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A stand-alone solar PV system for a home or office works independent from the public electricity grid and this is an advantage for areas where the grid is not available or not reliable. The disadvantages of a stand-alone system are that batteries typically last only five years and that the overall system efficiency is low compared with a grid-interactive system. Another challenge with stand-alone systems is that there may be under-utilisation of the available solar energy when the batteries are full and there is insufficient load or there may be shortage of energy during cloudy days. In the case of grid-interactive systems surplus energy can be exported to the grid while a shortfall in energy can be drawn from the grid.

The WattMon comes in handy here. The information that the WattMon system gives helps us to improve system configuration and system usage. When the WattMon relay system is released in the near future, loads can be switched on or off based on the charging state of the battery and loads can be added to absorb surplus solar energy that is available. In stand-alone systems that are located in buildings with grid supply, the WattMon can trigger a grid charge of the batteries to complement solar energy charging on cloudy days or on days with higher than average consumption.

I have been using the WattMon system in our stand-alone home solar system and find it extremely useful. Based on the data we got from the WattMon system we decided to provide the refrigerator with an automatic change-over switch that connects the refrigerator to the stand-alone system only when there is no grid supply so that we spare the battery from deep discharges. We also understand now that there are many days on which the battery is already fully charged by early afternoon and that there is surplus solar energy available for usage during the remaining part of the day. Thanks to WattMon we know now what is happening behind the scenes.

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