One Array, All Seasons
Creating a Solar Array Built for Winter’s Worst
- Introduction
- Choosing the Right Solar Panel Size
- Choosing Lithium Iron Phosphate
- Calculating the Solar Array Size
- Why Overbuild for Winter?
- Conclusion
Introduction
Our goal is to help you understand how to calculate the right solar panel capacity for your system, from meeting your load list to ensuring winter battery charging. If you haven’t yet read our articles on Load List and Battery Capacity, these are foundational steps leading to this discussion, so check those out first to build a complete picture.
We want you to be able to visualize and design your setup confidently, making informed choices as you select products for your solar system. Education is the foundation of this process, and we’re here to guide you every step of the way.
Don’t hesitate to reach out, your renewable energy journey begins here, and we’re excited to support it!
Choosing the Right Solar Panel Size
Modern solar panels often exceed 600 watts, and in our off-grid installations, we currently use panels of 400 watts or larger, while grid-tied systems typically use 500-watt or higher panels, these are all 24 volt panels. As manufacturers continue to produce higher-wattage panels, choosing the right size also depends on roof space if panels are mounted on a roof.
Different roof shapes and orientations affect placement to ensure maximum sunlight exposure. For ground or pole mounts, however, the panel size depends primarily on energy needs and project costs, offering more flexibility in design.
Choosing Lithium Iron Phosphate
Since our customer has chosen a Lithium Iron Phosphate (LiFePO4) battery, we’re targeting a capacity of 2,622 Wh to achieve three days of autonomy.
If you were using lead-acid batteries instead, you would follow the same steps but adjust for their different charging and discharge characteristics. For a similar three-day autonomy, you’d need approximately 4,720 Wh of capacity, as lead-acid batteries require a larger capacity to account for their lower usable energy range.
In the last article, we rounded these values up to 300Ah for the lithium battery and 500Ah for the lead-acid battery. This rounding ensures a practical margin of extra capacity and simplifies battery selection in terms of amp hours. We’ll use these values in our calculations moving forward.
Calculating the Solar Array Size
- Battery capacity: 300 Ah × 12V = 3,600 Wh
- Winter peak sun hours: 1.5 hours
- Required array output: 3,600 Wh ÷ 1.5 hours = 2,400W
Panel Selection and Configuration
Using 400W, 24V panels:
- Required panels: 2,400W ÷ 400W = 6 panels
So, 6 panels are required to meet winter charging demands.
Alternate Panel Example
If using 200W panels instead:
- Required panels: 2,400W ÷ 200W = 12 panels
For a lithium battery bank with 300Ah capacity:
- Using 400W panels: 6 panels are required.
- Using 200W panels: 12 panels are required.
This setup ensures sufficient power generation during the shorter winter days.
This means we’re designing for enough stored energy to handle cloudy days. This capacity was calculated in our previous article on determining the battery bank size, and it serves as the foundation for building the solar array.
To properly charge this battery in winter, we’ll need to consider a lower peak sun hour value. While summer peak sun hours might be around 3 hours, winter’s sunlight is often closer to 1.5 hours. This conservative approach ensures that our system is reliable year-round, even when sunlight is limited.
Why Overbuild for Winter?
Designing for winter’s minimal sunlight allows:
- Year-Round Reliability: Sufficient charging power across all seasons without needing additional panels.
- Less Generator Use: Reduced generator reliance, even in cloudy conditions.
- Battery Health: Steady charging power reduces deep discharges, which helps maintain battery health.
Conclusion
We’ve focused on determining the right number of solar panels needed to reliably charge our battery bank.
Using six 400W, 24V panels will indeed supply enough power to recharge our 300Ah battery, even with limited winter sunlight of around 1.5 peak sun hours daily.
However, remember that while our calculations aim to cover essential usage, real-world factors like extended lighting needs or especially dark, cloudy days can still strain the system. To handle these scenarios, it’s wise to keep a backup generator on hand to ensure continuous power availability. This setup adds resilience and reliability to the overall system.
But selecting the correct panel quantity is just the beginning. To effectively connect and control these panels, we’ll need to choose an appropriate solar controller. We’ll dive into this choice in an upcoming section to ensure optimal charging and battery health. For now, our focus is simply on ensuring the array has enough capacity to meet winter demands.
IOTG Solar…
Keeping you powered through education.