ZEMCH 2019 International Conference Proceedings April.2020 | Page 441
discharge were at 17:33 on August 23, 2019 and at 03:36 on August 24, 2019. About 92% of the battery
capacity was discharged and about 91% of the load was supplied to the battery. In this mode full
discharge voltage was reached such that the battery could not be used because the battery voltage could
not be maintained until the next PV charge.
Mode 2 was designed to charge with grid power when the battery voltage drops below the
reference voltage when PV charge is not possible. The battery began to discharge at 17:41 on August
27, 2019 and ended at 03:38 on August 28, 2019. It remained discharged for about 9 h and 45 min. The
total discharge power was 3.733 kWh (discharge peak power of 0.249 kW), and the load power at
discharge was 3.875 kWh. Similar to Mode 1, intermittent discharge occurred between 16 and 17 oʹclock,
before the discharge start time.
Under mode 3, charging started at 07:38 on November 05, 2019 and full charge was reached at
11:31 on November 05, 2019. The battery was fully discharged about 9 h and 30 min after the battery
discharge began at 17:38 on November 05, 2019. The discharge power was 1.739 kWh (discharge peak
power of 0.199 kW), and the load power at that time was 1.867 kWh. The battery was completely
discharged and battery voltage was not maintained until the charge of PV power the next day.
Under mode 4, the battery is preferentially charged by PV power, and then by grid power when
there is no PV power and the battery voltage reaches the full discharge protection voltage. In other
words, if the battery is likely to be discharged, the battery is charged with grid power. The battery
started to recharge at 04:03 on September 18, 2019, about 9 h and 30 min after it was first discharged at
18:31 on September 17, 2019. Based on the 2 days data, the total discharge power was 2.894 kWh
(discharge peak power of 0.199 kW), the load power at this time was 2.916 kWh, and the total power
charged from the grid was 0.214 kWh.
In the modes where PV power was supplied to the load first (modes 1 and 2), the charge/discharge
of the battery is determined by the load. Therefore, charge/discharge may occur frequently and the
battery may not be sufficiently charged. As the battery voltage drops rapidly after complete discharge,
it is necessary to reduce the battery idle time between discharge and charge. On the other hand, in the
m o d e s w e r e P V p o w e r w a s s u p p l i e d t o t h e b a t t e r y f i r s t ( m o d e s 3 a n d 4 ) , P V
Figure 4. Performance characteristics of BESS prototype with veranda PV applied the air conditionerʹs
load (July 07, 2019)
Optimal Operation Schemes of Residential Battery Energy Storage System with Veranda Photovoltaic System
for Apartment Houses in Korea
430