Sizing Your First Portable Solar System: A No-Nonsense Guide for Beginners

If you’re new to the world of solar power, the first thing you probably did was start browsing 100-watt, 200-watt, and 400-watt solar panels, trying to guess which one is right for you.

Let’s stop right there. That’s like walking into a grocery store and buying a random amount of food without knowing what meal you’re cooking or how many people you’re feeding.

The secret to choosing the right solar setup is to start with your needs, not with the hardware. Before you look at another solar panel, we’re going to look inside your backpack, your camper, and your tent. In the next 15 minutes, using just a pen and paper, you’re going to figure out exactly what you need. Let’s begin.

Step 1: Write Your “Energy Menu” - What Are You Powering?

Just like writing a grocery list, the first step is to list every single electronic device you plan to use or charge during a typical day off-grid. Be honest and thorough.

Your list might look something like this: * Smartphone * Laptop * Drone batteries * LED camp lights * A 12V portable fridge/cooler * Camera batteries

This is your “energy menu.” It’s the list of things that will be “eating” the power you generate.

Step 2: The Only Math You Need - Calculating Your Daily Watt-Hours

Now, we need to figure out how “hungry” each device on your menu is. We’ll measure this in a unit called Watt-hours (Wh). It’s the most important unit in solar planning. Don’t worry, it’s incredibly simple to calculate.

The Simple Formula: Watts (W) x Hours (h) = Watt-hours (Wh)

For each item on your list, you need to find its power consumption in Watts and estimate how many hours you’ll use it per day.

• For charging things (phone, laptop): Look at the device’s battery capacity, which is often already in Wh. If not, you can usually find it online.
  • Example: An iPhone 15 battery is about 13 Wh. If you charge it once from empty to full, that’s 13 Wh. A MacBook Air battery is about 53 Wh. A full charge is 53 Wh.
• For running things (lights, fridge): Look for a label on the device or its power adapter that shows its consumption in Watts (W).
  • Example: Your LED lights use 5 Watts. You run them for 4 hours each evening. That’s 5 W x 4 h = 20 Wh.
  • Pro Tip for Fridges: A 12V fridge is a big one. It might say “60W,” but it cycles on and off. A good real-world estimate is that it will run for about one-third of the day (8 hours). So, 60 W x 8 h = 480 Wh. This is often the largest item on anyone’s menu.

Let’s total up our example menu: * Smartphone (2 full charges): 13 Wh x 2 = 26 Wh * Laptop (1 full charge): 53 Wh x 1 = 53 Wh * LED Lights: 5 W x 4 h = 20 Wh * Total Daily Need: 99 Wh (We’ll leave the fridge out for this simple example for now).

The Critical “25% Safety Buffer”
The real world is messy. It might be cloudier than you expected, or you might use your laptop more. To avoid running out of power, always add a safety buffer. Multiply your total by 1.25.

• Our example: 99 Wh x 1.25 = 124 Wh. This is your real, safety-adjusted daily energy goal.

The X-Factor: Where You Live Matters (A Simple Guide to Sun Hours)

You have your target: 124 Wh per day. Now we need to figure out how big our solar panel “engine” needs to be to produce that much power. The key variable is Peak Sun Hours.

This doesn’t mean the number of daylight hours. It’s the average number of hours per day when the sun is strong enough to produce a panel’s rated power. Think of it as the number of hours your panel is “working at full strength.”

• Sunny Southwest (AZ, CA, NM): You can expect 5-6 peak sun hours.
• Most of the USA: A good average is 4-5 peak sun hours.
• Pacific Northwest & Northeast (WA, VT): You might only get 3-4 peak sun hours, especially outside of summer.

A 100W solar panel in Arizona (5.5 hours) can generate: 100 W x 5.5 h = 550 Wh per day.
That same 100W panel in Seattle (3.5 hours) might only generate: 100 W x 3.5 h = 350 Wh per day.
Your location makes a huge difference!

Step 3: Match Your Gear - Picking Your “Engine” and “Gas Tank”

Armed with your daily energy need (including the buffer) and your local sun hours, you are finally ready to choose your hardware.

Sizing Your Solar Panel (The Engine)

Your solar panel needs to generate more power each day than your daily need.

Panel Output = Panel Watts x Sun Hours

Let’s say you live in a place with an average of 4 sun hours. * A 100W panel will generate: 100 W x 4 h = 400 Wh per day. * A 200W panel will generate: 200 W x 4 h = 800 Wh per day.

Sizing Your Battery / Power Station (The Gas Tank)

Your battery is your energy storage. Its capacity should be at least your daily energy need, but ideally 1.5x to 2x larger. This gives you enough power to get through a cloudy day or use your devices at night.

Battery Capacity is measured in Watt-hours (Wh). A “500Wh” power station can store 500Wh of energy.

Putting It All Together: A Weekend Camper’s Real-World Example

Let’s go back to our camper. Their daily need was 124 Wh. They live in Colorado, averaging 4.5 sun hours.

1. Panel Choice: Their goal is 124 Wh. A 100W panel in their area generates about 450 Wh (100W x 4.5h). This is more than enough to cover their needs. The 100W panel is a perfect fit. There’s no need to spend more on the 200W panel.
2. Battery Choice: Their daily need is 124 Wh. A power station with a capacity of around 250 Wh would be ideal (124 Wh x 2). This gives them a full day of backup power.

Now, what if they added that 12V fridge? * New Daily Need: 99 Wh + 480 Wh = 579 Wh * With Safety Buffer: 579 Wh x 1.25 = 724 Wh * Panel Choice: A 100W panel (generating 450 Wh) is no longer enough. They need to step up. A 200W panel in their area generates 900 Wh (200W x 4.5h). This comfortably covers their 724 Wh need. The 200W panel is the right choice. * Battery Choice: Their daily need is 724 Wh. They should look for a power station with at least 750 Wh of capacity, and ideally 1000 Wh or more.

Conclusion: From “I Guess” to “I Know”

And that’s it. You’ve done it. You’ve replaced guesswork with certainty.

Sizing a portable solar system isn’t about complex engineering; it’s about understanding your own habits. By taking a few minutes to list what you’ll use and do some simple multiplication, you’ve transformed a confusing purchase into an informed decision. You no longer have to ask, “What size panel should I get?” You can now confidently say, “Based on my needs, this is the size I know will work.”