How a Solar Battery Fits the System
A solar battery stores the energy that a solar array produces but the load does not use at the moment of production. In a typical system, panels feed an MPPT charge controller or a hybrid inverter, the controller charges the battery, and the inverter supplies the loads from the battery or directly from the panels. Buyers searching for a solar battery are usually sizing a home system, an off-grid cabin, a small commercial site or a mobile power unit. The battery is the largest cost item after the panels in many of these projects, so sizing it correctly matters.
The sizing method has four steps: estimate the daily load, decide how many days of autonomy the system needs, set a depth of discharge, and check the array can recharge the battery in a typical day. The method works for lead-acid and lithium packs, but the values differ because the usable depth and the cycle life differ.
Step 1: Estimate the Daily Energy Load
List the loads that the system must supply, their power and the hours they run each day. Multiply power by hours to get watt-hours per day, then add the losses in the inverter and the wiring. A simple example is a load of 2,000 Wh per day with a 15 percent loss, which gives about 2,300 Wh per day from the battery.
Separate essential loads from optional loads. A system sized for essential loads only will be smaller and cheaper, and it will still keep the most important circuits running during a cloudy period. Buyers should agree on this split before they choose a battery size.
Step 2: Set the Days of Autonomy
Autonomy is the number of days the battery can supply the essential load without any solar input. One day is common for grid-tied systems with backup. Two or three days are typical for off-grid systems in regions with frequent overcast weather. Each extra day increases the battery bank size, so autonomy should be chosen with the site's weather pattern in mind.
Step 3: Convert Energy to a Battery Bank
The required usable energy equals the daily load multiplied by the days of autonomy. The rated energy equals the usable energy divided by the depth of discharge. For a LiFePO4 pack, the depth of discharge is set by the BMS and the design. The table below shows an example for a 2,300 Wh daily load with one day of autonomy at 90 percent depth of discharge.
| Item | Value |
|---|---|
| Daily battery energy | 2,300 Wh |
| Days of autonomy | 1 |
| Required usable energy | 2,300 Wh |
| Rated energy at 90 percent depth of discharge | About 2,560 Wh |
| Example pack | 12.8 V, 200 Ah (2,560 Wh nominal) |
The example uses catalog-based nominal energy for illustration. The usable energy of the chosen pack must be confirmed by the supplier, because it depends on the BMS limits and the test basis.
Step 4: Check Voltage and Current Compatibility
The battery voltage must match the inverter and the charge controller. Common LFP voltage classes are 12.8 V, 25.6 V and 51.2 V nominal. Larger systems usually choose a higher voltage to reduce current and cable size for the same power. At the same power, current falls as voltage rises. A 51.2 V battery therefore needs half the current of a 25.6 V battery and one quarter of the current of a 12.8 V battery, which allows thinner cable for the same load.
Check the continuous discharge current and the peak current of the battery against the inverter's maximum input current. A battery that stores enough energy but cannot deliver the peak current will limit the system.
Step 5: Check the Solar Input
The solar input must be sized to recharge the battery within a reasonable time. An all-in-one unit in the YueQi catalog lists an MPPT solar input with a voltage range of 60 to 500 V and a maximum input of 27 A. The 6.2 kW model lists a maximum solar input of 9,000 W, while the 4.2 kW model lists 6,200 W, a figure to be confirmed. Panel count, string voltage and the controller's input limits must all fit within these values.
- Confirm the open-circuit voltage of the panel string at the coldest expected temperature
- Confirm the maximum input power of the controller
- Estimate the number of sunny hours in your region and check the recharge time
Step 6: Plan Communication and Monitoring
A solar battery bank benefits from a communication link between the BMS and the inverter. CAN, RS485 and RS232 are common options, and the YueQi mobile storage models list all three. The link allows the inverter to read state of charge and alarms, and it helps the system avoid over-discharge. Confirm the protocol and the inverter brand before you purchase the battery.
Certification and Installation Notes
For cross-border trade, request UN 38.3 transport evidence for the lithium battery and the CE documents that apply to the product family. The YueQi catalog shows the CE mark and the UN 38.3 mark on its storage products, and certificate copies are available on request. Installation location, grid connection and local electrical rules depend on the destination market and must be confirmed with a qualified installer.
Summary
Sizing a solar battery is a sequence of simple steps: estimate the load, choose the autonomy, convert to a rated battery size, check voltage and current, and confirm the solar input and communication. A clear sizing sheet makes the supplier discussion faster and reduces the risk of a mismatch. Any figure in this article that depends on a specific model should be confirmed with the supplier in writing.
Next step
Send your application, target specification and estimated quantity with your inquiry, and we will confirm matching products, samples and document requirements in writing. See the product lines or request a quote.