Small-scale wind - Building for a Climate Change

It is unlikely that micro-wind power will play a significant role in bringing about the energy revolution of the coming decades. Three factors are involved: first the capacity or ‘load’ factor of turbines as a whole; at best this is around 30 per cent. This is the proportion of the rated capacity of a machine that can be delivered to a household or the grid. Second, wind speeds in a built-up area are unreliable and turbulent due to the configuration of buildings, streets and open spaces. Third, it is generally considered that an average wind speed of 7m/second or 16mph is necessary for the commercial success of wind power. Only about 33 per cent of the UK land area has such speeds (Mackay, 2008).

Figure 7.5 shows the distribution of average summer and winter wind speeds in the UK.The figure concentrates mostly on Scotland where the greatest concentration of wind farms is to be found. Very few cross the economic viability threshold of 7m/second.

The performance of a micro-turbine with a 1.1m diameter, assuming an above average wind speed of 6m/second, should deliver ~1.6kWh/day. Mackay (2008) describes an Ampair 600W micro- turbine positioned on a roof in a small town in the midlands of the UK.The average power generated is 0.037kWh/day.

Larger machines can serve a group of houses and an excellent case study is the Hockerton Housing Project in Nottinghamshire. It has installed two 5kW free-standing turbines as well as roof-mounted PVs over its four earth- sheltered homes. From June to September their output per month is mostly under 200kWh. What stands out from this record is that PVs have an important part to play in the energy mix at the domestic level, especially in combination with small-scale wind (6kW and above).

The triple helix vertical axis turbine (Figure 7.6) is appearing in increasing numbers of urban situations, such as the waterfront of Albert Dock, Liverpool. The machines produced by quietrevolution are rated at 6kW, producing an average of 10,000kWh/year assuming average wind speeds. Machines are 14m high and 3m in diameter, but need only be 8m high when

mounted on the roofs of high buildings such as the Fairview apartments in Croydon (Figure 7.7). The wind energy company Altechnica has patented a number of building integrated turbines that are deigned to accelerate wind velocity. Collectively they are known as Aeolian Planar or

Wing Concentrators. They are designed to exploit

the cubic relationship between wind speed and power output. This would mean that an increase of 25 per cent in wind speed would double the power output. These could also be described as ‘building augmented wind energy systems’. The development of this technology means that: • wind turbine size for a given output can be

reduced;

• annual output of a wind turbine can be increased substantially;

• wind turbine capacity factor can be increased substantially;

• wind turbines will ‘cut-in’ at a lower wind speed;

• simpler fixed yaw wind turbines become more feasible;

• sites with lower wind speed characteristics become more viable;

• urban sites become more viable; Stornoway Summer Winter Kinloss Kirkwall Stornoway Kirkwall Kinloss Leuchars Dunstaffnage Paisley Bedford St Mawgan 0 1 2 3 4 Windspeed (m/s) 5 6 7 8 Leuchars Paisley St Mawgan 100 km 9

Summer Winter Bedford

Dunstaffnage

Source: Mackay (2008, p264)

Figure 7.5 Average summer and winter wind speeds in the UK over the period 1971–2000 at a height of 10m

Source: Courtesy of quietrevolution Ltd

Figure 7.6 Triple helix wind generator by quietrevolution (qr5)

66 Building for a Changing Climate

• wind turbines can be productive for a greater proportion of a year;

• substantial CO₂ emissions are abated from what is effectively a ‘new’ energy source. The ‘Aeolian roof ’ combines a suitably profiled roof with a shaped fairing or plane designed to enhance wind speed along the apex of the building. The fairing or wing also protects the rotors. The system can accommodate cross-flow or axial turbines (Figure 7.8) and can generate power even at relatively low wind speeds and when there is turbulence. Structurally this is a robust system that minimizes roof loading. The prototype currently under test also indicates that vibrations are not transmitted to the structure.

The Building-Augmented variants of the patented Aeolian Wing™ Wind Energy Concentrator Systems family include several options including Aeolian Roof™ systems that are appropriate for a variety of roof profiles including curved, vaulted, shell and membrane roofs as well as dual-pitched, mono-pitched and flat roofs. The system is not only suitable for new buildings but also for retrofit application (Figure 7.9). Figure 7.7 Quietrevolution helical turbines, Fairview

Homes, London Road, Croydon

Source: Courtesy of Derek Taylor, Altechnica

Figure 7.8 Roof ridge accommodating cross-flow or axial turbines

System works with any current axial-flow & cross-flow wind turbines.

Altechnica Aeolian Roof Wing

Source: Courtesy of Altechnica

Figure 7.9 Aeolian system for terrace housing

Altechnica Patented Aeolian Roof on Curved Eaves Building (c) Altechnica

Axial-Flow Wind Turbines (cross flow turbines can also be used)

Source: Courtesy of Altechnica

Figure 7.10 The Aeolian Tower

Altechnica Aeolian Tower™

Altechnica’s Patented Aeolian Tower Wind Energy Systems™ with Aeolian Planar Concentrators™ on each corner.

68 Building for a Changing Climate

Altechnica has also designed the system to be adapted to high rise buildings (Figure 7.10).

Aeolian Tower™ systems are designed to be

incorporated into the sides and/or corners of buildings – particularly tall structures. Height increases the productivity of wind technology and side or corner installations reduce the visibility of wind energy exploitation on tall buildings. Again there is the potential for new- build and retrofit.

In document Building for a Climate Change (Page 81-85)