Analysis of wind power generation operation management risk in China

The Chinese government has made an important effort to diversify the country's energy mix and exploit different sources of renewable energy. Although China's installed wind power capacity has undergone a dramatic expansion over the past six years, the electricity generated from wind power has not increased as expected. Meanwhile, operational risks, such as high generation cost, mismatch between capacity and generation, intermittent wind power generation, power grid construction lag, deficient policy, and operation mechanism, have become increasingly prominent. If not controlled, these risks will negatively affect wind power development in China. Therefore, this paper established a quantitative analysis model of wind power operation management risk from two aspects, feed-in tariff and grid electricity (electricity being connected to the grid), based on an analysis of wind power operation management risk in China. Moreover, this study quantitatively assessed the risk of the operational management of a wind farm in Inner Mongolia. Finally, corresponding risk control strategies for the healthy development of wind power generation in China were proposed.     

Concept study of wind power utilizing direct thermal energy conversion and thermal energy storage

Present wind power is intermittent and cannot be used as the baseload energy source. Concept study of wind power utilizing direct thermal energy conversion and thermal energy storage named Wind powered Thermal Energy System (WTES) is conducted. The thermal energy is generated from the rotating energy directly at the top of the tower by the heat generator, which is a kind of simple and light electric brake. The rest of the system is the same as the tower type concentrated solar power (CSP). The cost estimation suggests that the energy cost of WTES is less than that of the conventional wind power, which must be supported by the backup thermal plants and grid enhancement. The light heat generator reduces some issues of wind power such as noise and vibration.     

Modelling and optimization of the smart hybrid renewable energy for communities (SHREC)

The future energy system in community level should be more ‘smart’ to secure reliability, enhance market service, minimize environmental impact, reduce costs and improve the use of renewable energy source (RES). Therefore, this paper proposes an energy integration system – smart hybrid renewable energy for communities (SHREC). It considers both thermal (heating and cooling) and electricity market in a large community level and highlight the interactions between them through utilizing RES, combined heat and power (CHP) and energy storages. A planning model based on CHP modelling is developed for the SHREC system. A linear programming (LP) algorithm is developed to optimize the SHREC system in a weekly period and the results are compared with an existing energy optimization software. We also demonstrate the model in a sample SHREC system during three typical weeks with cold, warm and mid-season weather in the year 2011. The results indicate that the developed modelling and optimization method is more efficient and flexible for the smart hybrid renewable energy systems.     

A new methodology for urban wind resource assessment

In the latest years the wind energy sector experienced an exponential growth all over the world. What started as a deployment of onshore projects, soon moved to offshore and, more recently to the urban environment within the context of smart cities and renewable micro-generation. However, urban wind projects using micro turbines do not have enough profit margins to enable the setup of comprehensive and expensive measurement campaigns, a standard procedure for the deployment of large wind parks. To respond to the wind assessment needs of the future smart cities a new and simple methodology for urban wind resource assessment was developed. This methodology is based on the construction of a surface involving a built area in order to estimate the wind potential by treating it as very complex orography. This is a straightforward methodology that allows estimating the sustainable urban wind potential, being suitable to map the urban wind resource in large areas. The methodology was applied to a case study and the results enabled the wind potential assessment of a large urban area being consistent with experimental data obtained in the case study area, with maximum deviations of the order of 10% (mean wind speed) and 20% (power density).     

Aggregated models of permanent magnet synchronous generators wind farms

This paper evaluates the responses of three aggregated models of a wind farm consisting of variable speed permanent magnet synchronous generator wind turbines when wind fluctuations or grid disturbances occur. These responses are compared with those of the detailed wind farm model, in order to verify the effectiveness of the studied aggregation methods for this type of wind farms. The equivalent wind farm models have been developed by adapting different aggregation criteria that already exist in technical literature and had been applied to other technologies. In this work, these methods have been modified to suit them to the permanent magnet synchronous generator technology. The results show that the three aggregated models provide very similar results to the detailed model, both in the evolution of active power when fluctuations in wind speed occur, and in the active power and DC-link voltage during the two simulated voltage dips. Notably, the aggregated model with an approximate mechanical torque offers excellent results.     

Assessing ecological risks of offshore wind power on Kattegat cod

Offshore wind power is expanding with particular development plans in the Baltic and the North Sea. To reassure an environmentally acceptable development, regulatory authorities need to make informed decisions even when evidence and experience are scarce. In this study Ecological Risk Assessment (ERA) has been applied on a wind farm project in Kattegat, proposed within a spawning ground for the Kattegat cod, a threatened population of Atlantic cod (Gadus morhua L.). Six stressors with potential impacts on cod and related to wind farms were investigated. Three of them – extreme noise from pile driving, noise from vessels, and disturbances due to cable-trenching – are related to the construction phase, while lubricant spills and noise from turbines together with electric fields from cables are related to the operation phase. The ecological risk was derived from the combined likelihood and magnitude of potential adverse effects from stressors to the cod population using a weight-of-evidence (WOE) ranking procedure. Available evidence was evaluated based on its reliability, and contradictory arguments were balanced against each other using evidence maps. The option of performing hazardous construction events (e.g. pile-driving) outside biologically sensitive periods was incorporated in the assessment. It was shown that the construction of the wind farm poses a high risk to cod, as defined by the ranked and combined likelihoods and magnitudes of adverse effects. However by avoiding particular construction events during the cod recruitment period ecological risks can be significantly reduced. Specifically for this case, ecological risks are reduced from high to low by avoiding pile-driving from December through June, which confirms previous indications that pile-driving is the most ecologically hazardous activity of offshore wind power development. Additional risk reduction is achieved by avoiding cable trenching from January through May. The study thus illustrates the effectiveness of time-planning for risk reduction. Importantly, the study illustrates how combined ERA and WOE methods can be valuable for handling uncertainties of environmental impacts within offshore industrial development.     

A numerical approach for planning offshore wind farms from regional to local scales over the Mediterranean

Renewable energy resources, such as wind, are available worldwide. Locating areas with high and continual wind sources are crucial in pre-planning of wind farms. Vast offshore areas are characterized by higher and more reliable wind resources in comparison with continental areas. However, offshore wind energy production is in a quite preliminary phase. Elaborating the potential productivity of wind farms over such areas is challenging due to sparse in situ observations. The Mediterranean basin is not an exception. In this study we are proposing numerical simulations of near-surface wind fields from regional climate models (RCMs) in order to obtain and fill the gaps in observations over the Mediterranean basin. Four simulations produced with two regional climate models are examined here. Remote sensing observations (QuikSCAT satellite) are used to assess the skill of the simulated fields. A technique for estimating the potential energy from the wind fields over the region is introduced. The wind energy potential atlas and the map of a wind turbine's functional range are presented, locating the potentially interesting sub-regions for wind farms. The ability of models to reproduce the annual cycle and the probability density function of wind speed anomalies are detailed for specified sub-regions.     

Evaluation of ground energy storage assisted electric vehicle DC fast charger for demand charge reduction and providing demand response

In 2012 there was approximately 2400 electric vehicle DC Fast Charging stations sold globally. According to Pike Research (Jerram and Gartner, 2012), it is anticipated that by 2020 there will be approximately 460,000 of them installed worldwide. A typical public DC fast charger delivers a maximum power output of 50 kW which allows a typical passenger vehicle to be 80% charged in 10–15 min, compared with 6–8 h for a 6.6 kW AC level 2 charging unit. While DC fast chargers offer users the convenience of being able to rapidly charge their vehicle, the unit's high power demand has the potential to put sudden strain on the electricity network, and incur significant demand charges.Depending on the utility rate structure, a DC fast charger can experience annual demand charges of several thousand dollars. Therefore in these cases there is an opportunity to mitigate or even avoid the demand charges incurred by coupling the unit with an appropriately sized energy storage system and coordinating the way in which it integrates. This paper explores the technical and economical suitability of coupling a ground energy storage system with a DC fast charge unit for mitigation or avoidance of demand charges and lessening the impact on the local electricity network. This paper also discusses the concept of having the system participate in demand response programs in order to provide grid support and to further improve the economic suitability of an energy storage system.     

Resource and revenue potential of California residential load participation in ancillary services

Increasing penetrations of intermittent renewable energy resources will require additional power system services. California recently adopted an energy storage mandate to support its renewable portfolio standard, which requires 33% of delivered energy from renewables by 2020. The objective of this paper is to estimate the amount of energy storage that could be provided by residential thermostatically controlled loads, such as refrigerators and air conditioners, and the amount of revenue that could be earned by loads participating in ancillary services markets. We model load aggregations as virtual energy storage, and use simple dynamical system models and publicly available data to generate our resource and revenue estimates. We find that the resource potential is large: 10–40 GW/8–12 GWh, which is significantly more than that required by the mandate. We also find that regulation and spinning/non-spinning reserve revenues vary significantly depending upon type of load and, for heat pumps and air conditioners, climate zone. For example, mean regulation revenues for refrigerators are $11/year, for electric water heaters are $24/year, for air conditioners are $0-32/year, and for heat pumps are $22–56/year. Both consumer choices, such as appliance settings, and policy, such as the design of ancillary service compensation and appliance standards, could increase revenue potentials.     

Biopower from direct firing of crop and forestry residues in China: A review of developments and investment outlook

This paper reviews developments in the direct-fired biomass power sector and provides an up to date investment outlook by calculating the Net Present Value of new investments, and the appropriate level of Feed-in-Tariff needed to stimulate future investment. An overview is provided of support policies, historical growth in installations, and main market players. A number of data sources is combined to build a database with detailed information of individual biopower projects. This data is used to describe technological and market trends, which are used in a cash flow model to calculate the NPV of a typical project. The NPV for new projects is estimated to be negative, and investment should be expected to stall without proper policy intervention. Increasing fuel prices, local competition over biomass fuel resources, lower than expected operational performance and a downturn in carbon markets have deteriorated the investment outlook. In order to ensure reasonable profitability, the Feed-In-Tariff should be increased, from the current level of 90.9 € MWh⁻¹, to between 97 and 105 € MWh⁻¹. Where possible, government organizations should help organize demand for the supply of heat. Local rural energy bureaus may help organize supply networks for biomass fuels throughout the country, in order to reduce seasonal and local fuel scarcity and price fluctuations.     

Wind tunnel test for the NREL phase VI rotor with 2 m diameter

The aerodynamic performance of the ‘NREL Phase VI’ rotor with a 2 m diameter was tested in the open jet test section. The original rotor with a 10.06 m diameter was tested in the NASA Ames tunnel and the test result was used as validation data for the computational model. The Reynolds number of the sectional airfoils in the original test is around 1.0E6 which is too high for a conventional wind tunnel with a diameter less than 5 m. The wind tunnel test to study the Reynolds number effect on the rotor performance from Re = 0.1E6 to Re = 0.4E6 was conducted in the KARI low speed wind tunnel with a 5 m × 3.75 m open jet test section. The torque generated by the blade was directly measured by the sensor installed in the rotating axis. The variation of the Reynolds number was achieved by changing the rotational speed. Two surface conditions, free transition and forced transition were employed in this test to study the surface trip effect. The test results for the free transition condition show that the power coefficient, Cp gradually increases with the Reynolds number, but the Cp for the forced transition condition does not vary with the Reynolds number. The maximum Cp for the free transition is 0.30 and it decrease to 0.22 for the forced transition conditions at the Reynolds number 0.4E6. The downstream flow velocity measured by 5-hole probe in the wind tunnel test was compared with BEMT calculation result. The comparison results show that the torque dependency on Reynolds number in the blade is mainly originated from the airfoil drag characteristics. A model to estimate the power of full scale blade was suggested based on these measurement results. The estimated power shows a good agreement with the full scale test result.     

Smart metering for residential energy efficiency: The use of community based social marketing for behavioural change and smart grid introduction

Community-based social marketing (CBSM) has shown to be very effective at inducing behavioural change due to its pragmatic approach. It has been found that nonintegrated intensive approaches towards changing individual's behaviour, such as education and economic self-interest are not successful.This paper will explain how a large urban electricity meter replacement program can achieve a reduction in peak demand and overall energy consumption through the use of advanced metering infrastructure (AMI or ‘smart meters’) coupled with CBSM, which in turn enables the progression towards a ‘smart grid’. In order to measure success the following targets were set:

• •Peak demand reduction (peak lopping) of 20% from the households participating in the Behaviour Change Programs (BCPs).
• •Peak demand shifting (load shifting) to reduce energy consumption during ‘super peak’ by 10% in BCP participating households.
• •Average total energy use reduction of 10% in BCP participating households.

The energy efficiency actions discussed with householders during eco-coaching, and other feedback communications, are identified by utilising the information regarding barriers and benefits generated from the research phase prior to coaching. These actions can include referral to other initiatives such as the provision of reduced cost solar PV power systems, direct load control devices for domestic air-conditioners, the time-of-use pricing product, the provision of in-home-displays (IHD) and other devices necessary for development of a ‘smart grid’.     

Off-grid electricity generation with renewable energy technologies in India: An application of HOMER

Renewable energy-based off-grid or decentralised electricity supply has traditionally considered a single technology-based limited level of supply to meet the basic needs, without considering reliable energy provision to rural consumers. The purpose of this paper is to propose the best hybrid technology combination for electricity generation from a mix of renewable energy resources to satisfy the electrical needs in a reliable manner of an off-grid remote village, Palari in the state of Chhattisgarh, India. Four renewable resources, namely, small-scale hydropower, solar photovoltaic systems, wind turbines and bio-diesel generators are considered. The paper estimates the residential, institutional, commercial, agricultural and small-scale industrial demand in the pre-HOMER analysis. Using HOMER, the paper identifies the optimal off-grid option and compares this with conventional grid extension. The solution obtained shows that a hybrid combination of renewable energy generators at an off-grid location can be a cost-effective alternative to grid extension and it is sustainable, techno-economically viable and environmentally sound. The paper also presents a post-HOMER analysis and discusses issues that are likely to affect/influence the realisation of the optimal solution.     

Comparative Life Cycle Assessment of a Thai Island's diesel/PV/wind hybrid microgrid

Hybrid microgrid systems are an emerging tool for rural electrification due in part to their purported environmental benefits. This study uses Life Cycle Assessment (LCA) to compare the environmental impacts of a diesel/PV/wind hybrid microgrid on the island of Koh Jig, Thailand with the electrification alternatives of grid extension and home diesel generators. The impact categories evaluated are: acidification potential (kg SO₂ eq), global warming potential (kg CO₂ eq), human toxicity potential (kg 1.4 DCB eq), and abiotic resource depletion potential (kg Sb eq). The results show that the microgrid system has the lowest global warming and abiotic resource depletion potentials of all three electrification scenarios. The use phase of the diesel generator and the extraction of copper are shown to significantly contribute to the microgrid's environmental impacts. The relative environmental impacts of the grid extension scenario are found to be proportional to the distance required for grid extension. Across all categories except acidification potential, the impacts from the home diesel generators are the largest. Sensitivity analyses show that maximizing the renewable energy fraction does not necessarily produce a more environmentally sustainable electrification scenario and that the diesel generator provides versatility to the system by allowing power production to be scaled significantly before more technology is needed to meet demand. While the environmental benefits of the microgrid increase as the installation community becomes more isolated, the choice of electrification scenario requires assigning relative importance to each impact category and considering social and economic factors.     

The improved CO2 capture system with heat recovery based on absorption heat transformer and flash evaporator

Absorption heat transformer (AHT) and flash evaporator (FE) are used to reduce the heat consumption of CO₂ capture processes and an AHT–FE-aided capture system is proposed. Analyses are carried out to verify the effectiveness in reducing heat consumption. Compared with the base CO₂ capture system of 3000 t/d CO₂ capture capacity from a 660 MW coal-fired power unit, the AHT–FE-aided capture system reduces the heat consumption from 3.873 GJ/tCO₂ to 3.772 GJ/tCO₂, and the corresponding energy saving is 2.62%. The economic analysis shows that the annual profit would be 2.94 million RMB Yuan. The payback period of the AHT–FE-aided capture system is approximately 2.4 years. Therefore, the AHT–FE-aided capture system is both economically and technically feasible for improving the CO₂ capture energy performance.     

Environmental assessment of electricity generation from an Italian anaerobic digestion plant

A standard ISO Life Cycle Assessment study was carried out to evaluate the environmental sustainability of electricity production from an anaerobic digestion (AD) plant using a mixture of dedicated energy crops, agricultural residues and livestock effluents as input materials. The functional unit was 1 MJ of electricity. System boundaries were from cradle to grave and covered all the phases from energy crops cultivation to the production of biogas and its use in a Combined Heat and Power plant to produce electricity. Liquid and solid digestate storage and spreading on agricultural land were included. Primary data were collected from the AD plant for all the above phases. Since heat produced is used only internally, no allocation was applied in the study. As regards digestate management, CH₄ emissions were calculated from literature, whereas four literature methods were applied for calculation of nitrogen emissions with the goal to perform a sensitivity analysis on LCA results. ILCD Handbook impact assessment methodologies were used. Results show that the main hotspots are energy crops cultivation and the management of digestate, mainly because of both nitrogen and methane emissions, affecting Global Warming, Acidification, Marine and Freshwater Eutrophication. Finally, a detailed Monte Carlo analysis, was carried out to evaluate the results uncertainty. The study represents the state of the art about the environmental performance of the AD plant with the use of sensitivity and uncertainty analysis, which both improve the reliability of results, and allows drawing general conclusions on how to mitigate the environmental impacts of AD process.     

Smart control of a horizontal axis wind turbine using dielectric barrier discharge plasma actuators

Rotating stall around a small-scale horizontal axis wind turbine was experimentally studied to characterize and assess smart rotor control by plasma actuators. Phase-locked Particle Image Velocimetry was used to map the flow over the rotor blade suction surface at numerous radial stations at a range of tip-speed-ratios. Flow separation occurred from the inboard of the blade and spread radially outwards as the tip-speed-ratio reduced. Plasma actuators placed along the span that produced a chord-wise body force had very little effect on the flow separation, even when operated in pulsed forcing mode. In contrast, plasma actuators along the blade chord that produced a body force into the radial directions (plasma vortex generators) successfully mitigated rotating stall. Torque due to aerodynamic drag was reduced by up to 22% at the lowest tip-speed-ratio of 3.7, suppressing stall over the outboard 50% of the blade. This was due to quasi-two-dimensional flow reattachment in the outboard region, and shifting of a fully stalled zone towards the hub in the inboard region because the plasma-induced body force counteracted the Coriolis-induced radial flow. This can significantly increase the turbine power output in unfavourable wind conditions and during start-up.     

Analysis of technology improvement opportunities for a 1.5 MW wind turbine using a hybrid stochastic approach in life cycle assessment

This paper presents an analysis of potential technological advancements for a 1.5 MW wind turbine using a hybrid stochastic method to improve uncertainty estimates of embodied energy and embodied carbon. The analysis is specifically aimed at these two quantities due to the fact that LCA based design decision making is of utmost importance at the concept design stage. In the presented case studies, better results for the baseline turbine were observed compared to turbines with the proposed technological advancements. Embodied carbon and embodied energy results for the baseline turbine show that there is about 85% probability that the turbine manufacturers may have lost the chance to reduce carbon emissions, and 50% probability that they may have lost the chance to reduce the primary energy consumed during its manufacture. The paper also highlights that the adopted methodology can be used to support design decision making and hence is more feasible for LCA studies.     

Estimating the offshore wind resources of the State of Ceará in Brazil

The onshore wind power is consolidated; the challenge is to reach the same level of maturity for offshore exploitation. Brazil has no offshore wind power plants and there are few studies in this direction. This paper aims to estimate the offshore wind resources in the State of Ceará, in Brazil. The investigation uses a mesoscale atmospheric computer model, the Regional Atmospheric Modeling System (RAMS), with horizontal resolution of 2 km, which estimates the offshore average wind speed, average wind direction, power density and turbulence taking into account the bathymetry data and navigation routes along the coast of Ceará. The wind potential was evaluated in three representative periods, La Niña, El Niño and Neutral year, analyzing the dry and rainy season for each period. The results indicate an average wind speed above 8 m/s and power density above 720 W/m² no matter the period evaluated, in the dry season. The predominant wind direction in the observed dry periods was from East to West and the turbulence intensity is smaller during dry season of El Niño. Besides, the bathymetry of the State of Ceará is shallow and the large ships route is far beyond the coast, offering no danger to future endeavors.     

Considering uncertainty in the optimal energy management of renewable micro-grids including storage devices

This paper proposes a new probabilistic framework based on 2m Point Estimate Method (2m PEM) to consider the uncertainties in the optimal energy management of the Micro Girds (MGs) including different renewable power sources like Photovoltaics (PVs), Wind Turbine (WT), Micro Turbine (MT), Fuel Cell (FC) as well as storage devices. The proposed probabilistic framework requires 2m runs of the deterministic framework to consider the uncertainty of m uncertain variables in the terms of the first three moments of the relevant probability density functions. Therefore, the uncertainty regarding the load demand forecasting error, grid bid changes and WT and PV output power variations are considered concurrently. Investigating the MG problem with uncertainty in a 24 h time interval with several equality and inequality constraints requires a powerful optimization technique which could escape from the local optima as well as premature convergence. Consequently, a novel self adaptive optimization algorithm based on θ-Particle Swarm Optimization (θ-PSO) algorithm is proposed to explore the total search space globally. The θ-PSO algorithm uses the phase angle vectors to update the velocity/position of particles such that faster and more stable convergence is achieved. In addition, the proposed self adaptive modification method consists of three sub-modification methods which will let the particles choosel the modification method which best fits their current situation. The feasibility and satisfying performance of the proposed method is tested on a typical grid-connected MG as the case study.