This is an introductory type guide to renewable energy.
In this guide, we outline and explain:
– What renewable energy is
– What some of it’s main uses might be across society
– The main types of renewable energy, along with examples
– Why different renewable energy sources might be considered renewable
What Is Renewable Energy? (A Definition)
Renewable energy might be generally described as energy that uses resources that are either essentially infinite because of how abundant they are, or, that they are replenished/renewed faster than they are consumed.
This may mean that these resources don’t face resource depletion issues.
It might be worth noting that, just because an energy source is renewable, it doesn’t mean it’s completely sustainable or eco friendly.
Renewable Energy vs Non Renewable Energy – What’s The Main Difference?
In comparison to renewable energy sources, non renewable energy sources may come from finite (scarce) resources, that are consumed faster than the rate at which they form or replenish in nature.
As a result, they may be subject to resource depletion issues.
Common examples of non renewable energy sources are fossil fuels – coal, natural gas, and crude oil.
Fossil fuels are finite, and can take millions of years to form in nature (whereby organic matter, such as the remains of decayed plants and animals, are exposed to heat and pressure, and eventually form into fossil fuels)
According to some reports, uranium may take even longer to form than coal, natural gas and oil.
For example, different research suggested nuclear may have formed in one or more supernovae, or, in the merger of neutron stars.
Processing & Refinement Of Resources
Something else to note about non renewable energy sources, is that resources like coal, oil, natural gas, and even uranium, usually have to be processed or refined in some way before they can be used.
Renewable energy sources generally don’t require processing or refinement – for example, sunlight, wind, and water don’t require processing or refinement before they can be used to generate electricity.
How Much ‘Non Renewable’ Resources Used For Energy Might Be Left
Lastly, some people question how many more years some ‘non-renewable’ resources used for energy might last.
We’ve also previously written a separate guide about how/why we might not run out of some mined resources (like some fossil fuels) in the future.
What Is Renewable Energy Used For?
Renewable energy can also be used for:
– Heating and cooling (such as space heating and cooling)
– Transport (for power or fuel)
Types Of Renewable Energy (& Examples)
– Main Types Of Solar Energy Systems
Solar PV (photovoltaic)
Solar Thermal, of Solar CSP (Solar Concentrated/Concentrating Solar Power)
Solar PV is the main type of solar energy system used for solar energy across different metrics like installed capacity, electricity generation, and so on
Solar CSP/Thermal is another type of solar energy technology
Three of the main types of solar thermal plants are Linear Fresnel, Tower, and Dish and Trough
– Solar PV vs Solar CSP: Other Main Differences
Solar PV might mainly be used for electricity generation (on a utility scale, on rooftops, at households, and in standalone applications)
Solar CSP might mainly be used for electricity, or heating water
Dispatchability, and also generating electricity while the sun is down, are two of the potential main benefits of Solar CSP over Solar PV
irena.org mentions that ‘One of the main advantages of a CSP power plant over a solar PV power plant is that it can be equipped with molten salts in which heat can be stored, allowing electricity to be generated after the sun has set’
On the other hand, Solar PV is used at a much larger scale than Solar CSP (Solar CSP makes up only a small % of installed capacity and electricity generation comparatively)
When They Can Be Used
Solar PV can only be used when the sun is out, whereas Solar CSP doesn’t always have this limitation
[Solar CSP] provides a dispatchable energy supply – that is, their power output can be adjusted based on grid demand.
This makes them more flexible than traditional solar PV plants.
Solar CSP might face more barriers to growth and implementation than Solar PV
On a household and individual level, greenmatch.co.uk mentions some of the cost, efficiency, flexibility and other differences between the two technologies at greenmatch.co.uk
– Main Types Of Wind Energy
And, onshore wind farms are located in inland areas
But, offshore wind farms are used in some locations, and may grow in the future
Offshore wind farms are located in bodies of water, such as the ocean, or even fresh water sources (like lakes, fjords and sheltered coastal areas)
wikipedia.org indicates that offshore wind farms are usually constructed ‘… in the ocean on the continental shelf’
– Onshore Wind vs Offshore Wind: Other Main Differences
Efficiency & Power Output
Offshore wind turbines might be more efficient than onshore wind turbines, and have a higher power output, because of higher wind speeds, greater consistency of wind, and less physical interference from land or human-made objects
wikipedia.org indicates that (paraphrased) the cost of offshore wind power has historically been higher than that of onshore wind generation, but the cost might be becoming more price competitive recently in some regions (such as Europe)
Design & Construction Of Turbines
The types of wind turbines used in the ocean and different bodies of water also have to be designed and constructed to function adequately in these environments
But, a list of those different hydro energy setups and power plants include:
Hydroelectric dams (also called ‘impoundment facilities’)
Run of river (also called ‘diversion’)
Pumped hydro storage
In addition to the above main forms of hydro energy, there are some developing forms of hydro energy too.
One example is companies that are developing technology to utilise the slow moving water and flat water (which makes up a large % of water on Earth).
In the past, utilising energy from this type of water hasn’t been commercially viable.
Geothermal power plants (on the utility level)
Geothermal heat pumps and other geothermal systems (on the residential level, or in buildings in general)
There’s different types of geothermal power plants, such as dry steam, flash steam, and binary cycle plants.
They may each make use of either steam/vapor or water differently, or, they may each convert geothermal energy to power differently.
There’s also different types of geothermal systems that can be installed in houses and residential or commercial buildings.
Biomass & Bioenergy
For example, sugar and food crops might be one major category of biomass, whilst wood might be another.
Algae is a newer type of biomass that might be used for biofuels.
Biomass can be combusted directly for electricity, or heat. This might be the traditional way to use biomass for bioenergy.
However, newer technologies can refine biomass for biofuels (for transport), for biogas, and other uses.
Other Notes On The Types Of Renewable Energy
eia.gov considers the five major types of renewables energy to be (paraphrased) solar energy, geothermal energy, wind energy, biomass from plants, and hydropower
How The Different Types Of Renewable Energy Work
For Solar PV …
A photovoltaic system like a solar panel uses solar cells/PV cells to absorb solar radiation/sunlight, and this sunlight is converted into electricity
The general process for Solar PV, in order, and paraphrased from vivintsolar.com and weforum.org, might include:
1. Sunlight (which is composed of light photons) hits solar cells (usually in a solar panel)
2. The solar cells (using the semi-conductive material silicon) convert sunlight into an electrical current which is DC electricity
3. The DC electricity is fed into an inverter that turns DC energy into AC electricity, which can then be used for everyday applications
4. Electricity may either be used directly, stored in an energy storage battery, or, fed back into the grid (if it’s tied to the grid)
For Solar CSP …
Solar thermal technology uses the Sun’s heat energy/thermal energy (radiation) for:
Heating (to heat water for example)
And, it can also be used for desalinating water
A paraphrased summary of how Solar CSP can work, from wikipedia.org, sciencedirect.com, cleanenergycouncil.org.au and irena.org, might be:
Solar CSP uses mirrors (lenses and reflectors) to capture the Sun’s thermal energy (infrared radiation) to heat a (thermodynamic) liquid or an oil, create steam, drive a heat engine/generator, and generate electricity
– What Equipment Wind Energy Uses
Wind energy mainly uses wind turbines
Wind turbines can come in different types and sizes (with different sized turbine blades and rotors too)
– How Wind Energy Works
Wind turbines capture mechanical energy from wind
Wind turns the turbine blades, and electricity is generated with a generator
Another way to explain the above is …
Paraphrased from irena.org, eia.gov, and weforum.org, the general steps to create electricity from wind energy might be:
1. Kinetic energy from wind hits a wind turbine’s blades
2. The blades get spun (kinetic energy is turned into rotational energy), and they spin an inner rotor i.e. the blades are connected to a drive shaft in the turbine
3. This drive shaft is connected to an electric generator, and the electric generator creates electrical energy (AC electricity)
– Factors That Can Impact Wind Energy
Offshore vs Onshore
Whether the wind turbine is offshore or onshore
The Type Of Wind Turbine Used
i.e. whether it’s a horizontal or vertical axis turbine, it’s size, the dimensions and length of the blades, the dimensions of the rotor, and so on
irena.org indicates that ‘Theoretically, when wind speed doubles, wind power potential increases by a factor of eight’.
Wind speeds and strength might be higher at high altitudes as well
Consistency Of Wind
i.e. how often it is blowing
Energy efficiency for wind energy might refer to how much energy one wind turbine can capture.
Power output can refer to how much power one wind turbine can generate in a given time period
All of the above factors might impact energy efficiency and also power output.
Hydro energy uses the mechanical energy from water.
Why The Different Types Of Renewable Energy Are Considered Renewable
Solar energy comes from the Sun.
Most reports indicate that the Sun is going to last for billions more years.
… the Sun is going to last for roughly another 5 billion years (theconversation.com)
In sunny areas, and on days where it isn’t cloudy, the Sun is available for most of the day before it sets.
Wind energy comes from the wind.
Wind is a result of the movement of air or the creation of air currents, which are caused by the uneven heating of Earth’s surface (on land and on water) by the Sun, along with other factors.
As we mentioned above, the Sun is expected to last billions more years, so, this natural process of wind being created might continue for at least that amount of time into the future
In areas with wind, the wind is generally available during both the day and night i.e. for most hours in the day.
Hydro energy comes from water.
Water on Earth comes from, and is replenished by the Earth’s hydrologic cycle (also known as the water cycle).
This is a natural process whereby water is continuously cycled or exchanged through a cycle of stages across the Earth’s land, ocean and atmosphere.
As long as this process continues in a particular geographic location on Earth, water will continue to renew, and be available to use for energy.
Hydro energy is generally available as long as a geographic area continues to receive an adequate amount of rainfall or snow (where snow melts and becomes water) needed to operate certain hydro energy projects.
Hydropower is called a renewable energy source because it is replenished by snow and rainfall. As long as the rain falls, we won’t run out of this energy source (lsa.colorado.edu)
wikipedia.org mentions that hydroelectric plants can have a ‘… varying electricity [output] because of variances in water availability and flow …’
hydropower.org mentions that for run of river setups: ‘… As long as the river is running, it provides a continuous supply of electricity (base load)’
hydropower.org mentions that for pumped hydro storage, it ‘Can operate independently of an inflow of water for weeks and months’
Geothermal energy comes from the heat (thermal energy) in the Earth’s core, which is available at the crust of the Earth
This heat comes from very hot water, or very hot steam, found in dry steam wells or hot water wells (which are also called reservoirs)
This water or steam can sometimes be accessed by drilling holes too
Geothermal energy will likely continue to be available as long as the Earth exists, as the Earth’s core will continue to radiate heat. There’s a lot of thermal energy in the Earth’s core.
Geothermal energy might generally be available all the time, as long as access to heat can be achieved (at reservoirs and other locations).
‘Reinjection’ is also a technique or method used to prevent hot water reservoirs from depleting.
Even in geothermal areas dependent on a reservoir of hot water, the volume taken out can be reinjected, making it a sustainable energy source (energy.gov)
Tidal energy utilizes tides and currents in the ocean
High and low tides are a result of the Moon’s gravitational pull on the Earth, and also the Earth’s rotational force.
This is a natural process that can continue indefinitely, or, as long as the Earth and the Sun are in existence.
The future of the moon seems to be closely tied to the future of the Sun (futurism.com)
There might be multiple high and low tides in coastal areas every 24 hours.
Tides might also be reasonably predictable.
Waves come from the wind blowing across the surface of ocean water
As we mentioned above, wind currents are a result of the Sun’s radiation and heating on Earth’s surface.
These are natural processes that can continue indefinitely.
Although wave conditions can be predictable, where and when waves will be available can be less predictable in a given area.
Wave patterns and creation can depend on the consistency and force with which wind blows across the water’s surface
Biomass & Bioenergy
Bioenergy can come from different types of biomass.
Biomass is organic matter, and organic matter gets it’s chemical energy from photosynthesis from the Sun.
Some types of organic matter can be replenished faster than they are consumed.
Additionally, organic matter is reasonably abundant.
Some types of bioenergy may have somewhat of an asterisk against them though, because if they involve bio-crops, there can be a question to how resource intensive they might be (using land, water, fertilizers, pesticides, and so on), and how sustainable this might be long term.
There’s also the potential environmental impact of growing biomass, combusting it, refining it, and so on.
Pros & Cons Of Renewable Energy
1. Various ‘Better Meets Reality’ guides
33. https://www.iea.org/wei2018/ (includes figures for auction amounts of onshore and offshore wind)
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