Various energy sources have their own advantages and disadvantages. The quality of energy reflects the difficulty of energy utilization and the friendliness of the environment. The advantages and disadvantages of energy quality are mainly evaluated from the following aspects:
(1) Energy flow density. Energy flow density refers to the amount of energy that can be obtained from a certain energy in a unit space or unit area per unit time. Traditional fossil energy, nuclear energy, and hydropower generally have a high energy flow density, while various renewable energy sources generally have a low energy flow density. The energy flow density of solar energy is only a few hundred watts, and the energy flow density of wind energy is tens to hundreds of watts. Therefore, the utilization of renewable energy such as solar energy and wind energy requires a larger receiving area.
(2) Storage capacity. As a long-term usable energy source, there must be sufficient storage capacity on the earth. Fossil energy is a non-renewable energy, and the storage capacity on the earth is limited, and there will always be a time when it is exhausted. Renewable energy such as solar energy and wind energy can be recycled and continuously supplemented. Therefore, the supply of human energy will eventually be obtained from renewable energy sources.
(3) The continuity and storability of energy supply. This refers to whether energy can be continuously supplied, whether it can be provided immediately when it is needed, and whether it can be stored in large quantities when not in use. Generally, conventional energy is easy to store, while renewable energy has high randomness and volatility and is difficult to store; fossil energy and nuclear energy are relatively easy to meet the requirements of these two aspects.
(4) Energy grade. Energy grade refers to the proportion of energy that can be converted into useful work components. Considering the ability to be converted into work and the difficulty of development and utilization, the grade of energy is divided into high and low, and there are low-grade energy that is more difficult to convert into electric energy, such as low-temperature thermal energy; there are also high-grade energy sources that are easier to convert into electrical energy, such as hydropower. As a secondary energy source, electric energy is the easiest to develop and utilize, and is the highest-grade energy source.
(5) Transportation costs and losses. The resource distribution of energy is often inconsistent with the demand distribution of energy utilization. The transportation process of energy from the development site to the use site also requires energy consumption, so the transportation distance is also a factor that affects energy use. Solar energy, wind energy, geothermal energy, etc. are difficult to transport; fossil energy and nuclear fuel can be transported over long distances, but the transportation cost is relatively high.
(6) Development costs and equipment costs. The exploration, mining, processing, and transportation of fossil energy and nuclear fuel require a large amount of manpower and material resources. The energy consumed in the development process is relatively high, and the cost is also relatively large. Renewable energy such as wind energy, solar energy and tidal energy are provided by nature. In the development process, energy consumption is very small and operating costs are low. However, due to the low energy flow density of wind energy, solar energy and other renewable energy sources, the low utilization rate of equipment, and the low energy conversion efficiency, the equipment cost of renewable energy is much higher than that of fossil energy to develop the same power of energy. However, with the advancement of technology, the price of renewable energy power generation equipment is falling rapidly. In 2012, the cost of wind power generation equipment per kilowatt has dropped from tens of thousands of yuan to more than 3,000 RMB.
(7) Impact on the environment. The pollution produced in the process of energy development and utilization has become the most important factor affecting the environment. For example, the process of burning fossil fuels not only emits CO2 and other greenhouse gases, but also emits toxic or corrosive substances (such as SO2, NOx, etc.). Nuclear fuel has the problems of uranium radioactive pollution and waste disposal; the construction of hydropower stations will inundate the land, affect the survival of aquatic animals, cause earthquakes, and hinder irrigation and shipping. If the planning and design are appropriate, these risks can be transformed into favorable factors. Renewable energy has less impact on the environment during the development and utilization stage, so renewable energy is also called clean energy.