A method for mapping the turbulence intensity and excess energy available to building mounted wind turbines over a UK City

A method for estimating the potential power available to building mounted wind turbines within turbulent urban air flows

De-centralised wind energy is proposed as a future renewable electricity generation technology. The opportunity for individuals or small organisations to generate power locally enables a
\nreduction in losses associated with long distance electricity transmission. As the majority of Europe's population live in close proximity to one-another, 'point of use' wind energy systems will
\npredominantly operate from within the urban environment. Urban winds are characterised by increased levels of 'gustiness' and a decreased energy content with respect to rural and offshore sites.
\nVertical axis wind turbine designs, capable of handling winds comprising frequent changes in direction , are proposed as the configuration of choice for the urban environment. The evaluation and
\noptimisation of urban, vertical axis wind turbines requires a broad systems-based approach, consisting of: an assessment and simulation of the urban wind resource, the development of unsteady
\naero-mechanical turbine performance prediction models and the inclusion of typical installation
\nlosses.
\nA wind turbine 's location is found to be far more important in terms of net energy extraction
\nthan a particular turbine 's aerodynamic efficiency. To quantify the influence of location on overall
\nenergy yield, an in-depth evaluation of the urban wind resource is completed , including the development of methods to predict terrain roughness heights (shown to be a key factor dictating a site's
\ntotal available wind energy and levels of gustiness) from single point wind speed data. When compared to offshore locations, urban winds are characterised by: a reduction in mean wind speeds, an
\nincreased 'gustiness' (from negligible values to 23% of the total available energy resource) and,
\ndepending on whether kinetic energy contained within an unsteady urban wind can be extracted, a
\nfall of between 65% and 75% of the total available wind energy resource. This large decrease in
\navailable energy is viewed to be extremely significant, indicating that, for an urban turbine to be
\ncompetitive with its offshore counterpart (at the same elevation) an increase in overall efficiency
\nof the decentralised urban wind turbine system (compared with the offshore system) of between
\n286% and 400% is necessary. Unfortunately short period gustiness is shown to be detrimental to
\nturbine performance, hence a wind turbine operating within a steady wind will always extract a
\nlarger proportion of the total available wind energy than a turbine operating within an unsteady
\nwind.
\nA time and space accurate free-vortex model capable of simulating turbine performance in a
\nfluctuating wind as well as accounting for turbine-turbine interactions has been developed. Combining this vortex model with formulations for inertial effects, active control models and installation losses, has enabled a systems based design optimisation of wind turbines operating within
\nurban environments.
\nRotor designs with very benign (flat topped) power curve characteristics, at the expense of
\nmaximum aerodynamic efficiency, are shown to limit the adverse effects of an urban wind's short
\nperiod gustiness on net energy output. For the small urban rotors considered (15m2), energy losses
\nincurred converting turbine shaft power to grid conditioned outputs (240V, 50Hz) are seen to drive
\na systems design and subsequent optimisation, with these installation losses sometimes exceeding
\ntotal aerodynamic generation, leading to negative net energy outputs (a net flow of energy from
\nthe national grid to the wind turbine system). Optimisation of both aerodynamic rotor design and
\nturbine control strategies illustrate that improvements from a baseline configuration (with an initial
\npositive net energy yield) of up to 267% are possible . Incorporating these improvements within a
\ntypical 15m2 urban wind turbine installation result in predictions of annual energy yields of up to
\n3200 KWh, amounting to ~ 13% of the total annual energy use of an average adult living in the
\nUK.
\nThe installation of turbines on the tops of tall buildings is suggested as a method to mitigate the
\nvery low energy yields observed for urban turbines. The space available for turbine installations
\non the tops of these tall buildings is limited and close spaced turbine operation is likely to result. A
\nstudy of turbine-turbine interactions shows that a blockage effect, similar to that observed in wind
\ntunnel tests, results in favourable turbine performance. Thus, in a wind with a strong prevailing
\ndirection, a close spaced turbine array is capable of a better steady-wind aerodynamic performance
\nthan the same number of isolated wind turbines.

Assessment of wind resources in two parts of Northeast Brazil with the use of numerical models

Urban distributed energy systems play a crucial role in the development of sustainable and low-carbon cities. Evaluating urban wind resources is essential for effective wind energy harvesting, which requires detailed information about the urban flow field. Computational fluid dynamics (CFD) has emerged as a viable and scalable method for assessing urban wind resources. This review paper synthesizes the characteristics of the urban wind environment and resources, outlines the general framework for CFD-aided wind resource assessment, and addresses future challenges and perspectives. It highlights the critical need to optimize wind energy harvesting in complex built environments. The paper discusses the conditions for urban wind resource assessment, particularly the extraction of boundary conditions and the performance of small wind turbines (SWTs). Additionally, it notes that while large eddy simulation (LES) is a high-fidelity model, it is still less commonly used compared to Reynolds-averaged Navier–Stokes (RANS) models. Several challenges remain, including the broader adoption of high-fidelity LES models, the integration of wake models and extreme conditions, and the application of these methods at larger scales in real urban environments. The potential of multi-scale modeling approaches to enhance the feasibility and scalability of these methods is also emphasized. The findings are intended to promote the utilization and further development of CFD methods to accelerate the creation of resilient and energy-efficient cities, as well as to foster interdisciplinary innovation in wind energy systems.

A new methodology for urban wind resource assessment

Predicting flow patterns that develop on the roof of high-rise buildings is critical for the development of urban wind energy. In particular, the performance and reliability of devices largely depends on the positioning strategy, a major unresolved challenge. This work aims at investigating the effect of variations in the turbulent inflow and the geometric model on the flow patterns that develop on the roof of tall buildings in the realistic configuration of the University of Birmingham’s campus in the United Kingdom (UK). Results confirm that the accuracy of Large Eddy Simulation (LES) predictions is only marginally affected by differences in the inflow mean wind speed and turbulence intensity, provided that turbulence is not absent. The effect of the presence of surrounding buildings is also investigated and found to be marginal to the results if the inflow is turbulent. The integral length scale is the parameter most affected by the turbulence characteristics of the inflow, while gustiness is only marginally influenced. This work will contribute to LES applications on the urban wind resource and their computational setup simplification.

A case application of WRF-UCM models to the simulation of urban wind speed profiles in a typhoon

PurposeThis paper aims to develop an optimal maintenance and spare parts policy for an urban micro wind power system, focusing on two urban micro wind farms (UMWF). The reliability and efficiency of these systems are sought to be enhanced by considering the relationship between urban wind parameters and wind turbine degradation.Design/methodology/approachA proportional hazards (PH) model is utilized to describe how urban wind conditions impact turbine degradation. The maintenance strategy includes preventive maintenance (PM), corrective maintenance (CM) and opportunistic maintenance (OM). A multi-objective optimization algorithm is developed to optimize the joint policy of OM plans and spare parts resource allocation.FindingsThe proposed maintenance and spare parts policy effectively balances the trade-offs between PM, CM and OM strategies. Numerical experiments demonstrate that the policy improves the reliability of UMWF, reducing downtime and maintenance costs while ensuring the availability of spare parts when needed. The results show a significant enhancement in system performance compared to traditional maintenance approaches.Originality/valueA novel maintenance policy and spare parts management approach for urban micro wind power systems is proposed. A multi-objective optimization algorithm is developed to optimize the OM schedule and maintenance spare parts resource management strategy for wind farms in urban wind environments.

Wind power offers the possibility of onsite generation of renewable energy for residential, commercial and industrial energy users in urban and suburban areas. This form of electricity production has generally been limited to rural and utility applications, but continued improvements have generated new interest in the potential of wind power in urban environments. There are several key elements that determine the viability of urban wind power, the most important of which are turbine technology, wind resources, costs and regulations. This paper will examine these elements with the goal of assessing the current status and future potential of urban wind power. Urban environments present a unique set of challenges to wind power, which demand turbine technology specific to these applications. Buildings create turbulent wind patterns, destroying the constant, steady winds on which utility scale turbines are dependant. Noise, shadow and vibration due to turbines is more important in urban applications, and turbine esthetics becomes a major focus. A new generation of wind turbines is now being produced with these concerns specifically in mind. There are a variety of solutions to these problems, which designers are beginning to explore. An essential element in the success of a turbine is the availability of wind resources. New turbine designs are being produced to utilize lower velocity winds. Additionally, engineers and architects can create better turbine locations through the integration of turbines with building design. Through this integrated design, buildings can contribute to the wind resources by increasing wind speeds and directing wind through the turbine. Available wind and turbulence, along with the characteristics of the particular turbine design, dictates how much electricity can be produced. The third critical aspect of urban wind power is the cost of producing electricity. To gain success, urban wind generators must be cost competitive with other urban applications of renewable energy technologies. The primary competition in this market is from solar photovoltaics, which currently produce power at about 50 ct/kWh. Utility scale wind turbines are not part of this market, and therefore do not compete with urban turbines. Urban turbines have the potential to produce electricity at costs of down to 10 ct/kWh. Future technology improvements, along with increased production, could significantly reduce the capital cost and further reduce the price of generating power. There are also opportunities for tax incentives, feed-in tariffs and other subsidies that can reduce the installed cost of wind power. Finally, regulations and policy can be a major obstacle to urban wind power. This includes zoning and building codes, as well as electronics certifications and interconnection regulations. This paper will examine existing and future turbine technologies, urban wind resource availability and the costs associated with producing energy via urban wind power. It will also identify roadblocks to the implementation and assess the overall viability of this type of renewable energy production.

A study of the wake effects on the wind characteristics and fatigue loads for the turbines in a wind farm

The interaction between nearby wind turbines in a wind farm modifies the power and loads compared to their stand-alone values. The increased turbulence intensity and the modified turbulence structure at the downstream turbines creates higher fatigue loading, which can be mitigated by wind farm and/or wind turbine control. To alleviate loads and maximize power possible strategies such as wake steering, where the turbine is yawed to redirect the wake such that it does not impinge the downstream turbine, have been studied. The work presented here focuses on situations where the wake is nevertheless affecting the downstream turbine, and more specifically how high loads can be avoided by yawing the wake-affected turbine. The analysis is conducted on a 2.3 MW machine, and the flow field is simulated using the Dynamic Wake Meandering model. The study investigates the impact on power and loads for different longitudinal interspacing and turbulence intensities. Optimal yaw strategies are defined for above rated regions where no power loss occurs. The potential load alleviation for different load sensors are studied, but the presentation is focussed on the blade root flapwise fatigue loading. For full wake at 3D interspacing and turbulence intensity of 5 %, around 35 % of load reduction on the 1 Hz Damage Equivalent Loads can be achieved at high wind speeds. Smaller reductions are achieved for higher atmospheric turbulence; the analogue case with 15 % turbulence intensity shows 17 % potential alleviation. The alleviation on the wind turbine lifetime is also calculated and compared for different turbulence intensities and mean wind speeds. Small reductions are achieved for sites with low mean wind speed and high turbulence intensity, but high reductions, of around 19 %, are accomplished in low turbulence intensity with high mean wind speed.

Wind resource assessment and wind farm modeling in Mossobo-Harena area, North Ethiopia

Urban wind energy has become a popular source of sustainable power in modern urban configurations. This study aims to analyze the technical and economic aspects of installing wind-harnessing devices near different common urban configurations. Computational fluid dynamics simulations utilized by Reynolds-Averaged Navier-Stokes equations and realizable k-ϵ turbulence model are used to model the turbulent urban canopy layer in the vicinity of four different urban settings namely an isolated high-rise building model, and 3 clusters of buildings with different central building heights, ranging from no building to a high-rise building model. Normalized wind power density (PD) and turbulence intensity (TI) contours were plotted to identify areas of interest to install urban wind turbines. To show the significance of this research, the levelized cost of energy was calculated for an urban horizontal axis wind turbine installed at locations with the highest wind PD and lowest TI values. The results indicated that while the highest wind PD locations and their values change with the selected configuration, promising regions can be identified for wind harnessing applications.

The central shaft is an important and indispensable part of a small scale urban vertical axis wind turbines (VAWTs). Normally, it is often operated at the same angular velocity as the wind turbine. The shedding vortices released by the rotating shaft have a negative effect on the blades passing the wake of the wind shaft. The objective of this study is to explore the influence of the wake of rotating shaft on the performance of the VAWT under different operational and physical parameters. The results show that when the ratio of the shaft diameter to the wind turbine diameter (α) is 9%, the power loss of the wind turbine in one revolution increases from 0% to 25% relative to that of no-shaft wind turbine (this is a numerical experiment for which the shaft of the VAWT is removed in order to study the interactions between the shaft and blade). When the downstream blades pass through the wake of the shaft, the pressure gradient of the suction side and pressure side is changed, and an adverse effect is also exerted on the lift generation in the blades. In addition, α = 5% is a critical value for the rotating shaft wind turbine (the lift-drag ratio trend of the shaft changes differently). In order to figure out the impacts of four factors; namely, tip speed ratios (TSRs), α, turbulence intensity (TI), and the relative surface roughness value (ks/ds) on the performance of a VAWT system, the Taguchi method is employed in this study. The influence strength order of these factors is featured by TSRs > ks/ds > α > TI. Furthermore, within the range we have analyzed in this study, the optimal power coefficient (Cp) occurred under the condition of TSR = 4, α = 5%, ks/ds = 1 × 10−2, and TI = 8%.

Assessment of urban wind energy resource in Hong Kong based on multi-instrument observations