Current Operation and Control
To get better insights on operation of the system and consumption on the island, a Leonics System Monitoring Device was installed on the island in September 2018. It collects data on the entire system as shown in the figure below. This data has been used to analyse typical load behaviour on the island.
As the load profile is substantial for the design of the microgrid, more detailed measurements in a resolution of 5 min have been taken. All recorded load profile data since the measurement unit was installed in end-September have been analyzed for consistency and is used to improve the accuracy of the new system design. The active power is obtained from the individual line current and voltage measurements. The data shows that the average daily consumption is around 230-250 kWh. The daily consumption reveals clear repetitive patterns with a short morning peak and a longer evening peak. The maximum daily peak power is drawn at approximately 5 am in the morning and is 18-25 kW. An evening peak occurs from 5 pm-10 pm and is about 12-18 kW. The usual daytime load (9 am-4 pm) fluctuates around 9-10 kW. Hence, the daily base load could be directly fed by a new AC-coupled PV array.
Current System Operation
Apart from the load profile, more measurements have been obtained to analyze and understand the operation of the current assets: PV generation, diesel genset and battery. The following patterns are apparent in the data set: The load is fed from the lead acid battery during the night and in most days the battery is completely discharged before the diesel genset is manually restarted around 4:30/6:00 am. This leads to blackout periods during the times where the battery is empty, and the diesel has not been turned on yet. As seen in the figure below, the length of blackout varies substantially between a couple of minutes and 90 minutes.
The morning peak is covered by a mixture of PV and diesel generation. Surplus from PV generation during the day is used to charge the battery. After PV cannot cover the load alone the battery is discharged, and diesel is turned on to cover the evening. Excess from diesel generation is fed into the battery. The diesel operates till 11 pm, afterwards the existing battery covers the load till it is fully discharged.