Is solar energy clean?

For decades we have been sold the idea that when we fully harness solar energy, all our problems of getting cheap and abundant energy, air pollution, and global warming will be solved.

For decades I have been warning that this optimistic approach is not true. If we were able to completely replace energy from fossil fuels (coal, oil and natural gas) by solar energy, some of our problems will not go away, they will just take longer to become unsustainable, especially the problem of global warming.

Why do I think this? Because the Earth receives a certain amount of solar energy. A part is used by plants to carry out the chlorophyll function, which transforms inorganic matter into organic matter, thus making life possible for all animals, including us, humans. Another part heats the oceans and the continents, allowing the Earth to maintain an almost constant temperature, despite the heat losses it suffers every day from the side opposite the sun. Finally, another part of the solar energy is reflected or diverted, in the atmosphere or on the surface, and is lost in outer space.

Suppose we manage to harness solar energy to meet all our energy needs. It is evident that we would get it at the cost of reducing the amount of solar energy reflected or diverted, so that a greater proportion of the solar energy reaching us every day would stay here, on Earth. Therefore, the average temperature of the Earth would rise. A little more slowly than if we get that same energy by burning fossil fuels, but in the long run the situation would also become unsustainable.

Is there any study that shows that this scenario can be true; that it is not just a speculation of a pessimistic? Well yes, there is.

An article published in the journal Physics World reports on a study by David Sailor's team at Arizona State University. This study shows that cities where solar panels have been placed on the roofs and terraces of many houses heat up significantly during the day: their average temperature becomes higher than normal. David Sailor explains it like this:

When you put [photovoltaic panels] on that white roof, the PV panels typically absorb in the order of 90% of the energy of the Sun. And the PV panels then do convert some of that energy to electricity, but typical panels today are only maybe 16–20% efficient. These panels are absorbing a tremendous amount of energy from the Sun, converting some of it into electricity, but then warming up because they’re not able to use all of the energy. So, these PV panels tend to be rather hot surfaces in the environment. 

To mitigate the problem, Sailor proposes that reflective panels be placed in close proximity to the solar panels, so that the reflected solar energy increases. And he seems to think that if we could increase the efficiency of the solar panels to get near 100% (which, of course, is unattainable) the problem would disappear. But he does not realize that, in such a case, if almost all the solar energy were to be converted into electricity, that electricity would eventually, sooner or later, turn into heat, so that the increase in temperature would still take place, although in a more distributed way, depending on where the electricity is used. But global warming would continue to increase.

This does not only affect solar energy. Another older study concluded that if all our energy were got from wind, the world would also warm up, not to mention the harmful effects that wind turbines have on fauna, flora and soil erosion.

If we remember that all forms of energy eventually end up being converted into heat, we will come to the conclusion that the only way to avoid global warming in the long term is to reduce total energy consumption. Using renewable sources does not change this situation, although it would make it possible to stop the increase in carbon dioxide in the atmosphere and some other harmful effects. These forms of energy are cleaner than fossil fuels, but they cannot be completely clean, precisely because they end up being converted into heat.

The same post in Spanish

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Manuel Alfonseca