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Module 5: Sizing Solar Panels for Your Solar Power System

We’ve already covered calculating your power need and sizing your battery bank, so the next step is figuring out the type and number of solar panels you’ll need to keep those batteries charged. 

By the end of this module, you should understand the following:

• What peak sun hours are and why they matter
• How to calculate the total solar panel wattage you should aim for
• How to choose the correct number and size of solar panels for your solar power system

Let’s get started.

How to Size Solar Panels: Step-by-Step Process

The easiest way to size solar panels is by breaking it down into a simplified three step process:

1. Find your peak sun hours
2. Calculate how much solar wattage you need
3. Decide how many panels actually meets those requirements

Step 1: Understand Your Peak Sun Hours 

Before you just start adding solar panels to your online shopping cart, you need to determine the number of peak sun hours you have in your area.

Peak sun hours are the number of full-sun hours you get per day. This is also when solar panels operate at close to their maximum efficiency. Basically, it’s your midday sunlight, where the angle of the sun means the sunlight is its most direct and powerful.

Hours where the sun is low on the horizon during sunrise or sunset don't count as peak sun hours, as your solar panels won’t be able to generate the same amount of energy during them. Sure, they might be able to generate some solar power, but these hours shouldn’t factor into your calculations. 

Think of it like applying sunscreen in the middle of the day, rather than in the early morning or at sunset. The sun is still up, but you can physically feel it is less powerful outside of those peak hours.

On average: 

• Most locations get 3 to 5 peak sun hours per day
• The most sunny locations can get 6+ peak sun hours
• North regions can get between 2 and 4 peak sun hours

If you live somewhere like Arizona, your number of peak sun hours are going to be different from those of someone living in Minnesota.

Still, your exact number of peak sun hours will depend on your location, the season, and the climate where you live, so it’s looking up your local average before you size your system.

Jackery offers a pretty handy chart that makes it easy to find your peak sun hours by state or by ZIP Code. Look up your area and make a quick note of how many peak sun hours you can reasonably expect in a typical day. 

Step 2: Calculate How Much Solar Panel Wattage You Need 

Once you have a rough idea of how many peak sun hours you can expect in a typical day, it’s time to calculate how much solar power you need your panels to generate.

This calculation starts with your battery bank size, because the goal is almost always to fully charge your battery bank with a single day of sunlight.

Again, if you’re unsure how big your battery should be, or you’re not sure how to size a battery bank, just go back and watch our video: Sizing Battery Capacity for Your Solar Power System

Example Calculation:

Let’s say you have a 10,000Wh (10kWh) battery bank and you can expect an average of four peak sun hours per day where you live.

To find your required solar panel wattage, divide your battery capacity by your peak sun hours:

Battery Capacity ÷ Peak Sun Hours = Required Panel Wattage 

In this example, that would play out like:

10,000Wh ÷ 4 hours = 2,500W of Solar Panels

What this means is that you’d need 2,500 watts of total solar panel capacity to recharge your 10,000Wh battery bank in a single day with solar power. 

Remember, non-peak sunlight still generates power, but it’s significantly less than peak sunlight. 

This is why we always recommend ignoring these hours of solar production in order to reliably size your solar array. Instead, view the power generated during those hours as a bonus that can help compensate for cloudy and rainy days.

Step 3: Choose the Number and Size of Solar Panels

Now that you know how many watts of solar power your panels need to generate, you need to decide how you’re going to achieve that. 

Solar panels come in a variety of wattages, so you need to come up with a combination of panels that comes close to achieving your required panel wattage.

Using our 2,500W required solar panel wattage example from above, you could reach your needs with:

• Six 400W panels = 2,400W
• Twelve 200W panels = 2,400W

Both combinations of panels would be close, but slightly under your target. Sure, you could theoretically use a series of twenty five 100W panels, but it would be overly complicated, inefficient, and not even the most cost-effective strategy. More realistically, you’ll be looking at using 200W to 400W panels.

⚡Solar Lab Tip: Oversize Your Solar Panel Array

If your budget allows it, we always recommend having a bit more solar panel capacity to make sure you’re able to charge your batteries each day. 

There’s no harm in generating too much solar power, but you can run into issues if you don’t generate enough. If your desired total wattage is 2,500W, you could play it safe and build a 2,800W solar panel array. 

Power you generate beyond your maximum solar input won’t do any damage, it will just get wasted.

While you’ll want the total wattage to come close to adding up to your desired wattage amount (in this example 2,500W), the wattage of the individual panels will depend on your space and budget constraints. 

400+ watt solar panels are larger and tend to be more expensive, but you need fewer of them. On the other hand, 200W panels are smaller, but you’ll need twice as many, so they’ll probably end up taking up quite a bit more space on your property. 

⚡Solar Lab Tip: Don’t Stress About Solar Panel Branding

A lot of solar panels are overpriced, especially when they’re manufactured by power station brands. 

Instead of buying overpriced panels, we recommend retailers like Shop Solar and Signature Solar, as both carry a huge range of panels in various wattages. They also offer discounts for bulk orders. Remember, panels should be a lot cheaper than your batteries.

Other Key Factors to Consider

Sizing your solar panels isn’t just about the raw math and calculating wattage totals, real-world installation also matters.

Where and how you are going to install your solar panels is something you really need to consider. 

Solar Panel Mounting Location

Where will your solar panels go, and how much space do you have available in that location? Options include:

• Roof solar panel mounts and racks
• Ground mounts
• RV or van roof racks
• Portable setup of folding solar panels

Each option requires different hardware and installation methods. The decision will affect the number of panels you can physically install in a given location. 

Keep in mind that lower wattage panels are physically smaller, so it might be more practical to go with less efficient panels if you are tight on space. 

⚡Solar Lab Tip: Consider Obstacles and Future Expansion

Sun hours don’t matter if your panels are shaded. Prioritize unobstructed sunlight, especially during peak hours when choosing a location for your panels.

Also, don’t forget that solar power systems are designed to be modular, meaning you should be able to expand them in the future. You can start small today, then add more panels in the future. Just make sure your inverter and charge controller can handle your future aims.

Solar Panel Sizing Made Simple

Sizing solar panels doesn’t require engineering software or a professional installer. You just need three numbers:

• Your battery capacity
• Your peak sun hours
• Your desired recharge time

Once you have those, the math is straightforward, and the rest comes down to space and budget.

If you’re just buying solar panels for a power station, try to get your solar panel wattage as close to the power station’s maximum solar input as possible. This will allow you to charge your unit as quickly as possible, which can be really important during emergency situations.   

Up Next: Module 6 – Sizing Your Power Inverter

Sizing a solar panel array doesn't have to be some overly complicated process. By understanding your sun hours, calculating the required wattage, and considering your space and mounting options, you can build an efficient and effective solar panel array.

Don’t get discouraged if you can’t afford to build your ideal solar array right at the beginning. You can always start out small and add more solar panels in the future when your budget allows you to do so.

Remember to keep your solar panel wattage information handy for when you size your inverter in the next step.