Sustainable energy is energy that renews itself automatically and to generate it is not necessary to use fossil resources such as coal. Wind and solar energy are two examples of sustainable, clean energy. The sun will keep producing light energy, and the rotation of our planet will keep generating wind. Notably zero-carbon energy sources are all forms of clean energy. Energy derived from biomass, biodiesel, are forms of renewable energy. The difference between green and renewable energy involves the possibility of replenishment, such as crops and biomass.

The IEA, i.e. the International Energy Agency, has recorded a major decline in the production of electricity using coal and has, instead, recorded an increase in the use of renewable energy sources tento it is true that, in 2021, the production of electricity from renewable sources increased by more than 8 percentage points compared to the most recent past. Solar and wind are set to contribute two-thirds of renewable growth. Noteworthy China alone should account for almost half of the global increase in renewable electricity in 2021. This trend should continue in the future and help in reducing CO₂ emissions.

Green, clean, renewable or sustainable energy do not affect our environment. Hydropower is often classified as sustainable energy, however some experts argue that it has too many social and environmental costs to be considered a sustainable or renewable resource in particular when the construction of dams disrupt local ecosystems.

The mantle of the Earth, under the crust, will always give off heat deriving from the core. Thanks to specific technology we can access this source of heat and use it especially in regions of volcanic and tectonic activity. Entire cities in Iceland, which is located in a volcanic active region near a mid-ocean ridge, geothermal energy supplies 90 percent of residents’ electricity needs.

The World Energy Conservation Day is celebrated annually on December 14 to highlight the importance of energy consumption and of its scarcity, as well as of its impact on the sustainability of the global ecosystem. March 18 is World Recycling Day and January 28 is World Day for Reducing CO₂ emissions.

Although free, solar energy can be associated with a high cost to use it: just think, for example, of the cost of the equipment needed to use solar energy. Apart from the high costs for their assembly, solar panels can be very expensive to buy and, subsequently, to maintain: to be able to use the energy of the sun, photovoltaic cells are required and, usually, there are hundreds of those that need to be connected between them to provide proper current flow. The electricity produced can be both used directly or stored in storage batteries. Early photovoltaic cells were extremely expensive, making the cost of solar electric panels prohibitive but advancement in technology and recent development of inexpensive semiconductor materials has helped greatly lower the cost to use it.

Although the initial construction and later maintenance costs are high, hydropower (which is derived from the flow of water), like other alternative energy sources, is totally clean and relatively cheap in the long run. However large-scale dams can have a significant impact on the regional environment. When the river is initially dammed, farmlands are sometimes flooded and entire populations of people and wildlife are displaced by the rising waters behind the dam. It must be underlined that sometimes the reservoir can flood hundreds or thousands of square kilometers. Moreover the decreased flow downstream from the dam can also negatively impact the environment changing it, as well as human and wildlife populations living downstream.

Wind energy is a form of clean and renewable energy, as to how it works, a wind turbine generator operates on a simple principle: The kinetic energy of the wind is trapped and collected by the blades on the wind turbines. The fact that these blades are similar to the wings on an aircraft, allows the wind to flow over the airfoil-shaped blades causing “lift”. This causes the turbine to turn. The turbine blades are connected to a drive shaft which turns a generator and thus electricity is produced. Wind energy does not produce air pollution, and can be virtually limitless. Constant wind and large available land are the main “disadvantages” for wind generators.

Natural gas production is often a by-product of oil recovery, as the two commonly share underground reservoirs. Natural gas is a limited resource, the current estimate of natural gas reserves is about 100 million metric tons and at current usage levels, this supply will last an estimated 100 years, and most of the world’s natural gas reserves are found in Eastern Europe and in the Middle East. Considering that natural gas is generally not contaminated with sulphur, it can be regarded as the cleanest fossil fuel.

Nuclear energy has the potential to become a true alternative energy source, and this has been proven over the years. Therefore, it can ensure a transition to more sustainable energy, eliminating the negative effects that climate change could almost certainly create in the future if nothing will have done about it. Concerns still exist about the safety of nuclear power plants however technology and innovation have advanced and have made nuclear energy safer and more affordable, and more countries around the world are starting to adopt nuclear power. Unfortunately old plants are still in operations and an accident might occur usually involving a meltdown of the core or leaks of radioactive material.

Biomass energy is generated using organic matter such as agriculture residues, plant material, and human waste. Wood combustion thus appears to be the most common source of biomass energy, but energy can also be generated by burning, for example, herbaceous (non-woody) plant material, or by burning animal manure (dung) or peat (i.e. partially decomposed animal and plant tissue). Humans started using these elements since they started using the fire. Today biomass can also be converted into a liquid biofuel such as ethanol or methanol.

Green energy is intended as the use of sustainable, clean and renewable energy sources used to produce energy instead of fossil fuels which represent the major source of CO₂ which contributes to the greenhouse effect thus to global warming and climate change threatening our environment. The more the use of green energy will be expanded the more we will help in protecting our environment and ourselves.