Page 48 - Energize October 2021

TECHNICAL

Hybrid inverter systems Figure 7 shows the instantaneous and daily readouts of an outback
Monitoring systems can provide information on the performance of the RM80 battery monitor used with an off-grid system.
array and the battery, as well as the inverter.

Monitors can provide all or some of the following:
• Instantaneous PV array voltage, current and power output, battery
voltage and state of charge (SOC)
• Instantaneous power consumption
• Hourly, daily or longer-term energy (kWh) generation on an
individual unit or combined basis
• Battery charge and discharge cycles, including battery max and
minimum volt and SOC.
• Graphic outputs (dashboards) showing performance over time.
• Failure, out of limit, low performance or decreasing performance
warnings. Figure 7: Battery monitor readouts
• Analytical functions based on performance over time and compared
with other systems. Figure 8 shows the results of 21 days of monitoring.

Figure 6: Monitoring system dashboard (Solar analytics) Figure 8: 21-day record from charge regulator
Fault or failure detection can be difficult even with information from The red battery voltage bars indicate that fully discharged condition
the monitor, and many systems offer diagnostic and analytic functions was reached. The controller would have disconnected the load at
to make this easier for the owner. Detection of low performance or this stage.
failure is derived from comparing performance with previous or pre-set
values. Some cloud-based systems can access weather data for the Maintenance
area, as well as performance of other systems in the neighbourhood, to Panel cleaning
give more accurate and meaningful reports. Washing/cleaning panels is an extremely important task which
needs to be done on all rooftop PV plant. This is location, and
Battery monitoring consequently, weather dependant. Soiling on PV panels affects the
Determining the state (capacity) of the battery used in a simple rooftop energy yield of the PV plant. In South Africa’s highveld region peak
PV system is not easy, and most users will not have the means to do this. power can decrease 30% to 40% due to the accumulation of dust
Other than inspection and checking of electrical connections, battery over a period of three months, when there is little or no rain, and
maintenance relies on an efficient battery monitor. Battery or charge when module cleaning is not performed. The accumulation of dust
monitors can provide instantaneous and daily records performance, and is more severe on panels which have low tilt , thus dependant on
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a loss of capacity may be determined by observation over time. the roof type. Common practice now for flat or low tilt East/west
mounting poses a problem for cleaning.
A charge control monitor provides the following information: Panel cleaning is probably the most important regular
• PV voltage and maximum and minimum current flow into controller maintenance. Bad soiling of the panel can result in a significant
from the PV. deterioration in output. Rooftop solar panel cleaning is much
• Current flow into battery more difficult than that for groundmount solar farms and is
• Current flow into inverter made difficult by the location of the panels and access to the
• Current flow in and out of battery installation. Cleaning methods will depend on the accessibility and
• Battery maximum and minimum voltage roof pitch and will vary from single story buildings to multi storey
warehouse etc.
Most charge regulators and hybrid inverters will have some form of Without the luxury of soiling monitors, the need to clean
battery-state recorder which will provide information on the daily panels can be determined by a drop in output of the panel array,
charge and discharge performance of the battery. taking seasonal factors into account. Cleaning operations can

energize | October 2021 | 46