Definition of Renewable Energy: Sources and Examples

Renewable Energy – Today’s global energy demand has tripled since 1950 and its use is estimated to have reached 10,000 million tons per year. Most of this energy is produced from non-renewable materials, such as coal, gas, oil and nuclear energy.

Petroleum is the most critical energy source among these energy sources. Given the dwindling availability of petroleum and the dangers of its use, efforts to find renewable and environmentally friendly energy sources are important.

As reported by the Center for Energy Studies, Gadjah Mada University (UGM), renewable energy is energy that comes from natural sources, such as sunlight, wind, rain, geothermal, and biomass. Several potential and abundant sources of renewable energy in Indonesia are wind, geothermal, hydropower, solar, biomass (biogas, solid biofuel, and liquid biofuel).

Definition of Renewable Energy

Renewable energy is energy that comes from “sustainable natural processes”, such as solar power, wind power, water currents, biological processes, and geothermal. To find out more about the use of renewable energy in modern society, see development of renewable energy. For general discussion, see future energy development.

Renewable energy.

The concept of renewable energy became known in the 1970s, as an effort to balance the development of nuclear and fossil fueled energy. The most common definition is a source of energy that can be quickly restored naturally and the process is sustainable. By this definition, nuclear and fossil fuels are excluded.

By definition, all renewable energy is also sustainable energy, because it is always available in nature for a relatively very long time, so there is no need to worry or anticipate that its sources will run out. Non-nuclear energy proponents do not include nuclear power as part of sustainable energy because the supply of uranium-235 in nature has a limit, say hundreds of years.

However, nuclear activists argue that nuclear is considered sustainable energy if it is used as fuel in fast breeder reactors (FBR: Fast Breeder Reactor ) because nuclear fuel reserves can “multiply” hundreds to thousands of times.

The reason is this, the nuclear reserves that energy experts talk about in the order of tens or hundreds of years are implicitly calculated with the assumption that the reactor used is an ordinary reactor (generally the BWR or PWR type), which incidentally can only burn U-235. On the one hand, the content of U-235 in nature is no more than 0.72%, the remaining approximately 99.28% is U-238.

Uranium type U-238 in “normal” burning conditions (used as fuel in normal reactors) cannot produce nuclear energy, but if it is mixed with U-235 and fed together into a breeder reactor, it is equivalent to the consumption/burning of U -235, U-238 undergoes a 1 neutron capture reaction and transforms into U-239.

In a matter of minutes U-239 decays while releasing beta particles and transforms back into Np-239. Np-239 also decays again while emitting beta particles to become Pu-239. This Pu-239, which although not available in nature, is formed as a by-product of burning U-235, has the ability to divide and produce energy like U-235.

You can imagine if all U-238, which is thousands of times more numerous than U-235, was successfully converted into Pu-239, how much increase would occur in the amount of nuclear fuel. The same thing happened to the atom [thorium-233] which, by capturing 1 neutron, changed its form to U-233 which has the ability to chain reaction (nuclear reaction).

That is why certain developed countries are reluctant to give up nuclear, even though the radioactive risks it receives are not light. Fast breeder reactors like those owned by North Korea are under strict supervision from the IAEA because they are capable of producing new Pu-239 fuel which is vulnerable to being misused for weapons of mass destruction. Nuclear opponents, on the other hand, tend to use the term “sustainable energy” as a synonym for “renewable energy” to exclude nuclear energy from the discussion of the energy group.


Main Source of Renewable Energy

1. Geothermal Energy

Geothermal energy comes from radioactive decay in the center of the earth, which heats the earth from within, as well as from the sun’s heat, which heats the earth’s surface. There are three ways to use geothermal energy, namely:

  • As a power generator and used in the form of electricity.
  • As a source of heat that is used directly using pipes into the bowels of the earth.
  • As a heat pump pumped directly from the bowels of the earth

Geothermal is a form of heat energy or thermal energy that is generated and stored in the earth. Heat energy is energy that determines the temperature of an object. Geothermal energy comes from energy from the formation of planets (20%) and radioactive decay of minerals (80%). The geothermal gradient, defined by the temperature difference between the Earth’s core and its surface, drives the continuous conduction in the form of heat energy from the core to the Earth’s surface.

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The temperature of the earth’s core reaches more than 5000 0 C. Heat flows by conduction towards the rocks around the earth’s core. This heat causes the rocks to melt, forming magma. Magma transfers heat by convection and moves up because magma in the form of molten rock has a lower density than solid rock. Magma heats the earth’s crust and water flowing in the earth’s crust, heating it up to 300 0 C. This hot water creates high pressure so that water comes out of the earth’s crust.

Geothermal energy from the Earth’s core is closer to the surface in some areas. Hot steam or underground water can be harnessed, brought to the surface, and can be used to generate electricity. Geothermal power sources are located in several geologically unstable parts such as Iceland, New Zealand, United States of America, Philippines and Italy.

The two most prominent areas so far in the United States are in the Yellowstone dome and in northern California. Iceland generates geothermal power and delivered energy to 66% of all Icelandic homes in 2000, in the form of direct heat energy and electrical energy through power plants. 86% of houses in Iceland use geothermal energy to heat their homes.

2. Solar Energy

Solar panels ( photovoltaic arrays ) aboard small yachts at sea can charge 12 V batteries to 9 amperes in full and direct sunlight conditions.

Since most renewable energy comes from “solar energy” the term is a little confusing. However, what is meant here is energy that is collected directly from sunlight.

Solar power can be used for:

  • Generate electricity using solar cells.
  • Generating electricity Using solar towers.
  • Heats the building directly.
  • Heating the building through a heat pump.
  • Heating food using a solar oven.
  • Heats water via a solar powered water heater.

Of course the sun does not provide constant energy to every point on earth, so its use is limited. Solar cells are often used to charge batteries during the day and the power from the batteries is used at night when sunlight is not available.


3. Wind Power

The temperature difference in two different places produces different air pressure, thus producing wind. Wind is the movement of matter (air) and has been known for a long time to drive turbines. Wind turbines are used to generate kinetic energy and electrical energy.

The energy available from the wind is a function of wind speed; when the wind speed increases, the output energy also increases up to the maximum limit of energy that the turbine can produce. Areas with stronger and more constant winds, such as offshore and upland, are usually preferred for developing “wind farms”.

4. Water Energy

Water energy is used because it has mass and is able to flow. Water has a density of 800 times that of air. Even the slow movement of water can be converted into other forms of energy. Water turbines are designed to obtain energy from various types of reservoirs, which are calculated from the amount of water mass, height, to water velocity.

Water energy is utilized in the form of:

  • Power generation dams, the largest of which is the Three Gorges dam in China.
  • Micro hydro built to generate electricity up to a scale of 100 kilowatts. Generally used in remote areas that have many water sources.
  • A run-of-the-river built by harnessing the kinetic energy of flowing water without the need for a large water reservoir.

5. Biomass

Plants usually use photosynthesis to store solar energy, air, and CO 2 . Biofuels ( biofuels ) are fuels obtained from biomass-organisms or products of animal metabolism, such as cow dung and so on. It is also a renewable energy source. Usually biomass is burned to release the chemical energy stored in it, except when biofuel is used for fuel cell fuel (eg direct methanol fuel cell and direct ethanol fuel cell ).

Biomass can be used directly as fuel or to produce other types of fuels such as biodiesel, bioethanol or biogas depending on the source. Biomass in the form of biodiesel, bioethanol and biogas can be burned directly in an internal combustion engine or boiler under certain conditions.

Biomass becomes a renewable energy source if the extraction rate does not exceed the production rate, because basically biomass is a material produced by nature in a relatively short time through various biological processes. Various cases of non-renewable biomass use have occurred, such as the case of Roman era deforestation, and what is happening now, deforestation of the Amazon forest. Peat is also actually a biomass whose definition as renewable energy is quite biased because the rate of extraction by humans is not proportional to the rate of growth of the peat layer.

There are three forms of using biomass, namely solid, liquid, and gas. In general, there are two methods of producing biomass, namely by growing biomass-producing organisms and using the leftover materials from living things processing industries.

a. Liquid Bio-Fuel

Liquid bio-fuels are usually in the form of bio-alcohols such as methanol, ethanol and biodiesel. Biodiesel can be used in modern diesel vehicles with little or no modification and can be obtained from waste vegetable and animal oils and fats. Depending on the potential of each region, corn, sugar beet, sugarcane and several types of grass are cultivated to produce bioethanol. Meanwhile, biodiesel is produced from plants or plant products that contain oil (oil palm, copra, castor seeds, algae) and has gone through various processes such as esterification.

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b. Solid Biomass

Direct use is usually in the form of flammable solids, either kindling or flammable plants. Plants can be cultivated specifically for burning or can be used for other purposes, such as processing in certain industries and processing waste that can be burned as fuel.

Biomass briquettes manufacture also uses solid biomass, where the raw material can be in the form of chunks or flakes of raw solid biomass or which have gone through certain processes such as pyrolysis to increase the percentage of carbon and reduce the water content. Solid biomass can also be processed by gasification to produce gas.

c. Biogas

Various organic materials, biologically by fermentation, as well as physico-chemically by gasification, can release flammable gases. Biogas can easily be produced from various industrial wastes that exist today, such as paper production, sugar production, livestock manure, and so on. Various waste streams must be diluted with water and allowed to naturally ferment, producing methane gas. The residue from this fermentation activity is fertilizer which is rich in nitrogen, carbon and minerals.

Small Scale Energy Sources

  • Piezoelectricity, is an electric charge resulting from the application of mechanical stress to a solid object. This object converts mechanical energy into electrical energy.
  • An automatic watch ( Automatic watch, self-winding watch ) is a watch that is driven by stored mechanical energy, which is obtained from the movement of the user’s hand. Mechanical energy is stored in the spring mechanism inside.
  • Electrokinetic runway ( electrokinetic road ramp ) is a method of generating electrical energy by utilizing the kinetic energy of cars moving on a runway installed on the road. A runway has been installed in the parking lot of a Sainsbury’s supermarket in Gloucester, United Kingdom, where the electricity generated is used to power a cash register.
  • Captures unutilized electromagnetic radiation and converts it into electrical energy using a rectifying antenna . This is one method of harvesting energy ( energy harvesting ).

Problems in Renewable Energy

1. Aesthetics, Habitat Endangerment, and Land Use

Some people dislike the aesthetics of wind turbines or bring up nature conservation issues when large solar panels are installed in villages. Those trying to take advantage of this renewable technology should do so in a preferred way, for example utilizing solar collectors as noise barriers along the way, integrating them as sun shades, installing them on existing roofs and even replacing the roof completely, also amorphous photovoltaic cells can be used to replace window.

Several renewable energy extraction systems create unique environmental problems. For example, wind turbines can be dangerous to flying birds, while hydropower dams can create barriers to fish migration—a serious problem in the Pacific Northwest which has reduced salmon populations.

Burning biomass and biofuels causes the same air pollution as burning fossil fuels, although this carbon released into the atmosphere can be reabsorbed if the biomass producing organisms are continuously cultivated. Another problem with many renewable energies, particularly biomass and biofuels, is the large amount of land required to cultivate them.

2. Concentration

Another problem is the variability and distribution of renewable energy in nature, except for geothermal energy which is generally concentrated in one particular area but is found in extreme locations. Wind energy is the most difficult to focus, so it requires a large turbine to capture as much wind energy as possible.

The method of utilizing water energy depends on the location and characteristics of the water source so that the design of the water turbine can be different. Utilization of solar energy can be done in various ways, but to get a lot of energy requires a large area of ​​capture.

For comparison, under standard testing conditions in the United States of America, the energy received by 1 m2 of solar cells having an efficiency of 20% will produce 200 watts. The standard test conditions in question are an air temperature of 20 0 C and an irradiance of 1000 W/m 2 .

3. Distance to Electrical Energy Receivers

Geographical diversity is also a significant issue, as some renewable energy sources such as geothermal, hydro, and wind can be located far from receiving electricity; geothermal in the mountains, water energy in the upper reaches of the river, and wind energy off the coast or in the highlands. The utilization of these resources on a large scale will likely require substantial investment in transmission and distribution networks and the technology itself in dealing with the associated environment.

4. Availability

One significant drawback is the availability of renewable energy in nature; some of them exist only occasionally and not all the time (intermittent). For example, sunlight which is only available during the day, wind energy whose strength varies at any time, water energy which cannot be utilized when rivers are dry, biomass has the same problems as those faced by agriculture (eg climate, pests), and so on. Meanwhile, geothermal energy can be available all the time.