Renewable energy sources (RES) can be replenished in a short period of time.
Renewable energy sources are all fuel types and energy carriers, different from the fossil ones.
Renewable energy is also known as green or clean energy, because the process of transformation of renewable energy sources into renewable energy does not produce green house gas emissions (toxins or pollutants) that are harmful to the environment.
There are lots of definition used in different countries and regions.
For example in the USA - "Renewable energy is natural energy that can be used again and again and will never run out". It's good to know that each state may adopt its own definition for legislation.
Here you can find some of the most popular, offficial and world recognized deffinition of Renewable energy sources (RES).
"Energy from renewable sources means energy from renew able non-fossil sources, namely wind, solar, aerothermal, geothermal, hydrothermal and ocean energy, hydropower, biomass, landfill gas, sewage treatment plant gas and biogases."
Source: Directive 2003/54/EC
"Renewable energy sources are energy resources that are naturally replenishing but flow-limited. They are virtually inexhaustible in duration but limited in the amount of energy that is available per unit of time. Renewable energy resources include: biomass, hydro, geothermal, solar, wind, ocean thermal, wave action, and tidal action." Source: EIA Glossary
Alternative energy: Fuel sources that are other than those derived from fossil fuels. Typically used interchangeably for renewable energy.
Type of RES There are five often used renewable sources - solar (thermal and PV), hydro, geothermal, wind, biomass (wood, wood waste, municipal solid waste, biogas, landfill gas). Other type of renewable energy is the energy from ocean (energy from tide); osmotic power (salinity gradient power) is the energy retrieved from the difference in the salt concentration between seawater and river water; cellulosic ethanol - process of producing enzymes which could enable a cellulosic ethanol, instead of building refineries that can process biomass and turn it into ethanol.
Advantages of renewable energy
- It can be used without depleting it.
- There is no green gas emissions, no pollution emissions - no contribution to global warming.
- Renewable energy is healthy and environmentally friendly.
- All forms of energy are expensive, but as time and technologies progresses, renewable energy generally gets cheaper, while fossil fuels generally get more expensive.
For example coal emits smoke and chemicals when it is burned to make electricity. Nuclear power plants create radioactive waste that is dangerous for thousands of years. Gasoline burned in our cars causes smog. Even natural gas contributes to the pollution problems.
Some renewable energy sources (wind and solar) don't emit smoke or create pollution when they are used. Others, such as biomass, almost always cause less pollution than fossil or nuclear alternatives.
Renewable energy can be use for power generation, hot water, space heating, transport fuels, off-grid energy services.
Disadvantages of renewable energy
- All forms of energy are expensive. This is because it is a new technology and as such has extremely large capital cost.
- It is difficult to generate the quantities of electricity for example that are as large as those produced by traditional fossil fuel generators. So if we use renewable energy we will need to build more energy facilities. The best solution is to have a balance of many different power sources.
- The reliability of supply. Renewable energy often relies on the weather for its source of power: hydro generators need rain to fill dams to supply flowing water; wind turbines need wind to turn the blades; solar collectors need sunshine to collect heat and make electricity. This can be unpredictable.
Renewable energy potential
When we speak about the renewable enrgy potential we need to know that there are two main types of potential: theoretical and technical potential of renewable energy sources (RES).
Theoretical RES potential - This is the all physically available renewable sources. E.g., the whole amount of solar energy, radiated to the entire territory during one year; concerning biomass - all forest and other plantations in the municipality/country..., which are suitable for energy use, concerning the hydro it could be all river flow and etc.
Technical RES potential - this is the part of the theoretical one, which remains available for energy use, when the existing technical and non technical (financial, legal, etc.) limitations are taken into account.
Renewable Energy Certificate (REC)
Each producer of renewable energy need to have a renewable energy certificate. This is a document that proofs that one megawatt-hour (MWh) of electricity that he produced is generated from a renewable energy resource.
Why the producer need it?
Because once the producer have got such a certificate he is able to sell that renewable electricity on the open market as a commodity.
The other famous alternative name of the Renewable Energy Certificate are also: Green Tags, Tradable Renewable Certificates (TRCs), and Renewable Energy Credits.