Load Shedding Proof: How to Design a Backup System That Actually Works

Load shedding is a fact of life in South Africa. But many businesses invest in backup systems that fail when needed most—undersized inverters, insufficient battery capacity, or systems that cannot handle their actual loads.

Common Backup System Failures

Undersized Inverter: System shuts down when multiple high-power devices start simultaneously.

Insufficient Battery Capacity: Batteries drain before load shedding ends, leaving you without power.

Incompatible Loads: Some equipment (motors, pumps) cannot run on modified sine wave inverters.

No Load Prioritization: System tries to power everything and fails instead of prioritizing critical loads.

Poor Installation: Wiring, grounding, or ventilation issues cause system failures or safety hazards.

The Right Approach to Backup System Design

A reliable backup system requires careful planning:

Step 1: Identify Critical Loads

Not everything needs to run during load shedding. Prioritize:

Essential Loads (must run):

• Computers and servers
• Internet and communications
• Security systems
• Refrigeration
• Critical lighting

Nice-to-Have Loads (can be shed):

• HVAC (can tolerate brief interruptions)
• Non-critical lighting
• Kitchen appliances
• Convenience equipment

Non-Essential Loads (shed immediately):

• Water heating
• Pool pumps
• Heavy machinery
• High-power equipment

Step 2: Calculate Power Requirements

For each critical load, determine:

Running Power (W): Continuous power consumption during normal operation.

Starting Power (W): Brief surge when equipment starts (motors, compressors can draw 3-5x running power).

Runtime Required (hours): How long must equipment run during load shedding?

Example Calculation:

• 10 computers @ 200W each = 2,000W running
• 2 servers @ 500W each = 1,000W running
• Internet equipment = 200W running
• Security system = 100W running
• LED lighting = 500W running
• Total Running Load: 3,800W
• Peak Starting Load: 4,500W (accounting for simultaneous starts)

Step 3: Size Inverter Capacity

Inverter must handle:

Continuous Load: Total running power of all critical loads.

Surge Capacity: Peak starting power when equipment starts simultaneously.

Safety Margin: 20-30% headroom for future expansion and unexpected loads.

Example:

• Running load: 3,800W
• Peak starting load: 4,500W
• Safety margin: 30%
• Required Inverter Capacity: 5,850W (round up to 6kW inverter)

Step 4: Calculate Battery Capacity

Battery capacity depends on:

Load (W): Total running power of critical loads.

Runtime (hours): How long must system run during load shedding?

Depth of Discharge (DoD): Maximum battery discharge (80% for lithium, 50% for lead-acid).

System Efficiency: Inverter efficiency (typically 90-95%).

Formula: Battery Capacity (Wh) = (Load × Runtime) / (DoD × Efficiency)

Example:

• Load: 3,800W
• Runtime: 4 hours (Stage 6 load shedding)
• DoD: 80% (lithium batteries)
• Efficiency: 93%
• Required Battery Capacity: (3,800 × 4) / (0.80 × 0.93) = 20,430Wh ≈ 20kWh

Step 5: Choose Battery Technology

Lithium-Ion (LiFePO4):

• Pros: Long lifespan (10+ years), deep discharge (80% DoD), fast charging, compact
• Cons: Higher upfront cost (R8,000-R12,000/kWh)
• Best for: Frequent cycling, space-constrained installations

Lead-Acid (AGM/Gel):

• Pros: Lower upfront cost (R3,000-R5,000/kWh)
• Cons: Shorter lifespan (3-5 years), shallow discharge (50% DoD), slower charging, bulky
• Best for: Budget-conscious installations, infrequent use

Step 6: Plan for Recharging

Batteries must recharge between load shedding events:

Grid Charging: Recharge from grid during non-load-shedding periods (slowest, cheapest).

Solar Charging: Recharge from solar panels during the day (faster, reduces grid dependence).

Generator Charging: Recharge from generator if grid and solar are insufficient (fastest, most expensive).

Recharge Time Calculation: Recharge Time (hours) = Battery Capacity (kWh) / Charging Power (kW)

Example:

• Battery capacity: 20kWh
• Charging power: 5kW (from grid or solar)
• Recharge time: 4 hours

Real Example: Sandton Office Building

A 200-person office needed backup power for critical operations during load shedding.

Critical Loads Identified:

• 150 computers @ 200W = 30kW
• 10 servers @ 500W = 5kW
• Internet and networking = 2kW
• Security systems = 1kW
• Critical lighting = 3kW
• Total: 41kW running load

Initial Quote (from installer):

• 30kW inverter
• 30kWh battery bank
• Cost: R450,000

Problem: System would fail because:

• Inverter undersized for starting surge (150 computers starting simultaneously)
• Battery capacity insufficient for 4-hour Stage 6 load shedding
• No load prioritization (trying to power everything)

Our Recommendation:

• Prioritize critical loads: 100 computers + servers + networking + security = 28kW
• 40kW inverter (handles starting surge + 30% margin)
• 50kWh lithium battery bank (4 hours runtime at 28kW load)
• Load shedding controls (automatically shed non-critical loads)
• Cost: R580,000

Results:

• System reliably powers critical operations through Stage 6 load shedding
• No unexpected shutdowns or failures
• Employees remain productive during outages
• ROI: Avoided productivity losses worth R100,000/month during Stage 4-6 load shedding

Hybrid Solar + Battery Systems

Combining solar with battery storage provides:

Daytime Recharging: Solar panels recharge batteries during the day, reducing grid dependence.

Load Shedding Protection: Batteries provide backup power during outages.

Cost Savings: Solar reduces grid consumption even when load shedding is not active.

System Sizing:

• Solar capacity: Size to cover daytime loads + recharge batteries
• Battery capacity: Size for evening/night loads during load shedding
• Inverter capacity: Size for peak load + starting surge

Common Mistakes to Avoid

Mistake 1: Undersizing for Starting Surge

• Motors, compressors, and electronics draw 3-5x running power when starting
• Inverter must handle simultaneous starting of multiple devices

Mistake 2: Ignoring Battery Recharge Time

• Batteries must fully recharge between load shedding events
• Insufficient recharge time leads to progressive battery depletion

Mistake 3: Using Modified Sine Wave Inverters

• Some equipment (motors, medical devices, audio equipment) requires pure sine wave
• Modified sine wave can cause equipment damage or malfunction

Mistake 4: No Load Prioritization

• Trying to power everything during load shedding often results in system failure
• Implement automatic load shedding to prioritize critical loads

Mistake 5: Poor Ventilation

• Batteries and inverters generate heat and require adequate ventilation
• Overheating reduces lifespan and can cause failures

Get Your Backup System Right

Our FREE energy audit provides the data you need for reliable backup system design:

• Detailed load analysis showing actual consumption patterns
• Critical load identification and prioritization
• Accurate inverter and battery sizing calculations
• Recharge time analysis
• Professional recommendations for system configuration

Design your backup system correctly: Call +27 10 595 3384 or visit powercentrix.co.za