|
Plug-ín Wind turbine, development specification.
by Hakan Falk, "Energy Saving Now", Nov. 2003
Technical Specification for VolksWind (VW) turbine.
Grid Inverter type similar to Soladin 120W, wind adoptation.
VAWT Darrieus or Savonius 150 Watt
Small swept area.
Efficiency 30% or better.
Small size with large security.
High wind speed resistant.
Turbulence friendly.
Low roof mount in urban areas.
Low noise.
Easy to install for low cost or DIY.
Low price and mass produced.
Introduction and design considerations.
Large wind turbine technology is already one of the larger future energy supplies and small wind turbines have a big potential. What is needed for a common use of wind are turbines that meet a specification that is flexible enough for general application and be possible to mount almost everywhere and plug-in to the grid. Wind Turbines on the market are often larger, mounted on high towers and need plenty of space around them for safety and efficiency. The only way is therefore to specify a flexible urban wind turbine and hope that this will encourage someone to develop in this direction. This development specification document is an attempt to define a small wind turbine for common use.
The wind turbine must be able to meet the following criteria:
Suitable for roof mounting in urban areas.
Pose no risks for its neighborhood.
Have a good efficiency.
Insensitive to turbulence and not breaking up.
Suitable for mass production and a low price.
Looking at the possible and most common types of win turbines we have,
- Savonius Vertical Axis Wind Turbine. (SVAWT)
An early style is generally called a Savonius Rotor. The spinning part of a weatherman's wind speed device (anemometer) is a Savonius Rotor. Sideways mounted cups catch the wind and cause the vertical shaft to spin. A Savonius Rotor has an advantage. It works equally well with wind from any direction. Savonius rotor have efficiencies as high as around 30%, It is common and popular with home builders, because of its aerodynamic simplicity and that it does not need considerations of wind directions.
- Darrieus Vertical Axis Wind Turbine. (DVAWT)
A very sophisticated cross-wind-axis turbine is the Darrieus Rotor. This design looks something like an egg-beater, with usually either two or three curved airfoils. This design is technically called a high-tip-speed cross-wind-axis turbine. The airfoils and the high airfoil velocities allows this style to have efficiencies as high as around 35%, over a fairly wide range of wind speeds. It is suitable for mass production and is the best choice of VAWT. The aerodynamic design is more complicated, but is easy when it is once in mass production.
- Wind Mill Horizontal Axis Wind Turbine. (WMHAWT)
Early version of this wind turbines, was the Dutch-style windmill, which was used primarily for milling grain for farms. Why it is so closely identified with The Netherlands, is the very large number of such wind turbines that was used there, for the purpose of serving as water pumps in the countries land recuperation from the sea. Its extremes of performance were of little importance, as were its low efficiency in converting the energy in the wind to useful work. More important was the utilization of renewable energy, easy design, robustness and suitability for repetition. Its low efficiency does exclude this type of turbines.
- Propeller type Horizontal Axis Wind Turbine. (PHAWT)
The traditional Propeller style is what is called a high-tip-speed wind-axis turbine. Because of the high tip speed, the theoretical efficiency can be higher, around 45%. This higher efficiency probably explains the usage of Propeller-style turbines on large wind farms. This is the best and also most common choice for HAWT.
We end up with two possible and logical designs for our urban wind turbine, either the DVAWT or the PHAWT.
Air flow and turbulence over the roof top.
Although I do not have much experiences from siting of wind turbines, I do have experiences of air flow and turbulence. I have a PPL and been flying gliders, but maybe more importance is my 8 years of experience from flying para gliders. The latter in the same air space as wind turbines normally are sited. Unfortunately, it is no more flying for me, after losing the sight on my right eye around 10 month ago. For the purpose of siting and choice of turbine type, I like to discuss the air flow over fixed objects, like a house.
When the wind encounters the house, it will build up a pressure zone in front and a vacuum zone at the back of the house. The wind will follow the longer route over the house with higher wind speed and energy content, but still without creating turbulence. When it reaches the top of the roof, it will be effected by the vacuum, turn downwards and develop turbulence at the back side. On the top of the roof the wind will have a gradual difference in angles, it is wind of higher but still laminar velocity and above that the more constant and slower laminar wind.
The PHAWT is dependent, for its efficiency, of incoming wind straight from the front and will not work well with the variance in angles in the zone nearest to the roof. Maybe it would work better, if it could also position itself vertically in the same way as horizontally. A PHAWT would therefore be mounted on a tower, to get higher and into the zone of the constant wind. As a consequence, the mounting is more expensive, complicated and risky, than the DVAWT. The characteristics of the DHAWT make it very suitable to work in the zone close to the roof and utilizing the higher wind speed there, it will somewhat compensate the differences in efficiencies between the turbine types.
Because of the above characteristics, I chose the Darrieus or Savonius rotor for the VolksWind turbine.
Sizing and installation.
To determine the suitable size of the VW turbine, I looked at pricing for available turbines, grid-tie inverters and the components. One important factor was installation costs and durability in high wind speeds, the turbine and its components must have break up risks that are much less than the best roof components. It seems that I could detect a definitive price jump around above 450 Watt and a comfortable size around 150 to 200 Watt.
A 150 to 200 Watt VW-turbine will be able to cover 10 to 15% of a household electricity use. It can have around 4 to 5 years pay back time and over 10 years life span. As with most wind turbines, it is financially very attractive and with a good subsidize plan, it would get a high pick up rate.
Comments.
This specification is done with the aim to publish and discuss it in a couple of trusted discussion lists, before it is made generally available. The goal is, if possible, to create one or more models of wind turbines that can be used in urban or semi-urban environment and that way expand the prospective user base for wind energy.
Plug-in technologies for "The Grid".
This article is a part of our series in "plug-in" technologies collection, others are,
The Grid.
Plug-in solar.
Plug-ín Wind turbine, a development specification. (this article)
Plug-in hydro power. (to come)
Plug-in HVAC cogeneration.
Plug-in cogeneration hybrid car. (to come)
Plug-in electrical vehicles. (to come)
According to technology investigations, it is estimated that around 30% of current grid supplies can be "plug-in" deliveries, without any changes to existing grids. It is already around 70% of the potential of supplies from such sources and achievable without any restructuring or new investments in "The Grid". The environment and technologies are "ready for use" and the only things missing are political will and decisions. Good implementation examples are already working and corruptive delays or rules are bound to be exposed and measured in the future.
Hakan Falk
© EnergySavingNow.com
© Copyright energysavingnow.com 2000.
© Copyrights to Software @ this site
|
|
"Disturbed children"
and
"Grumpy old men".
|
