Masaaki Takagi

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.

Power system stabilization by charging power management of Plug-in Hybrid Electric Vehicles with LFC signal

In the transport sector, Plug-in Hybrid Electric Vehicle (PHEV) is being developed as an environmentally friendly vehicle. The electric energy of PHEVs is charged mainly during nighttime when the electricity price is low. Therefore, we have proposed a charging power control of PHEVs to compensate the Load Frequency Control (LFC) capacity in the nighttime. In this study, we propose a control method based on Area Control Error (ACE) and frequency characteristic of PHEV KPHEV, which is a change in charging power divided by a change in frequency. ACE is a required adjustment in generation to keep the balance of supply-and-demand; hence, we can also keep the balance by adjusting the demand as much as ACE. LFC signal fLFC calculated by the following equation fLFC = −ACE/ KPHEV is dispersed to all PHEVs; then, PHEVs control the charging power on the basis of fLFC. We evaluated the proposed control method by using an interconnected 2-area model and obtained the following results. Charging power control based on the proposed method can effectively suppress tie-line flow deviation and frequency deviation, and it could substitute for LFC capacity.

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.

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.

EV charging schedule for load leveling by non-linearly-distributed start time

Large-scale deployment of electric vehicles (EVs) adds load to the current power system. Without control of the temporal dispersion of EV charging, a new rapid peak load may occur and cause severe problems in the power system. Therefore, we propose two algorithms for load leveling by decentralized autonomous control. The first algorithm uses an off-peak rate period, and the second changes the charging start time according to the charging duration. We evaluated the second algorithm in two cases: a linear case, where the start time varies linearly with the charging duration, and a quadratic case, where the start time varies non-linearly, that is, quadratically with the charging duration. In the linear case, a gradually sloped peak occurs in the morning. On the other hand, in the quadratic case, the charging hours are dispersed appropriately, and the daily load curve is almost flat in the night.