As more South African businesses adopt solar, battery energy storage is becoming the next logical step. But not all battery systems are designed the same, and if your goal is to save money through energy arbitrage, designing your BESS correctly from day one is critical.
Energy arbitrage is about charging your battery when electricity is cheap and discharging it when tariffs are high. It's a simple idea, but unlocking real value requires careful planning, precise sizing, and system-level thinking.
Start with Load and Tariff Analysis
Before sizing a battery, you need to understand your energy profile. How much power do you use? When does your consumption peak? What tariff are you on? With the rise of TOU tariffs like Eskom Megaflex, the gap between off-peak and peak prices can exceed R2.00/kWh — that's your arbitrage opportunity.
Right-Sizing the Battery (and Inverter)
For arbitrage-only systems (not backup), the design doesn't need to cover your full load. The battery size is based on how much energy you can reasonably shift each day. The inverter is then sized to match the desired discharge rate, not the full site load.
This approach lowers:
- Capital cost
- Installation complexity
- Maintenance requirements
Charge Sources: Solar or Grid?
Arbitrage systems can charge from two sources:
- Excess solar PV, which has a near-zero marginal cost
- Off-peak grid energy, typically available late at night or early morning at rates as low as R1.20/kWh
Well-designed BESS systems can switch between these sources automatically.
Controls, Monitoring, and Adjustments
No arbitrage system is complete without intelligent control. The battery must be programmed to charge and discharge at the right times based on tariff windows, load forecasts, and solar production levels.
Avoiding Common Pitfalls
Common issues include:
- Oversizing the battery for arbitrage use
- Oversizing the inverter for backup functionality that isn't needed
- Incorrect discharge schedules
- No post-installation performance tracking
A Smarter Way to Design Storage
When designed for energy arbitrage, a BESS doesn't need to be big. It just needs to be smart — matching your peak usage window, aligning with tariff gaps, charging from the lowest-cost source, and discharging when it counts.
