How to Size a Solar Panel Array For A Solar Power System

Sizing your solar panel array is one of the most important steps in designing a reliable and efficient off-grid solar power system. Whether you’re powering a home, cabin, RV, or mobile business, the right solar array ensures you produce enough energy to meet your needs—without overspending on equipment you don’t need.

In our previous article, we covered how to size a battery bank. Now, we’ll focus on the production side of the equation: how many solar panels you need, how much power they should produce, and how to make the most of your available space.

This solar panel array sizing guide includes:

• A simple five-step sizing process
• A downloadable worksheet and calculator
• A detailed solar panel size chart
• Real-world examples and pro tips

Why Proper Solar Panel Sizing Matters

An undersized solar array can leave you short on power when you need it most. An oversized system may waste your budget or exceed your charge controller’s capacity. The goal is to design a balanced system—one that generates enough daily watt-hours (Wh) to meet your consumption, considering your environment and use case.

Whether you're running a couple of lights and a fridge in your camper, or you're backing up your home during grid outages, the right solar array size is the foundation.

Step 1: Estimate Your Daily Energy Usage

The first step in sizing your solar array is understanding how much energy you use on a typical day. This is measured in watt-hours (Wh) or kilowatt-hours (kWh).

You can calculate this in two ways:

1. Review Your Utility Bill: If you’re on-grid, check your last power bill. Divide your total monthly usage (in kWh) by 30 to get your daily average.
2. Itemize Your Loads: For off-grid systems, make a list of every appliance or device you'll be powering. Include the wattage, how many hours per day you use it, and multiply.

Example:

Laptop: 60W × 5 hours = 300Wh
Fridge: 100W × 10 hours = 1,000Wh
Lights: 40W × 4 hours = 160Wh

Total: 1,460Wh or 1.46kWh per day

Use our Solar Array Sizing Downloadable Worksheet to log your devices and automatically calculate totals.

Step 2: Find Your Average Sun Hours

Your location’s solar potential—measured in average sun hours per day—determines how much usable power your panels will produce. A “sun hour” is one hour of full, direct sunlight that produces 1,000W per square meter.

Average sun hours can vary dramatically depending on your location. For example, look at the differences across these states:

• Arizona: ~6.0 sun hours/day
• Colorado: ~5.5 sun hours/day
• Michigan: ~4.0 sun hours/day
• Seattle: ~3.5 sun hours/day

Use tools like PVWatts Calculator or Global Solar Atlas to find your local average.

Step 3: Calculate the Required Solar Array Size

Now that you know your daily energy use and sun hours, it’s time to calculate how large your solar array needs to be.

Formula: Total Daily Use (Wh) ÷ Sun Hours × 1.25 = Solar Array Size (W)

The “× 1.25” accounts for system inefficiencies (inverter losses, shading, panel age, etc.)

Example: 1,460 ÷ 5 × 1.25 = 365W

That means you need a solar array rated at around 365 watts to meet your needs reliably.

Step 4: Choose Your Solar Panels

Next, choose your panel type. Panels come in various sizes and wattages. Here are the most common options:

Step 5: Calculate the Number of Panels Needed

Once you’ve selected a panel size, divide your required array size by the panel wattage to find the quantity.

Example: You need 750W of solar. You’re using 250W panels: 750 ÷ 250 = 3 panels

Pro tip: It’s usually more efficient to use larger, fewer panels if space allows. You’ll have fewer connections to manage and less wiring loss.

Real-World Examples

Off-Grid RV System

Daily Use: 1,200Wh
Location: Arizona (6 sun hours)
Array Size: 1,200 ÷ 6 × 1.25 = 250W

Use 1 × 250W panel or 2 × 100W panels for redundancy

Remote Cabin

Daily Use: 4,000Wh
Location: Colorado (5.5 sun hours)
Array Size: 4,000 ÷ 5.5 × 1.25 = ~910W

Use 3 × 300W panels or 2 × 400W + 1 × 100W panel

Home Backup System

Daily Use: 10,000Wh
Location: Texas (5.5 sun hours)
Array Size: 10,000 ÷ 5.5 × 1.25 = ~2,273W

Use 6 × 400W panels

Final Thoughts

Sizing your solar panel array doesn’t have to be complicated. With a few key data points, and the right tools, you can confidently build a system that meets your needs—day after day, season after season.

Still Need Help Selecting a Solar Array Size?

Reach out to our friendly portable power experts and we'll be happy to help!

Toll-free & text: 888-976-5443
Email: support@outboundpower.com