In this blog post, we will find out why we still need to save energy even though solar energy is infinite.
Yuval Noah Harari wrote “Sapiens.” In the fourth part of “Sapiens,” “The Scientific Revolution,” he argues that credit, the basic principle of capitalist society, has enabled us all to live in abundance. This means that the size of the economic pie has increased, so that the fact that someone takes a large share does not mean that the share of others decreases. Capitalism has a great advantage in that everyone can have a bigger piece of the pie.
However, all pies require raw materials and energy. Energy is especially essential for processing raw materials and maintaining human life. Can raw materials and energy be supplied indefinitely? Harari asks this question in this book. And immediately in the next chapter, he claims that solar energy can provide the infinite energy we need. He explains that the energy emitted by the sun in one second alone exceeds all the energy used by humankind in industry. But I have one question. So, is it really necessary to save energy?
My answer is “yes.” There are three reasons for this. The first is that it is impossible to completely convert solar energy. The second is that, according to the principle of mass-energy equivalence, a small mass contains a large amount of energy, but the amount of energy that can actually be used is very small. The third is that we need to think more deeply about what energy is.
First, the amount of energy that can be obtained from alternative energy sources is insufficient. Many people tend to think that alternative energy sources (solar energy, hydropower, geothermal energy, etc.) are diverse and that their supply is sufficient. In particular, many argue that solar energy is a good alternative energy source because it is abundant. However, we need to think about how much solar energy we can actually use. The amount of energy that the sun emits in one second and reaches the Earth is as much as 1 million exajoules (EJ). But how much of this can be converted through solar panels? The conversion efficiency of solar cells currently developed is only about 15%. In addition, the area of the Earth’s surface that can be used for solar panels is less than 6%. This is a calculation based on the assumption that solar panels are installed in all areas except for the sea, rivers, and mountains. In other words, the area that can actually be used and the power generation efficiency must be considered in addition to the total amount of energy reaching the earth. From this perspective, the energy that the sun emits in a year is less than 10 times the energy that humans use in industry in a year, suggesting that the amount of energy is not sufficient. Of course, the amount of 10 times may seem large by today’s standards, but since more energy will be needed in the future, the claim that solar energy is abundant is an exaggeration.
Second, the ways to obtain energy are limited. Many people cite the mass-energy equivalence (E=mc^2) and claim that energy is sufficient. However, the mass here does not simply refer to the mass of an object. This is “mass defect,” which refers to the energy that occurs when mass disappears. In other words, this energy is generated only in reactions that violate the law of conservation of mass, such as nuclear fusion and nuclear fission. Radioactive isotopes are required to cause these reactions, and the mass consumed in nuclear power plants is very small. Until the technology for stabilizing nuclear reactors is developed and we can secure enough radioactive elements, the nuclear energy we can obtain is still only at the level of nuclear power plants. In addition, such technology is accompanied by risks. Therefore, the amount of energy that can be generated using mass-energy equivalence is limited with current technology, and its risks cannot be ignored.
Third, we need to think about what energy is. Most energy is a relative concept. There is energy that is defined by absolute numbers, but there is also energy that is determined by the difference. For example, gravitational energy is defined by assuming an infinite potential position of zero. Similarly, thermal power generation, which obtains heat based on the energy stored in chemical bonds, also depends on how much the bonds can be broken rather than the energy stored in the compounds themselves. Therefore, it is quite difficult to define energy. In the end, what matters is how much energy we can convert into “electrical energy.”
So far, we have looked at the meaning of energy and the limits of energy that we can use. Depending on the definition, energy can appear to be abundant or scarce. However, the energy we should pay attention to is “electrical energy,” which we can easily convert. As we calculated earlier, solar energy and mass energy are very small to convert into electrical energy that we can use with current technology. That is why we need to save energy, not only because of the depletion of fossil fuels, but also because the types and amounts of energy we can convert are limited. Once fossil fuels are depleted, we will have no choice but to rely on solar energy or other alternative energy sources with low conversion efficiency. In the end, saving energy is the only way for our future, along with the development of technology.
