Mean Annual Energy Production Research Articles

Failure Consequence Cost Analysis of Wave Energy Converters—Component Failures, Site Impacts, and Maintenance Interval Scenarios

In the early stages of developing wave energy converter (WEC) projects, a quantitative assessment of component failure consequence costs is essential. The WEC types, deployment site features, and accessibility should all be carefully considered. This study introduces an operation and maintenance failure consequence cost (O&M-FC) model, distinct from conventional O&M models. The model is illustrated with case studies at three energetic Atlantic sites, each of which considers two types of generic floating WECs: a 300 kW point absorber (PA) with a hydraulic power-take-off (PTO) and a 1000 kW oscillating water column (OWC) with an air-wells-turbine PTO. This study compares 39 failure modes for PA and 27 for OWC in terms of direct repair costs and indirect lost production costs, examining the impact of location accessibility, capacity factors, and the mean annual energy production. The discussion revolves around the sensitive parameters. Recommendations for failure mitigations are presented, and the impact of planned maintenance (PM) during the operational phase is examined for 20 MW PA and OWC WEC projects. For a given WEC type, the method thoroughly evaluates how the location affects performance metrics. It offers a decision-making tool for determining optimal PM intervals to meet targets such as O&M costs, operating profit, or availability.

Numerical Study on the Performance of an OWC under Breaking and Non-Breaking Waves

A numerical model for the simulation of the performance of an oscillating water column (OWC) subjected to non-breaking and breaking waves is proposed in this paper. The numerical model consists of a hydrodynamic model specifically designed to simulate breaking waves and a pneumatic model that takes into account the air compressibility. The proposed numerical model was applied to evaluate the potential mean annual energy production from the waves of two coastal sites characterized by different hydrodynamic conditions: a deep-water condition, where the OWC interacts with non-breaking waves, and a shallow-water condition, where the OWC is subjected to breaking waves. The numerical results show that the effects of the air compressibility can be considered negligible only in numerical simulations of the performances of reduced-scale OWC devices, such as those used in laboratory experiments. We demonstrated that in real-scale simulations, the effect of the air compressibility within the OWC chamber significantly reduces its ability to extract energy from waves. The numerical results show that the effect of the air compressibility is even more significant in the case of a real-scale OWC located in the surf zone, where it interacts with breaking waves.

Practical power absorption assessment limits for generic wave energy converters

There lacks a generic representation of the wave power absorption of devices across dimensions, shapes, and resource conditions. A conventional resource assessment approach only evaluates the wave power based on wave characteristics, which is insufficient to capture the practical power absorption variations between WEC archetypes. In this paper, a novel WEC net power assessment (WNPA) method is proposed and is generally applicable to any arbitrary WECs design. Two theoretical upper bounds of wave power absorption are adopted and derived for different types of WECs. Numerical simulations are conducted to apply this novel technique to assess the net power available to different WECs at the Wave Energy Test Site (WETS), Hawaii and the PacWave site, Oregon over 11 years. By comparing the power potential for WECs oscillating in different degrees of freedom, the results indicate the surging mode may be the most energetic; regardless of shapes and ocean sites. When applied to three generic WECs (point absorber, terminator, and attenuator), the pitching terminator is shown to have lower absorption potential. Finally, the mean annual energy production (MAEP) of the three generic WECs at WETS and PacWave are compared, and a surging attenuator shows a significant wave power potential at PacWave.

Numerical Investigation into the Performance of an OWC Device under Regular and Irregular Waves

A numerical investigation into the hydrodynamic efficiency of an oscillating water column (OWC) device for the production of energy from sea waves under the conditions of regular and irregular waves is proposed. The numerical simulations were carried out using a two-dimensional version of a recently published three-dimensional free-surface nonhydrostatic numerical model, which is based on a conservative form of the contravariant Navier–Stokes equations written for a moving co-ordinate system. The governing equations are spatially discretized by a finite volume shock-capturing scheme based on high-order wave-targeted essentially nonoscillatory reconstructions and an exact Riemann solver. Time discretization was performed by a predictor-corrector method that took into account the nonhydrostatic pressure component. The proposed numerical model allowed us to highlight the significant differences between the hydrodynamic efficiency obtained under irregular waves and those obtained under regular monochromatic waves and provides more realistic evaluations of the OWC device performances. The results of the above comparison showed a reduction in the hydrodynamic efficiency of the OWC from 0.78 to about 0.54 when passing from regular waves to the corresponding irregular ones. The model was applied to assess the potential energy production obtainable by a set of OWCs at the Cetraro harbor (southern Italy). The numerical results show that, by adopting the optimal dimensions of the OWC, the estimated mean annual energy production obtainable at the Cetraro harbor is equal to 1540.52 MWh, which corresponds to the energy production of about 10 wind turbines with a nominal power of 60 KW.

Parametric study of a horizontal axis wind turbine with similar characteristics to those of the Villonaco wind power plant

<p class="JAREAbstract">The present paper focuses on the selection of parameters that maximize electrical energy production of a horizontal axis wind turbine using Python programming language. The study takes as reference turbines of Villonaco wind field in Ecuador. For this aim, the Blade Element Momentum (BEM) theory was implemented, to define rotor geometry and power curve. Furthermore, wind speeds were analyzed using the Weibull probability distribution and the most probable speed was 10.50 m/s. The results were compared with mean annual energy production of a Villonaco’s wind turbine to validate the model. Turbine height, rated wind speed and rotor radius were the selected parameters to determine the influence in generated energy. Individual increment in rotor radius and rated wind speed cause a significant increase in energy produced. While the increment in turbine’s height reduces energy generated by 0.88%.</p>

Estimation of the influences of air density on wind energy assessment: A case study from China

The distribution characteristics of air density in China were modelled on a high-spatial-resolution scale (4000 m × 4000 m) and the absolute error was calculated by comparing with constant air density. Daily mean air pressure and air temperature time series from 2403 meteorological stations for the period 1998–2018 were used to compute air density at the hub height of a typical wind turbine. The statistical air density distributions were applied in the study area and the influence of elevation on changes in air density was quantified. Mean annual energy production in the study area was estimated using extrapolated parameters of the Weibull distribution and adjusted power curves. Compared with energy production under the assumption of constant air density, the results demonstrate that over 33% of the study area had a mean air density less than 1.000 kg/m3 due to the effect of elevation. Values as low as 0.347 kg/m3 were observed in the Tibetan Plateau. Energy production was underestimated (0.04–1.76%) in the north-east and north when the variability of air density was considered, and wind resources were overestimated by more than 20% in approximately 13.1% of the study area. The results of this study will contribute to identifying suitable locations for developing the wind energy industry. The influence of air density on wind energy production at different elevations can now be quantified, allowing more efficient utilization of wind resources.

Experimental and numerical comparisons of self-reacting point absorber wave energy converters in irregular waves

An experimental and numerical comparison of the performance of two self-reacting point absorber wave energy converter designs is undertaken for heave motions in irregular waves. The experiments consist of a series of 1:25 scale model tests that feature re-configurable WEC body shapes, a feedback controlled power take-off, and a heave motion constraint apparatus. While both designs have the same float, the first design features a streamlined reacting body and the second design features a damper plate reacting body. A time domain numerical model, validated by the experimental results, is used to extend the comparisons of the designs in terms of power matrices, capture width matrices, and mean annual power production. Results indicate that the wave energy converter design with damper plate produces 41% higher mean annual energy production than the wave energy converter design with streamlined reacting body at a representative location near the West Coast of Vancouver Island, British Columbia, Canada.

Interannual variability of wind climates and wind turbine annual energy production

Abstract. The interannual variability (IAV) of expected annual energy production (AEP) from proposed wind farms plays a key role in dictating project financing. IAV in preconstruction projected AEP and the difference in 50th and 90th percentile (P50 and P90) AEP derive in part from variability in wind climates. However, the magnitude of IAV in wind speeds at or close to wind turbine hub heights is poorly defined and may be overestimated by assuming annual mean wind speeds are Gaussian distributed with a standard deviation (σ) of 6 %, as is widely applied within the wind energy industry. There is a need for improved understanding of the long-term wind resource and the IAV therein in order to generate more robust predictions of the financial value of a wind energy project. Long-term simulations of wind speeds near typical wind turbine hub heights over the eastern USA indicate median gross capacity factors (computed using 10 min wind speeds close to wind turbine hub heights and the power curve of the most common wind turbine deployed in the region) that are in good agreement with values derived from operational wind farms. The IAV of annual mean wind speeds at or near typical wind turbine hub heights in these simulations and AEP computed using the power curve of the most commonly deployed wind turbine is lower than is implied by assuming σ=6 %. Indeed, rather than 9 out of 10 years exhibiting AEP within 0.9 and 1.1 times the long-term mean AEP as implied by assuming a Gaussian distribution with σ of 6 %, the results presented herein indicate that in over 90 % of the area in the eastern USA that currently has operating wind turbines, simulated AEP lies within 0.94 and 1.06 of the long-term average. Further, the IAV of estimated AEP is not substantially larger than IAV in mean wind speeds. These results indicate it may be appropriate to reduce the IAV applied to preconstruction AEP estimates to account for variability in wind climates, which would decrease the cost of capital for wind farm developments.

WEC Design Based on Refined Mean Annual Energy Production for the Israeli Mediterranean Coast

WEC Design Based on Refined Mean Annual Energy Production for the Israeli Mediterranean Coast

Wave Energy Converter Annual Energy Production Uncertainty Using Simulations

Critical to evaluating the economic viability of a wave energy project is: (1) a robust estimate of the electricity production throughout the project lifetime and (2) an understanding of the uncertainty associated with said estimate. Standardization efforts have established mean annual energy production (MAEP) as the metric for quantification of wave energy converter (WEC) electricity production and the performance matrix approach as the appropriate method for calculation. General acceptance of a method for calculating the MAEP uncertainty has not yet been achieved. Several authors have proposed methods based on the standard engineering approach to error propagation, however, a lack of available WEC deployment data has restricted testing of these methods. In this work the magnitude and sensitivity of MAEP uncertainty is investigated. The analysis is driven by data from simulated deployments of 2 WECs of different operating principle at 4 different locations. A Monte Carlo simulation approach is proposed for calculating the variability of MAEP estimates and is used to explore the sensitivity of the calculation. The uncertainty of MAEP ranged from 2%–20% of the mean value. Of the contributing uncertainties studied, the variability in the wave climate was found responsible for most of the uncertainty in MAEP. Uncertainty in MAEP differs considerably between WEC types and between deployment locations and is sensitive to the length of the input data-sets. This implies that if a certain maximum level of uncertainty in MAEP is targeted, the minimum required lengths of the input data-sets will be different for every WEC-location combination.

Quantifying the robustness of optimal reservoir operation for the Xinanjiang-Fuchunjiang Reservoir Cascade

In this research we investigate the robustness of the common implicit stochastic optimization (ISO) method for dam reoperation. As a case study, we focus on the Xinanjiang-Fuchunjiang reservoir cascade in eastern China, for which adapted operating rules were proposed as a means to reduce the impact of climate change and socio-economic developments. The optimizations were based on five different water supply and demand scenarios for the future period from 2011 to 2040. Main uncertainties in the optimization can be traced back to correctness of the assumed supply and demand scenarios and the quality and tuning of the applied optimization algorithm. To investigate the robustness of proposed operation rules, we (1) compare cross-scenario performance of all obtained Pareto-optimal rulesets and (2) investigate whether different metaheuristic optimization algorithms lead to the same results. For the latter we compare the originally used genetic algorithm (Nondominated Sorting Genetic Algorithm II, NSGA-II) with a particle swarm optimization algorithm (MOPSO). Reservoir performance was measured using the shortage index (SI) and mean annual energy production (MAEP) as main indicators. It is found that optimal operating rules, tailored to a specific scenario, deliver at most 2.4% less hydropower when applied to a different scenario, while the SI increases at most with 0.28. NSGA-II and MOPSO are shown to yield approximately the same Pareto-front for all scenarios, even though small differences can be observed.

Influence of Hydropower Development on Flow Regime in the Zambezi River Basin for Different Scenarios of Environmental Flows

As the need for energy is increasing, the challenges in the future are to operate existing large hydraulic schemes in more sustainable ways and to develop future water resources projects that are able to achieve a better balance between environmental and socio-economic demands. In this context, scenarios combining different levels of environmental requirements as well as hydropower developments were simulated at a daily time step with a hydraulic-hydrological model (the Soil and Water Assessment Tool) over the Zambezi River Basin. For each scenario, the hydropower operation rules, the mean annual energy produced and the firm powers were considered. The impact on the flow regime was characterized by a hydrological alteration indicator and Pardé coefficients. In the present state, the total mean annual energy production is about 30,000 GWh with a firm power of about 3,000 MW. The impact of the dams on the flow regime is low in the Kafue flats and the Zambezi delta and high in the Mana Pools. The new run-of-river hydropower plants aim to increase the mean energy production by more than 90 % and the firm power by about 40 %. Releasing e-flows can reduce the impact in the Kafue flats and in the Zambezi delta, with a loss of less than 10 % of mean annual energy production and about 15 % of the firm power at Itezhi-Tezhi and Cahora Bassa. This reveals that a compromise between energy production and environmental sustainability can be reached.

Assessment of the wake effect on the energy production of onshore wind farms using GIS

In this study, we propose a method to estimate the mean annual energy production of a wind farm with a Geographic Information System (GIS). GIS allows for spatial modeling in many fields and has recently been applied in the field of renewable energy. The geographic features of a wind park are represented using spatial data such as topography, land cover, and wind resource. Wind resource layers contain data of the 16 wind directions, in which the wind rose is divided, including the frequency of the wind direction, the mean annual wind speed and the annual Weibull parameters k and C) estimated at 50m height. The wind turbines are represented by points including information about the roughness of the surrounding terrain. Roughness is calculated within a GIS process that models the variation of the land cover over the year around the wind turbine position. The mean annual energy production is calculated coupling the technical characteristics of the wind turbines models with the wind resource. In addition, the wake effect between wind turbines has been included. A parameter called “reduced efficiency coefficient” has been introduced to assess the impact of the layout of wind farm on the annual energy production in respect to the change of the wind direction. The reduced efficiency coefficient shows that relatively regular wind farm layouts designed for exploiting the wind speed blowing from the prevailing wind direction can cause significant energy losses. In particular, when the wind comes from directions perpendicular to the prevailing one, the wind turbines waste up to 60% of the available energy. The method has been tested, comparing the actual annual energy production of four wind farms in Kansas (U.S.) with the estimated mean annual energy production. The validation demonstrated an average underestimation of 3.56% of the annual energy production and an average underestimation of 1.11% of the capacity factor. The results are encouraging and the developed process enables the quantification of the annual energy production with low uncertainties.

Adapting Multireservoir Operation to Shifting Patterns of Water Supply and Demand

The aim of this study is to determine whether dam reoperation (the adjustment of reservoir operating rules) is an effective adaptation strategy to reduce the potential impacts of climate change and regional socio-economic developments. The Xinanjiang-Fuchunjiang reservoir cascade, located in Hangzhou Region (China), is selected as case study. We use a scenario-based approach to explore the effects of various likely degrees of water stress for the future period between 2011 and 2040, which are compared to the control period from 1971 to 2000. The scenario impacts are simulated with the WEAP water allocation model, which is interlinked with the NSGA-II metaheuristic algorithm in order to derive optimal operating rules adapted to each scenario. Reservoir performance is measured with the Shortage Index (SI) and Mean Annual Energy Production (MAEP). For the investigated scenarios, adapted operating rules on average reduce the SI with 84 % and increase the MAEP with 6.4 % (compared to the projected future performance of conventional operation). Based on the optimization results, we conclude that for the studied case dam reoperation is an effective adaptation strategy to reduce the impact of changing patterns of water supply and demand, even though it is insufficient to completely restore system performance to that of the control period

Wind energy potential assessment considering the uncertainties due to limited data

A new Bayesian approach is proposed to estimate the annual energy production (AEP) of a site where construction of wind turbines is considered. The approach uses long-term wind speeds of a nearby weather station and short-term wind speeds near the target site. Uncertainties exist due to the limited amount of data in the target site, in addition to the inherent uncertainties in the wind speed, the air density, the surface roughness exponent, and the power performance of the turbine. The proposed method systematically addresses these uncertainties and provides the distribution of the AEP. For illustration, we used the wind speed data near Yeosu, Korea, and the power performance curve of a 3MW turbine. For the site and the turbine studied, the range given by the 95% confidence interval corresponded to 8.9% of the mean AEP, and the range given by the 99% confidence interval corresponded to 11.9% of the mean AEP. Benefits of using the Bayesian approach compared to the classical statistical inference was also illustrated with the case study. The proposed approach provides a more conservative estimation considering the uncertainties due to the limited amount of data. Distributions of parameters of the prediction model are also provided, which enables a more detailed analysis of the prediction.

Simulation of a wind farm in swift current region in Southern Saskatchewan (Canada)

An attempt is made to simulate the Centennial wind farm consisting of 83 wind turbines. The farm is located in the Coulee municipality region near Swift Current, Southern Saskatchewan (Canada). The Wind Atlas Analysis and Application Program and other mapping programs were used for generating the annual energy production (AEP). Based on the generated wind atlas and using both the meteorological data for a period of 10 years (2000–2009), and a vector map with height contour and surface roughness lines, the total AEP for the wind farm was calculated. In addition, AEPs of the wind farm were individually calculated for 2007, 2008 and 2009. The results of the simulated model were compared to the actual values for 3 years. The average absolute deviation between the predicted and actual mean AEP values was found to be less than 7%.

Biomass Production of Short RotationEucalyptus camaldulensisDehn. Stands Growing on Peat Soil under a High Water Table in Israel

SYNOPSIS The growth and production of Eucalyptus camaldulensis Dehn. was studied under a four-year rotation on neutral and acid peat soils in the Hula Valley, Israel. The water table at the site was 1 m to 2 m for most of the year and the trees were planted at stocking densities of 1100, 1670 and 3300 trees per hectare. The local combination of fertile soil, high water table and high temperature created excellent growing conditions and produced remarkably high biomass tonnages and energy production values. Biomass production was not affected by either the type of peat or stocking per ha above 1670 stems. The mean annual increment of above-ground biomass and mean annual energy production were 51 t (o.d.) per hectare per year and 1008 MJ/ha per year for stocking densities of 1670 stems/ha.