Renewable energy is generally defined as energy that comes from resources which are continually replenished on a human timescale such as sunlight, wind, rain, tides, waves and geothermal heat.
Wind power – I did a specific post on wind already so I won’t write anything here but still wanted to include it on the list of sources of renewable energies.
Hydropower – there is energy in water that can be harnessed and used for power. Since water is ~ 800 times denser than air, even a slow flowing stream of water, or moderate sea swell, can yield considerable amounts of energy.
- Hydroelectric energy is usually meant for large-scale hydroelectric dams. The largest of which is the Three Gorges Dam in China
- Micro hydro systems are power installations that usually produce up to 100 kW of power. They are often used in water rich areas as a remote-area power supply or RAPS
- Run-of-the-river systems draw from kinetic energy from rivers and oceans without the creation of a large reservoir
Solar energy – applies energy from the sun in the form of solar radiation for heat or to generate electricity. This form uses either heat engines (concentrated solar power) known as photovoltaics. A list of other solar applications includes but is not limited to space heating and cooling through solar architecture, day lighting, solar hot water, solar cooking (CMU demo), and high temperature process heat for industrial purposes.
- Active solar techniques include the use of photovoltaic panels and solar thermal collectors to harness the energy.
- Passive solar techniques include adjusting a building to the sun, selecting materials with favorable thermal mass or light dispersing properties, and designing spaces that naturally circulate air.
Biomass – (plant material) can be a renewable energy source if the rate of extraction does not exceed the rate of production, as non-renewable biomass usage can easily occur.
- Ex: the Deforestation during the Roman period and the present Deforestation of the Amazon Rainforest.
Through photosynthesis, plants capture the sun’s energy. When the plants are burnt, they release the sun’s energy they contain. In this way, biomass functions as a sort of natural battery for storing solar energy. The best approaches vary from region to region according to climate, soils and geography.
In general there are 2 main approaches to using plants for energy production:
- Growing plants specifically for energy use (known as first and third-generation biomass)
- Using the residues (known as second-generation biomass) from plants that are used for other things.
Biofuel – include a wide range of fuels which are derived from biomass. This covers solid biomass, liquid fuels and various biogases.
- Liquid biofuels include bioalcohols, such as bioethanol, and oils, such as biodiesel
- Gaseous biofuels include biogas, landfill gas and synthetic gas.
Bioethanol is an alcohol made by fermenting the sugar components of plant materials and it is made mostly from sugar and starch crops. Ethanol can be used as a fuel for vehicles in its pure form, but it is usually used as a gasoline additive to increase octane and improve vehicle emissions. The energy costs for producing bio-ethanol are almost equal to, the energy yields from bio-ethanol.
Biodiesel is made from vegetable oils, animal fats or recycled greases. It can be used as a fuel for vehicles in its pure form, but it is usually used as a diesel additive to reduce levels of particulates, carbon monoxide, and hydrocarbons from diesel-powered vehicles.
Geothermal energy – is from thermal energy generated and stored in the Earth. Thermal energy is the energy that determines the temperature of matter. Earth’s geothermal energy originates from the original formation of the planet (20%) and from radioactive decay of minerals (80%). The geothermal gradient, which is the difference in temperature between the core of the planet and its surface, drives a continuous conduction of thermal energy in the form of heat from the core to the surface.
- From hot springs, geothermal energy has been used for bathing since Paleolithic times and for space heating since ancient Roman times, but it is now better known for electricity generation.