Battery Bank Configuration — Series vs Parallel
Configuring your battery bank correctly is one of the most important decisions in a solar energy system. Whether you need higher voltage, greater capacity, or both, understanding series and parallel battery connections ensures safe operation, optimal performance, and maximum battery lifespan. This guide covers the principles, practical examples, and critical safety rules for battery bank configuration.
Series Connection: Increasing Voltage
When batteries are connected in series, the positive terminal of one battery connects to the negative terminal of the next. This increases the total voltage while the capacity (Ah) remains the same as a single battery.
Example: Series Connection
| Configuration | Total Voltage | Total Capacity | Total Energy |
|---|---|---|---|
| 1 x 48V 100Ah battery | 48V | 100Ah | 4.8 kWh |
| 2 x 24V 100Ah in series | 48V | 100Ah | 4.8 kWh |
| 4 x 12V 100Ah in series | 48V | 100Ah | 4.8 kWh |
Series connections are used when you need to match the inverter's required battery voltage. Most Deye hybrid inverters operate on a 48V battery bus, so batteries must be configured to provide 48V nominal.
Parallel Connection: Increasing Capacity
When batteries are connected in parallel, all positive terminals connect together and all negative terminals connect together. This increases the total capacity (Ah) while the voltage remains the same as a single battery.
Example: Parallel Connection
| Configuration | Total Voltage | Total Capacity | Total Energy |
|---|---|---|---|
| 1 x 48V 100Ah battery | 48V | 100Ah | 4.8 kWh |
| 2 x 48V 100Ah in parallel | 48V | 200Ah | 9.6 kWh |
| 4 x 48V 100Ah in parallel | 48V | 400Ah | 19.2 kWh |
Parallel connections are the most common way to scale battery capacity in residential solar systems. Deye BOS-G batteries support up to 16 units in parallel, providing up to 80 kWh of storage from a single inverter.
Series-Parallel: Combining Both
Some systems require both higher voltage and greater capacity. In this case, batteries are first wired in series to achieve the target voltage, then series groups are wired in parallel for additional capacity. This is common in larger commercial systems.
How to Choose the Right Configuration
- Check your inverter's battery voltage range: Deye SUN-8K operates at 40-60V (48V nominal). Your battery bank must fall within this range.
- Calculate your energy needs: Determine how many kWh of storage you need based on your nighttime consumption and desired backup duration.
- Select the right combination: Use parallel connections to increase capacity while maintaining the correct voltage.
- Verify maximum parallel units: Check both the inverter and battery specifications for the maximum number of parallel batteries supported.
Critical Safety Rules
- Never mix battery types: All batteries in a bank must be the same brand, model, chemistry, and capacity. Mixing causes imbalanced charging and premature failure.
- Never mix old and new batteries: A new battery connected in parallel with a degraded one will be dragged down to the weaker battery's performance level.
- Use identical cable lengths: In parallel connections, use the same length and gauge of cable for each battery to ensure even current distribution.
- Install fuses on every parallel string: Each parallel battery should have an individual fuse or circuit breaker for fault isolation.
- Torque all connections: Use a torque wrench to tighten battery terminals to the manufacturer's specification. Loose connections cause arcing and fire risk.
- Commission batteries simultaneously: When adding parallel batteries, charge all units to the same SoC before connecting them together.
Common Mistakes to Avoid
- Mixing 12V and 24V batteries: This creates dangerous voltage imbalances
- Exceeding maximum parallel count: Too many parallel batteries can overwhelm the BMS communication bus
- Using different cable sizes: Causes uneven current flow and overheating of thinner cables
- Connecting batteries with different SoC levels: This causes massive equalisation currents that can damage batteries and blow fuses
- Forgetting to update inverter settings: When adding batteries, update the battery capacity setting in the inverter so the SoC calculation remains accurate
Deye Battery Configuration Options
Deye's BOS-G series LiFePO4 batteries are designed for simple parallel expansion:
- BOS-G5.1: 48V, 5.12 kWh per unit, up to 16 in parallel (81.9 kWh)
- Communication: CAN bus daisy-chain between batteries and inverter
- Auto-balancing: The BMS automatically balances SoC across parallel units
- Hot-swap: New units can be added to an existing system without full shutdown
Frequently Asked Questions
What is the difference between series and parallel battery connections?
Series connections increase voltage while keeping capacity the same — the positive of one battery connects to the negative of the next. Parallel connections increase capacity while keeping voltage the same — all positives connect together and all negatives connect together. Most residential solar systems use parallel connections to scale storage capacity at the correct voltage.
Can I mix different battery brands in a battery bank?
No, you should never mix different battery brands, models, chemistries, or capacities in the same battery bank. Mixed batteries have different charge/discharge characteristics, leading to imbalanced charging, reduced performance, premature failure, and potential safety hazards.
How many Deye BOS-G batteries can I connect in parallel?
Deye BOS-G5.1 batteries support up to 16 units in parallel, providing a maximum of 81.9 kWh of storage capacity. The batteries communicate via CAN bus daisy-chain and include automatic SoC balancing across all parallel units.
