How to calculate battery storage for solar system

How to Calculate Battery Storage Capacity for Solar Systems

Calculating the battery storage capacity of a solar system is a key step to ensure its efficient and reliable operation. This article will detail the calculation process and outline the necessary formulas for better understanding and application.

1. Understanding Solar Power Generation

• Total Power of Photovoltaic Panels:Assuming you installed 10 photovoltaic panels, each with a peak power of 500 watts.Ppv_total = Npv × Ppv_peak

  Where Npv is the number of photovoltaic panels, and Ppv_peak is the peak power of each panel.

  Thus: Ppv_total = 10 × 500 watts = 5000 watts = 5 kW

• Solar Irradiance:Assume the average sunlight duration per day is 6 hours, with a peak solar irradiance of 1000 watts/m².The conversion efficiency of the photovoltaic panels is 23%.

  Edaily = Ppv_total × Tsun × ηpv

  Where Tsun is the average daily sunlight duration, and ηpv is the conversion efficiency.

  Thus: Edaily = 5 kW × 6 hours × 23% = 6.9 kWh

2. Determining System Needs

• Household Electricity Demand:Assuming your household’s average daily electricity consumption is 10 kWh, but the demand varies at different times of the day.Daytime (6 hours): 5 kWh

  Nighttime (18 hours): 5 kWh

  Eload_daily = Eload_day + Eload_night

  Where Eload_day is the daytime consumption, and Eload_night is the nighttime consumption.

  Thus: Eload_daily = 5 kWh + 5 kWh = 10 kWh

3. Energy Balance

• • During the Day:Solar power generated: 6.9 kWhHousehold power consumption: 5 kWh

    Remaining power: 6.9 kWh – 5 kWh = 1.9 kWh

    Egap_day = Edaily - Eload_day

    Thus: Egap_day = 6.9 kWh - 5 kWh = 1.9 kWh

  • During the Night:Solar power generated: 0 kWhHousehold power consumption: 5 kWh

    Battery power needed: 5 kWh

    Ebattery_night = Eload_night

    Thus: Ebattery_night = 5 kWh

Therefore, the total energy that needs to be stored in the battery is:

Ebattery = Egap_day + Ebattery_night

Thus: Ebattery = 1.9 kWh + 5 kWh = 6.9 kWh

4. Choosing the Right Battery

• Actual Battery Capacity:Assuming you choose to use a lithium-ion battery with a charge/discharge efficiency of 90%.Eactual = Ebattery / ηbattery

  Where ηbattery is the battery’s charge/discharge efficiency.

  Thus: Eactual = 6.9 kWh / 0.9 = 7.67 kWh

5. Considering Backup Days

To cope with cloudy weather or insufficient solar power generation, it’s usually recommended to select a few additional backup days. Assume you want the system to operate normally even after 3 consecutive days without sunlight.

• Total Demand for 3 Days:E3days = 3 × Eload_dailyThus: E3days = 3 × 10 kWh = 30 kWh
• Actual Battery Capacity for 3 Days:E3days_actual = E3days / ηbatteryThus: E3days_actual = 30 kWh / 0.9 = 33.33 kWh

How to calculate the ROI of solar power station system