Sizing Your Solar Array and Battery Bank for Continuous Power
To determine the size of the solar array and battery bank needed to run a 120V 150W device 24 hours a day with a 3-day cloudy day buffer, we can break down the calculation into several steps. This guide will walk you through the process, ensuring you have reliable energy storage even during cloudy conditions.
Step 1: Calculate Daily Energy Consumption
The first step in sizing your solar system is to calculate the daily energy consumption of your device. This is done by multiplying the power (in watts) by the time (in hours).
Daily Energy Consumption:
Daily Consumption Power (W) x Time (h) 150 W x 24 h 3600 Wh
Step 2: Calculate Total Energy Requirement for Cloudy Days
Next, we need to determine how much energy the system needs for three cloudy days. This buffer will ensure you have sufficient energy stored even during extended periods of low sunlight.
Total Energy for 3 Cloudy Days:
Total Energy for 3 Days Daily Consumption x 3 3600 Wh x 3 10800 Wh
Step 3: Calculate Battery Bank Size
The battery bank size depends on the daily energy requirement and the battery's efficiency. To preserve battery life, we will only use 50% of the battery's capacity. This means the battery will need to store twice the amount of energy needed to cover three cloudy days.
Battery Capacity Required:
Battery Capacity Required Total Energy for 3 Days / 0.5 10800 Wh / 0.5 21600 Wh
Convert to Amp-Hours at 120V:
Battery Capacity Ah Battery Capacity Wh / Voltage 21600 Wh / 120 V 180 Ah
Step 4: Calculate Solar Array Size
To determine the solar array size, we need to consider the average sunlight hours available per day. For simplicity, let's assume an average of 5 hours of effective sunlight per day.
Daily Energy Production Needed:
Daily Energy Production Needed Daily Consumption 3600 Wh
Calculate the Required Solar Array Size:
Solar Array Size W Daily Energy Production Needed / Sunlight Hours 3600 Wh / 5 h 720 W
Summary
Battery Bank Size:
180 Ah at 120V or 21600 Wh
Solar Array Size:
720 W
Additional Considerations
Efficiency Losses: A common practice is to account for system inefficiencies, such as inverter losses and battery charge/discharge efficiencies, by adding an extra 25% to the solar array and battery bank capacities.
Adjusted Solar Array Size:
720 W x 1.25 900 W
Adjusted Battery Bank Size:
21600 Wh x 1.25 27000 Wh or 27000 Wh / 120 V 225 Ah
Final Recommendations
Battery Bank Size:
Approximately 225 Ah at 120V
Solar Array Size:
Approximately 900 W
This setup should provide sufficient energy to run your device continuously, even during extended cloudy periods.
By following these steps and understanding the key components, you can ensure a reliable and efficient solar energy system. Whether you're looking to power a small device or a larger system, the same principles apply. Make sure to consult a professional if you have specific requirements or complex needs.