Optimization of load shedding system

An optimization algorithm is presented for an underfrequency load shedding system which is composed of several stages that are tripped at preset frequencies. The optimization of this system is considered with respect to a cost function that includes a dynamic part, which is the integral of the deviation from nominal frequency, and a static part which is the total load shedding. The optimization is constrained by the requirement of minimum allowed frequency and limitation on the total load of the shedding system. A projected gradient method is used for the solution, and analytic expressions for the partial derivatives are used to simplify the computation. Results of applying the optimization to a model of the Israeli power system are given together with a study of the cost parameters     

Pricing option contracts on the strategic petroleum reserve

In this article we examine the pricing of option contracts on the strategic petroleum reserve (SPR) and consider how these can be used by both the government and refiners. We analyze the interaction between the call and put option contracts, taking into account the underlying game, in the infinite Markov decision process with discounting, explaining the relationship between the valuation of options on the SPR by refiners and the valuation of financial options on a marker crude in financial markets. We conclude that the values of both call and put options on the SPR increase with oil prices and decrease with total inventory. Furthermore, our analysis shows that a more active management of the SPR creates higher social welfare (although refiners profit less from inventories) and larger volatility in inventory profits, decreasing private investment in petroleum stocks.     

An automatic load shedding scheme including pumped-storage units

An automatic load shedding scheme considering the pumped-storage units at Taiwan Power Company (Taipower) is proposed in this paper. Taipower owns ten pumped-storage units which can be shed with higher priority when operated in pumping mode in order to restore the system frequency. In this way, the amount of customer load required to be shed can be significantly decreased. The system reliability and stability can also be enhanced. In the paper, a load frequency control model is developed. An automatic load shedding scheme that is adaptable to Taipower operation is thus developed. The proposed method has been validated through the utility data and compared with the utility shedding scheme. Test results solidify the feasibility and effectiveness of the proposed method for the applications     

Optimal dynamic load shedding policy for generation load imbalances including characteristics of loads

Modern electrical power systems are highly interconnected and heavily loaded. An emergency may occur as a result of a sudden increase in system load or unexpected partial or total outage of a generator. This paper presents an optimal dynamic load shedding policy for generation load imbalances. The effects of voltage and frequency characteristics of system loads, transmission lines, transformers and reactive power compensator are reported. Equality and inequality system constraints are also considered in the formulation of this nonlinear programming problem. The further effects of system average time constant, speed drop factor, load reduction ratio (load frequency sensitivity factor), system inertia, load shedding and spinning reserve are included. Furthermore a simple load distribution factor is considered in this algorithm. Results of the unified power system of lower Egypt have been presented to validate the algorithm and show its effectiveness. Copyright © 1999 John Wiley & Sons, Ltd.     

Direct load control of residential water heaters

In Norway there is a growing concern that electricity production and transmission may not meet the demand in peak-load situations. It is therefore important to evaluate the potential of different demand-side measures that may contribute to reduce peak load. This paper analyses data from an experiment where residential water heaters were automatically disconnected during peak periods of the day. A model of hourly electricity consumption is used to evaluate the effects on the load of the disconnections. The results indicate an average consumption reduction per household of approximately 0.5 kWh/h during disconnection, and an additional average increase in consumption the following hour, due to the payback effect, that may reach up to 0.28 kWh/h per household.     

Extreme water-hammer pressure during one-after-another load shedding in pumped-storage stations

The intermittent and unpredictable wind and solar power leads to the frequent transient processing of pumped-storage stations, increasing the probability of load shedding. When one turbine sheds its load, the other turbines in the same hydraulic unit become overloaded and may shed their loads, which is referred to as a “one-after-another (OAA)” load-shedding process. An extremely high water-hammer pressure (WHP), namely, high spiral case pressure (SCP) or low draft tube pressure (DTP), may arise in this case, directly threatening the safety of the PSS. The objective of this study was to theoretically determine the hydraulic connections between the turbines and reveal the mechanism of the rapid rise in the WHP under the OAA load-shedding conditions. Theoretical derivations inferred that the drastic pressure changes in a trail shedding turbine (TST) are caused by the hydraulic connection with the lead shedding turbine (LST) in the S region. Furthermore, numerical simulations and model experiments were performed for the OAA load-shedding process, which confirmed the validity of the theoretical analysis. Finally, an analysis was conducted on the distribution of the water inertia in the upstream and downstream branch pipes, and engineering measures were proposed to guarantee the safe operation of PSS systems.     

Comparative analysis of different grid-independent hybrid power generation systems for a residential load

Demand of electricity is rising all over the world, both in developing and developed countries due to escalation in world population and economic growth. The exploitation of renewable energy is imperative to mitigate energy crisis and to avoid the environmental downfall. The stochastic nature of many renewable energy sources sets techno-economic and functional limitations in their application for covering most types of energy needs. These limitations can be surmounted if a renewable and a conventional energy source are combined to formulate a hybrid generation power system.This paper examines the techno-economic feasibility of four hybrid power generation systems applied to cover the demand of a typical off-grid residence for a 20 years period. Each one of these hybrid power solutions should involve at least one renewable energy source technology and be able to cover all load needs. Four applications are investigated for each hybrid system, accounting to different geographical areas in Greece with diverse solar and aeolic profile. A comparative analysis is followed to set off the optimal solution based on a minimal total cost criterion.     

Assessment of a modified method for determining the cooling load of residential buildings

Cooling load calculations are essential in sizing air conditioning system equipment. In designing energy, efficient and renewable energy sourced cooling systems for buildings, it is important to have the exact values of cooling loads and seasonal cooling demands of buildings. In this paper new assessment method for more precise determining of cooling loads and seasonal cooling demands of residential buildings are developed, which are necessary for right solutions of cooling efficiency problems. Comparing to the method of ASHRAE, example and other methods it provides more correct results. Application of suggested method provides better accuracy in assessment of cooling loads especially for seasonal aspects, as they take into account the impact of more factors.     

An economic feasibility analysis of photovoltaics power during urban load shedding time

A first-order cost analysis of Photovoltaics power generation and DG power generation for urban emergency load is presented. Six years field data of two DG sets installed at IIT, Delhi for emergency load have been thoroughly analysed to find out the requirements for such power generation model.The unit cost of emergency load energy is calculated using different parameters. These are the interest rate of commercial loan at present value of Indian market, IREDA loan facility to promote PV, the depreciation cost, operation and maintenance cost of PV and DG sets, and fuel cost of DG set. It is found that the unit cost of PV electricity is cheaper or comparable with that from DG power at present market price.     

Optimal dispatching strategy for residential demand response considering load participation

To facilitate the coordinated and large-scale participation of residential flexible loads in demand response(DR),a load aggregator(LA) can integrate these loads for scheduling. In this study, a residential DR optimization scheduling strategy was formulated considering the participation of flexible loads in DR. First, based on the operational characteristics of flexible loads such as electric vehicles, air conditioners, and dishwashers, their DR participation, the base to calculate the compensati...     

基于动态负荷特性的家用光伏发电系统经济性评价

以家用光伏发电系统为研究对象,基于用户侧动态负荷特性与供给侧光伏发电出力特性的耦合解析,根据分布式光伏系统"自用为主、余电上网"的应用原则,构建家用分布式光伏发电系统经济性评价模型。应用该模型,以上海某家用光伏发电系统为例,分析其运行特性、经济性能及其影响因素。研究结果表明,现行政策下家用光伏发电系统的动态投资回收年限为12.4 a;在中国,促进光伏产业发展最实际、最有效的政策是提高上网电价。     

Solar home system electrification as a viable technology option for Africa's development

This paper is based on a review of the effectiveness of solar home systems (SHS) in Africa in meeting users expectations on a service based analytical approach. Various projects have deployed SHS on the promise that they are cost-effective, can meet end-user demands, have ability to alleviate poverty, can save time and reduce emissions. However, a close review of the actual cost of these systems given the services they provide indicates most of the promises remain unmet and hence questions the wisdom of using public funds to support the system at the expense of more appropriate technologies.     

Biochar as a viable carbon sequestration option: Global and Canadian perspective

Biochar production and mixing in soil are seen as the best options for atmospheric carbon sequestration, providing simultaneous benefits to soil and opportunities for distributed energy generation. The proximity of biomass source and biochar dispersal greatly reduces the energy and emissions footprint of the whole process. The viability of the whole biochar process is examined from two boundary points: is there enough biomass around to have significant impact on the atmospheric CO₂ levels and is there enough soil area for biochar dispersal. The answers are soundly positive, both for the world as a whole and for Canada, for which a more detailed analysis was done. However, the massive adoption of biochar solution is critically dependent on proper recognition of its carbon sequestration impact its soil improvement potentials. To that extent the International Biochar Initiative, together with national chapters, including recently formed Canadian Biochar Initiative, are actively promoting biochar related research and policy framework. This paper addresses the questions of availability of sources and sites that would benefit from its dispersal.     

A review and an analysis of the residential electric load curve models

Due to the growth of electric end-uses, the management of the variations in time of the electric power demand has become essential, especially in the residential sector. According to this issue, the anticipation of the power demand is of great interest. This implies a better knowledge of the electric load curve of the household stock. Papers about understanding and forecasting energy demand are numerous but studies on building's load curves are rare. In this paper we propose a cross analysis of some existing methods capable of building up a residential electric load curve. Two main types of load curve models have been identified in the literature: top-down and bottom-up methods. Even if the review presents two existing top-down approaches, the authors focused the further analysis on bottom-up models. For each of them we first identify its functional characteristics: finality and scope, input data required, output format, modeled appliances and end-uses covered, generation of the diversity and validation of the model. Secondly, we establish a bloc diagram representing its architecture with focus on the mathematical model chosen. Finally, the authors list the limits of the model in view of the criteria needed to build up an ideal, bottom-up and technically explicit load curve model for the residential sector.A cross reading of the different methodologies is proposed through a global table that characterizes and sums up the analyzed models. Moreover, a graphical representation of the models studied is proposed, according to three criteria (range of application, modelling of the diversity, time scale accuracy) that allows us to compare them “at a glance”. To conclude, an identification of the gaps among existing models is proposed. It consists of listing the end-uses, the appliances and other behavioural correlations which may affect the load curve and that are not included in the reviewed methodologies and need further research.     

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.     

Study of a fuel cell network with water electrolysis for improving partial load efficiency of a residential cogeneration system

A fuel cell energy network which connects hydrogen and oxygen gas pipes, electric power lines and exhaust heat output lines of the fuel cell cogeneration for individual houses, respectively, is analysed. As an analysis case, the energy demand patterns of individual houses in Tokyo are used, and the analysis method for minimization of the operational cost using a genetic algorithm is described. The fuel cell network system of an analysis example assumed connecting the fuel cell cogeneration of five houses. If energy is supplied to the five houses using the fuel cell energy network proposed in this paper, 9% of city gas consumption will be reduced by the maximum from the results of analysis. Two per cent included with 9% is an effect of introducing water electrolysis operation of the fuel cells, corresponding to partial load operation of fuel cell cogeneration. Copyright © 2005 John Wiley & Sons, Ltd.     

Marketing residential grid-connected PV systems using a Balanced Scorecard as a marketing tool

A strategic analysis of the electricity market in Western Australia yields a market potential for renewable energy in Western Australia. However, from a purely financial viewpoint the installation of grid-connected pv-systems still is not economically viable. In this paper a balanced scorecard (BSC) is developed to capture and visualize other than financial benefits. Therefore, the BSC can be used as a marketing tool to communicate the benefits of a privately owned GCPV system to potential customers.     

A comparative life cycle energy cost analysis of photovoltaic and fuel generator for load shedding application

Comparative life cycle energy cost analysis for different electricity generators (photovoltaic generator, kerosene generator and diesel generator) used during load shedding is presented. The parameters considered for calculation of the unit cost of energy are: the discount rate, inflation rate, IREDA loan facility to promote PV, operation and maintenance cost of PV and fuel generator (FG) set and the associated fuel cost. It is found that the unit cost of PV electricity is comparable to or less than that of FG generated electricity at present market prices.     

Btu tax as a revenue option: Its impact on agriculture in the USA

The paper investigates the impact of the imposition of a broadly based energy tax on the US economy in general and the agricultural sectors in particular. The analytical approach used in the analysis consisted of a general equilibrium model composed of 12 producing sectors, 13 consuming sectors, six household categories, classified by income, and the government. The effects of a 10 cents per million Btu tax on energy on prices and quantities are examined. The results are revealing. For example, a 10 cents per million Btu tax on energy imposed at the point of production would result in lower output by the producing sectors (by about $9.154 billion), an increase in the consumption of goods and services (by about $20.292 billion), and a reduction in welfare (by about $4.30 billion). The government would realize an increase in revenue of about $6.356 billion. If the Btu tax were imposed at the point of consumption, there would be lower output by the producing sectors (by about $5.88 billion), an expansion in the consumption of goods and services (by about $19.830 billion), and a reduction in welfare (by about $7.066 billion). The government would realize an increase in revenue of $6.688 billion. The agricultural sectors would be minimally impacted. For example, if a 10 cents per million Btu tax were imposed at the point of production, output in the program crops sector would rise (by $8.3 million), output in the livestock sector would decline (by $83 million), output in the all-other-agriculture-commodities sector would be reduced (by $118 million), and output in the forestry sector would rise (by $34.7 million). If the Btu tax were imposed at the point of consumption, output in the program crops sector would fall (by $38 million), output in the livestock sector would decline (by $42 million), output in the all other agriculture commodities sector would be reduced (by $94 million), and output in the forestry sector would rise (by $221 million).     

A procedure to group residential air-conditioning load profiles during the hottest days in summer

A methodology is proposed whereby residential customers can be grouped by their diurnal air-conditioner use profiles during the hottest days in summer. The procedure, illustrated with data from a load experiment study, involves three phases. The first is to form a subset of electricity use data corresponding solely to days when utilities are likely to face summer peaking problems. The second phase is to identify a characteristic diurnal A/C load profile for each customer which adequately represents his day-to-day behavior during these peak days. The final phase is to cluster these diurnal A/C load profiles into physically consistent discrete groups. The eventual practical applications of this methodology are that it could assist utilities in better planning and implementing cost-effective peak shaving strategies.