Short-term Energy Storage Research Articles

Stored energy - Short-term and long-term energy storage methods

This paper deals with the short-term and long-term energy storage methods for standby electric power systems. Stored energy is required in uninterruptible standby systems during the transition from utility power to engine-generator power. Various storage methods provide energy when the utility source fails. For batteries in cycling duty, Li-ion and Ni-MH cells are coming into wide use to displace VRLA batteries. For float duty, VRLA and NiCd batteries predominate. Flywheel-generator units are being offered to replace batteries in UPS. Fuel cells require a warm-up time and, hence, are suitable for long-term operation. Ultracapacitors are proposed to replace batteries for short-term discharge. CAED and hydrogen energy storage are suitable for large projects.

Dissemination of off-grid hybrid wind-diesel-battery power systems for electrification of isolated settlements of hot regions

Since the maturing of the wind farm industry, attention has been focused on the use of wind turbines for electricity production in remote areas. Generally, remote villages are driven by diesel generators. However, introduction/dissemination of wind energy conversion systems (WECS) into the existing diesel systems results in the reduction of the diesel fuel consumption and eventually allows atmospheric pollution to subside. A short-term energy storage integrated with wind-diesel system may compensate for fluctuations in the power output of the wind turbine and raise the fuel saving potential. The Kingdom of Saudi Arabia's (K.S.A) area is large, with large number of villages/settlements scattered all over the Kingdom. In the present study, hourly mean wind-speed data recorded at an airport, K.S.A., has been analyzed to investigate the technical and economic feasibility/viability of utilizing off-grid hybrid (wind-diesel-battery) power systems to meet the load requirements of a typical remote/isolated village with annual electrical energy demand of 13,244 MWh. The airport is located in the vicinity of the candidate settlement. The hybrid systems simulated comprise of various combinations (wind farms) of 600 kW commercial WECS supplemented with diesel generators and a short-term battery storage. The amount of battery storage capacity has been varied from 0 to 60 load minutes (equivalent to 0–60 min of average load). National Renewable Energy Laboratory's (NREL’s) HOMER software has been used to perform the technical and economic analysis of hybrid wind-diesel-battery power systems. The investigation indicates that for a hybrid system consisting of 3.6 MW (six 600 kW wind machines, 50 m hub-height) wind farm capacity together with 4.5 MW diesel system (three 1.5 MW diesel units) and a battery storage of 30 load minutes (equivalent to 30 min of average load), the wind penetration is 24%. The cost of generating energy from the above hybrid configuration has been found to be 0.078 US$/kWh (assuming a diesel fuel price of 0.1 $/liter). The simulation results highlight that the number of operational hours of diesel generators in wind-diesel system decreases with increase in wind farm capacity. The study also illustrates that for a given hybrid wind-diesel system, the decrease in diesel run time is further enhanced by inclusion of battery storage capacity. An attempt has been made to address the effect of wind penetration, effect of hub-height on energy production, cost of wind-diesel-battery systems, cost of energy production, excess electricity, un-met load, percentage fuel savings and decrease in carbon emissions, etc (for different scenarios such as wind-diesel without storage, wind-diesel with storage, as compared to diesel-only situation).

Supercapacitor Energy Storage for Wind Energy Applications

As wind energy reaches higher penetration levels, there is a greater need to manage intermittency associated with the individual wind turbine generators. This paper considers the integration of a short-term energy storage device in a doubly fed induction generator design in order to smooth the fast wind-induced power variations. This storage device can also be used to reinforce the dc bus during transients, thereby enhancing its low-voltage ride through (LVRT) capability. The topology is evaluated in terms of its ability to improve the performance both during normal operation and during transients. Results show that when storage is sized based upon the LVRT requirement, it can effectively damp short-term power oscillations, and it provides superior transient performance when compared with conventional topologies

Power quality improvement of a stand-alone power system subjected to various disturbances

In wind-diesel stand-alone power systems, the disturbances like random nature of wind power, turbulent wind, sudden changes in load demand and the wind park disconnection effect continuously the system voltage and frequency. The satisfactory operation of such a system is not an easy task and the control design has to take in to account all these subtleties. For maintaining the power quality, generally, a short-term energy storage device is used. In this paper, the performance of a wind-diesel system associated with a superconducting magnetic energy storage (SMES) system is studied. The effect of installing SMES at wind park bus/load bus, on the system performance is investigated. To control the exchange of real and reactive powers between the SMES unit and the wind-diesel system, a control strategy based on fuzzy logic is proposed. The dynamic models of the hybrid power system for most common scenarios are developed and the results presented.

Operational characteristics of energy storage high temperature superconducting flywheels considering time dependent processes

Technical and economical feasibilities of short-term energy storage flywheels with high temperature superconducting (HTS) bearing are widely investigated. It is essential to reduce the ac losses caused by magnetic field variations in HTS bulk disks/rings (levitators) used in the magnetic bearings of flywheels. For the HTS bearings the calculation and measurement of the magnetic field distribution were performed. Effects like eccentricity, tilting were measured. Time dependency of the levitation force following a jumpwise movement of the permanent magnet was measured. The results were used to setup an engineering design algorithm for energy storage HTS flywheels. This algorithm was applied to an experimental HTS flywheel model with a disk type permanent magnet motor/generator unit designed and constructed by the authors. A conceptual design of the disk-type motor/generator with radial flux is shown.

Influence of sexual maturity on feeding, growth and energy stores of wild Atlantic salmon parr

Maturing Salmo salar parr had significantly lower short-term energy stores (indicated by hepato-somatic index) in August, and significantly lower energy stores and growth rate (indicated by RNA : DNA) in September than immature parr captured from the same stream sites on the same date. There were no significant differences in gut fullness or protein concentrations, suggesting that up to early September the main energetic consequences of maturation were a reduction in allocations to growth and short-term energy storage, but not a mobilization of long-term stored energy in the form of proteins. These are the first observations of relative food intake and energy storage for maturing parr under natural conditions, and also the first to assess growth effects on wild fish before completion of the maturation process.

The utilisation of short term energy storage with tidal current generation systems

This paper is an investigation into how the coupling of tidal current turbines with energy storage mechanisms could result in an effective firm supply capacity. It is shown that the cyclic nature the tidal current resource ensures that even relatively small storage capacities could prove effective.

95/03977 Analysis of an underground electric heating system with short-term energy storage

95/03977 Analysis of an underground electric heating system with short-term energy storage

The load matching approach to sizing photovoltaic systems with short-term energy storage

This paper presents results obtained for sizing the photovoltaic array and the battery in PV systems with short-term energy storage. The method is based on maximizing the utilization of the array output energy, and minimizing losses associated with charging and discharging the battery. Results show that the two-dimensional problem of sizing the PV array and the battery can be replaced by a one-dimensional problem of sizing the array. Under the standard insolation model, the maximum electrical energy output from a 1 kW peak array over a 1 day period is approximately 6 kWh. However, due to the various losses in the system the useful daily dc energy is about 5 kWh. The array voltage at the maximum power point must be at least 1.35 times the battery open circuit voltage at full charge in the case of direct-coupled, or 1.6 if a power conditioning unit is used. The maximum depth of discharge of the battery is 65%. For maximum performance, the battery should be sized such that its state of charge varies between 0.35 and 0.85 per unit.

Wind diesel design and the role of short term flywheel energy storage

Wind diesel hybrid systems can often provide a cost effective solution to electricity supply in many rural and grid remote applications. The potential market for such stand alone systems is vast. The sizing and design of these systems to suite a given application is non-trivial. Design principles for wind diesel systems are presented with stress placed on the role of short term energy storage. It is shown that flywheels are the most appropriate form of energy storage. A user-friendly software package to help engineers design wind diesel systems has been developed over the last three years with support from the CEC's JOULE programme. The modelling and software development was undertaken cooperatively by several EEC and EFTA countries. An brief introduction to the software, which models both logistic and dynamic aspects of system operation, is provided and there is a discussion of its validation.

Night metabolism of recent photosynthate by sea ice algae in the high Arctic

Changes in intracellular distribution of recent (labelled) photosynthate during light-dark incubations were consistent with overnight consumption of low molecular weight compounds and carbohydrate, but continued protein synthesis, in sea ice algae from Resolute Passage, Canada, during April and May, 1986. Synthesis of labelled protein at night varied with preceding light availability but was always less than 30% of the daytime rate. Comparisons of labelled photosynthate dynamics against oxygen consumption and net changes of particulate matter composition and concentration showed that soluble polysaccharide was not the only major metabolic substrate, and that much of the carbon lost overnight was not recent, labelled photosynthate. Total net lipid synthesis was greatly underestimated by labelled photosynthate allocation. However, overnight consumption of the labelled lipid was directly proportional to photon flux density in the preceding light period, suggesting a short-term energy storage function for the small labelled portion of the total lipid pool. Arctic ice algae appear to incorporate only limited amounts of recent photosynthate into their large lipid pools even over a full 24 h photoperiod.

Thermal design of snow-melt road, utilizing short-term thermal energy storage under the road.

A theoretical analysis of a snow-melt road has been performed using a method of imaging line sources. The results showed that: (1) The snow-melt road proposed in this report is assumed to be a uniform concrete road which has a deep heat storage zone 2.9m under the road. (2) The heat loss through the road shoulder can be eliminated by a thermal insulator buried in the shoulder 50cm deep. (3) The power of the proposed type of heat storage is far superior to the standard one. Over 5 days, the surface heat flux of this road is larger than the standard one. (4) The optimal relation between the pitch, the depth of the buried heat transfer pipes and the temperature of water used are shown in the figures. A thermal design process is proposed.

Condition of larval anchovy (Engraulis mordax) in the Southern California Bight, as measured through lipid analysis

Northern anchovy larvae, Engraulis mordax, were collected on five cruises covering the Southern California Bight, one cruise in April 1984, four cruises in January, February and May 1986. The amounts of triacylglycerol, cholesterol and polar lipid were measured in individual anchovy larvae as indicators of their nutritional condition. There was a significant difference in each of the size-specific lipid components between the stations for four of the five cruises. This indicates that all the ocean habitats within a cruise were not equal in promoting growth (and presumably survival) in the anchovy larvae. There were also differences between cruises, where the percentage of the larvae judged to be in poor condition varied from 8 to 27%. Canonical correlation analyses revealed a significant relationship in most cases between the larval fish parameters and the physical and biological data collected from each occupied station. Cholesterol and triacylglycerol were the most important larval components, and the short-term energy storage component in the copepod Calanus pacificus was the most important station component. The data, however, are not sufficient to identify and characterize stations in the field which produce anchovy larvae in good condition.

Short-term thermal energy storage as a means of reducing the heat pump capacity required for domestic central heating systems

The effects upon the economics, size and performances of domestic central heating heat pumps by the incorporation of some thermal energy storage between the heat pump and the heat distribution system are studied with the aid of computer simulation programs. It is demonstrated that significant reductions in the capacity of the heat pump and system annual running costs can be made by using moderate quantities of heat storage without causing any detriment to the overall performance of the heating system. The results are being validated in the laboratory, where a phase-change material thermal energy store is linked to a heat pump and heat distribution system, and the performance of this system is being monitored.

Worldwide Applications of Ground-Coupled Heat Pumps, Conventional and Solar Assisted: ABSTRACT

The use of the ground as an energy source, sink or storage element for coupling to a heat pump has attracted renewed interest in recent years. Several system options have been developed, some of which use additional solar-derived energy. In applying ground coupling in a given situation, three major decisions must be made. First, it must be decided whether to use solar energy in the ground-coupled system, and if so, whether to design for long- or short-term energy storage. Second, the type of in-ground End_Page 957------------------------------ heat exchange device must be selected. These include the horizontal coil, the vertical heat exchanger, the buried water tank, and the buried flat plate. Third, the heat-exchange device must be sized relative to the heat pump, the load, and the solar components, if any. The ways in which these decisions have been approached in a variety of countries and climates have been analyzed as a base for assessing the outlook for ground-coupling applications in terms of economic, energy supply, and technology development scenarios which could work for or against ground coupling. These include availability and cost of the various forms of energy, in particular gas versus coal; availability of capital and interest rates; utility load profiles; and technical developments in air-to-air heat pumps, g s furnaces, and gas-fired heat pumps. The paper concludes with a discussion of research and development needs for ground coupling. End_of_Article - Last_Page 958------------

Dependability of Wind Energy Generators with Short-Term Energy Storage

Power fluctuations and power duration curves for wind energy generators, including energy storage facilities of a certain capacity, are compared to those of typical nuclear reactors. A storage system capable of delivering the yearly average power output for about 10 hours already makes the dependability of the wind energy system comparable to that of a typical nuclear plant.

Dependability of Wind Energy Generators with Short-Term Energy Storage

Power fluctuations and power duration curves for wind energy generators, including energy storage facilities of a certain capacity, are compared to those of typical nuclear reactors. A storage system capable of delivering the yearly average power output for about 10 hours already makes the dependability of the wind energy system comparable to that of a typical nuclear plant.