Albert Einstein



"It is a miracle that curiosity survives formal education"


GLOSSARY

Betz Limit:
Betz' law reflects a theory for flow machines, developed by Albert Betz. It shows the maximum possible energy that may be derived by means of a infinitely thin rotor from a fluid flowing at a certain speed. The limit is 59.3%.
wikipedia To top

Biomass:
Biomass is the only form of high grade renewable heat. It takes the form of by-products, such as straw, energy crops, and processed fuels, such as wood pellets which are generally imported. These fuels are used in straightforward combustion, and can include combined heat and power (CHP), or the more sophisticated but efficient anaerobic digestion, gasification and pyrolysis. Energy crops include short rotation coppice, willow, and perennial grass. To top

Breakeven wind speed:
This is the minimum wind speed required to keep the kites aloft with no net input of energy. This value may vary between designs but it is of fundamental importance to overall efficiency of the kite and lines: Some net energy will be required to keep the kites flying, for the proportion of time that wind speeds below this value are experienced. To top

Capacity factor (Net):
The ratio of the net electricity generated, for the time considered, to the energy that could have been generated at continuous full-power operation during the same period. wikipedia
Since wind speed is not constant, a wind farm's annual energy production is never as much as the sum of the generator nameplate ratings multiplied by the total hours in a year. The ratio of actual productivity in a year to this theoretical maximum is called the capacity factor. Typical capacity factors are 20-40%, with values at the upper end of the range in particularly favourable sites According to a 2007 Stanford University study published in the Journal of Applied Meteorology and Climatology, interconnecting ten or more wind farms allows 33 to 47% of the total energy produced to be used as reliable, baseload electric power, as long as minimum criteria are met for wind speed and turbine height. To top...

CCS:
CCS is an acronym of Carbon Capture and Storage. To top...
wikipedia

Dyneema:
This is a commercial name for ultra high molecular weight polyethylene. Dyneema fibers have a remarkable strength to weigh ratio. To top...
wikipedia

Energy intensity:
The energy required to achieve a unit of economic output. To top

HAWT:
Horzontal Axis Wind Turbine. Currently Nearly all wind turbines are of this type generally with 3 blades. To top...
wikipedia

Light Wind Energy Requirement to keep kites aloft:
Unlike conventional windmills, which in very light winds just rest on their solid structures, tethered aerofoils (kites) require some minimum wind speed to keep them aloft. With kites we have all seen children trying to provide this by running. During very light winds below 'breakeven wind speed' energy will be required to keep the kites aloft through a process of step towing or similar. Clearly more energy will be required in true nil wind than in a wind very slightly below the breakeven wind speed. To top...

Intermitancy:
See also Capacity Factor
Is the intermittent nature of wind power generation. For example the Standard HAWT 'cuts in' with wind speeds greater than 3.5m/s. (with little or no energy production until significantly higher wind speeds.)
The standard UK wind data suggests that for 12% of the time the wind speed at hub height would be less than the kick in speed so the turbine would not even be turning. To top...

Micro-Generation
Micro-generation is often, but not exclusively, renewable since it is the generation of energy by individuals and communities to meet their own needs. Although the UK lags behind many European countries, growing use of planning policy to require on-site renewable energy generation is having a positive effect on the use of micro-scale technologies. Typically technologies include: micro-wind, solar photovoltaics, solar thermal, CHP, biomass, ground source heat and cooling pumps, micro-hydro, and fuel cells. To top...

Rayleigh Model:
A Rayleigh distribution is commonly used to model wind speed and distribution. To top...
wikipedia

Reynolds number:
In fluid mechanics, the Reynolds number may be described as the ratio of inertial forces (vs_) to viscous forces (_/L) and, consequently, it quantifies the relative importance of these two types of forces for given flow conditions. To top...
wikipedia

Solidity Ratio:
Solidity Ratio is the Area of the Blade(s) of wind turbine divided by the total area of the wind that they sweep in their rotation. To top...

Standard:
For the purpose of the calculations in this web site some assumptions have been made. For example a Standard HAWT has been used to compare against.
Other 'standard' values have been assumed. Where possible this standard material or data has been taken directly from existing published data.

Standard HAWT
For the purposes of these illustrations the Standard HAWT has been taken to be the GE 3.6MW, link: GE-Energy with a hub height of 100m.
This is a relatively large HAWT designed for sea use.

Standard Wind Data
Wind data has been obtained from radiosonde (weather balloon) data base access at http://raob.fsl.noaa.gov. This data is provided by the National Oceanic and Atmospheric Administration (NOAA) and Earth System Research Laboratory (ESRL). The sites chosen can be located on the map at ESRL.
The three sites chosen for our analysis are AB, SH and VA. They were chosen because they:

1. Are within the British Isles
2. Record wind speeds at heights of less than 500m
3. Have consistent data over many years
(sites with more sporadic data recording were omitted.)
4. Two of the sites have almost uninterrupted access to the prevailing wind directly from the sea.

Some data 'sorting' was required to compare the sites.

Step Towing:
This is a process of winch towing a gliding aircraft higher into the air, than can be achieved by a single tow. It works in the following manner: The aircraft is initially towed up towards the winch as normal. Rather than release, it then turns and flies back towards its starting point on the ground still connected to the line that is now paid out. It arrives above its starting point turns back toward the winch and is towed up again. This is the first of series of steps and enables great altitude to be achieved from a short take off field. The process is not widely used in gliding due to the requirement for good synchronisation between line tension, paying out and aircraft position and direction. There are inherent dangers if these become out of sync. To top...

Swept Area:
This is the area, perpendicular to the wind direction, that is swept by a windmill. For a HAWT this can be imagined as a circle or hoop with the same radius as the windmill aligned perpendicular to the flow. The wind flow is generally assumed horizontal so the hoop must be standing vertical with the wind blowing straight through it. To top...

TCPA:
Town and Country Planning Association, link to www.tcpa.org.uk
To top...

Tethered Aerofoil:
In its most basic form this a kite. That is it is flying structure anchored to the ground to a fixed point via a tether or line. The tether can be lengthened or shortened and the kite can be ÔflownÕ in a cone of fight path options down wind of the tether with no power input just tension in the line. This project intends to extract energy from the line tension by using it to turn a generator while paying the line out. See animation: Animation
To top...

VAWT:
VAWT is an acronym for Vertical Axis Wind Turbine. These are an interesting alternative to the HAWT with various pros and cons. To top...
wikipedia
Avian Energy, Stretfield, Bradwell, Hope Valley. S33 9JT. | Email: info@avianenergy.co.uk