If solar energy is infinite, why do we still need to conserve energy?

Drawing on Yuval Noah Harari’s Sapiens, this article explores the importance of energy in capitalist societies and questions whether solar energy and mass-energy equivalence make it possible to obtain infinite energy. It goes on to discuss three reasons why we should conserve energy, pointing out current technological limitations and the efficiency of energy conversion.

 

Yuval Noah Harari is the author of Sapiens. In Part 4 of Sapiens, “The Scientific Revolution,” he argues that credit, a fundamental principle of capitalist society, has made it possible for us all to live in abundance. This means that the size of the economic “pie” has increased, so that when one person gets more, it doesn’t mean that others get less. Capitalism is great because it allows everyone to have a bigger piece of the pie.
However, every “pie” requires raw materials and energy. Energy, in particular, is essential for processing raw materials and sustaining human life. Can there be an infinite supply of raw materials and energy? Harari asks this question in the book, and in the very next chapter, he argues that solar energy can provide the infinite energy we need. He explains that the energy the sun emits in one second, and the fraction that reaches Earth, exceeds all the energy we use for industry. But this begs the question: do we really need to conserve energy?
The answer is yes. There are three reasons for this. The first is that solar energy cannot be fully converted. The second reason is that the principle of mass-energy equivalence states that a small mass contains a large amount of energy, but only a very small amount of mass is actually available. The third is that we need to think more deeply about what energy is.
First, the amount of energy we can get from alternative energy is not enough. Many people tend to think that alternative energies (solar, hydro, geothermal, etc.) are plentiful and that the supply is sufficient. Solar energy, in particular, is so abundant that many argue that it’s not a problem as an alternative energy source. However, we need to think about how much solar energy is actually available to us. Of the energy emitted by the sun in one second, about one million exajoules (EJ) reach the Earth. But how much of that can be converted by solar panels? Currently developed solar cells have a conversion efficiency of only about 15%, and less than 6% of the Earth’s surface is available for solar panels. This is based on the assumption that solar panels would be installed on all areas except oceans, rivers, and mountains, meaning that the total amount of energy reaching the earth is less than the area that can actually be harnessed and the efficiency with which it can be generated. From this perspective, the energy released by the sun in a year is less than 10 times the energy that humans use in industry in a year, which suggests that the amount of energy is not very sufficient. Of course, 10 times may seem like a lot by today’s standards, but in the future we will need even more energy, so the claim of solar energy abundance is overstated.
Second, there are limited ways to obtain energy. Many people argue that there is plenty of energy, citing mass-energy equivalence (E=mc^2). However, mass here does not simply mean the mass of an object. It’s “missing mass,” which is the energy that comes from the loss of mass. This energy is only available in reactions that break the law of conservation of mass, such as nuclear fusion or fission. These reactions require radioactive isotopes, and even in nuclear power plants, the mass consumed is very small. Until reactor stabilization technology improves and enough radioactive elements become available, nuclear energy is still only at the level of nuclear power plants. So there is a limit to the amount of energy that can be generated using mass-energy equivalence with current technology, and the risks are not negligible.
Third, we need to think about what energy is. Most energy is a relative concept. While some energies are defined by absolute numbers, many are determined by differences. For example, gravitational energy is defined by assuming a potential position of zero at infinity. Similarly, thermal power generation, which uses the energy stored in chemical bonds to generate heat, depends on the extent to which the bonds can be broken, rather than the energy stored in the compounds themselves. Defining energy is therefore quite difficult. In the end, what matters is how much energy we can convert into ‘electrical energy’.
So far, we’ve discussed what energy means and the limits of how much energy we can use. Energy can seem like a lot or a little depending on its definition. However, the energy we should be interested in is ‘electrical energy’, which we can easily convert. As we calculated earlier, solar energy and mass energy are too small to convert into electrical energy that we can utilize with current technology. So it’s not just the depletion of fossil fuels that we need to conserve energy. It’s because the types and amounts of energy we can convert are limited. Once fossil fuels are depleted, we will be forced to rely on solar energy or other alternative energy sources that are less efficient to convert. In the end, conserving energy while advancing technology is the only way to secure our future.