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What is an Energy Storing Wind Dam?

1. What is an Energy Storing Wind Dam?

An Energy Storing Wind Dam uses wind to pump water. This water is stored for electricity generation on demand via a hydro generator. Other applications include irrigation or any situation requiring a raised water source.

2. How Does an Energy Storing Wind Dam Work?

Instead of using electricity to drive a water pump, wind energy is used. A water pump is connected to a wind turbine via a common shaft so as when the wind blows the wind turbine drives the water pump. Below shows the difference between a motor/water pump assembly and a turbine/water pump assembly:

Figure 1: Motor/Water Pump Assembly     Figure 2: Turbine/Water Pump Assembly

3. What Does an Energy Storing Wind Dam Look Like?

A single Wind Dam turbine is approximately 4m in diameter (Figure 3). At this size it does not have the capacity to pump a large amount of water, however many stacked together are used to gain the desired pumping capacity (Figure 4). To make this possible each turbine module is placed inside a duct or tube to provide a separation between turbines to minimise interference. The opening of the duct is hexagonally shaped for optimal stacking and reduces to a circular shape centrally to accommodate the turbine.

Figure 3: Single Turbine Assembly     Figure 4: Multiple Turbine Assemblies In Series

This wall of turbines or Energy Storing Wind Dam requires a water source and an upper storage reservoir (Figure 5).

Figure 5: Energy Storing Wind Dam System

4. Wind Power: What's Been Done Before?

Most people know about Wind Farms which consist of many large diameter Free Field Turbines (Figure 6). These turbines drive generators, producing electricity instantaneously. However, if the wind isn't blowing, no electricity is produced. Hence when the wind blows and excess electricity is generated, there needs to be a way to store this excess energy for when the wind isn't blowing. 

Energy Storing Wind Dams solve this problem, not by storing electricity but by storing the potential to generate electricity through water storage and the use of a hydro generator.

Figure 6: Conventional Turbine

Figure 7: Wind Turbine Configuration   Figure 8: Energy Storing Wind Dam Configuration

5. Comparing an Energy Storing Wind Dam to Free Field Turbines

5.1 Location: An Energy Storing Wind Dam is a fixed stationary object where as a Free Field Turbines has the ability to rotate into wind. This gives each favourable advantages at different sites.

Free Field Turbines with the ability to yaw into wind favour open fields where they can handle wind from multiple directions. An Energy Storing Wind Dam being stationary has a restricted angle of wind that can be captured. However having a useful wind angle of up to 40° off centre and a bidirectional turbine, this allows 160° of useful wind.

Figure 9: Maximum Usable Wind Angle

Certain sites however are suited to this restriction. Positioned in a valley; a natural wind funnel, an Energy Storing Wind Dam utilises it surroundings very effectively. The ability to yaw into the wind is not necessary, leaving Free Field Turbines with costly redundant features.

The majority of sites will also have a prevailing wind which suits an Energy Storing Wind Dam as it can be set up in a direction to maximise operational time. The advantage of an Energy Storing Wind Dam being stationary is that it is more simplistic and will result in a longer lasting structure due to less moving parts. Being stationary gives the Energy Storing Wind Dam the simplicity to be built on or be added on to an existing environmental feature. This could be extending a current ridge line, blending the transition between nature and man made. The Wind Dam can either be extended along land or out to sea.

An Energy Storing Wind Dam's ability to recirculate water at an existing hydro station (Figure 10) could boost electricity production at peak times and store the potential during off peak times.

Figure 10: Recirculation of Hydro Dam water

5.2 Turbine Density: The number and size of turbines relates to the amount of energy extracted from the wind. Either one of these parameters has to change to increase the wind energy collected. With Free Field Turbines, blade diameters are reaching a maximum optimal size ( http://www.euros.de/Windtech_050716.htm ), therefore a greater number of turbines are required to increase the wind energy generation. Land however is scarce and adequate spacing is required between turbines to avoid interference for optimal performance.

An Energy Storing Wind Dam allows closely stacked turbines due to the separation attained by the ducts minimising interference. This means there is a greater turbine density or wind collection area i.e. the wind sees the Wind Dam as one large turbine.

Figure 11 shows a rough comparison between many small Energy Storing Wind Dam turbines and a large Free Field Turbine. The height and width is roughly the same however the area of turbines the wind sees is different.

Figure 11: Approximate Turbine Density Comparison

Additionally Figure 12 shows a rough comparison of land used for 8MW generation year average.

Figure 12: Land Usage Comparison

5.3 Complexity: A Free Field Turbine (Figure 13), while a marvellous piece of engineering is quite complicated due to its abilities to turn or 'yaw' into the wind, adjust the pitch of the blades, modify shaft speed via a gearbox for the electrical generator, and brake for out of control wind speeds. An Energy Storing Wind Dam configuration (Figure 14) consisting of a turbine and a water pump on a common shaft reveals a considerable difference.

Figure 13: Free Field Turbine Setup (Reference: www.nrel.gov/wind/animation.html)     Figure 14: Energy Storing Wind Dam Setup

6. Environmental Impacts

6.1 Bird Strikes: This is a concern with Free Field Turbines as birds quite often cannot make out the rotating blades.
With an Energy Storing Wind Dam there is a large static structure surrounding the turbines making it hard for birds not to see. Adding a coarse mess across the face of the Energy Storing Wind Dam would prevent this problem altogether with minimal loss in efficiency, otherwise not possible with a Free Field Turbine.

6.2 Flicker: A common complaint with Free Field Turbines is the sun shines through the spinning blades, creating a flicker effect.
An Energy Storing Wind Dam has each turbine positioned centrally in a duct making them less visible. Additionally being smaller turbines they spin faster reducing this effect,

6.3 Wind Shelter: Down-wind from an Energy Storing Wind Dam the air stream will expand, reducing its speed acting as a wind break to reduce wind effects at ground level. Gust effects are also dampened by the Wind Dam.

6.4 Shadow: The image of an Energy Storing Wind Dam blocking out all sunlight is not actually the case. A North-South positioned Wind Dam when the sun is low in the early morning and late evening would generate the largest shadow. However the Wind Dam will allow reflected light through the ducts openings, drastically reducing the shadow effect, due to the high porosity of the ducts. While an East-West positioned Wind Dam will have minimal shade throughout the day.

6.5 Noise: With the absence of a gear box and fewer moving parts, noise from an Energy Storing Wind Dam will be significantly less than a Free Field Turbine. Turbine noise will be the major source but since the turbines are smaller they will rotate faster producing a higher frequency noise. Higher frequency noises are easier to dampen than a lower frequency noise, just think how far away you can hear the sub in a car audio system compared to the higher frequency sounds. Duct material will also be a good sound absorber.

7. Energy Storing Wind Dam Adaptations

A solution to the problem of the restricted wind direction capture of the Energy Storing Wind Dam in an open field is to construct Wind Dam 'legs' that can be extended out in multiple directions. Positioned centrally can be a hydro generator for electricity generation.

Figure 15: Wind Dam Legs Concept, Plan View     Figure 16: Wind Dam Legs Concept, 3D

8. Future Scope...

The idea of a Wind Dam in present society is foreign and would seem to many people as obtrusive, but the way things are going with decreasing oil supplies we need to look towards a more sustainable society, and changes to the landscapes and the way we think about what is normal will have to be accepted to move into the future. An Energy Storing Wind Dam would be seen as a normal feature of the landscape for future generations to come, just as we have grown up with power lines, bridges, skyscrapers, the Eiffel Tower etc.