The role of energy storage in accessing remote wind resources in the Midwest

Replacing current generation with wind energy would help reduce the emissions associated with fossil fuel electricity generation. However, integrating wind into the electricity grid is not without cost. Wind power output is highly variable and average capacity factors from wind farms are often much lower than conventional generators. Further, the best wind resources with highest capacity factors are often located far away from load centers and accessing them therefore requires transmission investments. Energy storage capacity could be an alternative to some of the required transmission investment, thereby reducing capital costs for accessing remote wind farms. This work focuses on the trade-offs between energy storage and transmission. In a case study of a 200 MW wind farm in North Dakota to deliver power to Illinois, we estimate the size of transmission and energy storage capacity that yields the lowest average cost of generating and delivering electricity ($/MW h) from this farm. We find that transmission costs must be at least $600/MW-km and energy storage must cost at most $100/kW h in order for this application of energy storage to be economical.     

Evaluating the limits of solar photovoltaics (PV) in electric power systems utilizing energy storage and other enabling technologies

In this work, we evaluate technologies that will enable solar photovoltaics (PV) to overcome the limits of traditional electric power systems. We performed simulations of a large utility system using hourly solar insolation and load data and attempted to provide up to 50% of this system's energy from PV. We considered several methods to avoid the limits of unusable PV that result at high penetration due to the use of inflexible baseload generators. The enabling technologies considered in this work are increased system flexibility, load shifting via demand responsive appliances, and energy storage.     

Simulation of a combined wind and solar power plant

The combined generation of electricity by wind and solar energy is a very attractive solution for isolated regions with high levels of yearly wind energy and insolation. A computer model is developed for the simulation of the electricity system of a Mediterranean island, including a wind power plant, a photovoltaic power plant and a storage system. In order to obtain an overall view of the system performance and economic aspects, the model also incorporates a number of diesel generators. Daily simulations for the Greek island Kythnos show that such a combined system of moderate size can provide a large fraction of the electrical energy requirements. Various parameters calculated in the simulation can be used to improve the configuration of the system and to estimate the cost of the electrical energy unit.     

Forecast study of the supply curve of solar and wind technologies in Argentina,Brazil, Chile and Mexico

This paper forecasts the supply curve of non-conventional renewable technologies such as wind and solar generating stations in Argentina, Brazil, Chile and Mexico using technological and economic parameters. It also estimates the additional investment costs in solar and wind generation for reaching the renewable energy target in each of these countries. To assess the power supply profile from 1 axis tracking PV and horizontal axis wind turbine (three blade) stations, two different scenarios are developed for 2014 and 2025. Scenario 1 estimates the PV and wind annual electricity yield by using polycrystalline silicon (cSi poly) as semiconductor material for PV cells and a Vestas 90–3.0 MW turbine for the wind for 2014.Scenario 2 assumes a more efficient technology, such as CPV. In fact, the model employs 45% efficiency triple junction cells using ∼3500 m2 for each 1 MW installed capacity in 2025. Moreover, this scenario also assumes a more powerful type of turbine, i.e. Vestas 112–3.075 MW. The biggest potential for wind power is found to be in Argentina, followed by Brazil, Mexico and Chile. In addition, a 550 MW installed capacity CPV power station, using triple junction cells could generate up to 4 TWh in Chile in 2025.     

Technology mix alternatives with high shares of wind power and photovoltaics—case study for Spain

The shift to a low carbon society is an issue of highest priority in the EU. For electricity generation, such a target counts with three main alternatives: renewable energies, nuclear power and carbon capture and storage. This paper focuses on the renewables’ alternative. Due to resource availability, a technology mix with a high share of PV and wind power is gaining increasing interest as a major solution for several EU member states and in part for the EU collectively to achieve decarbonization and energy security with acceptable costs. Due to their intermittency, the integration of high shares of PV and wind power in the electricity supply is challenging. This paper presents a techno-economic assessment of technology mix alternatives with a high share of PV and wind power in Spain, as an example. Thereby, the focus is on the option of increasing wind curtailment versus substituting rigid baseload generation in favor of the more flexible gas turbines and combined cycle gas turbines.     

Combining hydro and variable wind power generation by means of pumped-storage under economically viable terms

Pumped hydro storage (PHS) systems which are located at isolated regions and are able to exploit the rejected wind energy amounts produced by local wind farms, seem to gain interest worldwide and to become essential in regard to higher shares of renewable-generated electricity. Despite the high wind potential encountered in many Greek island regions, the wind energy contribution to the electrification of these areas is significantly restricted due to imposed electrical grid limitations. In this context, the current work examines the economic viability of a wind-based PHS system (wind-hydro solution) which provides the local electrical grid of an Aegean Sea island, Lesbos, with guaranteed energy amounts during the peak load demand periods. Based on the maximization of the project’s net present value, the optimum system configuration is proposed while many other feasible solutions are revealed. According to the results obtained the implementation of this project demonstrates excellent technical and economic performance, while at the same time renewable energy sources (RES) contribution is doubled reaching almost 20% of the Lesbos island electrical energy consumption.     

Simulating reservoir storage for a wind-hydro hydrid system

A wind-hydro hybrid system is proposed to improve Brazil's use of its renewable energy portfolio. In this scheme, winds from local or remote locations supply extra generation, so that the hydroelectric outflow can be reduced accordingly to wind production. The water savings, in turn, lead to a significant improvement of the reservoir's storage. A simple model is developed and applied to the Itumbiara hydroelectric reservoir of midwest Brazil. Scenarios for different wind contributions are compared to historical observations from 1994 to 2011. Results suggest that, if implemented, the hybrid system should improve the country's energy security. Hydroelectric reservoirs might be able to confront interannual climate variability without risks to the energy supply. A positive impact on the multiple use of reservoirs is expected for fish-farming, irrigation, recreation, navigation and water supply.     

Grid flexibility and storage required to achieve very high penetration of variable renewable electricity

We examine the changes to the electric power system required to incorporate high penetration of variable wind and solar electricity generation in a transmission constrained grid. Simulations were performed in the Texas, US (ERCOT) grid where different mixes of wind, solar photovoltaic and concentrating solar power meet up to 80% of the electric demand. The primary constraints on incorporation of these sources at large scale are the limited time coincidence of the resource with normal electricity demand, combined with the limited flexibility of thermal generators to reduce output. An additional constraint in the ERCOT system is the current inability to exchange power with neighboring grids.     

Economic analysis of reactive power compensation in a wind farm: Influence of Spanish energy policy

Presently, renewable energies and especially wind energy are gaining a special relevance in the electrical market worldwide. This current rate of growth brings with it the need for the various wind farms to not limit themselves to producing energy but also provide stability to the network within its capabilities. So, the actual objective is to adapt the installations that produce wind energy in such a way that they give a maximum amount of support in any given moment to the electrical network. For this purpose, there are governing techno-economic parameters that influence the economic behavior of commercial wind farms. A complete cost-benefit analysis model is developed, focused on incorporating automatic capacitor banks into wind farms for the compensation of reactive power. This economic analysis is about doubly fed induction generator (DFIG) wind turbines. Although this kind of wind turbines have a certain capability in terms of modulating reactive power, this capacity is not enough to achieve the new requirements of reactive power regulation in Spain and it is necessary to invest in systems of external compensation.In this paper, we have studied the case of DFIG wind turbine and capacitor banks, although the used methodology can be applied to other technologies as well by simply amplifying the algorithms according to the specific characteristics of the option elected. Following this premise, a detailed analysis of the specific needs of a wind farm has been carried out, as well as a search for the optimum performance for the compensation of reactive power.     

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.     

Economic feasibility and optimisation of an energy storage system for Portland Wind Farm (Victoria,Australia)

This paper presents the details of a theoretical study of the economic advantages of using large-scale energy storage to complement a wind farm in a base-load dominated electricity grid. A computer model is developed which simulates the operation of several energy storage systems when used with the 190-MW Portland Wind Farm (PWF) located in Portland, Victoria, Australia. A variety of operating strategies are compared with the results of a dynamic programming model which finds the maximum possible revenue which a given system can generate for a set of input conditions. Three energy storage systems are modelled and costed: Pumped Seawater Hydro Storage (PSHS), Compressed Air Energy Storage (CAES), and Thermal Energy Storage (TES). It is found that CAES is the most profitable storage medium, requiring a capital expenditure of A$140 M and generating a rate of return (ROR) of 15.4%. The ROR for PSHS was 9.6%, and for TES was 8.0%. Therefore, a significant investment opportunity exists for the installation of an energy storage system in this wind farm. It is therefore highly recommended that CAES is investigated further with the aim of introducing large-scale energy storage to PWF and other similar wind turbine installations.     

System behaviour of compressed-air energy-storage in Denmark with a high penetration of renewable energy sources

In 2005, wind power supplied 19% of the 36 TWh annual electricity demand in Denmark, while 50% was produced at combined heat-and-power plants (CHP). The installed wind-turbine capacity in Western Denmark exceeds the local demand at certain points in time. So far, excess production has been exported to neighbouring countries. However, plans to expand wind power both in Denmark and in its neighbouring countries could restrain the export option and create transmission congestion challenges. This results in a need to increase the flexibility of the local electricity-system. Compressed-Air Energy-Storage (CAES) has been proposed as a potential solution for levelling fluctuating wind-power production and maintaining a system balance. This paper analyses the energy-balance effects of adding CAES to the Western Danish energy-system. Results show that even with an unlimited CAES plant capacity, excess power production is not eliminated because of the high percentage of CHP production. The optimal wind-power penetration for maximum CAES operation is found to be around 55%. The minimum storage size for CAES to fully eliminate condensing power plants operation in the optimized system is over 500 GWh, which corresponds to a cavern volume of around 234 Mm³ at an average pressure of 60 bar. Such a storage size would be technically and economically unfeasible. The analysis, however, did not include the potential role of a CAES plant in regulating the power services.     

Hydrogen storage and demand to increase wind power onto electricity distribution networks

An optimal power flow (OPF) methodology is developed to investigate the provision of a demand hydrogen as a means to maximise wind power generation in relation to a constrained electricity network. The use of excess wind energy to generate hydrogen for use as a transport fuel is investigated. Hydrogen demand is included in the objective function of the OPF, and a techno-economic analysis is presented. We conclude that using this method to generate hydrogen increases the utilisation of wind energy and allows for a hydrogen demand to be met at or near to the point of use. The OPF algorithm that has been developed optimises the amount of wind energy utilised, as well as minimising the amount of hydrogen demand not met. The cost at which the hydrogen is produced was found to be dependent on the operating methodology, component capital investment costs, level of hydrogen demand, and storage constraint.     

Understanding the variability of wind power costs

Wind power has a significant contribution to make in efforts to abate CO₂ emissions from global energy systems. Currently, wind power generation costs are approaching parity with costs attributed to conventional, carbon-based sources of energy but the economic advantage still rests decidedly with conventional sources. Therefore, there is an imperative to ensure that wind power projects are developed in the most economically optimal fashion. For wind power project developers, shaving a few tenths of a cent off of the kilowatts per hour cost of wind power can mean the difference between a commercially viable project and a non-starter. For civic authorities who are responsible for managing municipally supported wind power projects, optimizing the economics of such projects can attenuate stakeholder opposition. This paper attempts to contribute to a better understanding of how to economically optimise wind power projects by conflating research from the fields of energy economics, wind power engineering, aerodynamics, geography and climate science to identify critical factors that influence the economic optimization of wind power projects.     

Simulation and size optimization of a pumped–storage power plant for the recovery of wind-farms rejected energy

The hybrid wind–hydro power generation appears to be an attractive solution for isolated, autonomous electric grids in order to increase the wind energy penetration and cost-effectiveness. This work presents a numerical methodology for optimum sizing of the various components of a reversible hydraulic system designed to recover the electric energy that is rejected from wind farms due to imposed grid limitations. The algorithm is applied to study a practical case using time variation data of rejected power from a number of wind farms installed in the island of Crete, Greece. The free design parameters of the system include the turbine size, the size and the number of the pumps, the penstock diameter and thickness, and the reservoirs’ capacity, whereas some critical financial parameters are also considered. The numerical procedure combines an evaluation algorithm that simulates in detail the plant operation during a 12-month period, and an automated optimization software based on evolutionary algorithms. The economic analysis uses dynamic evaluation methods and the attainability of various objectives is examined using single or multi-objective optimizations. In addition, the developed numerical tool is used to perform several parametric studies and sensitivity tests in order to analyse in depth the influence of the most important parameters on the plant operation and economic behaviour. The results showed that a well optimized design may be crucial for the technical and economic viability of the examined system.     

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.