Selecting the right battery solution impacts the performance and longevity of any solar PV system. This could be for grid backup, improved self-consumption, or off-grid independence. With new emerging technologies like lithium-ion batteries in the solar industry, reliability, durability, and lifecycle costs must be weighed carefully. This comprehensive guide is for solar installers and resellers seeking to make informed, technically sound decisions that yield satisfied, long-term clients.
A Lithium-ion battery vs Lead Acid Battery Technologies
| Attribute | Lead-Acid | Lithium-Ion (LiFePO₄ Preferred) |
|---|---|---|
| Total Storage Capacity | Typically 100Ah–200Ah @12V (1.2–2.4kWh). Banks for residential use range from 8 kWh–25 kWh. | Modular packs from 2 kWh to 15 kWh. Scalable in parallel/series with built-in BMS. |
| Usable Capacity (Depth of Discharge – DoD) | ~50% usable DoD to protect lifespan | Up to 90–95% usable DoD with minimal impact on lifespan |
| Cycle Life (at 25°C) | High lifespan is significantly reduced above 30°C | 4,000–7,000+ cycles at 80–90% DoD (10+ years) |
| Round-Trip Efficiency | ~75–85% | 92–97% |
| Charge/Discharge Rate | Moderate to high; good surge support | Limited sustained discharge (1–2C); surge handling depends on BMS and inverter compatibility |
| Weight & Space | ~70–80kg per kWh usable | ~10–15kg per kWh usable; wall-mounted and compact options available |
| Temperature Sensitivity | Regular checks (electrolyte levels, equalisation) required unless sealed | Moderate; LiFePO₄ chemistry preferred for resilience in African climates |
| Maintenance | Regular checks (electrolyte levels, equalisation) are required unless sealed | Virtually maintenance-free |
| Cost Considerations | Low upfront cost; high lifecycle cost due to shorter lifespan | Higher upfront cost, lower lifecycle cost with fewer replacements needed |
Get Off Grid Tip: Lithium-ion batteries—especially LiFePO₄—are ideal for residential and light commercial use. Their compact form factor, high efficiency, and long lifespan provide unmatched value. Lead acid remains viable for cost-sensitive, low-cycle backup scenarios.
Factors to Consider When Choosing Battery Systems
Define the Application Type
Understanding the use case is non-negotiable in battery specification:
- Grid-Backup: These systems are designed for infrequent outages or load shedding. They prioritise fast charging and minimal battery wear. Sizing is guided by essential loads and short autonomy windows.
- Self-Consumption: Batteries must cycle daily, storing solar surplus for nighttime use. Efficiency and DoD become essential, with lithium-ion batteries offering clear advantages.
- Off-Grid: Batteries become the heartbeat of the entire system. Deep discharge tolerance, high cycle life, and stable long-term output are indispensable. LiFePO₄ is the de facto standard here.
Essential Load Assessment
An accurate load profile avoids both underperformance and wasteful oversizing.Prioritise core household or business functions, and steer clear of resistive loads unless budget and system size allow.
| Load | Power (W) | Time (hrs) | Diversity Factor | Energy (Wh) |
|---|---|---|---|---|
| LED Lighting | 200 | 5 | 1 | 1,000 |
| Fridge | 150 | 24 | 0.3 | 1,080 |
| Freezer | 150 | 24 | 0.2 | 720 |
| WiFi Router | 10 | 24 | 1 | 240 |
| Phone Charging | 50 | 1 | 1 | 50 |
| TV & Decoder | 170 | 4 | 1 | 680 |
| Miscellaneous | 100 | 24 | 0.4 | 960 |
| Total Daily Energy | – | – | – | 4,730Wh |
This sample profile aligns with many middle-income households across Southern Africa.
Battery Sizing
Use the daily load and desired backup duration to size the system:
- Multiply daily energy by the desired autonomy fraction:
- (4,730Wh÷24)×12=2,365Wh
- (4,730Wh÷24)×12=2,365Wh
- Adjust for usable DoD (e.g., 90% for LiFePO₄):
- 2,365÷0.9≈2.63 kWh gross capacity
- 2,365÷0.9≈2.63 kWh gross capacity
- Add a 15–20% margin for inverter inefficiency and ageing:
- ≈3.2–3.5kWh usable recommended
Right-sizing ensures optimal performance without financial overreach.
Charging Considerations
Battery size must be synchronised with solar input. Oversizing without sufficient PV yield leads to undercharged batteries, especially problematic in winter.
A 3.5 kWh battery recharging in 5 hours requires a consistent 700W surplus after meeting immediate load. In regions with 4.5–6.5 effective sun hours, the PV array design must reflect this.
Compatibility and BMS Integration
Battery management systems (BMS) regulate health, safety, and performance. For high-efficiency systems:
- Ensure BMS communicates via CAN or RS485 with the inverter.
- Improper pairing can lead to charging faults, erratic behaviour, or system lockouts.
- Always consult compatibility charts or rely on known pairings:
Smart systems are only as smart as their weakest link—don’t let integration be that point.
Environmental and Installation Considerations
Solar batteries are sensitive to their surroundings:
- Temperature: A Lithium-ion battery prefers 15–30°C. Ambient temperatures above 35°C can degrade life expectancy rapidly. Always position batteries in shaded, thermally stable environments.
- Ventilation: Flooded lead-acid batteries emit hydrogen gas—ventilation is non-negotiable. Sealed GEL/AGM options reduce this, but still benefit from airflow.
- Mounting: Assess weight loads. Lead-acid requires reinforced ground placement. Lithium-ion battery offers modular wall mounts or rack-mounted cabinets, ideal for constrained spaces.
- Compliance: Adhere strictly to SANS 10142-1-2, municipal codes, and utility interconnection rules to prevent issues with inspections or insurance.
Lifecycle Costing: What to Tell Customers
Long-term value wins the customer:
- Lead-acid may cost less upfront, but typically requires 1–2 replacements over 10 years.
- Lithium-ion, while more expensive initially, offers higher usable capacity, minimal degradation, and near-zero maintenance.
Encourage your customers to consider Dollar per usable kWh:
Battery Type Approx. $/kWh over 10 years
Lead-Acid $4–R5+
Lithium-Ion $2–R3
Selling on TCO (Total Cost of Ownership) reinforces long-term savings, reduced site visits, and peace of mind.
Battery selection is not a one-size-fits-all decision. It requires technical precision, local context, and an eye toward future scalability. As the backbone of energy storage, batteries must deliver efficiency, durability, and cost-effectiveness.
Disclaimer: The information provided in this article is intended for educational and informational purposes only. Every effort has been made to ensure accuracy. However, we advise that readers consult datasheets and installation manuals to verify information. For specific project requirements or additional guidance, please contact the Get Off Grid technical team.
