Congratulations! You have taken the jump and bought an off-grid solar system with a Lithium ion battery to protect against load shedding and reduce your bill. However, you’re not entirely sure if you are receiving the maximum benefit from your new purchase. This is part 1 in a series on how to maximise your free power from the sun, while ensuring you have sufficient battery capacity for load shedding.
Before diving into how to maximise your use of solar we need to understand how your inverter works and the logic it operates under. Two main settings decide how you utilise solar power.
Understanding your inverter
1. How your load is powered and; 2. How your battery is charged.
Your inverter receives power from the utility, battery and from solar. This setting determines which source of power the inverter uses to power your loads and how it balances or switches between the various sources. There are 4 main options:
UTI – only utility provides the power to your house. Solar and battery will only be used if the utility is not available.
SOL – solar provides power to your loads as first priority, if there is insufficient solar power available, battery will be used to power the loads at the same time. Utility is only used when solar is not available (e.g at night) or the battery drops to it’s low voltage setting.
SBU – solar provides power to your loads as first priority, if there is insufficient solar power available, battery will be used to power the loads at the same time. Utility is only used when the battery drops to its low voltage setting.
*Please note there is a subtle difference between SOL and SBU – SOL will switch over to utility when solar is unavailable,
even if the battery is full. SBU will continue using the battery until its low voltage point.
SUB – solar provides power to the loads as first priority, if there is insufficient solar to power the loads, utility tops it up. Battery is only used when solar is not sufficient and there is no utility available.
Charger source priority
This setting decided what source of power the inverter uses to charge the battery – there are 3 options.
CSO – solar energy charges the battery. Utility is only used if solar is not available.
SNU – solar energy and utility both charge the battery.
OSO – only solar energy is used to charge the battery.
How do you determine the optimum combination of output source and charger source for your inverter?
From the above we can eliminate UTI as an option as it does not make use of free solar power and will not reduce your bill. Equally a charge setting of SNU doesn’t make sense as it uses utility to charge the battery even when there is solar energy available. So which of the remaining settings makes the most sense? The key is deciding how much you want to cycle your battery.
If you want to preserve your battery for load shedding and maximise its life span, then SUB and CSO make the most sense. Solar energy will be used when it is available, with utility topping it up as necessary, e.g. if a cloud moves over the panels, or the sun starts going down. The battery will be charged by solar, however if the battery is depleted going into night time, the utility will charge it. Thus you should always have spare battery capacity to carry you through load shedding.
Should your priority be maximising the amount of solar power you receive and using this energy into the night, then SBU and OSO are a good match. Only solar power will charge the battery and the system will use battery to top up solar power as needed. It will continue using the battery into the night until it reaches its low voltage point – typically at 50% of capacity. You will then only have the remaining
50% of the battery to use in the case of load shedding. This is efficient, but risky if there are days of cloudy weather or heavy load shedding.
Thirdly is an option that balances the risk of load shedding with making good use of solar power. This is to use SOL and OSO. Solar energy will power your loads, with battery topping it up as necessary. The battery will also be charged by solar power. When night falls and the panels stop producing, the inverter will switch to utility power. At this stage the battery will be close to fully charged unless there was extreme cloudy weather. A slightly more conservative variant of this option is to use CSO for charging – the utility will be used to charge the battery when solar power is not available – this should ensure that you have a full battery going into the night.
Now that you have an understanding of how your inverter works and which settings produce the best results depending on your requirements, part 2 will deal with optimising your load.