Thinking about adding solar power to your RV? That’s a fantastic step towards energy independence and unlocking the freedom of boondocking!
One of the first and most crucial steps in going solar is figuring out how much solar power you actually need – this is often called “sizing your system.” It can seem a bit technical, but with a clear approach, you can get a very good estimate.
As someone who has embraced solar on my RV, I can tell you that understanding your daily power consumption is the most critical step in sizing an RV solar system. You need to calculate your daily amp-hour (Ah) usage to determine the solar panel wattage and battery bank capacity required. This is spot on – it all starts with knowing what you use.
If you undersize your solar system (not enough panel wattage or battery capacity), you’ll find yourself running out of power, especially on cloudy days or if your consumption is higher than expected. This leads to frustration and often means relying on your generator more than you’d like.
If you oversize your system significantly, you’ll spend more money than necessary on panels and batteries, and you might be carrying extra weight you don’t need.
The goal is to find that sweet spot: a system that reliably meets your typical daily energy needs with a reasonable buffer for less-than-ideal conditions, without breaking the bank or overloading your RV.
This is the cornerstone of sizing your solar system. You need to figure out how much 12-volt DC power all your appliances and devices consume in a typical 24-hour period.
1. List All 12V DC Devices: Go through your RV and list everything that runs on 12V DC power.
This includes:
2. Determine Amperage Draw: For each device, find out how many amps it draws when it’s running. This is often on a label on the device itself, in its manual, or can be found online. If you have a battery monitor with a shunt (like a Victron BMV or SmartShunt), it can show you the real-time amperage draw of your system.
3. Estimate Daily Hours of Use: For each device, estimate how many hours it will run in a typical 24-hour period. This will vary greatly based on your habits.
4. Calculate Daily Amp-Hours (Ah) per Device: Multiply the Amps by the Hours of Use for each device. (Amps x Hours = Amp-hours).
5. Sum Total Daily Amp-Hours: Add up the daily Amp-hours for all your 12V DC devices. This is your total daily DC load.
If you plan to use an inverter to run 120V AC appliances (coffee maker, microwave, TV, laptop charger, etc.) off your batteries, you need to account for their power consumption too.
Real-World Tip: If you're planning to go fully off-grid without relying on a generator, one of the most accurate ways to estimate your energy needs is to track your actual power usage over a few days of dry camping. Use a battery monitor to measure your total amp-hours used each day, then take the average across 2–3 days. This gives you a realistic picture of your daily consumption. Once you have this figure, consider sizing your solar panel array at least 20% larger than your calculated needs. This extra capacity provides a buffer for cloudy days, seasonal changes, and future upgrades.
Once you know your total daily Amp-hour usage, you can size your battery bank.
1. Days of Autonomy: Decide how many days you want to be able to go without significant solar input (e.g., very cloudy days). One day is a minimum, two to three days provide a good buffer.
2. Depth of Discharge (DoD):
3. Calculation (Lead-Acid Example):
4. Calculation (Lithium Example):
Now, determine how much solar panel wattage you need to replenish your daily Amp-hour usage.
1. Peak Sun Hours: This is a critical factor. It’s not the total hours of daylight, but the average number of hours per day when the sun’s intensity is sufficient for your panels to produce near their rated wattage. This varies significantly by location and time of year. You can find peak sun hour maps online (e.g., from NREL). A conservative average for many parts of the US might be 4-5 hours, but it can be less in winter or northern latitudes, and more in summer or the southwest.
2. System Losses: Solar systems have losses (wiring, controller inefficiency, panel temperature, etc.). A common estimate is around 15-25% loss.
3. Calculation:
Product Example (Solar Panel): Zamp Solar KIT1021 Legacy Black 95 Watt Solar Panel Deluxe Kit
The charge controller regulates the power from your solar panels to safely charge your batteries. There are two main types:
Product Example: Zamp Solar ZS-10AW 5 Stage Solar Charge Controller
Controllers are rated by Amperage (e.g., 30A) and sometimes Voltage (e.g., 100V max panel input). Ensure the controller can handle the total amperage from your solar array (Panel Watts / Battery Voltage) and that the panel array’s open-circuit voltage (Voc) doesn’t exceed the controller’s max input voltage.
Sizing an RV solar system involves a bit of homework, but getting it right is key to a successful and satisfying off-grid experience. The most important part is accurately assessing your daily power consumption. From there, you can determine the battery bank and solar panel array needed to keep you powered up.
Don’t be afraid to slightly overestimate your needs if your budget and RV space allow – it’s better to have a little extra capacity than not enough. And remember, you can often start with a smaller system and expand it later if needed.
Happy boondocking!
I’m Bill Rowell, the founder of RVupgrades.com. In 2002, I launched the business to help fellow RV enthusiasts find unique and hard-to-find products. Over the years, it’s grown to offer more than 15,000 items, with a warehouse in Eastlake, Ohio. Having owned and repaired nearly every type of RV, I bring over two decades of hands-on experience to the table. For me, this isn’t just a business – it’s a passion and a way of life that I love sharing with the RV community.
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