What is clean energy? What are the clean energy sources?

Due to the impact of climate change, renewable energy has been widely recognized worldwide as an alternative to fossil energy. The United Nations Climate Change Conference in Paris in 2015 became a watershed in the development of renewable energy, re-emphasizing the importance of renewable energy development. The conference pointed out that by doubling the proportion of renewable energy by 2030, that is, renewable energy will account for 36% of the total final energy consumption, to control climate change and achieve sustainable development goals.

What is clean energy?

Clean energy, namely green energy, refers to the energy that does not emit pollutants and can be directly used for production and life, including renewable energy. In a narrow sense, green energy refers to renewable energy, such as water energy, biological energy, solar energy, wind energy, geothermal energy, and ocean energy. These energy sources can be restored and replenished after consumption, and little pollution is produced. In a broad sense, clean energy includes the selection of energy with low or no pollution to the ecological environment, such as natural gas, clean coal, and nuclear energy, in the process of energy production and consumption. New energy refers to the secondary energy technologies developed in recent years, such as fuel cells and new secondary batteries.

What are the clean energy sources?

Hydrogen energy

Hydrogen energy has always been regarded as the ultimate energy source. Compared with other fuels, hydrogen has the cleanest combustion products, basically only producing pollution-free water, and the water produced by combustion can continue to produce hydrogen and be reused. Secondly, the specific energy of hydrogen combustion is high, and the calorific value of hydrogen is the highest among all fuels except nuclear fuel, which is three times that of gasoline. Moreover, it is “as light as a feather”. As the lightest substance we know, even liquid hydrogen after pressurized liquefaction is less than 1/10 of the density of steel. This low density makes it possible to reduce the weight of fuel, increase the payload of transportation tools, and thus effectively reduce transportation costs.

The use of hydrogen energy will make mankind bid farewell to carbon-based energy. Hydrogen was 40 times more expensive to produce than oil in 2000, by 2010 it had fallen to 15 times, and today it costs about twice as much as oil, with break-even in sight.

The main way to realize hydrogen energy is to rely on the reaction between hydrogen and oxygen to convert chemical energy into electrical energy. Since the by-product of the hydrogen-oxygen reaction is water, there is no environmental pollution problem, so people hold great expectations for hydrogen as a fuel. Since the 1960s, hydrogen energy was first used in the fields of rocket and space shuttle launches. With the progress of science and technology and the emphasis on environmental protection, the application of hydrogen energy has gradually expanded to automobiles, aircraft fuel, and hydrogen fuel cells.

To use hydrogen as an energy source, the problems of hydrogen storage and transportation must be solved. It is not economical and safe to store hydrogen in high-pressure cylinders or in liquid or solid state. It is reported that about 50% of the total hydrogen energy research funds of the U.S. Department of Energy are used for hydrogen storage research.

A fuel cell (FC) is an electrochemical device that converts chemical energy directly into electrical energy. Simply speaking, it is a device for electrochemical reaction between reactant fuel and oxygen in the air to obtain electric energy and heat energy. The energy conversion process is that chemical energy is directly converted into electric energy and heat energy, and the formed electric energy is low-voltage DC electric energy. The fuel and oxidant pass through the two poles from both sides respectively. Its working process is equivalent to the reverse reaction process of electrolyzing water. The electrode is the place where fuel and oxidant are converted into electricity, water, and energy. The fuel (mainly hydrogen) emits electrons on the anode. The electrons are transmitted to the cathode through the external circuit and combined with the oxidant. They pass through the ionic conductor of the electrolyte between the two electrodes. The chemical reactions of the fuel and the oxidant at the two electrodes. Electrolyte interfaces form a circuit to generate current. It is the fourth power generation technology after hydropower, thermal power, and nuclear power.

Nuclear

Nuclear energy is a clean energy for sustainable development, which has been recognized as the only alternative energy that can replace conventional energy on a large scale. The statistical results show that the CO2 emission of France is only 15% of that of its neighboring countries because its electricity supply mainly depends on nuclear energy. The main reason is that the operation of nuclear power plants will not emit CO2, SO2, and dust.

Solar

Compared with other energy sources, solar energy has many advantages, such as: (1) The total amount of solar energy received by the earth in a year is far greater than the demand for energy by human beings. (2) It is widely distributed and does not require mining and transportation. And (3) that method has no exhaustion problem and can be used for a long time. (4) Safety and sanitation, no pollution to the environment, etc. Therefore, solar energy will play an important role in the future energy structure. At present, its development and utilization has been highly valued and great progress has been made.

The main technologies used in the utilization of solar energy are photoelectric conversion and photothermal conversion. Photoelectric conversion materials and photothermal conversion materials play a key role in these technologies. The main photoelectric conversion materials are silicon and germanium semiconductor materials. Recently developed GaAs and CdS materials can be used to manufacture large area solar cells at a low cost, and the main products are solar panels. In developed countries such as Europe and the United States, there are finalized products of silicon solar panels. The main photothermal conversion materials are light absorption materials and phase change energy storage materials, such as blackened metal plates, multi-layer light absorption, anti-reflection films, inorganic hydrated salts, fluorite, and metal alloys. Organic paraffin, polyols, polyethylene, and other solid-liquid and solid-solid phase change energy storage materials.

Wind energy

Wind energy is the kinetic energy produced by the movement of air. A form of solar energy conversion. Due to the uneven heating of the earth’s surface caused by solar radiation, the pressure distribution in the atmosphere is unbalanced. Under the action of a horizontal pressure gradient, the air moves along the horizontal direction to form the wind. The total reserves of wind energy resources are very large, and the energy that can be developed by technology in a year is about 5.3 X 10 ^ 13 kWh. Wind energy is a renewable clean energy with large reserves and wide distribution, but its energy density is low (only 1/800 of water energy) and unstable. Under certain technical conditions, wind energy can be developed and utilized as an important energy source. Wind energy utilization is a comprehensive engineering technology, which converts the kinetic energy of wind into mechanical energy, electric energy, and heat energy through wind turbines.

From the strategic perspective of sustainable development, it is imperative to develop and utilize clean energy. Clean energy not only solves the crisis of energy shortage, but also solves the contradiction between energy and environment. And energy materials are all kinds of energy.