Times Of Low Demand Research Articles

Residual Demand Modeling and Application to Electricity Pricing

A model for residual demand is proposed, which extends structural electricity price models to account for renewable infeed in the market. Infeed from wind and solar is modeled explicitly and withdrawn from total demand. The methodology separates the impact of weather and capacity. Efficiency is modeled as a stochastic process. Installed capacity is a deterministic function of time. The residual demand model is applied to the German day-ahead market. Price trajectories show typical features seen in market prices in recent years. The model is able to closely reproduce the structure and magnitude of market prices. Using simulations it is found that renewable infeed increases the volatility of forward prices in times of low demand, but can reduce volatility in peak hours. The merit-order effect of increased wind and solar capacity is calculated. It is found that under current capacity levels in the German market wind has a stronger overall effect than solar, but both are even in peak hours.

Soil water dynamics and water use in a western juniper (Juniperus occidentalis) woodland

This study sought to quantify changes in landscape hydrology associated with changes in juniper cover and understory vegetation. We identified rates of surface evaporation in the absence of plant cover and determined rates of soil water depletion in four cover types. Vegetation treatments were installed in a randomized block design with five replications. Additionally, juniper trees were instrumented with Granier (1985) sap flow sensors to monitor transpiration rates. At the local scale juniper removal resulted in 20% greater over-winter accumulation of soil water, and demonstrated evidence of increased, generally complementary rates of transpiration in the released understory. Juniper utilizes the same resources as understory vegetation and successfully competes for shallow soil water before tapping into deeper resources. Stand-level estimates of transpiration for these woodlands averaged 0.4 mm per day during the summer months. Only 48% of the cool-season precipitation was retained in the top 90 cm in vegetated treatments but little is known about relative importance of processes governing water loss and depletion during the winter months. Resolving water use during times of low transpirational demand, will be crucial to link positive effects of juniper removal with subsurface water yield at the local scale and help further explain increased water availability observed at the watershed-scale.

Agent Cooperatives for Effective Power Consumption Shifting

In this paper, we present a directly applicable scheme for electricity consumption shifting and effective demand curve flattening. The scheme can employ the services of either individual or cooperating consumer agents alike. Agents participating in the scheme, however, are motivated to form cooperatives, in order to reduce their electricity bills via lower group prices granted for sizable consumption shifting from high to low demand time intervals. The scheme takes into account individual costs, and uses a strictly proper scoring rule to reward contributors according to efficiency. Cooperative members, in particular, can attain variable reduced electricity price rates, given their different load shifting capabilities. This allows even agents with initially forbidding shifting costs to participate in the scheme, and is achieved by a weakly budget-balanced, truthful reward sharing mechanism. We provide four variants of this approach, and evaluate it experimentally.

Residual Demand Modeling and Application to Electricity Pricing

A model for residual demand is proposed, which extends structural electricity price models to account for renewable infeed in the market. Infeed from wind and solar is modelled explicitly and withdrawn from total demand. The methodology separates the impact of weather and capacity. Efficiency is modelled as a stochastic process. Installed capacity is a deterministic function of time. The residual demand model is applied to the German day-ahead market. Price trajectories show typical features seen in market prices in recent years. The model is able to closely reproduce the structure and magnitude of market prices. Using simulations it is found that renewable infeed increases the volatility of forward prices in times of low demand, but can reduce volatility in peak hours. The merit-order effect of increased wind and solar capacity is calculated. It is found that under current capacity levels in the German market wind has a stronger overall effect than solar, but both are even in peak hours.

Rapid Startup SOFC Modules

The compact 200W SOFC module is characterised by its rapid startup capability. The module can be run on hydrogen, as well as on reformate from hydrocarbon fuels or alcohols. The stack temperature can be raised to 700°C in less than 5min by electric heaters placed in all bipolar plates. The heating power may be drawn from a battery which can be later recharged at times of low power demand. Only about 4 Wh of electrical energy are needed to heat one installed cell. As the nominal output is 10W per cell, the startup energy is recovered in about 24min of operation. The complete and functional modules are packaged in sealed metal containers. The current 200W demonstration module has a diameter of 100mm (4 inches) and is 100mm tall. The suspended stack of 16 planar cells of 60mm × 60mm size can deliver up to 200W of DC power when operated at around 850°C. However, the design of the module can be expanded to power levels of 1kW or more by increasing the number of cells per stack or by enlarging the active area.

Nuclear energy: Status and future limitations

The status of nuclear energy today and its potential evolution during the next 10–20 years is discussed. Nuclear energy contributes only about 14% of the world’s electric energy mix today, and as electric energy contributes itself only about 16% to the end energy use, its contribution is essentially negligible. Still, nuclear energy is plagued already with a long list of unsolved problems. Among the less known problems one finds the difficulties that nuclear plants cannot provide power according to needs, but have to be operated at full power also during times of low demand and regions with large contributions from nuclear power need some backup hydropower storage systems. The better known problems, without solutions since at least 40 years, are the final safe storage of the accumulated highly radioactive nuclear waste, that uranium itself is a very limited and non renewable energy resource and that enormous amounts of human resources, urgently needed to find a still unknown path towards a low energy future, are blocked by useless research on fusion energy. Thus, nuclear energy is not a solution to our energy worries but part of the problem.

How to deal with negative power price spikes?—Flexible voluntary curtailment agreements for large-scale integration of wind

For the large-scale integration of electricity from renewable energy sources (RES-E), the German system seems to reach its limits. In 2009, the electricity wholesale market experienced serious negative prices at times of high wind and low demand. The feed-in system in Germany consists of a fixed feed-in price, a take-off obligation and a RES priority rule, and in practice only very restrictive use of RES-E curtailment. Exactly the latter is the problem. We argue that the overall performance of the system would improve seriously by lifting the restrictions on the use of voluntary curtailment agreements, while retaining the priority rule as such. Since generators of RES-E can only improve under this system reform, investment conditions improve, leading to higher installed RES-E capacity. This in turn implies that reduced wind output due to curtailment can actually be offset by higher wind output in all periods in which there is no problem.

Universal SOFC Module for Rapid Start-Ups

The compact SOFC module characterized by its rapid start-up capability has been further improved. An optimized afterburner with catalytic ignition has been added, as well as innovative heat exchangers for fuel-exhaust-to-fuel and air-exhaust-to-air. The current module can be run on hydrogen, as well as on reformate from hydrocarbon fuels or alcohols. The stack temperature can be raised to 700°C in less than five minutes by electric heaters placed in all bipolar plates. The heating power may be drawn from a battery which can be later recharged at times of low power demand. Only about 4 Wh of energy are needed per installed cell. As the nominal cell output is 10 Watts, start-up energy is recovered in about 24 minutes of operation. The complete and functional modules are packaged in sealed metal containers. The current 200 Watt demonstration module has a diameter of 100 mm (4 in) and is 100 mm (4 in) tall. The suspended stack of 20 planar cells of 60 mm x 60 mm size can deliver up to 200 Watts of DC power at around 800°C. However, the design of the module can be expanded to power levels of 1 kW or more.

Quick-Start and Seal-Less Planar SOFC Module

A compact SOFC module has been developed for portable, mobile and stationary applications and for hybrid operation with batteries. The bipolar plates of this SOFC generator are equipped with electric heating elements. During start-up, the stack can be brought to operating temperature of 600°C in three minutes. The power may be drawn from a battery which can be later recharged at times of low power demand. For stationary application, heating energy may be drawn from the grid. The module can also be rapidly brought to operating temperatures with heat generated externally by the combustion of fuel. To minimize this initial energy consumption, a number of innovative features have been integrated in design and operation of stack and system of this innovative SOFC solution. The stack is suspended inside a hermetically sealed can to minimize heat losses by conduction and to avoid gas leakage from the stack by pressure equilibration.

Endogenous Investment and Pricing under Uncertainty

I analyze investment and pricing incentives in a differentiated products framework with uncertain demand. Firms choose production capacities before observing demand and choose prices after demand is realized. Unlike previous models, when firms are identical, symmetric pure-strategy equilibria exist, even in the presence of very low capacity costs. The equilibrium outcomes are significantly different from the equivalent Cournot model. Firms choose to underutilize their capacity at times of low demand, and hold more capacity than predicted by Cournot. I show with a simple policy example that even the sign of the comparative statics may differ between the two models.

São Miguel Island as a case study on a possible usage of Electric vehicle to store energy

Energy systems operation in isolated areas is frequently based on imported fossil fuels, which is a problem in different dimensions including environmental, economic and security of supply, with the latter being particularly relevant for any isolated system like Islands. Renewable energy is regarded as a solution to this problem, mainly in its transformation to electricity. This, however, excludes the impact of the transportation sector that represents a significant component of the imported fuels consumption. Other main limitation associated to renewable electricity consists on the need to increase the storage capacity that might attenuate the effect of intermittence of renewable energy sources and the disparity between supply and demand. In both problems - that are associated with renewable energy management - Plug-in Electric Vehicles (PEV) could be a part of the solution in that the use of vehicle to grid (V2G) technology can provide storage of electric energy during low demand times and use it to match the demand in peak hours and/or to avoid fossil fuel consumption.Therefore, some of the main questions are: could the large scale PEV penetration lead to increases in the fraction of electricity produced from renewable? Is the usage of PEV batteries as a storage system truly the best solution?São Miguel Island is the main electricity consumer in the whole Azores’s archipelago. There is no power connection to any major grid or even with other Islands. This work analyses a case study of isolated electricity grid, where energy systems modelling is used to assess to different roll out scenarios for large scale PEV penetration and discuss the possibility to increase the potential for the use of renewable electricity.

Standing the Test of Time Variations

In his News Focus story “Renewables test IQ of the grid” (10 April, p. [172][1]), D. Charles describes the widely held belief that large-scale use of renewables will become viable with a smart electric grid and short-term energy storage devices (such as pumped storage and batteries). However, the problems of integrating renewables with the electricity grid in a low-carbon world are much larger. Renewables are a time-varying source of energy that does not automatically match the demand-side time variations. Electricity demand varies daily, over a 3-day weather-related cycle, weekly, and seasonally. The seasonal variation in electric demand in much of the country is greater than a factor of 2, with seasonal mismatches between renewable production and demand. In a low-carbon world, the major energy options (nuclear, fossil fuels with carbon-dioxide sequestration, and renewables) have high capital costs and low operating costs. These high–capital-cost systems for electricity generation operate most economically when they are at full load all the time. For renewables, this is the maximum output given solar or wind conditions. To optimize their operation and to meet the storage needs of renewables requires systems that can store large amounts of energy and can do so on a daily to seasonal basis. The only existing such technologies are large hydroelectric dams—but there is not enough water storage capacity to meet the need. There is limited ongoing work on several new technologies. For example, in nuclear-hydrogen peak electricity systems, the nuclear reactor operates at steady state on a continuous basis ([ 1 ][2]). At times of low electricity demand, steam and electricity from the reactor are converted to hydrogen and oxygen by a solid-oxide high-temperature electrolyzer. At times of peak electricity demand, the reactor sends electricity to the grid and the electrolyzer is operated in reverse on hydrogen and oxygen from storage as a high-temperature fuel cell to produce electricity. Large-scale seasonal hydrogen storage is economical with use of current underground natural gas storage technologies. Eliminating greenhouse gas emissions from electricity production and large-scale use of renewables is not possible until we develop multiple, seasonal, energy storage systems with fast response capability to address mismatches between electricity production and demand. ![Figure][3] Hydroelectric dam. Dams such as this one can store large amounts of energy on a flexible schedule, but they have insufficient water storage capacity globally to be our sole renewable energy source. CREDIT: JUPITERIMAGES 1. [↵][4] 1. C. W. Forsberg, 2. M. S. Kazimi , 4th OECD-NEA Information Exchange Meeting on the Nuclear Production of Hydrogen, 14 to 16 April 2009, Oakbrook, IL; . [1]: /lookup/doi/10.1126/science.324.5924.172 [2]: #ref-1 [3]: pending:yes [4]: #xref-ref-1-1 View reference 1 in text

Implementation and control of electrolysers to achieve high penetrations of renewable power

The mass deployment of electrolysers, within a power system serving a region of high wind resource, as the enabling mechanism for achieving five key objectives is assessed (that is: a very high installed capacity of wind power plant (WPP); zero wind curtailment during times of low demand; a very high load factor for thermal power plant; an electricity supply of low-carbon intensity; and a hydrogen supply of low-carbon intensity). Three electrolyser implementation cases were simulated for three days characterised mainly by wind availability and emphasis was placed on maximizing the smoothness of the load profile (LF) applied to thermal power plant. If zero-carbon hydrogen is to be produced a daily load factor for thermal power plant of 90% is the upper limit, but load factors of up to 100% are achievable if a carbon intensity of 3 kgCO 2 / kgH 2 is permitted. For wind penetrations exceeding approximately 30% of system maximum demand, the electrolyser stock must include implementations close to WPP if curtailment is to be avoided. To achieve very high wind penetrations and very high load factors for thermal power plant requires a large stock of electrolysers—for the system investigated approximately 1.1 MW of electrolyser capacity is required per installed MW of wind power.