Autorización de equipos

This study was instigated from London's need to reduce CO2 emissions via the employment of renewable energy sources. Being a densely populated, urban area the London's topography does not lend itself to traditional turbine placement, hence more bespoke methods are required for successful integration. Two such sites are displayed in south London's Elephant and Castle: the Strata tower's BIWTs (three 18 kW HAWTs) and LSBUs Tower Block mounted 6 kW HAWT.

A literature review has shown there to be an existing body of research into noise, vibration and wind regime concerns associated with UWTs that demonstrates they can have a potentially detrimental effect on energy yield thus questioning their practicality within the urban environment.

It has been shown that hitherto no studies have specifically focused on the urban potential for BIWTs. As their integration is bespoke, typically determined by the architecture, it is unknown whether

existing guidelines for roof mounted wind turbines could be directly applied. It is probable that each installation would merit its own assessment and analysis procedure.

The purpose of this study has been to investigate the differences between roof mounted and BIWTs in order to quantify and assess the aforementioned concerns with the hope of demonstrating how a successful UWT installation can be achieved.

In order to achieve an efficient BIWT a multifaceted approach is presented, comprised of: (i) local noise surveys to inform acceptable turbine operating ranges, (ii) acoustic modelling of manufacturer provided data and/or acoustic testing of the proposed turbine across all applicable wind speed

ranges, (iii) vibration assessment of the turbine system, housing and any lower residential floors to (iv) the obtainment of site specific wind data to inform architectural design, turbine selection and

placement and (v) CFD modeling of local topography and the turbine mount and/or enclosure. It is imperative to assessment the potential for any local residential annoyance due to turbine generated noise pollution in the built environment. Key turbine noise issues have been highlighted and investigated for both installations. For the LSBU site it has been shown through measurement and simulation that any turbine generated noise propagated into the Tower Block is within regulations, therefore not likely to disturb any occupants although it has been shown that may faintly be detected through an open window in the upper levels. Noise levels at the nearest residential buildings are slightly in breach of established guidance but only at wind speeds above 6 m/s; a speed only recorded for 13 % of the time over a 2 year period. Below 6 m/s wind speeds other, pre-established environmental noise sources have been shown to dominate the existing aural environment.

For the Strata site it has been demonstrated that turbine generated noise is of great enough distance from local residential areas at to the street level that any noise would have diminished far below existing environmental noise levels. The isolation of the turbine venturi and lower maintenance level has also been shown to effectively reduce any structurally transmitted noise to levels far below regulation standards. Noise propagating from outside, detracting around the tower and into residents via the external facade has also shown to be of negligible level to cause any likelihood of complaint. It has therefore been shown that the Strata BIWT can comply with all relevant guidance.

An investigation into the likelihood of annoyance via turbine induced vibration was also undertaken for both sites. The LSBU site proved an interesting case as in spite of initial turbine mount measurements being far below levels likely to be perceived or cause complaint as laid out in BS 6472-1:2008 and BS 6841:1987, physical and visual manifestations of the turbine vibration were being observed on the 5th and 6th floors of the LSBU Tower Block.

The typical use of vibration measurements synchronised to the anemometry time interval, although useful in determining problems, was shown to be lacking in ability to quantify acceptable wind speed ranges due to impulsive gusts being associated with lower averaged wind speeds.

Therefore, in order to get a deeper insight into the fluctuations in Peak acceleration per averaged wind speed period the high resolution MAPS method was developed and utilised to present a more representative trend of peak vibration as a function of wind speed to determine operational limits. Via the MAPS method, high-resolution sampling within an office of complaint amplified levels were recorded within 10, 12.5, 16 and 31.5 Hz 1/3 octave bands as wind speed approaches and exceeds 7 m/s. Further analysis explains the observed increase to likely be due to amplified resonance of the turbine tower via the turbines blade passing frequency around this wind speed as well as an

unfortunate coincidence of high gust-speed blade passing frequency and structural resonance of the tower block itself. Initial site inspections did not foresee such a rare phenomenon and due to the extremely high ratio of structural to turbine mass no isolation or damping was suggested or installed. Effective isolation design is offered in chapter 7.1 to reduce any structurally transmitted vibrations to levels far below cause for complaint.

Vibration measurements recorded at the Strata site demonstrated that no likely cause for complaint would arise at any residential level within the range of monitored wind speeds. All measurements more than adequately met BS 6472-1:2008 and BS 6841:1987 guidelines.

This demonstrates that vibration must be appropriately considered for any UWT placement to ensure no structural natural frequencies are excited and to prevent any vibration transmission via appropriate mounting, isolation or damping where necessary.

Atmospheric measurements were recorded at LSBU to assess the local wind resource available to both sites. These measurements confirm that site specific, hub-height data is intrinsically essential in order to accurately estimate energy yield. As demonstrated in Table 73 the publicly available NOABL database gave 6 m/s as the average wind speed at LSBU hub-height for 2014 compared to the measured 0.8 m/s recorded at the LSBU CEREB site, different again to the 3.47 m/s average

recorded at hub height next to the LSBU turbine. This not only demonstrates the need for site specific data but further highlights how important it is to specifically mirror the hub position to avoid any topographical interference.

NOABL Heathrow CEREB LSBU

6 m/s 0.8 m/s 3.47 m/s

Table 73: Compares measured average wind speed figures from the LSBU sites with the average data available from the UK database NOABL for 2014.

A 2 year set of wind data was extrapolated to predict the Strata site's expected energy yield using the log profile law in Equation 5, which was shown to be more suitable for turbine heights over 100 m within a rough surface area. This was juxtaposed to the Weibull prediction method, which was show to be a better fit to the urban environment as it allows for a higher standard deviation in wind speed fluctuations per wind speed bin via the shape and scale factors.

CFD simulations have proved a useful tool in potential turbine site evaluation to facilitate the local wind flow assessment across specific roof mounted and BIWT structures to inform optimal turbine placement. CFD assessment further allows for potential sites to be evaluated with varying parameters to maximise the energy capture potential. Results indicate that if pre-installation CFD analysis had been employed and optimisation tips adhered to the LSBU site could see a four-fold increase in energy yield and the Strata site a 4.5 MWh per annum increase as figures show in Table 74.

Site Existing kWh pa Post-Optimisation kWh pa Ave Wind Speed increase

m/s

LSBU 2950 12671 1.5 m/s

STRATA 11521 15873 0.5 m/s

Table 74: Compares existing site energy yield with estimated yields post-optimisation proposals via the utilisation of CFD simulation.

This increased in yield would increase each sites ROI and generated percentage of electrical needs to the figures displayed in Table 75. While the ROI is still not an attractive investment on its own for the Strata site the percentage of electrical needs does go up to a fraction under the 8 % required by GLA's policy 4A.9.

As it stood, predicted yield figures presented by the Strata planning committee was enough to be granted planning permission, therefore rendering the turbine installation a sound investment in spite of its initial installation cost.

ROI Existing ROI Post-

Optimisation % Electrical Needs Existing % Electrical Needs Post-Optimisation LSBU 1 % 6.9 % 0.3 % 1.7 % STRATA 0.5 % 0.6 % 6.1 % 7.6 %

Table 75: Compares ROI and percentage of electrical needs data for each site pre and post site optimisation.

The LSBU site, as it stands, neither provides a substantial percentage of building electrical needs nor presents a sound investment but if advised optimisation were to be heeded a healthy IRR of 6.1% could be reaped and its price per kWh reduced from 28.2 pence to 6.5 pence, therefore making it viable, clean alternative to fossil fuelled electricity.

Both study sites have demonstrated strengths and weaknesses; while neither site poses a noise threat, structural borne vibration was an issue for LSBU. Energy wise the Strata site has a huge potential albeit at a substantial set up cost where as the current LSBU site is under-achieving. Nevertheless, by employing appropriate, vibration installation design, CFD modelling and noise

propagation simulation techniques in advance it has been shown that both site's downfalls could have been avoided to produce two unobtrusively effective electrical generation sites.

This thesis has highlighted key factors to consider at the planning stage of turbine placement, intrinsic within the urban environment. With these factors in mind detrimental installation mistakes can be avoided to make wind turbines an effective and feasible method of urban green energy production to contribute towards lowering London's carbon footprint.