1. Introduction
The integration of photovoltaic (PV) systems with energy storage batteries has emerged as a critical solution for enhancing energy self-sufficiency and reducing reliance on traditional power grids. In single-family residences, the operational efficiency of PV-energy storage battery systems is heavily influenced by electricity pricing models, such as tiered pricing and time-of-use (TOU) tariffs. This study investigates optimal operation strategies for residential PV-energy storage systems under these pricing schemes and evaluates their economic and technical performance through numerical simulations.
2. System Modeling
2.1 Power Balance Equations
The energy flow in a PV-energy storage battery system follows these power balance principles:
$$ P_L = P_{pv2L} + P_{b2L} + P_{gim} $$
$$ P_{pv} = P_{pv2L} + P_{pv2b} + P_{gex} $$
where \( P_L \) is the residential load, \( P_{pv2L} \) and \( P_{b2L} \) represent power supplied by PV and energy storage batteries, respectively, and \( P_{gim}/P_{gex} \) denote grid import/export power.
2.2 Energy Storage Battery Model
The state-of-charge (SOC) dynamics of the energy storage battery are governed by:
$$ E_{t+\Delta t}^{ES} = E_t^{ES} + \left( \xi P_{ES,ch} \eta_{ch}^{ES} – \frac{(1-\xi) P_{ES,dis}}{\eta_{dis}^{ES}} \right) \Delta t $$
with constraints:
$$ SOC_{min}X_{ES} \leq E_t^{ES} \leq SOC_{max}X_{ES} $$
where \( X_{ES} \) is the battery capacity, and \( \eta_{ch}^{ES}/\eta_{dis}^{ES} \) represent charge/discharge efficiencies (0.9).
3. Electricity Pricing Mechanisms
| Pricing Model | Time Period | Rate (CNY/kWh) |
|---|---|---|
| Tiered Pricing | 1-240 kWh/month | 0.4883 |
| 241-400 kWh/month | 0.5383 | |
| >400 kWh/month | 0.7883 | |
| TOU Pricing | Peak (07:00-09:00, 17:00-23:00) | 0.807 |
| Off-peak (02:00-04:00, 11:00-17:00) | 0.269 | |
| Standard (Other hours) | 0.538 |
4. Operation Strategies
4.1 Conventional Operation Mode (Tiered Pricing)
Prioritizes self-consumption of PV generation with energy storage battery dispatch sequence:
- Direct PV-to-load supply
- Excess PV charges energy storage battery
- Grid import when PV/battery insufficient
4.2 Hybrid Operation Mode (TOU Pricing)
Combines self-consumption optimization with strategic battery charging during off-peak periods:
$$ \text{Charge Strategy} = \begin{cases}
\max(P_{pv2b}, P_{grid2b}) & \text{if off-peak} \\
\text{Conventional mode} & \text{otherwise}
\end{cases} $$
5. Performance Metrics
5.1 Economic Analysis
Net Present Value (NPV) calculation:
$$ NPV = \sum_{y=1}^{25} \frac{R_y – C_{O\&M,y}}{(1 + dr)^{y-1}} – Inv $$
where \( Inv = U_{batt}X_{ES} + U_{PV}C_{PV} \), with battery costs ranging 1,000-2,500 CNY/kWh.
5.2 Technical Performance
Self-consumption rate (\( \phi_{sc} \)):
$$ \phi_{sc} = \frac{\int_{t_1}^{t_2} \min(L(t), P(t)+S(t))dt}{\int_{t_1}^{t_2} P(t)dt} $$
6. Results and Discussion
6.1 Self-Consumption Analysis
| PV Capacity (kWp) | SC (No Battery) | SC (10kWh Battery) |
|---|---|---|
| 4 | 85% | 97% |
| 8 | 67% | 89% |
| 12 | 50% | 78% |
6.2 Economic Viability
Optimal energy storage battery capacities for different cost scenarios:
| Battery Cost (CNY/kWh) | Optimal Capacity (kWh) | Max NPV (kCNY) |
|---|---|---|
| 2,500 | 0 | 42.1 |
| 1,500 | 3.2 | 58.7 |
| 1,000 | 6.5 | 74.3 |
7. Conclusion
The study demonstrates that energy storage battery integration significantly improves PV self-consumption rates (15-30% increase) while achieving positive NPV across most scenarios. For tiered pricing systems, smaller batteries (3-5kWh) provide optimal returns, whereas TOU pricing enables larger battery deployments (6-8kWh) through strategic off-peak charging. The results emphasize the critical role of energy storage battery systems in maximizing residential PV benefits under evolving electricity market structures.