Design Specification

Battery Energy Storage System (BESS) for a 2 kW Grid Connection

Executive Summary

Design a scalable Battery Energy Storage System (BESS) that allows a property with a 2 kW utility limit to safely support significantly larger loads using a hybrid inverter and LiFePO₄ batteries. The system prioritizes:

• Power outage protection
• Peak shaving (never exceed 2 kW grid import)
• Future solar integration
• Modular battery expansion

1. System Architecture

      Utility Grid (2 kW Max)
               │
      Main Breaker + SPD
               │
      Hybrid Inverter (10 kVA)
         ┌─────┴─────┐
         │           │
   House Loads   Battery Bank

2. Design Targets

| Parameter | Target | |---|---:| | Grid Import | ≤2 kW | | Initial Battery | 20 kWh | | Expansion | 60+ kWh | | Inverter | 10 kVA | | Continuous Load | Up to inverter/battery limits (≈8 kW practical) |

3. Normal Operation

• Load <2 kW: Grid powers load and charges batteries.
• Load >2 kW: Grid stays capped at 2 kW, battery supplies the remainder.
• Grid outage: Battery powers the entire installation.

4. Worst-Case Runtime

| Battery | 5 kW | 8 kW | |---|---:|---:| |20 kWh|~3.6 h|~2.2 h| |40 kWh|~7.2 h|~4.4 h| |60 kWh|~10.8 h|~6.6 h|

5. Components

• 10 kVA Hybrid inverter with grid import limiting
• 48 V LiFePO4 rack batteries
• Battery rack cabinet
• DC fuse and isolator
• AC breakers
• SPD
• Earthing
• Monitoring

6. Approximate Budget

| Item | Cost (INR) | |---|---:| |10 kVA Hybrid Inverter|120,000| |20 kWh LiFePO4|350,000| |Protection + Installation|90,000| |Monitoring|15,000| |Estimated Total|575,000–700,000|

7. Safety

• Dedicated battery room or ventilated cabinet
• Correct cable sizing
• DC fuse near battery
• Isolation switches
• Surge protection
• Fire extinguisher
• BMS monitoring

8. Future Solar

Solar Panels
      │
 MPPT Input
      │
Hybrid Inverter
      │
 Battery
      │
 House

The initial system is solar-ready without purchasing PV modules today.

Appendices

A. Expansion Roadmap

Phase 1: Grid + Battery Phase 2: Add Solar Phase 3: Add Generator

B. Recommended Cable and Protection

Use cable sizes and breaker ratings based on the selected inverter manufacturer's installation manual and local electrical code.

C. Maintenance

• Monthly: Visual inspection
• Quarterly: Tighten terminals
• Annually: Capacity and insulation tests

D. Daily Energy Flow

Charge whenever grid demand is below 2 kW and discharge only when load exceeds 2 kW or during outages.