Abstract
This article investigates the optimal operation strategies and their economic and operational effects for solar energy storage system (SESS) in detached residential buildings under various electricity pricing models. The study models building electricity consumption and photovoltaic (PV) system power generation for a sample detached residential building. We develop two operational strategies—regular operation mode and hybrid operation mode—for the PV-storage system under tiered and time-of-use electricity pricing scenarios. We analyze the net present value (NPV) and self-consumption rate (SC) for four different storage unit prices ranging from 1000 to 2500 yuan/(kWh) as the storage capacity increases. The results show that the larger the installed PV capacity, the higher the initial NPV. The self-consumption rate gradually increases with the storage capacity under the regular operation mode, while it remains relatively constant under the hybrid operation mode. The optimal storage capacity for both modes, considering economic viability, is found at the peak of the NPV curve, and different PV installed capacities lead to varying initial NPV values and rankings.
1. Introduction
Solar energy, a widely adopted renewable energy source, has immense potential for power generation due to its cleanliness, abundance, and renewability . Initially, PV systems were primarily employed in large-scale power plants and public buildings. However, the significant reduction in PV system costs and the promotion of renewable energy policies globally have led to their increased adoption in residential applications .
Despite this growth, enhancing the consumption of PV-generated electricity in detached residential buildings remains a challenge. The integration of energy storage system (ESS) effectively improves the self-consumption capability of PV systems and mitigates distribution network pressure and transmission losses . The declining cost of solar energy storage system and supportive policies from national energy authorities have facilitated the flexible dispatch of energy in residential buildings through ESS installation.
This study focuses on the optimal operation strategies and their effects under different electricity pricing models for solar energy storage system in detached residential buildings. The primary objectives are to analyze the economic performance and self-consumption rates under tiered and time-of-use electricity pricing scenarios and to provide practical guidance for residents considering solar energy storage system installation.
2. Literature Review
Solar energy systems have been studied extensively for their technical and economic feasibility in various applications. Studies have shown that solar energy can significantly contribute to sustainable development goals and reduce greenhouse gas emissions . However, integrating solar energy into residential buildings requires careful consideration of energy storage solutions to ensure efficient utilization of generated power .
solar energy storage system play a vital role in improving the reliability and flexibility of renewable energy systems . In residential contexts, distributed solar energy storage system allow local energy production and storage, enhancing energy self-sufficiency and reducing reliance on the grid . Studies have shown that appropriate solar energy storage system sizes and operation strategies can optimize the economic performance and self-consumption rates of PV systems .
Despite these advancements, few studies have comprehensively examined the impact of different electricity pricing models on the operation strategies and performance of solar energy storage system in residential buildings. This gap motivates the current study, which aims to fill this knowledge void by analyzing the effects of tiered and time-of-use pricing on the operation and performance of solar energy storage system.
3. Methodology
3.1 Modeling Framework
The study adopts a modeling framework that integrates building energy consumption, PV power generation, and solar energy storage system operation. The framework is implemented using TRNSYS software to simulate building energy consumption and PV power generation. The simulated data is validated against measured data to ensure accuracy.
3.2 Building Energy Consumption and PV Generation Modeling
The study considers a sample detached residential building located in Beijing with a floor area of 380 m² and an annual electricity consumption of approximately 15,000 kWh. The building is fully electrified, with an independent HVAC system, lighting, kitchen appliances, and outdoor irrigation systems. The building’s energy consumption is simulated using TRNSYS, and the results are validated against measured data.
PV power generation is modeled for different installed capacities ranging from 4 to 12 kWp, considering a PV panel material with a maximum output power of 130 W. The simulated annual power generation varies from 4,372.47 to 13,117.41 kWh for the respective installed capacities.
3.3 Electricity Pricing Models
Two electricity pricing models are considered: tiered pricing and time-of-use pricing. The tiered pricing model follows the Beijing residential tariff structure, with three tiers at different electricity consumption levels. The time-of-use pricing model adopts the structure from the Gansu Provincial Development and Reform Commission, with peak, off-peak, and flat-rate periods.
3.4 Solar Energy Storage System Operation Strategies
Two operation strategies are designed for the solar energy storage system:
- Regular Operation Mode: Under tiered pricing, the PV system supplies power directly to loads when available. Excess power is stored in solar energy storage system or exported to the grid if the ESS is full. During periods of insufficient PV power, solar energy storage system supplies power to loads or the grid supplies power if solar energy storage system is depleted.
- Hybrid Operation Mode: Under time-of-use pricing, the system operates in regular mode during peak and flat-rate periods. During off-peak periods, solar energy storage system charges at maximum power, regardless of PV output, to maximize storage.
3.5 Economic Indicators
The economic performance is evaluated using the net present value (NPV) and self-consumption rate (SC). The NPV considers system costs, operation and maintenance expenses, and revenues over a 25-year lifetime with a discount rate of 2%. The SC measures the proportion of PV-generated power consumed locally.
4. Results and Analysis
4.1 Building Energy Consumption and PV Generation
The simulated annual energy consumption of the sample building is 15,430.3 kWh, with a deviation of less than 5% from measured data, validating the simulation accuracy. The simulated PV generation varies from 4,372.47 to 13,117.41 kWh for installed capacities of 4 to 12 kWp.
4.2 Operation Strategies and Performance
4.2.1 Regular Operation Mode
Under tiered pricing, the self-consumption rate increases with solar energy storage system capacity for all PV installed capacities. Without an solar energy storage system, the self-consumption rate ranges from 85% (4 kWp) to 50% (12 kWp). With an ESS, the self-consumption rate approaches 100% for sufficiently large ESS capacities.
The NPV curves show that larger PV capacities lead to higher initial NPVs. The optimal solar energy storage system capacity for economic viability is at the NPV peak. For storage unit prices below 1500 yuan/(kWh), some NPV curves exhibit an initial increase followed by a decrease, with the peak indicating the optimal capacity.
4.2.2 Hybrid Operation Mode
Under time-of-use pricing, the self-consumption rate remains relatively constant with increasing solar energy storage system capacity. Thesolar energy storage system charges at maximum power during off-peak periods, regardless of PV output, leading to minimal changes in self-consumption rates.
The NPV curves show significant economic benefits under the hybrid operation mode. The NPV remains positive for all PV capacities and most solar energy storage system capacities for storage unit prices below 2000 yuan/(kWh). The optimal solar energy storage system capacity for maximum NPV shifts to larger values as the storage unit price decreases.
5. Discussion
5.1 Comparison of Operation Modes
The regular operation mode exhibits a gradually increasing self-consumption rate with solar energy storage system capacity, while the hybrid mode maintains a relatively constant rate. The hybrid mode significantly outperforms the regular mode economically, with positive NPVs across a wider range of solar energy storage system capacities.
5.2 Optimal Solar Energy Storage System Capacity
The optimal solar energy storage system capacity for economic viability is located at the peak of the NPV curve for both modes. The optimal capacity shifts to larger values as the storage unit price decreases, reflecting the balance between investment cost and operational benefits.
5.3 Sensitivity to PV Capacity
Larger PV capacities lead to higher initial NPVs but do not necessarily result in the highest economic performance due to excess power generation during sunny periods. The optimal solar energy storage system capacity balances the trade-off between PV output and storage needs.
6. Conclusion
This study comprehensively analyzes the operation strategies and effects of solar energy storage system in detached residential buildings under different electricity pricing models. The regular and hybrid operation modes exhibit distinct self-consumption and economic performance characteristics. The hybrid mode outperforms the regular mode economically due to its ability to exploit off-peak electricity prices for solar energy storage system charging.
The optimal solar energy storage system capacity for economic viability is located at the peak of the NPV curve, shifting to larger values as the storage unit price decreases. The study provides valuable insights for residents considering solar energy storage system installation in detached residential buildings, highlighting the importance of considering different electricity pricing models and solar energy storage system operation strategies.