Comprehensive Guide to Sizing Your Off-Grid Solar Power System

Welcome to our comprehensive guide on how to size your off-grid solar power system. Whether you’re a seasoned enthusiast or just starting your solar journey, understanding how to properly size your system is crucial for optimal performance. In this guide, we will walk you through the step-by-step process of determining the number of solar panels, batteries, controllers, and inverters required for your specific needs. So let’s dive in and get started!

Step 1: Load Sizing

The first step in sizing your off-grid solar power system is to determine the load or devices you want to run. It’s essential to calculate the wattage of each item and the duration you plan to run them. Multiply the wattage by the hours to get the watt-hours. If you have multiple appliances, add their watt-hours together to obtain the total watt-hours.

For example, let’s consider three loads: a TV, a fridge, and a coffee maker. The TV consumes 125 watts and runs for 4 hours per day, resulting in 500 watt-hours. The fridge consumes 700 watts and runs for 8 hours per day, totaling 5600 watt-hours. Lastly, the coffee maker consumes 1500 watts and runs for 30 minutes a day, giving us 750 watt-hours. The total load consumption in this case is 6850 watt-hours.

Step 2: Solar Wattage Sizing

Next, you need to determine the wattage of the solar panels required to meet your load consumption. The peak solar hours vary depending on your location, so it’s important to find out the peak hours for your state. Divide the total load watt-hours by the peak hours to obtain the required wattage.

In our example, let’s assume we are located in Tennessee, which has an average of 4 peak hours. Dividing the total load of 6850 watt-hours by 4 peak hours gives us 1712.5 watts. However, it’s essential to consider efficiency losses. If you’re using a PWM controller with approximately 79% efficiency, divide the wattage by 0.8 to refine the wattage. For an MPPT controller with around 94% efficiency, divide the wattage by 0.94. If you plan to use an inverter, repeat the process by dividing the value by 0.9.

Considering an MPPT controller and an inverter, the refined wattage for powering your appliances is 2023.82 watts. Now that we know the required wattage, let’s move on to sizing the controller.

Step 3: Controller Sizing

To ensure your controller can handle the required wattage, refer to the controller specification sheet. It will indicate the wattage capacity of the controller. For instance, if you have a 30 Amp controller, it can handle up to 400 watts on a 12V system.

In our example, with a required wattage of 2023.82 watts, it may be challenging to find a controller that can handle such a high wattage. However, you can explore solar kits that offer higher wattage capabilities. Remember to consider the voltage of your system when selecting a controller.

Step 4: Battery Sizing

Now, let’s determine the size of the battery bank needed to store the energy generated by your solar panels. It’s crucial to ensure your battery bank has sufficient capacity to meet your energy requirements. To size your battery, double your initial watt-hour value to allow for a 50% discharge.

In our example, the total load consumption was 6850 watt-hours. Doubling this value gives us 13700 watt-hours. To find the amp-hours needed, divide the watt-hours by the voltage of your battery bank. If you’re using a 12V system, divide by 12V. If you’re using a 24V system, divide by 24V. If you’re using a 48V system, divide by 48V.

Assuming we are using a 24V system, the battery capacity required is (13700 watt-hours / 24 volts) * 2, which equals 570.83 amp-hours. This can be achieved by wiring six 200Ah batteries in series-parallel.

Step 5: Inverter Sizing

The final step is to size your inverter, which converts the DC power stored in the battery bank into AC power for your appliances. To determine the size of the inverter, add up the wattages of all the items you want to run simultaneously. It’s recommended to choose an inverter with a higher wattage capacity than the total load wattage. Additionally, ensure that the inverter matches the voltage of your battery bank.

In our example, the total load wattage is 700 watts (fridge) + 125 watts (TV) + 1500 watts (coffee maker) = 2325 watts. Therefore, a 2500 watt inverter or higher is required, considering a 24V system.

Congratulations! You now have a comprehensive understanding of how to size your off-grid solar power system. By following these steps, you can determine the number of solar panels, batteries, controllers, and inverters needed to meet your energy requirements. Remember to consider efficiency losses and select components that align with the voltage of your system.

If you want to dig deeper into solar power calculations or explore wiring lengths and gauge sizing, check out our recommended resources below. Happy solar sizing!

Note: For information specific to BONJOUR SOLAR solar panels and BONJOUR SOLAR batteries, please refer to the manufacturer’s documentation and specifications.