Yumiko Iwafune

Economic Value of PV Energy Storage Using Batteries of Battery-Switch Stations

The Japanese government has set a power sector goal for photovoltaic (PV) power usage to reach 53 million kW by 2030. To achieve the large-scale introduction of PV, a large storage capacity, in the form of pumped storage systems or batteries, is needed to store surplus electricity from PV plants. At the same time, in the transport sector, the electric vehicle (EV) is being developed as an environmentally friendly vehicle. To promote the diffusion of EVs, we need infrastructure that can charge EVs in a short time; a battery-switch station is one solution to this problem. This study 1) proposes the use of the station batteries as a countermeasure for surplus electricity from PVs and 2) conducts two relevant analyses. In the first analysis, we calculate the marginal value of a battery and an inverter using the Optimal Generation Mix Model (OPTIGEN). In the second analysis, we set the annual lease fee for the inverter and the battery, and calculate the optimum installed capacity of these devices. The results showed that the marginal value of the inverter/battery decreases with increasing inverter/battery capacity. The optimum installed capacity of the inverter/battery is derived from the intersection of the line of marginal value with the line of the annual lease fee. The stations gain an additional profit by leasing batteries to utilities.

Optimum operation scheduling model of domestic electric appliances for balancing power supply and demand

High penetration of variable renewable generations such as Photovoltaic (PV) systems will cause the issue of supply-demand imbalance in a whole power system. Activation of residential power usage, storage and generation by sophisticated scheduling and control using the Home Energy Management System (HEMS) will be needed to balance power supply and demand in the near future. In order to evaluate the applicability of the HEMS as a distributed controller for local and system-wide supply and demand balances, we developed an optimum operation scheduling model of domestic electric appliances using mixed integer linear programming. Applying this model to one house with dynamic electricity prices reflecting the power balance of the total power system, it was found that the adequate changes in electricity prices bring about the shift of residential power usages to control the amount of the reverse power flow due to excess PV generation.

An Integrated Computational Infrastructure for a Virtual Tokyo Concepts and Examples

Summary The evaluation of tradeoffs between technologies and policies for mitigation of environmental problems requires a systematic investigation of effects over the entire region under consideration. When attempting to model such large complex systems, issues such as usability, maintenance, and computing efficiency often become major modeling barriers. In this work a software prototype for integrating the services of computational models over the Internet, called DOME (distributed object-based modeling environment) is used to facilitate the construction of virtual Tokyo—a simulation platform for evaluating holistically the tradeoffs between various technologies for reducing the emissions of greenhouse gases. In making steps toward this ultimate goal, two models have been developed that use data defining spatial land-use distributions and the flows of goods expressed as an input-output table to provide information on the spatial and temporal characteristics of an urban region. Integrated, these models form a preliminary virtual Tokyo model when applied to Tokyo-specific databases. Given this platform, process models are applied to examine the effectiveness of using photovoltaic (PV) modules on the demand side to reduce conventional electric power generation and, thereby, also reduce carbon dioxide emissions. The results of introducing PV modules on the rooftops of buildings in Tokyo under various installation conditions are presented as a working example of the prototype. For full deployment on usable rooftop space, PV power generation could reduce carbon dioxide emissions from electric power generation by more than 12%. Future work will use the same methods as presented in this paper to examine cost, a critical determinant in the actual feasibility of PV module installation.

Energy storage of PV using batteries of battery-switch stations

In the power sector, the Japanese government has set the goal of that the introduction of PV will reach 53 million kW by 2030. However, large-scale introduction of PV will cause several problems in power systems such as surplus electricity. We need large capacity of pumped storages or batteries for the surplus electricity, but the construction costs of these plants are very high. On the other hand, in the transport sector, Electric Vehicle (EV) is being developed as an environmentally friendly vehicle. To promote the diffusion of EV, it is necessary to build infrastructures that can charge EV in a short time; a battery switch station is one of the solutions to this problem. At a station, the automated switch platform will replace the depleted battery with a fully-charged battery. The depleted battery is placed in a storage room and recharged to be available to other drivers. This means switch stations always have the constant capacity of battery. We propose the use of stations batteries as a countermeasure for surplus electricity of PV and evaluate the economic value of the proposed system. We assumed that 53 million kW of PV is introduced in the nationwide power system and considered two countermeasures for surplus electricity: (1) Pumped storage; (2) Battery of station. The difference in total annual cost between Pumped case and Battery case results in 695.7 billion yen. Hence, if a utility leases batteries from stations fewer than 695.7 billion yen, the utility will get a cost advantage in Battery case.

Short-term forecasting of residential building load for distributed energy management

It is expected that energy management systems (EMS) on the demand side can be used as a method for enhancing the capability of balancing supply and demand of a power system under the anticipated increase of renewable energy generation such as photovoltaics (PV). Energy demand and solar radiation must be predicted in order to realize the optimal operation scheduling of demand side appliances by EMS, including heat pump water heaters, PV systems, and solar powered water heaters. This paper presents a day-ahead forecasting method for electricity consumption in a house to contribute to energy management. Ten forecasting methods are examined using real survey data from 35 households over a year in order to verify forecast accuracy. A daily battery operation model is also developed to evaluate the effect of load forecasts.

Estimation of appliance electricity consumption by monitoring currents on residential distribution boards

Energy management systems (EMS) on demand sides are expected as a method of controlling electricity supply and demand balance in power grids including large amount of PV power generations. EMS is supposed to determine the optimal daily operation of energy appliances including energy storage factors economically and efficiently to satisfy consumers desire taking account of forecasted energy demand and PV generation.

Electricity pricing for PHEV bottom charge in daily load curve based on variation method

For fuel economy of power system, Plug-in Hybrid Electric Vehicle (PHEV) should be charged late at night to level a load curve. This paper proposes an electricity pricing algorithm for load leveling, using variation method. Variation method is a mathematical technique that can bring a value of integral functional to the extreme value. We formulate a cost minimization problem of PHEV owners, regarding the integral functional as an electric bill. By solving the problem, we get the electricity price curve that can realize the ideal bottom charge while PHEV owners minimize their electric bill. We analyze the difference in results between the proposal and the target case, where PHEVs are ideally charged to raise bottom demand. The ratio of the reduction of the proposal case to the target case resulted in 99.8%. It is verified that the proposed algorithm is effective in bottom-up of daily load curve.

Operation of heat pump water heaters for restriction of photovoltaic reverse power flow

Japanese government plans to introduce photovoltaic (PV) systems 20-fold by 2020 compared to the 2005 level, and then grid-connected PV systems are expected to increase rapidly. At the same time, however, there is concern that a large scale PV systems introduction might bring an excess of supply when the electricity demand is low such as in spring or autumn in Japan. Meanwhile, heat pump water heaters (HPWHs) are highly efficient water heaters and have been introduced rapidly. If hot water is stored in the daytime using HPWHs, it will contribute to absorb economically a part of the excess of PV output. In this paper, we propose a use of residential HPWHs in the daytime as a means of PV reverse power flow restriction. And we evaluate how the difference of the actual demand patterns influences on PV reverse power flow restriction and HPWH power consumption.

Reduction of PV Reverse Power Flow through the Usage of EV's Battery with Consideration of the Demand and Solar Radiation Forecast

This paper presents an evaluation of the usage of electric vehicle battery as an energy storage device for surplus power generated by Photovoltaic power generation system (PV) installed at home. The main goals are the reduction of the reverse power flow caused by PV power generation, and the mitigation of the dependency on the power system grid to charge the EVs battery. We conducted a study based on the forecast of electricity load and solar radiation. The study shows that by using PV-EV system, yhe amount of power bought from power utility can be reduced while keeping. The study shows that by using PV-EV system, the amount of power bought from power utility can be reduced while keeping the reverse power flow level controlled.

Evaluation of EV charging load contributing to stabilize PV output with consideration for rapid charge

There are growing concerns around the world about global warming issues, and the various countermeasures to reduce global warming by greenhouse gas are proposal. In the transport sector, Electric Vehicle (EV) is mentioned as one of the solutions to reduce CO2 emissions and heavy dependence on oil. In order to promote the introduction of EV, it is necessary to build charging infrastructures that EV can be charged rapidly. The purpose of this research is to evaluate EV charging that includes rapid charge in charging station (ST). In order to calculate EV charging load, the traffic simulator utilizing the multi-agent method is employed. In this paper, the EV charging load in a day is calculated by the traffic simulation and evaluated in order to assess the influence of EV charging on the grid system and the applicability of EV in the smart-grid system.