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This paper was a collective effort of Pavi Dhiman, Shiza Charania, Bagavan Marakathalingasivam and I
One of the biggest lessons that we’re taught growing up is that nothing is forever. Things come and go and that is the process of life. However, there are some major exceptions to this and that is energy.
Understanding Energy
Energy is one of the few things that have been constant since the dawn of time. It first began with the sun and with the Industrial Revolution cam coal, steam power engines and this continued. Now we’re here in the modern era where energy is found in abundance, however, as the population of the human species increases, so has the energy consumption. We are currently burning over a million terajoules of energy daily.
There are a variety of ways of producing energy, but the most abundant types are detrimental to the environment, including nuclear and fossil energy; as they heavily rely on oil, coal and natural gas. Not only do they negatively impact the environment, but they are also expensive to build, in fact, it costs about $9B to build a nuclear power plant.
That’s a lot of money for a power plant that is taking a massive toll on our planet.
The status quo has many pressing issues, the main one being a lack of cheap and low carbon-producing energy. The overarching term to describe all these issues is climate change. This term is thrown around a lot, but the climate crisis is directly correlated to the way we produce and use energy on a day-to-day basis; the production of energy is responsible for 87% of global greenhouse gas emissions. However, this stat only tells us one side of the story as the energy industry is facing decades of transformation. There are 2 major problems that the world faces today: the majority of our energy production creates a lot of greenhouse gas emissions and millions of people worldwide lack access to energy.
Problem 1: Energy Poverty
This problem is directly correlated with the left side of the graph above. The countries in low-income countries tend to have lower emissions. In actuality, US citizens emit more CO2 in 4 days than people in low-income countries do in an entire year all because people in low-income countries don’t have access to modern-day technology and energy. This problem is coined under a rather popular term called energy poverty. The graphs below prove this point further.
This lack of energy and technology access has led to some of the worst problems that the human race has faced. Looking at the graphs below, it’s evident that when it comes to access to sources for cooking and heating, they have been relying on solid fuel sources; this includes firewood, dung and crop waste. This is a foreign concept to individuals living in developed countries. Although this is a makeshift way to produce food, it comes at a detrimental cost for those living in energy poverty. This results in indoor pollution; the World Health Organization (WHO) has described this as the “world’s largest single environmental health risk.” This is a huge problem for those living in low-income countries as it is the largest risk factor for early death; in fact, it is responsible for over 1.6 million deaths every year. Using wood as a primary source of energy negatively impacts the surrounding environment as well. Poverty is often linked with deforestation and relying on fuelwood is one of the key reasons for this link. In these low-income countries, specifically in East, Central and West Africa, more than half their energy is supplied by fuelwood. These factors are huge contributors to the overarching problem of energy poverty.
Problem 2: Rising Greenhouse Gas Emissions
As mentioned previously, the problems with energy have 2 sides.
The second problem is one that is discussed a lot and it’s related to the right side of the first graph; greenhouse gas emissions are simply too high. (Graph is below for reference).
We touched on how the emissions are relatively low for low-income countries earlier. There must be a greater focus on the richer countries. In Europe, the richest 1% produce 43 tonnes of CO2 every year; this is 9x as much as the global average for global greenhouse gas emissions. To avoid misconceptions, it’s not just the rich that are contributing to the overarching problem of climate change. The majority of the world’s population is responsible for this, but the rich have a larger contribution to the problem.
When discussing climate change, the Paris Agreement is almost always brought up. The goal of this agreement is to keep the increase of the average temperature below 2 degrees. In order to reach this goal, current energy production methods must slowly reach the net-zero emission mark.
The word poverty is often associated with poorer people and countries, but even high-income countries often suffer from energy poverty. There are very few countries that are close to zero; those countries happen to be those that suffer from energy poverty. These countries that meet those standards are located in Africa: Malawi, Burundi, and the Democratic Republic of Congo. To make matters worse, currently developed countries only make up ~15% of the world’s population, but when it comes to energy consumption, they consume over 75% of worldwide primary energy.
Overall, these problems are major contributors to the overall energy problem that exists in our world.
The Future Projection of Energy
To get around these problems with energy, it’s important and necessary to understand what the future of energy will look like. Our current methods of generating electricity and energy through fossil fuels are something that we need to move away from.
So what will the future look like?
Companies are bound to still produce fossil fuels in 2040, but there’s going to be a rise in the renewable energy sector. It’s expected that almost 70% of the world's energy will come to form renewable sources; this also means that nearly 80% of the carbon emissions will be cut from the air. There must be key changes to be made, but to understand these changes, we need to look at future trends. There are a couple of key trends that will transform the energy sector; these trends will change the way we produce energy.
Decarbonization
This trend is one of the most talked-about trends in the modern world; it revolves around transitioning into a world where the use of carbon-free energy is encouraged and promoted. As mentioned earlier, in order to reach the goals set by the Paris Agreement, countries will have to adopt energy production methods that have a net-zero carbon emission rate.
Carbon reduction has been a hot topic in the energy sector for quite a while.
The emphasis on cutting carbon emissions is going to prompt businesses in all sectors to cut down on their emissions. There are many new carbon-reducing technologies that are breaking into the market that businesses can make the most of. The term electrification gets thrown around when the topic of decarbonizing comes up. For clarity, this would mean switching to electric vehicles. At the moment, fossil fuels are dominating the market and the energy sector; in the United States, fossil fuels are responsible for over 60% of their electricity generation.
So…What’s Next!?
In order for us to become emission-free, the solution is simple, renewable energy sources. This includes wind, solar and biofuels. Leveraging the utilization of these sources of energy has the potential to eliminate over 7 million deaths from air pollution and global warming. However, as promising as this sounds, there are major limitations with each source of energy. The main problem with current renewable energy production methods is that they aren’t consistent for 24 hours. There are periods when they produce more energy than others.
What I want to focus on is the future of wind energy. Wind energy has been an emerging source of energy worldwide and currently is able to provide over 16 million houses in the United States with energy. It’s also expected that Wind Energy alone can cut out over a 1/3 of global annual carbon emissions by 2050.
The big question is…if it has all this potential, why aren’t we making the most of it right now…?
Breaking-Down Wind Energy
Before jumping into the major flaws of wind energy, it’s vital to understand how wind turbines actually work.
The overarching goal of wind turbines is to convert Earth’s natural wind into electricity. The way a wind turbine converts wind energy into electricity is through the use of the aerodynamic force from the rotor blades of the wind turbine. They are made up of many airfoil cross-sections that consist of different sizes and shapes from the root all the way to the tip. These airfoils employed by the blades make the wind turbines turn. As the wind flows, the pressure on one side of the blade decreases. This imbalance that is generated creates lift and drag. In other words, a lift force is produced when a fluid moves over the airfoil.
Through this lift force, the wind turbine is able to rotate. The rotation of the wind turbine isn’t directly connected to a generator as these turbines have a very low rate of rpm (rotations per minute). If we were to connect the blade to a generator, we wouldn’t be able to generate much electricity and it would be a huge waste of money and space. However, to ensure that this doesn’t happen, the blades are connected to a gearbox. Within this gearbox, the speed is increased through the use of a planetary gear set arrangement. By using this, a high-speed ratio is produced; this ratio is approximately 1:90. There’s also a brake in the nacelle to ensure that during windy conditions, wind turbines don’t over-generate electricity and break down. Following this, power cables are connected all the way to the base. At the base of the wind turbine, there’s a transformer that acts as a connection between the wind turbine and the overall distribution grid.
Now that we have a rough understanding of how these wind turbines work, let’s look at the 3 biggest problems with them.
Problem #1: Efficiency
Out of all the major drawbacks of wind turbines, their poor efficiency is what is stopping wind turbines from being our sole source of energy supply. For context, wind efficiency is essentially the amount of kinetic energy in the wind that is converted into electricity that we can use. However, there are limitations to how efficient wind turbines can be due to the laws of physics.
The laws of physics that prevent wind turbines from being efficient is called Betz’s Limit. This limit says that the maximum efficiency of a wind turbine is 59.3%; this is a theoretical limit. However, this number is a theoretical value and most wind turbines only reach an efficiency between 25 and 45%. Wind turbines can’t be 100% efficient/extract all the energy from wind as that would mean that the wind velocity would be reduced to 0. With no velocity in the wind, the air/wind particles would all pile in the surrounding area of the wind turbine.
Another major drawback is that it’s not possible for a wind turbine to convert all 59.3% of the kinetic energy into electricity. In this conversion process, some of this energy is lost. This is due to the way that the modern day generators are produced and engineered. On average, a generator is able to convert about 80% of the total kinetic energy that a wind turbine captures. To understand this from a mathematical perspective, if the wind turbine captures 50% of the available energy and the generator converts 80% of that: 0.5 x 0.8 = 0.4. This would mean the wind turbine is only 40% efficient.
Problem #2: Cost
Another major drawback is how expensive a single wind turbine is. On average, a commercial wind turbine (2 megawatts) costs anywhere between $2.6–$4M. The typical cost is $1.3M per megawatt of electricity producing capacity. The costs of the wind turbine increases as the size of the wind turbines increase; wind turbines have an average height of 280 feet.
The upfront capital cost of wind turbines makes up about 84% of the total installation cost. In the pie chart above, here’s a more in-depth breakdown of the categories:
- Turbine Cost: this includes the blades, tower and the transformer
- Civil Works: this is the construction costs that are needed for on-site preparation and the foundations of the tower as well
- Grid Connection Costs: This includes the transformations, substations and the connection to the local distribution network
- Other Capital Costs: these costs can vary; includes construction of buildings, control systems and project consultancy costs
For these turbines, the biggest components are the rotor blades, tower and the gearbox. Putting these 3 items together, they can account to anywhere between 50% and 60% of the turbine cost. The rest of the items make up for a total of 13%. Overall, the turbine itself can cost between 64% and 84%; the grid connection, civil works and other costs account for the rest.
Along with these initial costs, there are manufacturing costs as well. Per wind turbine, it costs about $42000-$48000 to maintain annually. However, this number doesn’t stay consistent throughout the life span of a wind turbine; it increases as the wind turbine ages. This is because the wind turbine wears down due to the harsh environments and weather conditions they often face. The maintenance cost is broken down further into 6 costs:
- Insurance
- Land rent
- Service, repair and spare parts
- Administrative tasks
- Power
- Miscellaneous
Problem #3: Space
The third major problem with a wind turbine is that they require a lot of space. On average, a single wind turbine requires 1.5 acres of space. To put this into context, that’s about a football field, just for a single wind turbine. The scary part is, wind turbines are only going to continue growing in size and taking up space. Since 2000, wind turbines have been growing in height and blade length.
Another factor that impacts the amount of space a wind turbine takes up is its hub height. The hub height is the distance from the ground to the middle of the turbine. This contributes greatly to how much space a wind turbine takes up. The hub height has increased 59% since 1999; as of 2020, the hub height is about 90 meters. To put this into perspective, that’s as tall as the statue of liberty. Research has shown that the hub height for offshore turbines is projected to grow even taller to almost 150 feet.
These turbine towers are growing in height to capture more energy; as the altitude of the blade increases, the wind speeds increase. However, in the future, the energy demand is going to increase and it’s not going to be sustainable to increase the height of wind turbines. This will lead to higher costs and an imbalance in the energy sector.
Introducing Off-Wind Energy
At Off-Wind Energy, we’re leveraging 3D and 4D printing to create adaptive off-shore wind turbines that provide a 7.8x increase in efficiency, while also reducing costs by over $5 000 000.
Understanding Floating Off-Shore Wind Turbines
First of all, what even are off-shore wind turbines?
As mentioned earlier, wind turbines are huge! This means if we wanted to implement them, we’d have to use a lot of potential lands that could be used for so much more. This is where offshore wind turbines come in. You see, the surface of Earth is only 29% land, and with the amount of infrastructure needed to power cities, it’ll be really hard to fit extra wind turbines in there. But what about the rest of the Earth? You see, 71% of the surface is made of water, so why can’t we just put wind turbines there? That would essentially get rid of the whole spacing issue, right?
That’s exactly where offshore wind turbines come in.
Off-shore wind turbines are a new source of renewable energy that uses wind turbines placed off-shore to generate electricity. Off-shore wind speeds are usually faster than on land, which would increase energy production (they can be as large as 12 MW). Offshore wind speeds are usually steadier than on land, which makes it a more reliable source of energy.
Now, there are different methods that are used for implementing these turbines:
- Mono Pile: These off-shore turbines are held up by a steel pile driven 10–20m into the seabed. They tend to place these in shallower waters/next to the water
- Gravity: This the most common of the foundations, as it uses a large concrete/steel base that rests on the seabed and relies on gravity to hold it up
- Tripod: Involves the use of tripod piles which are generally driven 10–20m into the seabed (dependent on the soil conditions). They are designed for deeper waters, however, haven’t really been used too often
The current problem with these current methods is that up to 80% of the world’s offshore wind resource water is deeper than 60m, which means that all of these are almost useless.
That’s exactly why floating off-shore wind turbines, are the way to go
Floating offshore wind is an emerging method based on floating structures, which allows us to reach depths far greater than 50m — allowing us to be able to use the full 100% of offshore resources. Now, these wind turbines are over 100 metres high and weigh thousands of tons…. how are we going to get them floating? The solution involves a little bit of middle school science.
These floating wind turbines use floating offshore wind platforms (FOWP), which are concrete/steel/hybrid structures that provide buoyancy and stability to wind turbines. These ‘floating structures’ are then established by moorings and anchors which will distribute the masses/weights.
There are different types of platforms to help maintain stability:
- Barge: The beam and length (length and width) of the object are significantly larger than the draught (height) — mimics the structure of a ship. Since the floating platform has a large surface area when contacting with the water, it gives more stability to the overall structure.
- Semi-submergible: This design focuses on maximizing the volume, while still minimizing the surface area exposed to water — causes displacements of the mass of water and provides buoyancy. Technically, this would be a sphere but obviously, that isn’t practical to manufacture so the volumes are divided into multiple vertical cylinders, joined by beams and braces to create the surface that the turbine can be installed. The stability is dependent on the size and distance between them.
- Spar: Most of the weight is placed at the lowest point to provide its stability. The buoyancy is provided through the geometry of the cylinder, while its stability is done through the weight at the lowest point. So, as the turbines become larger they require longer cylinders for the weights (which is difficult when it comes to manufacturing)
- Tensioned Legs Platform (TLP): This type of design doesn’t really float once the turbine is installed. The geometry of 3–5 arms reduces the volume of each of the arms, therefore, the platform floats without the turbine installed. To prevent the structure from turning over due to the center of gravity rising (before instillation), reusable floats are attached to the TLP platform which can allow towing to the offshore anchorage sites. Then the cables/tendons are connected and the structure floats.
The choice between any of these types of floating platforms depends on the sea and seabed conditions, wind speeds, size of the turbine, depth of the harbours, etc.
Our solution uses the Semi-Submersible Turbines.
Even though we’re combatting the problem with space, one of the bigger problems we mentioned previously was the inefficiencies of current wind turbines. A core reason for this is because wind conditions constantly changing, and so most turbines can only operate at 25–65% of their maximum capacity.
That’s exactly, why the next part of our solution involves the use of 4D printing to create adaptable blades that can adjust for the wind conditions… without any sensors/external motors.
Mimicking the Structure of a Plant-Leaf to Enable Adaptive Blades
This sounds super complex, but let’s break this down.
Earlier, we touched on a concept that prevents wind turbines from being efficient and that was Betz’s law. Essentially, this law prevents the efficiency of the turbine from crossing 59.3%, this is the max efficiency a turbine can operate at. This is primarily due to the geometry of the wind turbines and that is exactly what our solution tackles.
Understanding Adaptive Blades
In the last couple of years, the energy demand has been on the increase. To match this expectation of the consumer, wind turbines have been increasing in size to increase the amount of energy that can be captured by a single turbine. However, this decision has many repercussions, such as increased costs and a negative impact on the environment.
To get around this issue, there have been talks and discussions of smart/advanced wind turbine blades that can control themselves; this would get rid of the need for a control system. Theoretically speaking, if turbines were to make these changes, the loss would go down and more energy would be produced, this results in these turbines being economically sustainable in the long run.
So far, there have been 2 types of adaptive blades that have been considered: bend-twist coupling (BTC) and sweeping. The one that our solution employs is Bend-Twist Coupling. The goal of bend-twist coupling (BTC) is to improve the aeroelastic response of wind turbine blades. BTC can be used to lower the fatigue loads on wind turbine blades.
BTC can be achieved in 2 manners: passive and active. In an active manner, the controllers and electromechanical systems are put in place to change the blade shape. In a passive manner, anisotropic properties are used so that during operation (wind loads), the BTC can be observed/seen.
Flexible Wind Turbine Blades
On the other hand, we have flexible wind turbines; they serve the same purpose as adaptive wind turbine blades: to help wind turbines maximize efficiency and adapt to changing weather conditions. Recently, fluctuations in the power supplied by wind turbines have been reported in California. In the report, they outlined that insects and contamination resulted in lift loss, which essentially reduced the amount of energy being produced.
Flexible wind blades are elastic and they adapt in accordance to the direction of the wind. The more accurate term to describe this adaptation is deformation. There are 2 categories the deformation that can fall into, pre-bending deformation and pitch angle change.
Pre-bending deformation is in the direction of the wind and it was made to help solve the tower clearance problem within wind turbines. Pre-bending deformation helps ensure that there’s enough distance between the blade and the tower during operations. But the key benefit is that the blade loads are reduced and the aero structural efficiency is significantly improved. The second type of deformation was pitch-angle change. This proposed deformation is to help increase the efficient working zone of the wind turbine.
Our Solution
Now that we’ve gone over the main ways wind turbines can adapt to changing weather conditions and wind speeds, let’s go over the solution and structure that we’re proposing. To get around Betz's law, we’re going to create plant leaf-mimetic wind turbine blades.
Those are some big words, but let’s break them down
Let’s rewind a bit, how do we know that mimicking the structure of a plant leaf onto a wind turbine will actually work?
Research has shown that there are lots of similarities between the structure of plant leaves and current wind turbines.
Environment
The plant leaf and the blade are both made to operate in a natural environment. By operating in a natural environment, both are exposed to the adversities and inconsistencies of nature, specifically the wind speeds and loads.
The Inner Topology Structure
The plant leaf consists of 2 primary veins: the principal vein and the lateral vein. The lateral vein is located symmetrically at the bi-lateral of the principal vein. On the other hand, wind turbines are made as spanwise spar. The spar is the main structural portion of the wing/blade, it goes spanwise at 90 degrees (right angels). The spar carries the loads and is composed of shear webs and a composite skin structure. This structure is similar to the topology pattern of a plant leaf.
These similarities are a reflection of how effective plant leaves can be when dealing with environmental stresses. This comparison also proves how plant leaves can be used as a blueprint to design future wind turbine blades to maximize the efficiency of wind turbines.
Now that we know plant leaf structures can work, let’s jump into understanding how they work
Understanding the Structure of Plant Leaf Veins
Plant leaves are grown in a manner that they are able to sustain their psychological abilities while also adapting to the different environmental stresses they face in their life span. This plant leaves consist of many leaf veins and their structure is essential to adapt to environmental stresses. The veins of plant leaves have evolved into a self-optimizing architecture based on their genetic code. This genetic code is a result of billions of years of evolution; nature has organically created complex and ingenious topologies for solving many structural/engineering problems and improving the design of structures in our everyday lives. Despite the exciting nature of these biological systems, there have been some difficulties finding the growth process of branching patterns. The status quo of approaching this type of modelling is through case studies as modelling them by hand would be highly inefficient. The leaf veins are living organ that has a psychological function, but can also adapt to a variety of different environmental loads. By doing so, it is able to evolve itself into the optimal structure with 2 major structural patterns: (1) medial axis pattern and (2) closed-loop pattern.
The morphogenesis of leaf veins is classified as 2 different growth processes. (1) A continuous growth process which includes sprouting, branching and degenerating. This allows for a complicated dichotomous hierarchical system to be formed. (2) The second is a continuous optimization process where both the growth rate and direction are adjusted so it can make it possible for the layout of the leaf to be purely dependent on the surrounding environment. This leaf vein structure that is able to self optimize and adjust to environmental stresses is key to improving the efficiency of wind turbines as they are under environmental stress (wind loads) for prolonged periods of time.
Moving on from the self-optimization portion, the next biggest thing is the medial axis pattern that plant leaf veins consist of. This is a phenomenon in almost all biology, this phenomenon was explored in the section above. Essentially, the medial axis skeleton forms the composite structure that has the primary function of supplying reinforcement. To prove this understanding, an experiment was conducted to explore the mechanical property and bionic study of compliant structures of plant leaves.
In this experiment, 5 fresh and mature leaf samples were taken; each of these represent the typical leaf network within nature. A total of 6 samples were taken: ficus altissima, pineapple, kemirinoten, madagascar palm, ficus viren, and royal palm. These plant leaves seem chosen at random, but there’s justification for each one. The royal palm and madagascar palm are monocotyledon plants (grass-like flowering plants) with a parallel pulse, the others are dicotyledonous plants with network veins. The 6 plants are quite different in thickness, shape outline, leaf texture and vein distribution; showing these samples are equally representative of nature.
For each plant, there were 15 samples that were taken; each sample with a similar shape/size. Using different measuring techniques, the thickness, density, mesophyll modulu, leaf vein modulu and poison ratio was calculated. Following this, the data collected is imported onto a trilinear coordinate measuring system; this system used measures the plant leaf data. In this data, the coordinate data of the main vein and lateral vein are the ones that are used, the smaller/minor veins are neglected as they don’t play a significant role in the mechanical/structural performance. Following this, the leaf structure is simplified; this means that the cross section and thickness of the veins become smaller from the root (medial axis) to the top (leaf rim). The geometry of the leaves is built on a tool called ANSYS APDL. The model is then imported onto Hypermesh (a commercial software) to make the topology optimization. By doing so, the leaves are made to withstand loads from different directions and forces.
The results of this experiment showed that the structure of the plant leaf is very similar to the natural vein network in the environment where it was tested with multiple loads. The main vein remained unchanged and the lateral vein had minor changes as the load changed. This goes to show that the network of plant leaf veins has the ability of adapt to different environmental stresses and loads. Furthermore, the analysis showed that the internal energy can be sustained at a relatively small value and vein growth is activated by environmental stress. This adaptability of plant leaf veins goes to show it’s a viable structure to mimic for wind turbine blades.
Understanding 4D Printing
If you aren’t familiar with 3D printing, it’s essentially a new method that can allow us to create a physical object from a digital (3-dimensional) design. This works by laying down layers of a liquid/powdered form of plastic, metal or cement, and then combine all these layers together.
4D printing is the process of 3D printing an object which transforms itself into another structure as a result of environmental stimuli, such as temperature, light, etc. These objects transform due to the influence of external factors like external energy input, which can be anything from temperature to light. There are 3 main characteristics of 4D printing:
- Ability to change in a way that is parallel with the desired functionality
- Material distribution; made of smart materials
- The structure is additively manufacturable
Programmable Materials
4D printers use 3D printers, the only difference is the input (material) that is used to build the object. With 4D printing we use “smart materials.” There are many ways to classify smart materials:
- Materials that can sense and react to stimuli on their own. They don’t need an external material to carry out the functions.
- Materials whose response is not encountered
- Materials whose response to a stimulus is different from the stimulus itself
Depending on how these smart materials react to stimulus, they can fall into any of the following groups:
- Shape Changers: these are SMs that respond to stimuli via strain/stress. Some may change in size or shape.
- Optical Sensors: in this group, the response of the material is perceivable by the eye. This includes thermochromic materials, triboluminescent materials or switchable mirrors
- Convertors: these materials react in a signal that can be used as a stimulus for other smart materials.
- State Changers: smart materials usually have a single condition in order to change; state changers are SMs whose conditions change in response to different stimulus.
The most common smart materials can be either a hydrogel or shape-memory polymer. Hydrogels have swelling/shrinking behaviours when solvent molecules either enter or leave the polymer networks. Shape memory polymer on the other hand is a smart material that produces shape changes due to external stimulus conditions. These shape-memory polymers are also known as programmable materials since they’re able to execute their 3D “genetic code” whenever it’s triggered. Coupling the potential of 4D printing with smart materials will help change the future of wind turbines and energy production. The material that will be employed for the 4D printing of the proposed wind turbine blades is Polylactic Acid (PLA).
Understanding Polylactic Acid (PLA): A Biodegradable Plastic for Turbine Blades
Polylactic Acid (PLA) is a thermoplastic polymer, which is a plastic polymer that can become moldable at a specific rise in temperature. Now, PLA is different from most thermoplastic polymers as it’s derived from renewable resources (corn starch and sugar cane); whereas normal plastics are derived from the distillation and polymerization of nonrenewable petroleum reserves. PLA Is both biodegradable and can be produced by existing manufacturing equipment that are normally used in the petrochemical industry, making it more cost efficient to produce.
There are different types of PLA, but each have similar characteristics since they’re all made form the same renewable source, lactic acid. The benefit from this is that it naturally degrades when exposed to the environment — there’s a high potential for short lifespan applications where biodegradability is highly beneficial but is also extremely robust in normal applications.
PLA is classified as a thermoplastic polyester due to the way it responds to heat → it becomes liquid at their melting points (150–160 degrees Celsius in the case of PLA). These polyester can be heated to their melting point, cooled, and reheated again without any significant degradation.
Overview of the Production of PLA
First, the corn starch is converted into sugar through wet milling. This wet milling separates the starch from the kernels. Next, acid or enzymes are added to these components that are separated, it is then heated to convert the starch into dextrose (sugar). One of the most common fermentation methods involves adding Lactobacillus bacteria to dextrose.
This then creates lactic acid, which is converted into lactide, a ring-form dimer of lactic acid. These lactide molecules bond together to create the polymer. Polymerization is small pieces of raw material polylactic acid plastic which can be converted into an array of PLA plastic products. Corn starch is mainly used since it includes the building blocks of the lactic acid/monomers which is polymerized into PLA. Polymerization uses metal catalysts (normally tin octoate) in a combination with lactide to make larger PLA molecules. The metal-catalyzed reaction leads to racemization, which goes from optically active (can rotate the PLA to the polarized side) to optically inactive (cannot rotate to the polarized side). This racemization reduces stereoregularity (where configurations and patterns within the chain follow a simple rule) when compared to the starting material.
The Challenge with PLA
One of the biggest problems with implementing PLA is that the polyester is hygroscopic. This means that it absorbs moisture from the air, meaning its not suitable for outdoor and construction applications where components can be exposed to sunlight, heat and humidity really quickly. Additionally, thermal degradation — the process that leads to the appearance of different compounds, such as linear and cyclic oligomers or lighter molecules with different lactide — is another problem with PLA.
Leveraging Beeswax Coatings
Following the environmental concerns and inefficiencies of recycling packaged materials, the development of biodegradable materials has been promoted. The current state of biodegradable materials isn’t the most favourable as the costs are high. The alternative to this is Thermoplastic Starch materials (TPS), they are cheap biodegradables, but they have some major drawbacks; deficient mechanical properties and high hygroscopicity. To get around this entire problem, these biodegradable materials must be cheap and have sufficient mechanical capabilities; in order to this, the Thermoplastic Starch materials must be blended with the biodegradable polyesters, specifically polylactic acid.
Employing this beeswax coating has the potential to reduce the hygroscopicity of starch based materials (PLA); this is a direct result of its hydrophobic nature. Beeswax is composed of 4 primary components: mixture of esters, hydrocarbons, fatty acids and alcohol. Another coating that has been used is lipid coating, it serves as a great moisture barrier. The use of the lipids coating will serve as an effective barrier to water vapour, but the main reason it is not being employed is because it reduces the mechanical strength of the matierals, is brittle and there is a lack of homogeneity.
Producing Beeswax Coating
Trays
The ingredients that are mixed in the tray are as follows: (52.5 g.100 g−1 starch, 17.5 g.100 g−1 glycerol, and 30 g.100 g−1 PLA). These ingredients are all manually mixed and are produced into pellets. The pellets produced are then extruded with a screw diameter of 20 mm and L/D ratio 34, five heating zones, flat-die slot gap of 1.74 mm coupled with a calender to create biodegradable sheets; each sheet has a homogenous thickness. These sheets are then thermopressed, this allows the production of the trays to occur.
Coatings
These trays are then coated with beeswax (BW) emulsion with slight modifications. The beeswax is melted in water at 65 degrees and then it is combined with ethyl alcohol and Tween 80. The trays are then coated by immersion in BW emulsion for 3 seconds and are then dried at room temperature for a week (7 days).
Understanding 3D Printing Concrete Wind Turbines
3D printing, also known as additive manufacturing is the process of making a 3-dimensional object from a blueprint held in a digital file. 3D printing technology employs layer-by-layer fabrication technology to produce structures directly from a computer-aided design, also known as CAD. 3D printing technology is quite versatile and has a broad array of applications. For the purpose of this prototype we’re proposing, we will be leveraging the use of 3D printing to 3D print concrete wind turbine towers. When manufacturing wind turbines and wind plants, manufacturers build wind turbines as tall as possible to capture the faster winds. However, the major problem with this is that, as wind turbines get taller, the diameter of the tower becomes extremely large. It becomes extremely difficult to transport these towers on roads. However, the workaround to this is to manufacture these towers on-site; this can be accomplished by utilizing 3D printing. In order to accomplish this, an automated concrete manufacturing process is adopted to workaround the transportation and logistics constraints that exist. Concrete 3D printing is a technology that has been rapidly developing in the last couple years; its design flexibility allows the possibilities of construction to be limitless. Among the benefits, the cheaper cost of concrete 3D printing stands out; with this, the access to renewable energy will be further hastened.
Breaking Down the Cost of a 6MW Turbine
The Backend of Calculations
Our Efficiency
What sets Off-Wind Energy turbines apart from the status quo is our efficiency in electricity created and our costs. To begin with efficiency, our turbines surpass Betz’s law (the law of the maximum efficiency stated previously). Normal turbines have an efficiency of roughly 15–25% which is how the typical offshore turbine output was calculated. On the other hand, with our 4D printed smart materials and cost-efficient turbine, we have a 90% efficiency capacity all because of our adaptable blades. However, can wind turbines ever be 100% efficient. Having a 100% efficient wind turbine means that the turbine should convert each molecule of air passing by the wind turbine which is nearly impossible because that means that the air around the turbine would completely stop, leaving no moving air or wind meaning there is nothing to rotate the rotor and start the turbine. A confusing paradox in itself!
This efficiency relies on the adaptable blades as they replace the pitch motion controller in a normal turbine. This controller is a control system which mitigates the excessive movement of a turbine and prevents it from moving in harsh weather conditions. Due to our 4D printed blades, the PLA responds to environmental stresses and stops during harsh weather conditions. Plus, due to the beeswax coating, the water permeability of the PLA significantly decreases by over 65%, preventing the plastic from biodegrading. This is a key component of the turbine because as the depths of the water increase, the wind speeds increase and the weather conditions become harsh.
Efficiency also significantly increases because the turbines are offshore. Whether it’s a coastal storm or an afternoon summer breeze, wind speeds are much faster near the ocean due to the limited friction over the water. Land typically has mountains, coastal barriers and man-made structures which add resistance to the wind flow, but the ocean is clear of barriers.
Overall, when implementing these turbines, there is a preferred set of criteria to meet to gain the most optimal output. The wind speeds are best suited when they are from 5m/s — 25m/s and since these are floating wind turbines, they can range in depths from 50m — 1000m. However, to be able to transfer the electricity from offshore to onshore, the turbines must be less than 200km from the shore.
Powering Homes With One Farm (5 of the 6MW Turbines):
Dimensions of our Wind Turbine
The current Off-Wind Energy turbines are 103m in tower height, have a rotor diameter of 150m and the blades are each 75m in length. Normally the cables would be over 200km however, we use a wireless system.
The reason for current offshore turbines to be larger is because larger wind turbines can reduce the overall average cost per megawatt-hour over its lifetime. This number extends to over 23% of the average fixed-offshore turbine. This is because the plant with larger wind turbines will need fewer machines to generate the same amount of energy resulting in less installation vessel trips and overall less maintenance, reducing the overall costs.
Design:
The type of turbines for the Off-Wind turbines are in the spar structure. These structures can be put in the deep depths of the ocean and provide an early market share of over 90%!
A common question is, why offshore turbines?
Why not just make larger onshore turbines or keep them closer to the shore? Currently, over 80% of the world’s Maritime Water is not used for any offshore energy production. This is due to the fact that the electricity they generate is often 2x as expensive as near-shore turbines and 3x as more as land-based turbines. Then again:
It’ll always be cheaper to build turbines on land but thats where the emissions-reduction targets have to be reached
Long term, floating wind turbines can also decrease the cost of energy production more than that of fixed wind turbines in the long term. Overall, floating turbines have a higher energy capacity factor with lower carbon emissions.
Current Offshore:
The current offshore turbines are fixed turbines which have a levelized cost of energy (LCOE) as $140/mWh whereas onshore turbines are $60/mWh. However, as new advancements (like Off-Wind Energy’s turbines) come into the market and project risk declines, the economics automatically decrease.
PLA Blades
The cost of PLA per kilogram is roughly $20, keep reading to see the cost breakdown of the beeswax coated PLA below. Now because we are 4D printing these blades and although the initial investment cost for these printers is high due to them being fairly new in the market, however, printing they are similar to 3D printers in the way that they result in a 50% reduction of costs. This results in a final cost of all three blades when 4D printed to be $597, 159.
Printed Towers
The towers of the wind turbine are made of tubular steel which is able to resist to the ocean's constant waves and tides. Typically, the cost of the tower is 20% of the wind turbine's cost. With an average cost of $3,000,000, resulting in a tower cost of $600,000. Again, as the towers are 3D printed, the cost for the towers results in a rough 50% cost reduction resulting in a tower cost of $300,000. Keep reading to see more about the cost breakdown.
Implementation:
Currently, 90% of the globally installed offshore wind capacity operates in the North Sea and near the Atlantic Ocean. The highest specific producibility is in Northern Europe near the North and Baltic Sea. The current location of offshore wind energy is limited where some of the largest wind farm projects have 1400 MW produced with over 170 turbines.
Offshore turbines are also preferred due to more stronger and consistent turbines further out as the potential is also in waters deeper than 60m. Currently, 2.4 billion people live within 100km of the shoreline which can deliver major-scale power directly to global markets. With floating turbines, we can remove the water depth constraints increasing the competitiveness. The floating turbines themselves also have an estimated 200 000 tonnes reduction of CO2 emissions per year 👇
Knowing that 90% of the global offshore wind resources are in deep waters, there’s great potential for wind in Asia, west coast North America and across Europe. Now, these turbines can be implemented all across the world but, we have major potential areas which can have a significance impact with floating offshore turbines and by using Off-Wind’s turbines, we could even eliminate the need for fixed turbines.