Charging time while appliances are running
Panel power is shared between the active loads and battery charging. The planner first applies PV/controller conversion losses and the controller output limit. It supplies the active loads, then sends any surplus to the battery within its charging-power limit and target charge.
When solar is insufficient, the battery supplies the deficit until its reserve or discharge-power limit is reached. Remaining appliance demand is reported as unserved energy. No grid or generator supply is assumed.
Worked example: why daytime consumption changes charging time
A 1,000 W array with 5 peak sun hours and 20% PV/controller conversion losses supplies 4,000 Wh/day at the DC bus before controller clipping. If 2,000 Wh of daytime AC appliances run while solar is available, a 90% efficient inverter requires approximately 2,222 Wh for those appliances.
That leaves at most 1,778 Wh of solar input for charging before standby and other limits. At 95% charging efficiency, approximately 1,689 Wh can be stored. This simplified energy example assumes suitable overlap; the planner’s schedule and power limits can reduce the amount further.
Why a bigger battery may still run down
If daily solar energy remains below daily consumption and conversion losses, increasing storage alone does not remove that continuing deficit. The comparison keeps the entered charge percentage constant, so a larger battery also begins with more stored energy. Look at the full simulated period and the ending charge, not just the first night.
How to enter a realistic scenario
- Enter nominal battery capacity, present capacity, starting charge, reserve and charging target.
- Add appliances and set their daily operating windows. Imported appliance hours are preserved, but start times are assumptions that you must review.
- Enter array watts, local seasonal peak sun hours and losses. Confirm whether solar is actually available to the backup system.
- Enter controller, battery and inverter limits. A zero rating means “not checked”.
- Compare reduced load, added panels or added battery capacity and inspect unserved energy and ending charge.
What the solar recharge model includes
The model uses 15-minute energy steps and repeats the same daily appliance schedule and smooth daylight profile for one to seven days. Daily PV energy before controller clipping equals array watts × peak sun hours × (1 − PV loss fraction). The daylight shape distributes that energy across the entered solar window; it is an assumption, not measured irradiance.
Losses are applied once along each relevant energy path. Direct solar-to-load energy does not incur battery charge/discharge losses. Battery charging uses a one-way charge efficiency, and discharge uses a separate one-way discharge efficiency. Controller limits apply before loads and storage; battery charging limits apply to surplus after loads.
Charging stops at the entered target. “First time to target” is elapsed time from the selected start; if the battery starts at or above target, the result instead shows its first recovery to target after discharging below it.
Common solar-charging questions
Are peak sun hours the same as daylight hours?
No. Peak sun hours describe daily solar energy as equivalent hours at reference irradiance. Daylight duration describes the clock-time window in which the model distributes that energy. Enter a local seasonal resource value rather than treating the example as a forecast.
Will my grid-connected solar recharge a battery during a blackout?
Only if the equipment and configuration support it. Some systems shut down solar production during an outage, even if the battery can supply backup loads. Choose “Not confirmed” to exclude solar until you have checked.
Why might actual full charging take longer?
Near-full absorption, current taper, cell balancing, battery protection, temperature and changing sunlight are not fully described by an energy-only model. A calculated 100% target is particularly uncertain.
Does scheduled energy coverage certify my inverter or wiring?
No. The continuous-energy model caps power but does not simulate an inverter tripping and restarting, short startup pulses, surge duration, wiring, protection or compatibility. Review the separate starting check and manufacturer requirements.
Can I use hourly weather data or a local solar forecast?
This release uses manually entered solar resource and an illustrative daily shape. It does not retrieve weather or connect to your inverter. A later location-based model would be a separate feature.
Check continuous battery runtime without solar.
Method and sources
These tools use an energy-balance model with editable assumptions. The sources below explain battery monitoring, solar-and-storage behaviour and backup-system limitations; they do not certify this calculator or your installation.
- Victron SmartShunt manual: state of charge, efficiency and remaining-time estimates
- European Commission PVGIS: solar production and off-grid energy balance. This release does not request PVGIS data; enter your own local peak sun hours.
- Australian Government Solar Consumer Guide: batteries and backup capability
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