**6. Suggested utilization system of EVs and their used batteries**

**Figure 7** presents the basic concept of load leveling which is developed for a small-scale EMS employing EVs, used EV batteries and RE generators including photovoltaic (PV) and wind. Four main continuous steps are proposed: (1) forecasting of the possibly generated RE and building load, (2) load leveling calculation including peak-shift and peak-cut, (3) value recalculation and correction, and (4) charging and discharging controls of both EVs and used EV batteries. The first step, load and RE forecasting, is basically conducted by EMS for 24 hours ahead. Furthermore, because the electricity amount in Japan is measured for a duration of 30 min, the electricity amounts (kWh) in this study are also measured and calculated as the total summation for a duration of 30 min.

**Figure 7.** Developed load leveling concept utilizing EVs and their used batteries.

To forecast both load and possibly generated RE, EMS initially sends a request to meteoro‐ logical agency to deliver the local weather forecast information. This weather information is very crucial for calculating the electricity which can be potentially generated by RE, such as PV and wind. Because the amount of RE generation is significantly smaller than the total load, in this study, this generated electricity from RE is used directly for peak-cut, hence it will be delivered directly and consumed entirely without being stored in the battery. Moreover, the weather information is also used to forecast the fluctuating load of the office building, especially to calculate the demand of air conditioning (cooling and heating) and lighting. The outputs from this first step include the predicted power generation from RE and daily load curves of the next day (defined as day starting from 00:00 to 24:00).

As the building load and possibly generated electricity from RE have been predicted, EMS will calculate the achievable load leveling (peak-cut) for the next day. In order to realize it, EMS sends a request to VIS to calculate and send the information related to the available EVs, including their battery SOCs, which will potentially participate for the load leveling program. This information is required to estimate the total available electricity which can be supplied by the EVs for load leveling.

In order to perform the given request by EMS, VIS initially collects the traveling schedule from the EV drivers (planned departure time and predicted arrival time). Next, EMS forwards this information, as well as calculates the total availability of EVs and their batteries, together with basic information including EV's ID. This registration of traveling schedule is conducted up to 24 hours before the planned departure. Finally, using the data from the first and second steps, EMS is able to estimate the peak-cut threshold which can be applied for the next day.

In this study, a peak-cut threshold is determined as the maximum electricity which is pur‐ chased from the electricity grid. To calculate this peak-cut threshold, some important factors need to be considered including price of electricity at the corresponding time, contracted power capacity, possibly generated electricity from RE, available electricity supply from other sources with low price, and potential energy storage.

In case that the electricity which is consumed by the office building rises resulting in the condition that the purchased electricity from the grid increases and reaches nearly the calculated peak-cut threshold, EMS immediately sends the control command to both connect‐ ed EVs and used EV batteries to release their electricity supporting EMS to cover the demand. Therefore, the electricity purchased from the grid can be kept to be the same to or lower than the calculated peak-cut threshold. As a result, a higher price of electricity during peak-load time or penalty due to higher capacity than the contracted one can be avoided.

When EVs are not connected to the designated charging stations, such as in motion or being parked in other places, the information of EVs is sent wirelessly to VIS in an interval of several seconds to minutes (adding and renewing the information). Thereafter, VIS transmits the updated data to EMS. EMS will recalculate the potential availability of electricity from EVs. Moreover, EMS also recalculates the building load based on the present real load of building and real weather which is measured using thermometer and hygrometer. Next, EMS renews its energy management plan, especially the calculated peak-cut threshold.

Furthermore, when EVs arrive at the office building and are plugged to the designated charging stations, EV start to communicate directly with EMS and bypassing VIS through the charging lines. EMS will read the information from EVs and update the previous data received from VIS, especially the battery SOC. As EVs are connected directly to EMS via charging station, EVs are completely under EMS management. Therefore, their charging and discharg‐ ing behaviors are controlled completely by EMS. After receiving the updated data from EVs, EMS recalculates the peak-cut threshold accurately. As the electricity demand reaches the updated peak-cut threshold, EMS sends the control command to EVs and used EV batteries to discharge their electricity. After finishing the load leveling, EMS can manage the charging for EVs, hence another peak-load due to uncoordinated EV charging can be avoided.
