The transition is inevitable, and we all agree that in future energy sources will be renewable, as there will be no other. In these days it has become clear that, in my opinion, this will mean more than just a change in the type of energy. We have to make a transition from an economic, social and political model, but we have not yet internalised that this will bring about a very radical change. In the end, when discussing the topic, the debate moves to the technological part. In fact, we carry the myth of technological progress that's very well embedded, at least in the last 150 years, it's very difficult to deal with a myth that's so deeply rooted in our society. And that's what I want to get here today: that we're not so optimistic.

I'm going to focus on the technological limits of renewables, which they do. Yesterday Marc [Gavaldà] and Rosa [Lago] made us reflect on the ecological debt that we are generating, above all by oil production. It's a pity, because if oil, coal, etc. We could build a very beautiful society. Pollution is, in principle, the only defect that these fuels have. It was later seen that economic power oppresses us even when we are in foams.

Renewables, on the other hand, are much less polluting, but they have a problem: it is the same source that uses the biosphere. Every system (biospheres, ecosystems…) uses energy, which is renewable. Therefore, if we use renewables on a large scale, we will compete with the biosphere. Or we're already competing. That's important. Sometimes we forget that obstacle. But be careful! These ecosystems that we want to protect as ecologists not only use photosynthesis, but there are also other forms of energy. Wind, for example, is fundamental to the functioning of the ecosystem. We may have ample room for manoeuvre before acting on the wind system, but we note that the biosphere is very complex: 400 parts per million CO2 are being enough to transform the Earth's climate. Very few studies have been carried out on the impact of wind on ecosystems, that is, on the climate change that would lead to the appropriation of wind. But those studies say yes, the use of wind causes climate change. The change is smaller than the one that produces carbon, but in a model of constant growth, in the end, it wouldn't be that small. Be careful.

Another example is deserts. It talks about putting up a lot of photovoltaic panels and you tend to think that the desert is completely arid. But some ecologists think that the Amazon wouldn't be so rich if it wasn't where the Sahara is, there are some interactions. What effect will the Sahara have on filling panals or mills? There's no research on it, and I would appreciate it. Of course, it's a question of scale. Another problem with renewables is low energy density. As you get little energy per square meter (much less than you get with fossils or nuclear), you need plenty of room for the facility. And so you'll inevitably have to compete with other resources that humanity needs, and with the biosphere. Competition has already started: 90% of the photovoltaic panels installed in Castilla y León are located in a place where once there was an agricultural area. But we will have an answer for some, because after all half of the agricultural land has been abandoned. OK. Again, scale will be the key.

It is also mandatory to mention the consumption of materials. I repeat a phrase that Pedro [Prieto] often says: energies are renewable, but we perceive them through non-renewable systems that use materials and are not renewable. Silver, for example, is the biggest constraint on the development of PV technology. If this technology is not modified, PV energy is very expensive. Mirrors can be made of aluminum, but this technology is pending development; aluminum reflects less light than silver, so you lose efficiency. And the territory it needs to occupy to get the same energy is wider.

To be truly renewable, these materials should be recycled, but we are a long way from achieving it. Nature is based precisely on recycling, and we do not even approach it. On the other hand, you need energy to recycle. Consequently, we are entering a vicious circle, and since the system we have built is very weak from a technological point of view, we cannot overcome it. We don't know how to do it.

And now, a parenthesis to talk about biofuels: it's ridiculous to say they're renewable. Among other reasons, because they own the soil, and the soil is not renewable, at least at our scale. This would be enough to close the debate on the renewability of biofuels. And they don't just need land, they need water, fertilizers ... And the energy density is ridiculous, less than 0.5 watts per square meter. It's absurd. We are occupying 50 million hectares for biofuels, of which we only get 0.2% of our energy consumption. This tells us how far the energy despair we live, like fracking, comes from. We tend to everything, and, unfortunately, we are also repeating with renewables the error of a model that has no other basis than to grow at all costs.

Finally, one of the arguments that is used proudly when talking about renewable energy is that it is a sector that generates many jobs. But if we do calculations, be careful ... Suppose we want a renewable world for the future, with the same consumption as today. In the field of solar energy or biofuels, approximately 30% of the population should work on this. Unemployment would end yes, but also the social structure, with all its complexity. We could argue whether this change has its good side, and if it does, but let's take it carefully.

In conclusion, let us say that in the future we will be 100% renewable, as we will have no other solution, but consuming much less than now. The model will be very different and we will surely not see 200 meters high wind mills, because in order to do so we would have to use a lot of fossil fuels. In fact, only a small part of the fossil energy needed for transition will be available at the end of the fossil age. I do not think there is a technological solution to this. The solution is cultural, not technological.