Abstract
The global push for clean and sustainable energy has increased the adoption of renewable energy systems, notably solar photovoltaic (PV) technology. However, the intermittency and variability of solar energy pose significant challenges to grid stability and reliability. Battery Energy Storage Systems (BESS) offer a viable solution to this challenge by providing energy buffering, peak shaving, load shifting, and grid support services. This paper discusses the role of BESS in stabilizing intermittent PV power generation, presents a basic model of a grid-connected 3-phase 4-wire PV-BESS system, and includes a capacity sizing methodology to design an optimal energy storage system.
1. Introduction
The growing integration of renewable energy into power systems introduces variability that challenges system operators and planners. Solar energy, although abundant, is inherently intermittent—its generation is limited to daylight hours and affected by weather conditions. These characteristics result in energy supply mismatches with demand, leading to instability in power quality, frequency regulation, and voltage support.
To mitigate these issues, Battery Energy Storage Systems (BESS) can be coupled with PV systems. A properly sized and controlled BESS ensures that excess energy generated during high irradiance periods can be stored and released during low-generation or high-demand periods, making the power output more stable and dispatchable.
2. Role of BESS in Grid-Connected PV Systems
2.1 Key Functions
Energy Shifting: Stores excess daytime energy for evening or night-time use.Peak Shaving: Reduces load on the grid during peak demand by supplying stored energy.
Grid Stability: Provides frequency and voltage regulation.
Power Quality: Mitigates voltage sags/swells and harmonic distortions in a 3-phase 4-wire system.
2.2 System Overview
A typical PV-BESS integrated system connected to a 3-phase 4-wire grid consists of:
- PV array
- DC/DC converter
- Battery storage bank
- Bidirectional inverter
- Grid interface (with or without transformer)
- Control system (EMS – Energy Management System)
3. Modeling and Analysis of Grid-Connected PV-BESS Systems
3.1 Assumptions
- System is grid-tied (3-phase, 4-wire, 400V or 6.9kV system)
- PV production follows a typical diurnal curve
- Load demand is known or estimated
- BESS has defined charge/discharge efficiency
3.2 Mathematical Model
Let:
: Energy generated by PV system per day (kWh)
: Energy required by the load per day (kWh)
: Surplus energy available for storage
: Round-trip efficiency of BESS (typically 85%–95%)
Then,
4. Capacity Sizing of BESS
4.1 Load and PV Data
Assume:
Daily Load: 
PV Capacity: 1 MWp
Peak Sun Hours (PSH): 5 hours/day
PV Output:
Excess Energy:
BESS Efficiency:
4.2 Required Storage Capacity
If the goal is to store this surplus and discharge during the night (over 12 hours):
Required BESS power rating:
Resulting BESS Specification:
Energy capacit: 2,700 kWh (2.7 MWh)
Power capacity: 225 kW
Nominal DC voltage: e.g., 1000 V
Battery type: Li-ion / Ni-Cd (depending on application requirements)
5. Design Considerations
5.1 Technical
Depth of Discharge (DoD): Typically 80% for Li-ion
Charge/Discharge cycles per day: 1–2
Thermal management and safety systems
Communication protocols with grid controller
5.2 Economic
CapEx of BESS: $300–$600/kWh
Payback period based on load profile, arbitrage, and grid tariffs
Lifecycle: 10–15 years depending on usage profile
6. Conclusion
The integration of BESS with PV systems provides a strategic solution to the intermittency of solar energy and improves overall grid reliability. A well-modeled and sized BESS ensures optimal energy usage, reduces peak demand, and supports voltage/frequency stability in 3-phase 4-wire systems. As renewable energy penetration grows, energy storage becomes indispensable for resilient and sustainable power systems.
7. References
IEEE Std 1547-2018 – Interconnection and Interoperability of Distributed Energy Resources with Associated Electric Power Systems Interfaces
IEC 62933 – Electrical Energy Storage (EES) Systems Standards
R. Lasseter et al., “Microgrids and Distributed Energy Resources,” IEEE PES, 2019
CIGRÉ TB 762 – Battery Energy Storage Applications and Technologies