To select the PV power, PCS power, and energy storage battery capacity in a microgrid system based on load power and irradiation conditions, the core principle is to achieve "supply-demand balance" — ensuring that PV power can meet load demand as much as possible, PCS can match the power conversion needs of PV and energy storage, and the battery capacity can compensate for the gap between PV generation and load consumption (especially in low-irradiation or no-irradiation periods). Below is a step-by-step, practical selection method, combined with the microgrid system:
1. Basic Parameter Definition (Prerequisite)
First, clarify the two core input parameters:
Load Power:
Calculate the maximum load power (P_load_max, unit: kW) : The peak power of all loads in the microgrid (e.g., 50kW for a remote base station, 200kW for a small industrial park).
Calculate the daily load energy consumption (E_load, unit: kWh) : E_load = P_load_avg × 24h (P_load_avg is the average load power throughout the day, which can be obtained by statistics of actual load operation data).
Irradiation Conditions:
Obtain the local average daily solar irradiance (H, unit: kWh/m²·day) : Query the local meteorological data (e.g., 4.5 kWh/m²·day in subtropical regions, 3.0 kWh/m²·day in high-latitude regions).
Determine the effective sunshine hours (T, unit: h) : T = H / 1kW/m² (e.g., H=4.5 → T=4.5h; it represents the time when the PV power generation reaches the rated power per day).
2. Selection of PV Power (P_PV, unit: kW)
PV power is mainly determined by the daily load energy consumption and local irradiance, with the goal of covering most of the daily load demand (considering 70%~90% coverage to avoid excessive PV waste or insufficient generation).
Formula & Calculation:
P_PV = (E_load × Coverage Rate) / (T × PV Generation Efficiency)
PV Generation Efficiency (η): Comprehensive efficiency of PV modules + inverter (usually 0.8~0.85, considering dust, shading, and line loss).
Coverage Rate: Generally 70%~90% (higher for areas with stable irradiance, lower for areas with frequent cloudy/rainy weather).
Example:
If E_load=200kWh/day, H=4.5kWh/m²·day (T=4.5h), coverage rate=80%, η=0.8:P_PV = (200 × 0.8) / (4.5 × 0.8) ≈ 44.4kW → Choose 45kW PV system (round up to the nearest standard specification).
Key Notes:
If the microgrid needs to operate off-grid for a long time, appropriately increase PV power (10%~20% redundancy) to cope with low-irradiation days.
If the microgrid is grid-connected, PV power can be slightly lower (70% coverage) because the grid can compensate for the shortage.
3. Selection of PCS Power (P_PCS, unit: kW)
PCS (Bidirectional Power Converter) is the "bridge" between PV/energy storage and the microgrid, so its power must match the PV power and energy storage discharge power, while meeting the load power demand.
Core Principles:
Example:
If P_PV=45kW, P_load_max=50kW, battery discharge rate=0.8C, battery capacity=100kWh (P_battery_discharge_max=80kW):Max(P_PV, P_battery_discharge_max, P_load_max) = 80kW → P_PCS choose 88~96kW (1.1~1.2×80kW).
4. Selection of Energy Storage Battery Capacity (E_battery, unit: kWh)
The battery capacity is used to compensate for the gap between PV generation and load consumption, ensuring stable power supply during no-irradiation periods (night, cloudy days) or grid outages.
Formula & Calculation:
E_battery = (E_load × (1 - PV Coverage Rate) + E_backup) / (Battery DOD × Battery Efficiency)
PV Coverage Rate: Same as the coverage rate used in PV power selection (70%~90%).
E_backup: Backup energy for emergency power supply (e.g., 1~3 days of load energy consumption for off-grid microgrids; 0.5~1 day for grid-connected microgrids).
Battery DOD (Depth of Discharge): Maximum allowable discharge depth (lithium iron phosphate batteries: 80%~90%, lead-acid batteries: 50%~60%; DOD=0.8 is commonly used).
Battery Efficiency: Charging and discharging efficiency (usually 0.9~0.95).
Example:
Based on the previous example (E_load=200kWh/day, coverage rate=80%, E_backup=1 day load (200kWh), DOD=0.8, battery efficiency=0.9):E_battery = (200×(1-0.8) + 200) / (0.8×0.9) = (40 + 200) / 0.72 ≈ 333.3kWh → Choose 350kWh energy storage battery (round up).
Key Notes:
Off-grid microgrids: Prioritize increasing backup energy (1~3 days) to ensure continuous power supply when PV generation is insufficient.
Grid-connected microgrids: Focus on peak shaving and valley filling, so E_backup can be smaller (0.5~1 day), and the capacity can be adjusted according to the peak-valley load difference.
5. Summary of Selection Logic (Combined with the Document’s Microgrid Integrated Cabinet)
The microgrid integrated cabinet (mentioned in the opened document) integrates PV access, PCS, energy storage, and STS/ATS. When selecting parameters for this cabinet:
First confirm the load’s maximum power and daily energy consumption (the core basis for all selections).
Combine local irradiance data to determine PV power (cover most load demand).
Determine PCS power based on PV power, battery discharge power, and peak load (ensure seamless switching and stable power supply).
Calculate battery capacity based on the PV coverage gap and backup requirements (ensure no power interruption in off-grid mode).