Renewable Energy Technologies Explained
Electricity is an inseparable part of modern life, and almost nothing in the world runs without it. For a long time now, the majority of global electricity demand has been met by fossil fuels , but in recent decades, concerns over greenhouse gas emissions and climate change have inspired a clean energy revolution.
Even though fossil fuel combustion takes up a major share of worldwide electricity generation, renewable energy sources are set to take over our grids in the foreseeable decades, with governments, organizations, and companies across the planet working to secure a green future.
Before we take a deep (slightly technical yet comprehensible) dive into the major renewable energy technologies, let’s touch upon how electricity is generated the traditional, dirty way – fossil fuels.
An overview of conventional fossil fuels
There are three main fossil fuels – coal, oil, and natural gas – formed from millions of years of decomposition of organic life that got buried in the Earth after death. Coal is usually extracted from coal mines, while oil and natural gas come from exploration, drilling, and extraction carried out either on land (onshore) or at sea (offshore).
The basic concept behind fossil fuels is combustion. The burning of coal or oil, for example, creates explosive amounts of heat, which turns water into high-pressure steam. This steam is used to drive a turbine, whose rotating blades drive a generator, thus producing electricity.
Such combustion emits carbon dioxide, among other pollutants, and CO2 is the evil behind everything going wrong with climate change. Our mastery over coal as an energy source and the popularity of energy-dense oil have been the backbone of economic development, powering everything from?early?ships & locomotives to heavy machinery & transportation networks.
The burning of fossil fuels emits carbon dioxide, among other pollutants, and CO2 is the evil behind everything going wrong with climate change.
To this day, fossil fuels are indispensable to our mobility and electricity demands, and over the course of mere decades (from the 1980s to 2014), humanity has released almost 750 billion tons of CO2 – the main driver of anthropogenic (human-induced) climate change and its slew of adverse effects.
Power generation is one of the highest carbon-emitting industries, along with the transportation sector (also driven by fossil fuels, mainly petroleum), and both combined accounted for more than half of all GHG emissions in the US in 2021 . This is driving the demand for non-combusting, clean energy sources to power our future, which is where the following renewables come in.
Solar
Solar radiation from the sun can be converted into electricity in two ways:
Photovoltaics (PV): Also called solar cells, solar PV converts light directly into electricity through the photovoltaic effect, whereby light falling on a single solar cell (made of a semiconductor, usually silicon) generates an electric current. In solar PV, solar modules (assemblies of solar cells) generate the required electricity from solar radiation.
Concentrated Solar Power: Abbreviated as CSP, here, a network of mirrors or lenses reflect and/or concentrate sunlight toward a single point. This concentrated sunlight generates crazy amounts of heat – enough to vaporize water into steam, which is used to drive a turbine attached to a generator, in turn generating electricity. Anyone who’s ever played with sunlight falling on and through a magnifying glass knows the impressive potential of concentrated solar power.
Wind
Wind energy is primarily extracted through giant wind turbines. Strong winds drive the blades of a wind turbine, thus driving a generator (placed in the hub) and producing electricity.??
Wind farms are usually put up in windy areas, either on land (onshore) or on the relatively shallow waters of a sea just past the nearest shore (offshore).
They occupy vast areas of land, as each wind turbine needs to be as far away from the others as possible, so that the incoming flow of wind hits all the turbines unobstructed. Closely spaced wind turbines experience disrupted airflow due to interference from others, thereby reducing efficiency.
Onshore wind farms, located on land, are easier to build and are closer to where electricity is needed. When situated in windy regions, such as on hills or near the coast, they provide reliable electricity for most of the year.
However, wind speeds on land can drop and experience unpredictable fluctuations in strength and direction, so onshore wind turbines are unable to reach their full potential. ?
Moreover, wind turbines are tall, and the rotating blades themselves span 50 meters in diameter in most cases. When hit with fast winds, the blades turn just as fast, generating not just electricity but also a loud, constant hum. This noise can disrupt the lives of communities living nearby.
Many of the above disadvantages are solved with offshore wind farms. The winds at sea are much stronger and more consistent, and they maintain their momentum and direction year-round, which translates to greater power generation than onshore wind.
Also, since they’re based at sea, no community is impacted by noise, and the submerged structures on which offshore wind turbines stand have been implicated in artificial reefs, benefiting marine life as well .
One downside, however, is that offshore wind turbines are difficult to construct; they need to be built and transported to sea, which is a complicated and expensive affair. Any maintenance work also needs to be planned in advance, since unforgivingly strong winds and sea waves both increase the frequency of preventive maintenance/repair work and make it challenging to do so.
Hydro
Hydropower utilizes the massive energy potential of flowing water to generate the required electricity. As of 2023, hydropower accounted for the largest share of the global installed capacity of renewable energy .
Hydropower infrastructure takes three forms:
Run-of-river: This type of facility utilizes the kinetic energy of flowing water directly to drive turbines connected to generators.
Impoundment: Usually consists of a reservoir (or dam) that holds water with the help of underwater ‘gates’. When the gate is closed, more water accumulates upstream of (before) the station. Once open, water is diverted through a tube (called a penstock) to drive a turbine (and thus a generator) before ending up downstream. The gates open and close based on electricity demand, meaning that in times of low demand, the gates remain closed, and periods of higher demand see them open for longer to allow maximum flow.
Pumped storage: Pumped storage is similar to a rechargeable battery. It is a closed system consisting of two reservoirs – one upstream and another downstream. Water from the upstream reservoir flows through a dam (thus generating electricity as planned) and ends up in the downstream reservoir. Water in the downstream reservoir can then be pumped back up into the upstream reservoir, and the process repeats. Obviously, it takes energy to pump water this way – usually provided through excess renewable electricity from an adjacent wind or solar farm. And there you have it – a rechargeable battery charged by the surplus electricity of the wind or solar farm.
Geothermal
Geothermal energy comes from the natural heat near the Earth’s surface. This sub-surface heat is not available everywhere and is only common in specific geological zones, such as at the boundaries of two tectonic plates locked in a turbulent, frictional battle.
Take The Ring of Fire, for example, which is located along the boundary of multiple tectonic plates pushing and sliding against one another. Apart from the regular occurrence of earthquakes, the heat generated is so dramatic that the rock melts and turns into magma, often making its way to the surface in the form of lava and volcanoes.
According to National Geographic, around three-fourths of Earth’s volcanoes sit along The Ring of Fire .
Generally speaking, the molten rock under the Earth’s surface doesn’t always come spewing out with volcanic ferocity. Often, it stays put under the surface, heating up rocks and sub-surface groundwater (aquifers) in the vicinity. This is where geothermal power plants come in.
Most geothermal power plants draw pressurized, superheated water from underground geothermal hotspots. As this naturally superheated water expands under its own pressure and is forced upward into a lower-pressure zone, it gets converted into steam, which is used to drive a turbine-generator setup. Often, the steam turns back into water after doing its job, and this condensation is funneled back into the underground reservoir in a closed, sustainable loop.
Controversial sources: Biomass and nuclear
Biomass and nuclear often get listed under the renewable energy category. But biomass is not really clean, and nuclear energy is not really renewable.
Biomass involves burning dead plant matter and other solid material to release heat, which can be used to generate steam and produce electricity.
Normally, living plants use up the sun’s radiation in photosynthesis, storing energy in the process. It is this energy that gets released when they are burned. Since the sun is renewable and vegetation always grows, biomass is considered renewable.
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"burning biomass releases carbon dioxide and other particulate matter, which can pollute the environment"
Preparing the raw materials to be used in biomass power plants, unfortunately, is anything but straightforward. Any plant feedstock must first be dehydrated and compressed into blocks (briquettes), which can be energy-intensive. Furthermore, burning biomass releases carbon dioxide and other particulate matter , which can pollute the environment.
Coming to nuclear, nuclear power plants are based on nuclear fission. In a controlled reaction, the nuclei of radioactive atoms (usually uranium and plutonium) are excited with an external energy source, causing them to split and release high amounts of energy. This energy is captured to heat up and vaporize water, thus driving a steam turbine to harvest electricity.
The water circulated throughout the reactor serves to keep the system cool and functional. Nuclear fission, apart from being clean and carbon-free, is extremely energy-dense, releasing a huge amount of energy per weight of fuel – several million times greater than fossil fuels .
Coming to its downsides, nuclear fission is extremely risky, as evidenced by history-defining catastrophes such as the Chernobyl disaster, Three Mile Island accident, and Fukushima Daiichi Nuclear Accident.
A failure to control the nuclear fission reaction (e.g., through the unavailability of enough water for cooling) can result in a deadly meltdown, proving fatal to any life in and around the power plant. Also, there is the inevitable problem of dealing with the radioactive waste and by-products of uranium fission.
There is widespread consensus that nuclear fission isn’t even renewable, as it depends on uranium-235, which is a finite resource mined from the Earth.
There is widespread consensus that nuclear fission isn’t even renewable, as it depends on uranium-235, which is a finite resource mined from the Earth – expected to be fully exhausted by the end of the century if current energy trends continue . And with all safety regulations mandated in the construction and operations of nuclear power stations, building one has become discouragingly expensive.
The challenges of renewables
It’s no mystery that fossil fuels are driving and accelerating climate change, be it through power generation or vehicular emissions. Based on a Statista Research Department publication, since 2000, the share of fossil fuels in global electricity production has never dropped below 60% .
Despite the clean and green label of renewable energy sources and the urgency of climate action, why do fossil fuels still dominate?
Putting the complex geopolitical variables aside, there are a number of technological and cost-related hurdles. Solar and wind energy are only as good as the weather, and sunlight and strong breezes come and go. Solar energy plays harder-to-get than wind, as the sun shines only during the day. This is why solar and wind farms are located in sunny and windy climates, and herein comes another problem.
Solar and wind energy are only as good as the weather, and sunlight and strong breezes come and go.
Such ideal locations for solar and wind energy infrastructure are, in most cases, far away from where electricity is needed – cities. Energy transportation thus becomes a wasteful affair, as power transmission lines normally lose at least 6% of the electricity they carry (so longer power lines that tap into remote solar and wind energy farms lose more during transmission).
Also, renewable energy technologies place special demand on the supply of (paradoxically) finite material resources, particularly metals, to build their conversion systems – solar panels, turbines, and generators – let alone the breathtaking amounts of steel and concrete required to lay the foundations of hydroelectric power stations.
The extraction of the above raw materials and production into final products are extremely polluting processes, especially the former.
Energy density is also a major issue with solar and wind. Even though technological advancements continue to make leaps in terms of efficiency and new materials, solar panels and wind turbines are still nowhere near the conversion potential of fossil fuels.
According to estimates by a Stanford University professor in a 2020 Forbes article, if solar and wind were to completely replace fossil fuels, the world would need at least 4 million wind turbines covering an area the size of Germany, in addition to solar panel installations spread over a region the size of Greece .
Now let’s talk hydro. Hydropower accounts for more than half the total renewable energy capacity.
Hydroelectricity is often deemed a reliable source of renewable energy, as opposed to solar and wind energy. However, the construction of the infrastructure that taps into the impressive potential of water reflects a disregard for the site’s local communities as well as nature.
Large-scale projects so far have brought clean electricity and benefits to a substantial number of energy-deprived households. But the net environmental and social impacts involve an overall detriment to ecosystems and people.
A few environmental and social implications of hydroelectricity are as follows:
Case study: Three Gorges Dam
As a case study, let us consider the construction of the largest hydroelectric power plant in the world – China’s Three Gorges Dam. This truly massive engineering marvel became fully operational by 2012 and has the potential to power more than a million households for a month with just an hour’s worth of power generation.
Although widely lauded for its impressive scale, the project has become known as one of the most controversial renewable energy projects globally (not unlike other sizeable hydroelectric power stations worldwide).
Since the start of its construction in the mid-1990s, more than a million people were displaced from their lands, and their homes were demolished to make way for the Three Gorges hydropower complex, leading to communal fragmentations and livelihood losses that were never adequately recompensed by authorities. The relocation of these displaced communities negatively impacted their ability to earn fair wages.
In terms of its environmental impact, the water upstream of the Three Gorges Dam has been worsening erosion along the banks of the Yangtze River and the base of its two cliffs on either side. This erosion, combined with changing water levels, has been implicated in the occurrence of fatal landslides on several occasions.
Green hydrogen – a gamechanger for transportation
On a concluding note, we look into the exciting prospects of the wonder fuel of the future – green hydrogen. Hydrogen is one of the most abundant elements in the universe, and one of its greatest benefits to humanity lies in mobility – e-mobility, to be more accurate.
Conventional battery-powered electric vehicles (BEVs) are marketed as green, clean, whatever. But this is far from the case. The Lithium-ion batteries powering EVs carry troubling secrets that never get public attention. To be honest, what’s true of Lithium-ion battery production is true for most manufacturing in general – polluting extraction processes, inhumane labor, and others.
The thing with EVs is that you need to charge the vehicle regularly, and that requires electricity. If you live in a place where most of the electricity in the grid comes from fossil fuels, EVs are no better than traditional engines.
The sustainability of EVs really depends on where you use them. Driving an EV in countries like Iceland (whose electricity comes almost entirely from renewables) is way more sustainable than in the US or India (where most electricity is still of fossil fuel origin).
"a true breakthrough for transportation is destined to come from hydrogen"
But Lithium-ion batteries are still not that energy-dense and are made from a finite resource (Lithium). Sodium-ion batteries could solve the resource scarcity, as Sodium is much more abundant in the Earth’s crust than Lithium, with considerably improved energy density and lifespan. But a true breakthrough for transportation is destined to come from hydrogen.
Hydrogen fuel cells form the heart of hydrogen-powered vehicles. The basic operating principle of a fuel cell electric vehicle (FCEV) can be explained as follows: the chemical energy contained in hydrogen (along with oxygen from the air) is used to produce electricity and water.
The inner workings of a fuel cell are a bit tricky and demand a long, detailed explanation, but this video explains it well. What’s important to note is that hydrogen fuel cells are much more efficient and energy-dense than batteries, and they have a significantly greater lifespan.
Hydrogen does not occur in raw form naturally and must be isolated into a usable fuel. Traditionally, hydrogen is created from a CO2-emitting process called steam methane reforming, which uses natural gas and steam.
This method releases carbon dioxide as a by-product, so the resulting hydrogen is dubbed grey hydrogen. Nowadays, the CO2 released during this very process is captured and stored deep underground (carbon capture and storage, or CCS), so hydrogen produced in this manner is called blue hydrogen.
Green hydrogen comes from the electrolysis of water to separate the hydrogen and oxygen atoms. Electrolysis requires electricity, and when this electricity comes from renewable energy sources, the hydrogen is termed green hydrogen. The concept of using renewable electricity this way (or even other purposes, such as direct electrification for EVs) falls under the umbrella term ‘power-to-x’.
Green hydrogen is truly as groundbreaking and versatile as it sounds, but an almost negligible percentage of hydrogen is green hydrogen (most of it, more than 90%, is still grey or blue). If green hydrogen became the dominant norm, the opportunities would be endless, as hydrogen can help decarbonize so many sectors , including the hard-to-abate steel industry and long-haul, heavy-duty transport.
Conclusion
So there you have it – the range of innovative renewable energy systems and an emerging, planet-saving fuel to power a low-to-almost-no-carbon future. A transition to 100% renewables is certainly beyond challenging, requiring careful attention to a range of stakeholders and socio-political considerations.
But the combined potential of renewables and green hydrogen would mean carbon-free electricity & transportation – two sectors that account for the majority of carbon dioxide emissions globally. Decarbonize these and we’re more than halfway there already.