1.2: Things to be chosen" What things, what choice?

In this book, the term “energy” will sometimes refer to “energy as understood by a physicist” – but primarily, to its meaning in the “engineer’s language”. More specifically, it will refer to forms of energy that can be either used directly, or can be converted in order to obtain:

• Electric power, to be sent to a single user, or to many users;
• Thermal power, to be used for heating homes, cooking, making hot water, and in a range of industrial technologies; and
• Mechanical power, for propelling vehicles, pumping water, lifting loads, etc..

Now, it’s common knowledge that there are old, well-established methods of exploiting available, but depletable, energy resources – we will call them “traditional”. And that there are newer methods, believed (not by everybody, though!) to be “clean” and more friendly to the planet and environment than the “traditional” ones, and based on resources that are not being depleted in spite of extracting power from them. One can think of such sources as “non-depletable” – however, they are commonly referred to as “renewable”, and we will use this term further on¹.

Table \(PageIndex{1}\): Major resources of energy

Traditional			Renewable
Coal and Lignite
Petroleum derivatives
Natural Gas Hydropower	→	→	Hydropower
Nuclear power (generations I-III)	→	→	Nuclear power (newer generations)
^Wind power	→	→	Wind power
^Biofuels	→	→	Biofuels
^Geothermal power	→	→	Geothermal power
^Solar power	→	→	Solar power
			Wave/Tidal power

The major “traditional” and “renewable” resources are shown in Table \(\PageIndex{1}\). Some resources are shown in both columns. Why? For reasons one may call “historical”. Hydro-power has been used by humans for thousands of years, and, reportedly, the very first hydroelectric power station was built in 1868, even a few years earlier than the first coal-fired station. Oil and natural gas-fired stations emerged only in the XX-th century. Hence, “by seniority” hydro-power has the right to be called “traditional”. On the other hand, hydro-power is very clean, does not emit any atmospheric pollution and it does not deplete any existing resources – actually, the sources of river and stream water the hydro-power plants use are constantly “renewed” by precipitations. Therefore, it is listed in both columns in the table, and the small arrows are meant to show that the “status” of hydropower has changed: when nobody was worried about the CO₂ emission, it was thought of as yet another method of generating electricity – but now, due to its zero-emission property, is considered an important member of the family of technologies of harnessing renewable energy resources.

Nuclear power is also shown in both columns. The first nuclear power plants emerged in the 1950-s, so they are “relatively young” by age, but they quickly became a major component in overall electric power generating systems in many countries (e.g., about 20% in the US, nearly 80% in France). However, in the past there was a number of minor and medium-scale potentially hazardous accidents in nuclear power plants all over the world, and three of real catastrophic scale: Three Mile Island in 1979, Chernobyl in 1986, and Fukushima in 2011. In all three cases the principal reason for the disaster was the malfunctioning of the main cooling systems. Thus, because of safety concerns, the existing facilities, using older Generation I through III reactors of previous generations, have no future and will certainly be shut down when the reactors reach their allowed lifespan. Yet, much effort has been devoted in recent years to designing new types of reactors (often referred to as “Generation IV” ones), which will be “intrinsically safe”, because the cooling systems will never stop working, even if everything else fails and human operators make all possible errors. One unquestionable advantage of nuclear power plants is that such facilities do not emit CO₂. In order to create a future “zero-emission” electrical utility industry, all power plants using mined combustible fuels (coal, oil and natural gas) need to be gradually eliminated and replaced by facilities using only renewable resources. However, in the opinion of some renowned expert teams, such an ambitious goal may not succeed unless nuclear power generation becomes a meaningful “component” of such industry. It is why nuclear power is listed in the right-hand column² in Table 1.

Solar energy, wind energy, geothermal energy and energy from bio-fuels are thought of as the “backbone” of the future zero-emission energy system – but all these energy forms have been used by humanity, at a minor scale, for thousands of years. Therefore, they cannot be totally ignored in the list of “Classical” energy resources – but they are listed in the left column in Table \(\PageIndex{1}\) using a small font.

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¹Even though, in the author’s opinion, “non-depletable” would be a better term than “renewable” because the former better describes the actual physical situation.

²In fact, the nuclear power sector does use mined material as fuels. Currently, it’s the “fissile” ²³⁵U isotope which comprises only 0.7% of the natural Uranium. The reminding 99.3% is almost exclusively ²³⁸U which is non-fissile. However, there are not yet exploited technologies in which the nonfissile ²³⁸U, and a non-fissile Thorium isotope, ²³²Th, can be used as fuels. The combined global resources of ²³⁸U and ²³²Th are not “undepletable”, of course, but they are sufficient to satisfy the energy needs of humanity for many thousands of years, so they may be thought of as “nearly renewable”.