02 Alternate Energy Sources
Wind:
Three (3) Wind Generating Technologies & 4 wind production sizes.
Horizontal Axis Wind Turbine (HAWT),
Vertical Axis Wind Turbine (VAWT) &
Kite turbines.
1. Horizontal Axis Wind Turbine (HAWT)
Horizontal Axis Wind Turbines are the most popular and biggest in size. As mechanical engineer Dr. Rosemary Barnes with 15 years of work experience says in one of her YouTube videos Should Wind Turbines Have TWO Blades? you can have as many balanced and stable blades as you want in a turbine that will work as efficiently as any other turbine as long as two parameters are accounted for.
The speed of rotation and
the width of the blades.
In HAWT turbines the rotational blade TIP speed is greater than that of the axis at its base due to linear speed. (In order for a blade tip to keep up with its bases Angular or Rotational speed it has to travel a greater distance and thus rotate faster in order to keep up).
A turbine’s blade tip speed is what creates noise when it rotates. The faster the tip speed the louder the noise. In order to have low turbine noise a slow axial rotational speed is required. In order for a wind turbine to have a single blade and remain stable and balanced its blade would have to be relatively wide. The more blades a turbine has the thinner they are. However, the more blades you have the more expensive and complicated the turbine is.
A single bladed turbine is unbalanced and a double blades turbine is not stable when turning to follow the wind direction. This doesn't mean that they don't exist, it is that they are more complicated to make efficient.
The cheapest and most common trade-off for HAWT is the 3 blade solution. Horizontal wind turbines mostly fall in 4 categories,
small for sailing boat, camp or small hut size of 80-600W,
medium for a few households or big offices / businesses of 5-20kW,
old large grid production of hundreds of kW, and
extremely large offshore wind turbines like those of Chinese “MingYang”, Danish “Vestas” and US “General ElectricGE” that can generate up to 16+MW of electrical power per turbine.
One of these offshore turbines such as the General Electrics Haliade-X can single-handedly produce up to 12MW of electricity, which is enough to power 16,000 European households. Its slightly larger sibling the 13MW turbine can generate enough energy in ONE rotation to power a UK household for 2 days.
A single blade of a Haliade-X is 107m long (27m longer than the wing span of the new fully double decked Airbus A380 creating a 220m rotor diameter and standing at a height of 260m). The main problem that these extremely large wind turbines face on land is their transportation to a working site. The width of the bases or length of the blades can be such that its really difficult to get them under or over bridges or through tunnels. A Swedish engineering and industrial design company named MODVION has come up with a design that will enable HAWT basses to be built and assembled in multiple modules made of Wood. These modules however are just as sturdy and long lasting as their steel counterparts and also lighter. The reason that this modularity is important is that the longer the turbine blades are (thus allowing them to get stronger and more constant wind) the wider and sturdier the tower's base needs to be. The extra height gives cleaner and more constant wind for the blade’s rotation.
A quite significant problem that an HAWT “grid placed” Offshore wind farms faces is that of their spacing. HAWT turbines are sensitive to the wind direction. In order to work efficiently they need a constant wind that doesn’t change direction frequently. In a HAWT wind farm where the turbines are placed one behind the other in a square grid the turbines placed in rows behind the front row get dirty and reduced wind. ‘Dirty’ in the sense that as the wind goes through the front turbine blades it gets twisted and swirled by the rotating blades and scattered behind them. Thus when the wind reaches the other rows it is no longer flowing steadily and in one direction and its speed has been reduced. One way of mostly countering this is by placing the turbines in a triangular grid and further apart so that the wind direction and force is optimal for all turbines no matter which row they are in.
2. Vertical Axis Wind Turbine (VAWT)
Vertical Axis Wind Turbines mostly fall under two categories,
Drag Type “Savonium” and
Lift Type “Darrieus” turbines.
Drag type turbines use the weight of the blades to assist in their rotation whereas Lift type turbines use aerodynamically shaped blades to assist with their rotation. Because of the blade orientation and compactness VAWT turbines are quieter because their rotational blade TIP speed is usually smaller than that of HAWT turbines. Their blade orientation combined with their low working noise makes them ideal for residential use. However this doesn't mean that they are not efficient. Even though they are not as well researched as HAWT turbines their industrial sizes such as the 50kW SunSurfs WT3 by SunSurfs or the 750kW Vertical Sky® A32 by Agile Wind Power are not to be frowned upon. Whereas HAWT turbines need big, complicated gear systems to keep them pointing into the wind VAHT turbines are omni-directional meaning that they can be spun by wind that comes to them from any direction. VAWT design, size and shape make them extremely robust and ideal for use in ALL wind speeds as they can practically work from a slight breeze all the way up to close to a hurricane. The fact that all of their moving parts that need servicing are found at their base makes them very easy to service unlike their HAWT counterparts where the blades and moving parts are found at the top of their tower some 260m high. VAWT after wind is less turbulent than that of HAWT turbines creating significantly less problems to the turbines behind them when in a farm and in some cases even improving the performance of nearby surrounding VAWT turbines. The overall size, compactness and silence of VAWT turbines makes them ideal for residential use. Their size and ability to work in minimal real or artificial wind make them ideal as a stand alone power supply. Artificial, meaning the type of wind created by a passing cars on a street or a busy highway, as shown by the Israeli “Alpha311' or the Turkish “Enlil”. Both of these VAWT’s not only produce electric power but they also contribute to scientific research by powering equipment mounted on them to measure air quality, earthquakes, connectivity for autonomous vehicles and wi-fi boosters.
3. Kite turbines
The third wind generating technology is that of Makani. Makani is a US based company with a goal to harvest energy from a kite. Turbines are connected to a kite which flies in loops called crosswind flight. The electric power generated by the kite’s turbines is sent to the grid via the kites tether. The wind speed combined with the apparent wind created by the loops the kite flies in, turn the kites turbines with great speed. One of Makani's prototypes whose kite length was equal to that of a small jet-planes wingspan, was able to generate 600kW of electricity
Solar:
Two (2) solar generation technologies
Photovoltaic (PV), and
Heliostat (Concentrated Solar Assisted Thermal Power Generation)
1. The first is Photovoltaic
Photovoltaic cells / panels come in lots of different types, technologies and means of application. There are 2 relatively simple technologies that can significantly increase traditional static panel productivity.
Bi-facial panels, and
Solar Tracking.
Bi-facial panels, as their name suggests, create electric power from both sides of the panel. The top side directly from the sun whereas the bottom side mostly from indirect reflected light from the ground, clouds or surrounding panels. Well installed bi-facial panels can have a 25-30% increase in electrical production.
Solar tracking, again as the name suggests, is when a panel is rotated by some sort of a mechanism to directly face the sun as it traverses the sky. Solar tracking can be,
single, or
dual axis.
In a single axis tracking system the panels are attached on two opposing sides of a panel thus rotating on a single axis usually from east to west to follow the sun. In a dual axis tracking system a panel array of 10-18 panels can be balanced on a pole that allows the panel array to rotate on two axis north-south & east-west thus making sure that the panels are always pointed at the most optimal direction for power production. Solar tracking can add an extra 25-40% increase in electrical production depending on whether it is single or dual axis rotation and how accurate it is. When bi-facial and solar tracking are combined, solar panels electric production can be increased up to and above 50%.
Solar power is a electromagnetic energy reaction that works when light photons strike a pv cells semi-conducive surface and knock electrons off it. Some of the electrons are lost on the boundary layer (PN Junction, Depletion Layer) between the positively and negatively saturated charged sides of a silicon panel but the remaining freed electrons are used as electric power. Not all solar photons however can be used to create electricity as not all have enough energy (are of the appropriate wavelength) to knock electrons off the pv semi-conducive surface. About 30% of the photons can be used for electricity production in silicon based cells, the other 70% are lost as heat.
In the early to mid 1950s the first silicon solar cell was invented and had an ‘efficiency’ (indicator of the amount of solar light that is finally converted to electricity) of about 6%. By 1959 the efficiency had been increased to 10%. Today the average silicon solar cell has an efficiency of 15-20% with the greatest efficiency being around 23%. Scientist have predicted that the maximum efficiency of silicon based solar panels is 29%
Solar electric production can be created with many different technologies.
Solar Roof Tiles such as those developed by USA TESLA or UK Developed ErgoSun are much easier and simpler to install on tiled roof tops than the traditional PV panels which require specialized brackets on a mounting frame system to support them on the roofs beams. Solar roof tiles are easier because the TESLA or ErgoSun tiles are the PV system. These special tiles provide a 2 in 1 solution unlike the traditional system where you install a pv system over an already tiled roof. A building with 900 ErgoSun tiles installed on its roof has a power production capacity of 13.5kW with NO bulky panels covering it.
Solar windows are another proposition. Companies like SolarWindow, Ubiquitous Energy (from MIT), joint research teams like that of the University of Minnesota and University of Milano-Bicocca and many others have come up with techniques for turning windows into electrical producing systems for various tasks. The SolarWindow company, for example, has created a Electricity-Generating Organic Liquid Coatings & Processes for Glass, Flexible Plastics & Films. It can be applied in various color tint and transparencies to match existing or planned color palettes. The liquid coating can be used to create electricity with both natural and artificial light.
USA Ubiquitous Energy have created another solution, this is a transparent glass that absorbs and converts infrared & ultraviolet light into electricity allowing the uninterrupted flow of visible light through. The absorption of the infrared light also contributes to the reduction of heat behind the glass.
A team of researchers led by Professor Joondong Kim at South Korea's Incheon National University besides creating a transparent solar cell have also created a smart window that gets darker as the light intensity increases.
Swiss Insolight has created a system for agrivoltaics that with the use of dynamic adjustments it created an optimal amount of shade for plant growth and converts the excess light into electricity.
On a similar line of thought UK based SolarGaps have created an auto tracking solar blinds that also creates electricity.
Two rapidly advancing technologies that can significantly increase photovoltaics are,
Carbon NanoTubes (CNT), and
Ferroelectric Crystals.
One research team from Rice University USA is working on using Carbon Nanotubes to capture the infrared light ie heat that the pv cells cannot convert to electricity. The carbon nanotubes convert (by focusing) the broadband infrared heat into narrow band light that can be easily converted to electricity. The researchers from Rice University say that the theoretical efficiency of photovoltaic cells coated with CNT can be increased from the max 29% of the silicon based cells to 80%.
Ferroelectric Crystals are dielectric crystals that spontaneously have a positive and negative charge (electric polarization). This polarization is naturally occurring ie without the aid of some sort of electric field and its direction can be switched with the application of an electric field. In an attempt to increase the theoretical 29% maximum electric yield of silicon based solar cells, researchers at Martin Luther University Halle-Wittenberg Germany stared experimenting with other materials for use in the photovoltaic process. They used ultra thin Ferroelectric Barium Titanate which does not absorb much sunlight and criss-cross overlaid it with ultra thin layers of Strontium Titanate, and Calcium Titanate to make a lattice. Strontium Titanate, and Calcium Titanate are Paraelectric Materials meaning that they become electrically polarized under an applied electric field. They found that in order to get the best current flow Barium Titanate had to be alternately criss-crossed with both Strontium Titanate, and Calcium Titanate. They finally ended up with a product that contained 500 such layers of a thickness of 200 nanometers. This product achieved a 1000 times increase in current flow compared to a similarly thick product of pure Barium Titanate. The specific orientation of the crystals, and their different alternating crystalline properties (Ferroelectric & Paraelectric) in their layering is what seems to have given them this incredible increase in current flow.
2. The second solar technology is thermal power generation via CSP (Concentrated Solar Power).
CSP can be found in four technologies,
Dish-Engine,
Linear Fresnel reflector,
Parabolic trough &
Power tower.
And comes in two versions and target groups.
1. Residential, small office / business version that mostly uses evacuated tubes, a system where a smaller tube or pv is suspended within a larger tube and the air is pumped out from between them. The evacuated air is critical in this system as it creates a thermal barrier between the outside and the solar collector or pv thus significantly increasing the systems performance. Evacuated tubes or something similar can be used in 3 ways. Solar water heating for a households, a hotels or businesses hot water needs. Solar Cooling systems to lower the work done by a HVAC condenser when cooling a house or building. Solar cooling can reduce the electrical consumption of a condenser by up to 50%. Another way of using evacuated tubes is in a combined pv and heating system. Here, inside the bigger outer glass tube of the evacuated system a small horizontal pv system is installed. The very low height (25cm from the ground) making it discreet, and the spacing depending on the latitude of installation and the reflective surface surrounding the big outer tube, all help increase the original electric performance by 40% making for a very good rooftop energy density compared to other pv systems.
2. Grid scale CSPs. The history of CSPs goes all they way back to Ancient Greece 214-212BC where it was said to have been used by Archimedes as a weapon to set fire to Roman boats. It wasn't until 1866 when Frenchman, Auguste Mouchout used parabolic troughs to boil water and use it’s steam to run a solar steam engine that this method resurfaced. In 1968 the first CSP power plant was developed by Italian Professor Giovanni Francia. This plant only generated energy it didn't store it. Solar reflectors surrounded a central receiver which boiled water and used its steam to create electricity with the use of a turbine. Alterations were made to this design and in 1982 the U.S. Department of Energy along with a consortium began testing a prototype of the first grid scale CSP towers of 10MW. From 1996-1999 the U.S. Department of Energy along with a consortium began testing solar heat storage so that electrical power could be produced 24/7.
Originally molten salt was used as a heat storage medium and expensive hardware was used to keep the concentrated, reflected sunbeams focused on one point. These CSPs originally and still use molten salt which is commonly stored at about 500-700C. However new technologies keep on appearing for the heat storage and production.
Spain built CSP plants in the early 2010s until it got into trouble on two issues. The first and more important was that Spain's electrical grid couldn't handle all the power that the CSP's were generating & thus had to subsidize them. Then the world economic crisis hit and the Spanish government ceased CSP subsidies altogether and the technology ceased to develop. However new technologies have started to appear for heat storage and production.
A newer version of the CSP tower uses simple motors and AI technology to track the sun and keep the sun rays focused on the receiver. This system significantly improves the CSPs heating capability and increases the solar heat created on the receiver to 1000-1500C. To store this intense heat, however, it was determined that rocks were a better solution than molten salt. Also the heated rocks could store the heated energy for about a week rather than the 10 hours or so of the molten salt.
Another material that has been developed by a group of Australian researchers. Is able to store heat at temperatures ranging from 200-1400C. This material comes in the form of Miscibility Gap Alloys (MGA) that can be stacked as modular blocks in insulated storage tanks for use in a range of applications.
Hydro:
Hydro has four (4) power generating technologies and 2 mediums of implementation.
The generating technologies are
Tidal / Current turbine based,
Wave piston (like that from wavepiston.dk, or concepts like those of Blue Energy - Ocean Power),
OWC (Oscillating Water Column) or artificial blowhole and
Ocean Mechanical Thermal Energy Conversion (OMTEC).
The mediums of implementation are fresh and salty water. As water is close to 800 time denser than air and density describes the mass (how much of something) of a unit volume (is in a specific amount) of a material ie mass/volume.
Water has the potential to significantly create more power than air as its density means it has more momentum (mass * velocity) and so can push or spin something with greater force (mass * acceleration). However, mostly due to its environment (water) and partly due to technology hydro power technology has fallen behind in comparison to other renewable sources like wind and solar. Although quite significant in its overall global electric power production 16% of total (gas, call, nuclear and all renewable energy) and about 60% of all renewable (Wind, solar etc) hydro is only half used. I say half because nearly all of the hydro power that makes up the 16% of total Electrical power is based on fresh water and not salt. 15,9% fresh to 0,4% Salt.
Close to all of the freshwater hydro power created is created by either,
One way (Hydro Turbines), or
Two way (Barrage / Range tidal systems).
Both of these systems require a dam of sorts along a river.
Fresh water Hydro Turbines which are also the oldest and most common / known create 98% of the hydro power. They require a dam to store the vast amount of water needed to guarantee the constant flow and pressure of water needed to turn their turbines as it leaves the dam.
Barrage tidal systems 2 of which are well known in the world are found at the estuary of the river Rance in Brittany in northern France and the Sihwa Lake in South Korea.
The first and oldest French system was constructed in 1966 and generates about 240MW. The second Korean one was build in 2011 and generates about 254MW of power.
The barrage system is almost the same as the hydro turbine system except that because its near or at the river estuary, its dam is not as tall and it takes advantage of the predictable tides which cause the water to flow both downstream and upstream.
As mentioned previously the amount of electric power produced by salt water is minuscule. However as technology increases and the electrical grid is decentralized more and more by wind turbines and solar farms the technology of hydro power is quite rapidly catching up.
From a 72m long and 2x20m rotor diameter tidal hydro turbines it is possible to create a total of 2MW with the Orbital 02. Or with 2x16m rotor diameter prototype tidal turbines, such as those at Strangford Lough Ireland by Simec Atlantis Engergy it is potentially possible to create 1.2MW. As with wind power, however, there are many types of turbines that can be used in hydro power. As smaller decentralized and localized mini stations are used to feed the grid with power the need for smaller scale technology is needed and hydropower is starting but steadily coming up with new and promising designs.
In the freshwater sector hydro turbines ranging from 2 to 200kW exist that can be easily installed in rivers, streams, canals or waterways with slow moving water. Turbines like Greek Kouris Centri Turbine (KCT), German Blue Freedom Kinetic, Belgian Turbulent and American WaterRotor Energy Technologies inc. These and many more have hydro turbines that range from 2-30kW in power. The good thing about these turbines is that as they are slow rotating and relatively small in size so that multiples units of them can be placed in a river bed nearly one after the other without harming the local aquatic life or impacting on each others performance, so as to meet the power needs of a village or small town found near them.
In the salt water (sea or ocean) sector, besides the various hydro turbines mentioned earlier there are also the other three technologies that are better suited to this environment. Wave piston (like that from wavepiston.dk or concepts like those of Blue Energy-Ocean Power), OWC (Oscillating Water Column) or artificial blowhole and Patrick McNulties Ocean Mechanical Thermal Energy Conversion (OMTEC). Both Wave pistons and OWCs require waves to generate electricity. OMTEC requires the vast depth of the Oceans at around 1000m and about 4-8C and the hotter the better ie mostly tropical water surface of 22-30C. This 15-26C temperature difference is necessary to create a sustainable net positive energy production system.