1. Introduction
The integration of renewable energy sources into microgrids has necessitated the development of robust energy storage systems to ensure grid stability, enhance power quality, and manage fluctuating energy demands. Among various storage technologies, battery-based solutions dominate due to their scalability and adaptability. This study focuses on evaluating the performance of two prominent battery types—Lead Carbon (LC) and Lead Acid (LA) batteries—within a microgrid-integrated energy storage system. Through experimental comparisons, cost analyses, and control strategy simulations, we identify the optimal battery choice for long-term operational efficiency and economic viability.
2. Performance Comparison of Energy Storage Batteries
2.1 Key Performance Indicators
The performance of LC and LA batteries is evaluated based on:
- Cycle Life: Number of charge-discharge cycles before capacity degradation.
- Depth of Discharge (DOD): Usable energy capacity per cycle.
- Charge/Discharge Rate: Power delivery efficiency.
2.2 Mathematical Modeling of Cycle Life
The cycle life NdNd of each battery type correlates inversely with DOD. Empirical relationships derived from experimental data are:
For Lead Acid (LA) Batteries:Nd(DOD)=4,469×DOD−0.491−4,054(1)Nd(DOD)=4,469×DOD−0.491−4,054(1)
For Lead Carbon (LC) Batteries:Nd(DOD)=5,967×DOD−0.987−4,653(2)Nd(DOD)=5,967×DOD−0.987−4,653(2)
The equivalent cycle count NeqNeq for a specific DOD level is:Neq(DOD)=NdNd(DOD)(3)Neq(DOD)=Nd(DOD)Nd(3)
The total operational cycles NtotalNtotal over a 15-year lifespan are:Ntotal=∑i=1nNeq(DODi)(4)Ntotal=i=1∑nNeq(DODi)(4)
2.3 State of Charge (SOC) Dynamics
SOC is calculated during charging (Pb>0Pb>0) and discharging (Pb<0Pb<0) phases:
Charging:SOC(k)=SOC(k−1)+Pb(k−1)⋅Kp⋅ΔtQB(5)SOC(k)=SOC(k−1)+QBPb(k−1)⋅Kp⋅Δt(5)
Discharging:SOC(k)=SOC(k−1)+Pb(k−1)⋅ΔtKp⋅QB(6)SOC(k)=SOC(k−1)+Kp⋅QBPb(k−1)⋅Δt(6)
Here, KpKp is efficiency, QBQB is battery capacity, and ΔtΔt is the sampling interval.
3. Cost Analysis Over 15-Year Lifespan
A comparative cost analysis (Table 1) highlights the economic superiority of LC batteries due to fewer replacements and lower capital costs.
Table 1: Lifetime Cost Comparison of LA and LC Batteries
| Battery Type | Expected Lifespan (Years) | Replacement Count | Battery Cost (10k USD) | PCS Cost (10k USD) | Total Cost (10k USD) |
|---|---|---|---|---|---|
| LA Battery | 4.26 | 3 | 620 | 80 | 628 |
| LC Battery | 5.71 | 2 | 450 | 80 | 458 |
The LC battery reduces total costs by 27%, underscoring its economic feasibility for energy storage systems.
4. Charge-Discharge Control Strategy
Effective management of energy storage systems requires dynamic power allocation between hybrid storage units (e.g., batteries and supercapacitors).
4.1 Power Allocation Rules
- Case 1: PHESS=0PHESS=0
If DOD≥DODmaxDOD≥DODmax, discharge halts:PHESS−i(i)=0(7)PHESS−i(i)=0(7)If DOD<DODmaxDOD<DODmax, discharge power is:PHESS−j=−PHESS(i)⋅CHESS−j(DODmax−DOD)∑jCHESS−j(DODmax−DOD)(8)PHESS−j=∑jCHESS−j(DODmax−DOD)−PHESS(i)⋅CHESS−j(DODmax−DOD)(8) - Case 2: PHESS>0PHESS>0
If SOC≥SOCmaxSOC≥SOCmax, charging halts:PHESS−i(i)=0(9)PHESS−i(i)=0(9)If SOC<SOCmaxSOC<SOCmax, charging power is:PHESS−j=−PHESS(i)⋅CHESS−j(SOCmax−SOC)∑jCHESS−j(SOCmax−SOC)(10)PHESS−j=∑jCHESS−j(SOCmax−SOC)−PHESS(i)⋅CHESS−j(SOCmax−SOC)(10)
4.2 Two-Stage Filtering for Power Smoothing
A two-stage filtering strategy mitigates high-frequency power fluctuations:
- Stage 1: Supercapacitors absorb rapid fluctuations.
- Stage 2: LC batteries smooth residual low-frequency variations.
5. Simulation and Experimental Validation
5.1 Simulation Setup
- Platform: MATLAB/Simulink.
- Parameters:
- Microgrid capacity: 7 MW.
- Hybrid modules: 10 units (500 kW each).
- Time constant: 2,400 s.
5.2 Results
- Supercapacitors exhibited frequent, high-magnitude charge-discharge cycles (Figure 1).
- LC Batteries demonstrated stable, low-frequency cycles (Figure 2).
- The hybrid energy storage system reduced peak power stress on LC batteries by 40%, extending efficiency duration by 22%.
6. Conclusion
The LC battery outperforms LA batteries in cycle life (5.71 vs. 4.26 years), cost efficiency (total savings of 170k USD), and operational stability. The proposed hybrid energy storage system with two-stage control effectively balances rapid response and long-term energy storage, making it ideal for renewable-dominant microgrids. Future work should explore advanced materials and AI-driven predictive maintenance to further optimize energy storage system performance.