Your Off-Grid Power Budget: A Step-by-Step Guide to Sizing an RV Solar System

One of the most common questions newcomers to the solar world ask is, “How many solar panels do I need for my RV?” The honest answer is: it depends. It’s like asking, “How much food do I need for a trip?” The answer depends entirely on how many people you’re feeding and what kind of meals you’re planning.

Instead of guessing, the professional way to approach this is to create a power budget, also known as an energy audit. It’s a simple process of figuring out exactly how much electricity you use in a typical day. Once you know your “appetite,” sizing your “pantry” (your solar panels and batteries) becomes a straightforward math problem.

Let’s walk through the three simple steps to create your own off-grid power budget.

Step 1: Audit Your Appliances - What Are You “Eating”?

The first step is to make a list of every single electrical device you plan to use in your RV or on your boat. Be thorough! Don’t forget the small things like phone chargers and the “phantom loads” from devices on standby.

For each device, you need to find two pieces of information:
1. Its Power Draw (in Watts): This is usually found on a sticker on the device or its power brick.
2. Your Estimated Daily Use (in Hours): Be realistic. How long do you actually run that water pump or watch TV each day?

Let’s create a sample audit worksheet. You can draw this out on a piece of paper or create a simple spreadsheet.

My Daily Energy Audit Worksheet

In this example, our total daily “appetite” for energy is 755 Watt-hours (Wh). This is the single most important number you need.

Step 2: Convert to Battery Language - Sizing Your “Pantry”

Solar panels don’t directly power your devices; they charge your batteries. Therefore, we need to translate our Watt-hour budget into a language batteries understand: Amp-hours (Ah).

The formula is easy: Amp-hours = Watt-hours / Voltage.
For most RV and boat battery systems, the voltage is 12V.

• Our Example: 755 Wh / 12V = 62.9 Ah

So, on a typical day, this user will draw about 63 Amp-hours from their battery bank.

Now you can size your battery bank. A crucial rule for battery health (especially for lead-acid types) is to never discharge them below 50%. This means you need a battery bank at least twice the size of your daily usage.

• Minimum Battery Size: 63 Ah x 2 = 126 Ah

For a comfortable buffer and to account for cloudy days, a good rule of thumb is to multiply your daily usage by 3 or 4. * Recommended Battery Size: 63 Ah x 3 = ~190 Ah

So, a 200Ah lithium or AGM battery bank would be a great fit for this user.

Step 3: Size Your “Harvest” - How Many Panels?

Now we know we need to replenish 63 Ah back into our batteries every day. This is where the solar panels come in. But a 200W panel doesn’t produce 200 watts all day long. The sun moves, and clouds happen.

To account for this, we use a concept called “Peak Sun Hours.” This is a simplified metric that represents how many hours of “peak,” or ideal, sunshine a specific location gets per day, on average.

Simplified Peak Sun Hours Map (USA Average) * Southwest (AZ, NM): 5-7 Hours * Southeast (FL, GA): 4-5 Hours * Midwest (OH, IL): 3.5-4.5 Hours * Northeast & Northwest (NY, WA): 3-4 Hours

Now, let’s calculate the daily yield of a single 200W panel, like the BougeRV Yuma 200W. We need its Maximum Power Current (Imp), which is about 8.5A.

Daily Amp-hour Harvest = Panel Imp x Peak Sun Hours

Let’s see how our 200W panel performs for a user who travels across the country: * In Arizona (6 Peak Sun Hours): 8.5A x 6 hrs = 51 Ah/day * In Ohio (4 Peak Sun Hours): 8.5A x 4 hrs = 34 Ah/day * In Washington (3 Peak Sun Hours): 8.5A x 3 hrs = 25.5 Ah/day

Now, we can finally answer the question, “How many panels do I need?” Our user needs to replenish 63 Ah per day.

• In Arizona: They need 63 / 51 = 1.2 panels. So, two 200W panels (400W total) would be more than enough.
• In Washington: They need 63 / 25.5 = 2.4 panels. Here, three 200W panels (600W total) would be a much safer bet to ensure their needs are met, even in less sunny conditions.

By following these three steps—Audit, Size the Battery, and Size the Panels—you have created a robust power budget. You are no longer guessing. You are making an informed decision based on your unique lifestyle and travel plans, ensuring your off-grid power system is a source of freedom, not frustration.