TINY OFF-GRID HOUSE WIND TURBINE & WEATHER MONITORING
Photo courtesy of Wikimedia Commons
Wind turbines use the kinetic energy of the wind and centripetal force to create mechanical energy that rotates blades and rotors, which turns a turbine, located in the nacelle assembly, that creates direct current (DC) electrical energy. The renewable energy of the wind and gravity, produces no carbon fuel combustion or emissions.
The catalyst of wind energy is the Sun. Wind is created when heat from the sun warms an area creating an area of low pressure which causes winds to flow in from cooler areas with high pressures. Wind energy is one of the earliest forms of renewable kinetic energy harnessed by humans. Early architecture incorporated passive winds to cool homes. Sixth millennium BCE Ceramics from the Eastern European Cucuteni-Tryptillian culture depict boats with sails. As early as the ninth century A.D., in central Persia windmills were used to grind grain in to flour and pump water. As of 2013, over 240,000 commercial-sized wind turbines worldwide produce 4% of the world’s electricity. At the time of this writing, Middelgrunden, 2.174 Miles, 3.5 km, from Copenhagen, is —currently— the worlds largest offshore wind farm generating over 40 MW of clean energy. According to Bloomberg Green reports, Denmark obtains over 40% of its electricity from wind power. Unlike coal, gas and nuclear power plants, wind turbines do not need the steam energy of water to rotate turbines to generate electricity. This avoids the use of over 6 million gallons of water annually. Offshore wind turbines on the oceans are not inhibited by size constraints and generate more energy due to higher ocean wind speeds.
Photo courtesy of Wikimedia Commons
The Tiny Off-Grid House will research the use of a Gorlovka Helical blade vertical axis wind turbine (VAWT) 600W 24V DC, 1.5m start up to 250 RPM, crowning a telescoping tower. The Gorlovka type is an evolutionary advancement on the Darrieus type with vertical blades. A vertical axis wind turbine has fewer moving parts reducing maintenance, is smaller and lighter since there is no heavy nacelle containing all the gears on top like in a horizontal wind turbine. Also, they are quieter.
There are three types of wind turbines:
Vertical Axis Wind Turbine (VAWT) Savonius (Drag type)
Horizontal Axis Wind Turbine (HAWT)
VAWT Darrieus (Lift type)
Savonius wind turbines technology has been used since early civilization. They are less efficient because of the drag created by the diagonally connected wind blades.
A wind turbine nacelle contains the blades hub connected to the main shaft connected to the gearbox where low aerodynamic torque is converted in to high speed shaft that turns a generator where DC electrical power is generated. Also, contained in the nacelle is a disc brake system to stop the rotation of the blades during excessively high wind conditions or during seasonal bird migrations.
Horizontal axis wind blades are most efficient since all the blades are in contact with the wind at the same time creating torque.
A horizontal axis wind turbine can maximize wind energy by making adjustments to its position in response to changing wind directions. The yaw rotation of the nacelle around the vertical axis of the tower faces the blades in to the wind. The pitch rotation of the blades around the lengthwise axis of the blade allows the blades to have increased contact with the wind.
A huge advantage of the Savonius and Darrieus Helical vertical axis wind turbines (VAWTs) is that they are omnidirectional (taking advantage of the wind from any direction) without the need for pitch and yaw mechanisms to orientate them in to the direction of the wind. The blades always rotate in the same direction; regardless of the direction of the wind. This creates less moving parts and reduces maintenance.
While one vertical blade at a time is creating torque. The remaining blades continue to rotate from the centrifugal force caused by inertia 15 - 20 RPM.
Earlier models of vertical axis wind turbines had a propensity to stall out and stop spinning depending on the angle of wind flow. Higher winds speeds were required for the higher starting torque of VAWT’s. During low wind pressures, some early models required a mechanical boost to get the blades rotating. Modern deigns have lower minimum operational windspeeds and higher cut-off wind speeds.
Blade Structural Design
The upstream wind first striking the front of the airfoil blade is called the leading edge, while the rear is the trailing edge.
Wind load (against the blades) and gravity (pushing down on blades) propel the HAWT blades to rotate. The blades are designed to have a strong inner main spar (spine) that can handle the load from gravity; yet have flexibility against wind resistance.
Another contributing natural force on the blades is the temperature; since colder air is more denser than warmer air, the heavier cold air provides more kinetic energy to turn the blades.
The orientation and twist shape of a horizontal axis wind turbine functions like an airplane propellers while a vertical axis wind turbine functions more like an airplane vertical stabilizer (Fin). Both use Bernoulli’s Principle to creates an area of low pressure as a result of faster air flow on the downwind side of the blade and an area of slower high pressure on the upwind side creating drag which causes the blade to move.
A HAWT works less efficiently with two blades than with three blades; however, more than three blades only produces marginal gains in efficiency, at higher material cost. The three blades are thicker closer to the hub which enables the blades to withstand wind loads.
The Gorlovka Helical blade vertical axis wind turbine (VAWT) is an evolutionary improvement of the straight blades H type Darrieus wind turbines. The helical 60° twist of the airfoil blades alleviates any torque concerns normally associated with the standard H type VAWT’s. The helical VAWT is quieter due to slower speeds along the blades edges.
The three Helical blades are designed like airplane wings creating lift; causing the turbine shaft to rotate. As the blades rotate around a vertical shaft Each of the three blades come in contact with the wind at the same time, at a different angle. A generator at the base of the shaft converts the winds kinetic energy in to electricity. On an industrial level, a generator located at the base is more economical to maintain that one up high on a HAWT.
The design of a VAWT blade reduces noise and the moving shadows caused by rotating HAWT blades. The omnidirectional compactness of the VAWT blades makes them ideal for urban environments.
A 600 Watt, 16.66 current, 24 Volt VAWT exposed to an average of 12 hours of “rated wind speeds” of 7.0 - 10.0 mph has the potential to generate 7.2 KWh of electrical energy for the Tiny Off-Grid House. Rated wind speeds provide sustained rotations at a force sufficient for optimal electrical production.
Wind speeds are usually measured in meters per second (m/sec). The cut-in winds speeds start rotations of the blades to generate electrical energy. At cut-out speeds the turbine shuts down to avoid damage from excessive wind speeds. The wind turbine has an electrical magnetic brake for over speed protection
The theoretical maximum efficiency a wind turbine can achieve is 59.3% known as The Betz’s Limit. The upstream wind speed should be higher than the downstream wind speed. Since some of the wind kinetic energy is converted to mechanical power that rotates the blades the downstream wind speed will be lower.
Note: The efficiency of a wind turbine can never be 100% because if the upwind speed is 100% the downstream wind speed will be 0% which means there is no air escaping downstream to rotate the blades.
All wind turbines must avoid topological and structural obstructions that blocks the productive flow or create turbulent feed winds. However, wind turbines can be strategically positioned at the mouth of land mass or structures that creates wind funnels.
Since winds are unpredictable, the excess electrical energy produced is best stored in batteries for use during times of low or no winds.
If the wind turbine is installed on or near the roof—without obstructing the solar array—the roof can act as a force multiplier doubling the kinetic energy of the windspeed impact on the wind turbine by deflection.
Wind turbine energy production has often been attacked by those with false-altruist concerns alleging they cause the majority of bird fatalities. According to the Audubon Society Fall 2019 Climate Issue, “citing a wide array of reasons, state lawmakers have passed legislation to hamper wind development. These moratoriums ban new turbines altogether, rather than promote the strategic siting of wind farms to maximize windenergy capture and minimize bird deaths. ”Strategic siting”, that is, to avoid migration routes and nesting grounds.
Studies have shown that collisions between birds and “stationary” skyscrapers huge transparent glass window panes, communication towers, result in 58% of avian fatalities; compared to collisions involving “rotating” wind turbine blades; which cause 0.01% of bird fatalities. Also, birds are less active at night or during high wind speeds when the wind turbines would be most active. Wind turbine position planning often involves strategic installation away from the habitual migratory routes of birds and their nesting grounds. The oil industry and utilities have done far more to endanger birds and their habitats. A 2009 - 2012 study found wind turbines accounted for 0.27 bird fatalities per gigawatt hour (GWh) compared to fossil fueled power stations 9.4 bird fatalities per gigawatt hour. Source Benjamin K. Sovacool
“According to research from The Smithsonian Migratory Bird Center and U.S. Fish and Wildlife Service Cats, species Felis silvestris catus, are second only to habitat loss as the largest human related cause of bird deaths. It’s estimated that Cats kill 1.3 - 4 billion birds each year in the U.S. alone, with 69% of those kills attributable to feral or unowned Cats” along with 6.3 - 22.3 billion mammals annually.
The 2010 Deepwater Horizon oil spill disaster killed or injured over a million birds. According to a New York Times 12/24/19 article “Habitat loss and pesticide exposure already have brought on widespread bird-species declines. The number of adult breeding birds in the United States and Canada has plummeted by 2.9 million since 1970.” In a 2017 Memorandum (M-7050), the Migratory Bird Treaty Act of 1918 was revised—weakened—to encourage the growth of business development and emasculated the prosecutorial authority of the U.S. Fish and Wildlife Service, the agency responsible for protecting migratory birds, over the benefit of business and energy utilities “when the underlying purpose of that activity is not to take birds”—according to the Interior Department. So if an oil tanker accidentally spills millions of gallons of oil killing or harming millions of nesting birds along with sea life, the Corporation(s) will not be held legally liable for fines for misfeasance conduct that never “intended” the “killing of migratory birds, their nesting areas, or their eggs!”
A twenty-five peer reviewed study, published in the June 2018 issue of The Journal of the Acoustical Society of America, have found that living in proximity to industrial wind turbines does not create a risk to human health.
Offshore wind turbines do not appear to harm fish and other marine animals populations. Infact, research shows that the underwater base of the offshore wind turbines increase marine populations by providing safe breeding habitats in the form of artificial reefs. The area surrounding the offshore wind turbines becomes a marine sanctuary because no fishing or trawling is allowed in this protected area.
Studies have shown that the energy and resources used in constructing an industrial scale wind turbine has its equivalent energy generated within 6 months; displacing 2,365 tons of CO2 every year of its 25 years lifespan.
Photo courtesy of AcuRite
Weather Monitoring:
Solar PV electrical production, Agriculture, fishing and Bee keeping requires specific information on local weather conditions. This up-to-date information can increase productivity and safety.
The benefits of having your own independent local weather monitoring station provides specific, up to date, information of weather conditions in your local area. Commercial weather monitoring agencies (National Oceanic and Atmospheric Administration NOAA or The Weather Channel) are dependable but may not provide relevant weather reports specific to “your local area.” Weather conditions from one local area to another can vary greatly especially during changing weather storms.
The AcuRite Atlas® 01007M-Bundle Weather Station provides remote monitoring from iOS and Android mobile devices or high definition touchscreen color display; with weather alerts. Along with an optional lightning detector. Four micro solar modules power an internal aspirating fan that maintains accurate temperature readings within +/- 1°F.
Sensors measures: wind speed, wind direction, temperature, humidity, rainfall, UV index and light intensity; with data transmission every 10 - 30 seconds, depending on respective measurement.
An Anemometer measures wind speed using three or four cups that spins on a fixed vertical rod.
A wind vane determines wind direction using a horizontal rod, with a larger end, that spins on a fixed vertical rod.
Rain precipitation measurement sensors use optical sensors or tipping bucket gauges to measure the size and number of rain drops.
When you live off-grid you have to become aware of the weather forecast. The ability of the AcuRite Weather Station to measure in realtime the UV index and light intensity should facilitate monitoring and research of the Tiny Off-Grid House solar PV electrical production in relation to weather conditions.
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