Energy return on investment (EROI) of mini-hydro and solar PV systems designed for a mini-grid

With dramatic cost declines and performance improvements, both mini-hydropower and solar photovoltaics (PV) now serve as core options to meet the growing demand for electricity in underserved regions worldwide. We compare the net energy return on energy invested (EROI) of mini-hydropower and solar electricity using five existing mini-hydropower installations in northern Thailand with grid-connected solar PV simulations. Both assessments use a life cycle perspective to estimate the EROI. We find that distributed mini-grids with penetrations of solar PV up to 50% of annual generation can exceed the EROI of some fossil-based traditional centralized grid systems. The analysis will help planners and engineers optimize mini-grids for energy payback and utilize local resources in their design. The results suggest higher EROI ratios for mini-hydropower plants than solar PV, though mini-hydropower plants typically yield lower EROI ratios than their large-scale hydropower counterparts.     

Energy auditing of diversified rice–wheat cropping systems in Indo-gangetic plains

The field investigations were carried out for energy use analysis in terms of different input requirements and outputs harvested under the diversified rice–wheat cropping systems at the research farm of Project Directorate for Cropping Systems Research, Modipuram, Meerut, India during the year 2000–2004. The experiments were conducted on rice (Oryza sativa L.)–wheat (Triticum aestivum L. emend. Fiori and Paol) system involving 8 sequences using diversification, furrow irrigated raised bed system (FIRB) of sowing wheat, use of summer period for deep ploughing or raising legume crops for seed or green manure to study the energy dynamics of different diversified cropping systems. Results revealed that total energy use was highest in rice–potato–wheat (i.e. 77,601 MJ/ha in flat bed & 75,697 MJ/ha in raised bed) followed by rice–wheat–sesbania (i.e. 48,770 MJ/ha in flat & 47,830 MJ/ha in raised bed) and rice–wheat–greengram (i.e. 48,414 MJ/ha in flat & 47,482 MJ/ha in raised bed). In overall, the raised bed sowing of wheat in the cropping system consumed 6–11% less fertilizer energy than flat bed while saved up to 4.2% energy through irrigation. The total output energy of the system was recorded significantly higher in rice–potato–wheat system (i.e. 222,836 MJ/ha in flat bed & 218,065 MJ/ha in raised bed) in comparison to rice–wheat–greengram (i.e. 177,477 MJ/ha in flat bed & 175,125 MJ/ha in raised bed), rice–wheat–sesbania (i.e. 172,000 MJ/ha in flat bed & 168,919 MJ/ha in raised bed) and rice–wheat system (i.e. 156,085 MJ/ha in flat bed & 151,862 MJ/ha in raised bed). The significantly higher net return of energy was obtained in rice–potato–wheat system as compared to other systems. This system required about 75% more input energy but provided about 42% more output energy compared to conventional rice–wheat system. About 10% higher output energy was obtained through growing greengram in summer for grain and foliage incorporation while 14% gain obtained by green manuring sesbania, when compared to deep summer ploughing after wheat harvest.     

Modelling of energy systems with a high percentage of CHP and wind power

This paper presents the energy system analysis model EnergyPLAN, which has been used to analyse the integration of large scale wind power into the national Danish electricity system. The main purpose of the EnergyPLAN model is to design suitable national energy planning strategies by analysing the consequences of different national energy investments. The model emphasises the analysis of different regulation strategies and different market economic optimisation strategies.At present wind power supply 15% of the Danish electricity demand and ca 50% is produced in CHP (combined heat and power production). The model has been used in the work of an expert group conducted by the Danish Energy Agency for the Danish Parliament. Results are included in the paper in terms of strategies, in order to manage the integration of CHP and wind power in the future Danish energy supply in which more than 40% of the supply is expected to come from wind power.     

Large-scale integration of wind power into the existing Chinese energy system

This paper presents the ability of the existing Chinese energy system to integrate wind power and explores how the Chinese energy system needs to prepare itself in order to integrate more fluctuating renewable energy in the future. With this purpose in mind, a model of the Chinese energy system has been constructed by using EnergyPLAN based on the year 2007, which has then been used for investigating three issues. Firstly, the accuracy of the model itself has been examined and then the maximum feasible wind power penetration in the existing energy system has been identified. Finally, barriers have been discussed and suggestions proposed for the Chinese energy system to integrate large-scale renewable energy in the future. It is concluded that the model constructed by the use of EnergyPLAN can accurately simulate the Chinese energy system. Based on current regulations to secure grid stability, the maximum feasible wind power penetration in the existing Chinese energy system is approximately 26% from both technical and economic points of view. A fuel efficiency decrease occurred when increasing wind power penetration in the system, due to its rigid power supply structure and the task of securing grid stability, was left primarily to large coal-fired power plants. There are at least three possible solutions for the Chinese energy system to integrate large-scale fluctuating renewable energy in the long term: Redesigning the regulations to secure grid stability by means of diversifying the participants, such as including hydropower and CHP plants; integrating large-scale heat pumps combined with heat storage devices to satisfy district heat demands and developing electric vehicles to promote off peak electricity utilisation.     

The value of compressed air energy storage with wind in transmission-constrained electric power systems

In this work, we examine the potential advantages of co-locating wind and energy storage to increase transmission utilization and decrease transmission costs. Co-location of wind and storage decreases transmission requirements, but also decreases the economic value of energy storage compared to locating energy storage at the load. This represents a tradeoff which we examine to estimate the transmission costs required to justify moving storage from load-sited to wind-sited in three different locations in the United States. We examined compressed air energy storage (CAES) in three “wind by wire” scenarios with a variety of transmission and CAES sizes relative to a given amount of wind. In the sites and years evaluated, the optimal amount of transmission ranges from 60% to 100% of the wind farm rating, with the optimal amount of CAES equal to 0–35% of the wind farm rating, depending heavily on wind resource, value of electricity in the local market, and the cost of natural gas.     

Performance investigation of an integrated wind energy system for co-generation of power and hydrogen

In this paper, a wind turbine energy system is integrated with a hydrogen fuel cell and proton exchange membrane electrolyzer to provide electricity and heat to a community of households. Different cases for varying wind speeds are taken into consideration. Wind turbines meet the electricity demand when there is sufficient wind speed available. During high wind speeds, the excess electricity generated is supplied to the electrolyzer to produce hydrogen which is stored in a storage tank. It is later utilized in the fuel cell to provide electricity during periods of low wind speeds to overcome the shortage of electricity supply. The fuel cell operates during high demand conditions and provides electricity and heat for the residential application. The overall efficiency of the system is calculated at different wind speeds. The overall energy and exergy efficiencies at a wind speed 5 m/s are then found to be 20.2% and 21.2% respectively.     

A review of energy storage technologies for wind power applications

Due to the stochastic nature of wind, electric power generated by wind turbines is highly erratic and may affect both the power quality and the planning of power systems. Energy Storage Systems (ESSs) may play an important role in wind power applications by controlling wind power plant output and providing ancillary services to the power system and therefore, enabling an increased penetration of wind power in the system. This article deals with the review of several energy storage technologies for wind power applications. The main objectives of the article are the introduction of the operating principles, as well as the presentation of the main characteristics of energy storage technologies suitable for stationary applications, and the definition and discussion of potential ESS applications in wind power, according to an extensive literature review.     

Analysis of wind climate and wind energy potential of regions in Turkey

Investments in wind plants have increased rapidly as a result of changes to legal regulations in Turkey over the last five years. This has also led to an increase in the number of wind potential analyses in various regions of the country. This study analyzes the wind climate features of three regions in Turkey and their energy potential. In order to determine the features of wind in these regions, a five-layer Sugeno-type ANFIS model established under the MATLAB-Simulink software was used and the relationship between wind speed and other climate variables determined. In the second phase, WASP software was used to complete the wind energy potential analyses using wind speed data. The final phase includes calculations of the amount of electricity to be obtained technically and capacity usage rates of the installed turbines if wind farms are established in the selected areas. The comparative tables and graphics of the said areas were obtained. In conclusion, the selected areas are well located for the installation of parallel-connected wind plants to the national network in terms of the reliability of wind, the dispersion of wind potential and capacity usage rates.     

Thermodynamic performance assessment of wind energy systems: An application

In this paper, the performance of wind energy system is assessed thermodynamically, from resource and technology perspectives. The thermodynamic characteristics of wind through energy and exergy analyses are considered and both energetic and exergetic efficiencies are studied. Wind speed is affected by air temperature and pressure and has a subsequent effect on wind turbine performance based on wind reference temperature and Bernoulli’s equation. VESTAS V52 wind turbine is selected for (Sharjah/UAE). Energy and exergy efficiency equations for wind energy systems are further developed for practical applications. The results show that there are noticeable differences between energy and exergy efficiencies and that exergetic efficiency reflects the right/actual performance. Finally, exergy analysis has been proven to be the right tool used in design, simulation, and performance evaluation of all renewable energy systems.     

Life cycle energy and greenhouse emissions analysis of wind turbines and the effect of size on energy yield

Wind turbines, used to generate renewable energy, are typically considered to take only a number of months to produce as much energy as is required in their manufacture and operation. With a life expectancy of upwards of 20 years, the energy produced by wind turbines over their life can be many times greater than that embodied in their production. Many previous life cycle energy studies of wind turbines are based on methods of assessment now known to be incomplete. These studies may underestimate the energy embodied in wind turbines by more than 50%, potentially overestimating the energy yield of those systems and possibly affecting the comparison of energy generation options. With the increasing trend towards larger scale wind turbines, comes a respective increase in the energy required for their manufacture. It is important to consider whether or not these increases in wind turbine size, and thus embodied energy, can be adequately justified by equivalent increases in the energy yield of such systems. This paper presents the results of a life cycle energy and greenhouse emissions analysis of two wind turbines and considers the effect of wind turbine size on energy yield. The issue of incompleteness associated with many past life cycle energy studies is also addressed. Energy yield ratios of 21 and 23 were found for a small and large scale wind turbine, respectively. The embodied energy component was found to be more significant than in previous studies, emphasised here due to the innovative use of a hybrid embodied energy analysis approach. The life cycle energy requirements were shown to be offset by the energy produced within the first 12 months of operation. The size of wind turbines appears to not be an important factor in optimising their life cycle energy performance.     

Momentum analysis of wind energy concentrator systems

The momentum theory is applied to wind energy concentrator systems. Both the concentration of the mass flow through the turbine and the augmentation of the specific energy drop over the turbine are taken into account. It is shown that the power coefficient of a system can be written as the product of three factors: a mass concentration coefficient an energy augmentation coefficient and an extraction coefficient. By this splitting, the relative importance of the three components in the power output of a system can be analysed.     

A joint probability density function of wind speed and direction for wind energy analysis

A very flexible joint probability density function of wind speed and direction is presented in this paper for use in wind energy analysis. A method that enables angular–linear distributions to be obtained with specified marginal distributions has been used for this purpose. For the marginal distribution of wind speed we use a singly truncated from below Normal–Weibull mixture distribution. The marginal distribution of wind direction comprises a finite mixture of von Mises distributions. The proposed model is applied in this paper to wind direction and wind speed hourly data recorded at several weather stations located in the Canary Islands (Spain). The suitability of the distributions is judged from the coefficient of determination R².

The conclusions reached are that the joint distribution proposed in this paper: (a) can represent unimodal, bimodal and bitangential wind speed frequency distributions, (b) takes into account the frequency of null winds, (c) represents the wind direction regimes in zones with several modes or prevailing wind directions, (d) takes into account the correlation between wind speeds and its directions. It can therefore be used in several tasks involved in the evaluation process of the wind resources available at a potential site. We also conclude that, in the case of the Canary Islands, the proposed model provides better fits in all the cases analysed than those obtained with the models used in the specialised literature on wind energy.     

Economic assessment of the engineering basis for wind power: Perspective of a vertically integrated utility

If wind park configurations are globally coordinated across the service area of a power utility, then electricity can be generated for the grid with substantial cost advantages. Based on this premise, the paper introduces a model by which large scale assessment of grid connected wind based power generation may be undertaken for a utility service area. The model can be useful to the policy maker for decisions regarding suitable wind portfolio standards (WPS) definition. The utility on the other hand, may use the model to study its service area for prospective wind based generation. Aspects of the problem modelled include cost-of-energy from individual generating units, daily load variations for the utility with emphasis on limited penetration, features of wind at prospective installation sites, makes of wind energy conversion systems (WECS) available, and recovery of expenditure through revenue. Application of the model to an assessment exercise for the state of Andhra Pradesh (India) is presented as an example.     

Design requirements for medium-sized wind turbines for remote and hybrid power systems

This paper provides an overview of the design requirements for medium-sized wind turbines intended for use in a remote hybrid power system. The recommendations are based on first-hand experience acquired at the University of Massachusetts through the installation, operation, and upgrade of a 250-kW turbine on a mountain top with difficult access in Western Massachusetts. Experience with the operation of this turbine and the design of its control system, together with a long history in the design and analysis of hybrid power systems, has made it possible to extend the work in Western Massachusetts to remote or hybrid power systems in general. The University test site has many attributes of more remote sites and the overall wind turbine installation is typical of one that could power a hybrid wind system. For example, access to the site is limited due to steep terrain, snow, and environmental restrictions. Also, the power lines feeding the turbine exhibit voltage sags and phase imbalance, especially during start-up. This paper is based on the experience gained from the operation of this wind turbine and assesses the requirements for the design and operation of medium to large wind turbines in remote locations. The work summarizes lessons learned relative to: (1) sensors, communication, and control capabilities; (2) grid connection issues; and (3) weather-related problems. The final section of the paper focuses on design requirements to ensure successful installation and the completion of maintenance and repairs at remote sites.     

A simplified model for estimating yearly wind fraction in hybrid-wind energy systems

This article presents a simplified algorithm to estimate the yearly wind fraction, the fraction of energy demand provided by wind generator, in a hybrid-wind system (typically a PV-wind) with battery storage. The novel model is drawn based on the simulation results, using 8-year long measured hour-by-hour wind speed data from five different locations throughout the world. The simulation program simulates the battery state of voltage (SoV) and is able to predict the wind fraction for a period of time, typically monthly or yearly. The yearly wind fraction values obtained from the simulations are plotted against the ratio of energy to load for various battery storage capacities to obtain wind fraction curves. The novel method correlates the yearly wind fraction with the parameters of the Weibull distribution function, thus, offering a general methodology. The yearly wind fraction curves are mathematically represented using a 2-parameter model. The novel algorithm is validated by comparing the simulated wind fraction values with those calculated from the simplified algorithm. The standard error of estimation of the WF from the simplified algorithm is further presented for each battery capacity.     

Efficiency of wind energy utilization for electricity and heat supply in northern regions of Russia

The paper describes a method for assessing the economic efficiency of wind energy utilization within small autonomous systems for both electricity and heat supply. The obtained analytical solution allows the simplification of calculations in comparison to the methods of chronological modeling and numerical algorithms for application of the convolution method.The economic effect of using wind turbines is assessed for remote communities of the extreme north of Russia with a maximum electric load of 200 kW for the turbines with a capacity from 30 to 800 kW, taking into account variation of possible growth rates of fossil fuel price for back-up sources of electric and heat energy.The calculations performed have shown that at the existing and forecasted rates of fuel price escalation, the economic effect of using surplus (as a result of mismatch in production and consumption) electric energy for heat supply will be 1.5–2.0 times higher. In this case, the optimal capacity of wind turbines can substantially exceed electric load power (two to four times).     

Dynamic model of wind energy conversion systems with PMSG-based variable-speed wind turbines for power system studies

In order to study the impact of a wind farm on the dynamics of the power system, a significant issue is to develop appropriate equivalent models that allow characterizing the dynamics of all individual wind turbine generators (WTGs) composing the park. In this sense, with the advance of power electronics, direct-driven permanent magnet synchronous generators (PMSGs) have drawn increased interest to wind turbine manufacturers due to their advantages over other variable-speed WTGs. These include the possibility of multi-pole design with a gearless construction that offers slow speed operation and reduced maintenance since no brushes are used, elimination of the excitation system, full controllability for maximum wind power extraction and grid interface, and easiness in accomplishing fault-ride through and grid support. In this way, this paper presents a comprehensive dynamic equivalent model of a wind farm with direct-driven PMSG wind turbines using full-scale converters and its control scheme. The proposed simplified modelling is developed using the state-space averaging technique and is implemented in the MATLAB/Simulink environment. The dynamic performance of the wind farm and its impact on the power system operation is evaluated using the phasor simulation method.     

The spectrum of power from wind turbines

The power spectral density of the output of wind turbines provides information on the character of fluctuations in turbine output. Here both 1-second and 1-hour samples are used to estimate the power spectrum of several wind farms. The measured output power is found to follow a Kolmogorov spectrum over more than four orders of magnitude, from 30 s to 2.6 days. This result is in sharp contrast to the only previous study covering long time periods, published 50 years ago. The spectrum defines the character of fill-in power that must be provided to compensate for wind's fluctuations when wind is deployed at large scale. Installing enough linear ramp rate generation (such as a gas generator) to fill in fast fluctuations with amplitudes of 1% of the maximum fluctuation would oversize the fill-in generation capacity by a factor of two for slower fluctuations, greatly increasing capital costs. A wind system that incorporates batteries, fuel cells, supercapacitors, or other fast-ramp-rate energy storage systems would match fluctuations much better, and can provide an economic route for deployment of energy storage systems when renewable portfolio standards require large amounts of intermittent renewable generating sources.     

Designing an index for assessing wind energy potential

To meet the increasing global demand for renewable energy, such as wind energy, an increasing number of wind parks are being constructed worldwide. Finding a suitable location requires a detailed and often costly analysis of local wind conditions. Plain average wind speed maps cannot provide a precise forecast of wind power because of the non-linear relationship between wind speed and production. We suggest a new approach to assess the local wind energy potential. First, meteorological reanalysis data are applied to obtain long-term low-scale wind speed data at specific turbine locations and hub heights. Second, the relation between wind data and energy production is determined via a five parameter logistic function using actual high-frequency energy production data. The resulting wind energy index allows for a turbine-specific estimation of the expected wind power at an unobserved location. A map of the wind power potential for Germany exemplifies our approach.