Size Matters: Choosing Solar Panels to Keep Your RV’s Batteries Juiced

How to Size Solar Panels for Charging RV Batteries

Traveling full-time in an RV offers unparalleled freedom and adventure, but it also presents unique challenges, particularly when it comes to power management.

Boondocking, or camping without hookups, requires a reliable way to keep your batteries charged, and solar panels are an excellent solution. However, selecting the right size solar panel for your RV battery is crucial to ensure you have enough power for your daily needs.

Recommended article: This Solar Panel Is Easy To Setup And Works With RV Batteries

This guide will walk you through the process of determining the appropriate solar panel size, helping you enjoy your off-grid adventures without worrying about power shortages.

Understanding Your RV Battery Capacity

To properly size your solar panels, you first need to know your RV battery’s capacity measured in amp-hours (Ah). This tells you how much energy the battery can store. Don’t worry if you’re not familiar with battery specifications – here’s how to easily find the amp-hour rating:

1. Look at the Battery Label Most RV batteries will have the amp-hour (Ah) rating printed right on the label or casing. It may show a number like 100Ah for a typical 12V battery. If you see this Ah number, that’s all you need!
2. Use the Reserve Capacity (RC) Rating If there’s no amp-hour number, look for a “Reserve Capacity” or RC rating in minutes. This tells you how many minutes the battery can deliver a certain amount of power. To convert RC to amp-hours, simply multiply the RC number by 0.6. For example, if the RC is 100 minutes, the amp-hour capacity is approximately 100 x 0.6 = 60Ah.
3. Check for Amp and Hour Ratings
   Some batteries list two numbers – one for amps (A) and one for hours (h). To calculate amp-hours, just multiply these two numbers together. For instance, if it shows 5A and 20h, the amp-hour capacity is 5 x 20 = 100Ah.

Once you know the amp-hour rating, you have the key number for sizing your solar panel system. Most RVs come with 100Ah or smaller batteries from the factory.

For longer battery life and capacity, it’s recommended to upgrade to two larger 6V batteries and wire them in series.

Or use two 12V batteries wired in parallel, which adds up the amp-hour ratings. For example, two 100Ah batteries provide 200Ah total capacity. You can add a third or a fourth one as well, as long as the batteries and all of your wiring supports and can handle it.

No matter which method you use, write down the amp-hour number somewhere handy. This will let you properly match your solar panel’s size to your battery capacity in the next steps.

RV Batteries Setup Examples

These are the three most typical battery setups in RVs and campers (the battery capacity varies though).

Single Battery Setup:

Battery: One 12V 100Ah battery

Capacity: 100Ah

Dual Battery Setup (Parallel):

Batteries: Two 12V 100Ah batteries

Capacity: 200Ah (maintains 12V, doubles Ah).

Dual Battery Setup (Series):

Batteries: Two 235Ah 6V batteries

Capacity: 235Ah at 12V (doubles voltage, maintains Ah)

Lead-Acid Battery Depth of Discharge

For lead-acid batteries like those commonly used in RVs, it’s important not to discharge them below 50% state of charge on a regular basis. Deeper discharges significantly reduce the battery’s lifespan and capacity over time.

So when sizing your solar panel system, calculate the battery capacity you’ll actually use by taking 50% of the total amp-hour rating. A good goal is to be able to reliably recharge that usable capacity from 50% to 100% each day.

Lithium Battery Advantages

An increasingly popular upgrade for RVs are lithium-ion batteries like lithium iron phosphate (LiFePO4). While more expensive upfront, lithium batteries provide several advantages over lead-acid:

1. Deeper Depth of Discharge: Lithium batteries can be safely discharged down to 20% remaining capacity without degradation, unlike the 50% limit for lead-acid.
2. Lighter Weight: Lithium batteries weigh significantly less per amp-hour than lead-acid, reducing weight.
3. Longer Lifespan: With proper care, lithium batteries can last 5-10 years versus 2-5 years for lead-acid batteries.
4. Faster Charging: Lithium batteries can be recharged much faster, up to their full capacity.

If upgrading to lithium batteries like the Battle Born line (click to view their 100Ah battery on Amazon.com), size your solar panel system to recharge from 20% to 100% state of charge daily. This unlocks their full capacity potential.

However, lithium RV batteries also require specific lithium-ready chargers and battery monitoring systems. Consult professional installation guidance when upgrading.

Sizing Your Solar Panel

A rule of thumb is to get enough solar panel wattage to fully recharge your batteries’ usable capacity in one sunny day. Here are some example sizing calculations:

Lead-Acid Batteries

*Assumes 6 peak sun hours per day with the panel angled towards the sun

Lithium Batteries

For lithium iron phosphate (LiFePO4) batteries, you can size your solar panel for recharging from 20% to 100% state of charge each day:

*Assumes 6 peak sun hours per day with the panel angled towards the sun

So if you have 200Ah battery capacity, the usable 100Ah capacity at 50% discharge can be recharged by a typical 200W solar panel in about 8 hours of peak sun exposure. A larger 300W panel would do it faster.

The key factor is the panel’s wattage rating, not physical size. Higher wattages from more efficient monocrystalline panels require less space.

Calculating Your Power Usage

Next, estimate your daily power consumption. List all the devices you use, including lights, fridge, fans, and electronics, and note their power ratings (in watts) and usage hours. Sum up the watt-hours (Wh) for all devices to get your total daily power consumption.

Example

To validate if a 100W or 200W solar kit is sufficient, estimate your daily 12V load by adding up battery draw from devices like:

• LED lights: 0.3A per light x hours used
• Water pump: 4A x hours used
• DC fan: 4A x hours used
• 12V TV: 3A x hours used
• Furnace fan: 8A x hours used

As an example, if you use 12 LED lights for 2 hours, the water pump 0.5 hours, a fan for 1 hour, and the furnace fan 0.5 hours daily, your total draw is:

(0.3A x 12 lights x 2 hours) + (4A x 0.5 hours) + (4A x 1 hour) + (8A x 0.5 hours) = 28Ah per day

A 100W solar panel producing 6A could recharge a 28Ah draw in under 5 hours of peak sun. This matches the general guidance that a 100W panel works for smaller RV battery banks.

If you know how many watt-hours you use daily, convert your daily power consumption to amp-hours (Ah) by dividing the total watt-hours by your battery voltage (usually 12V). For instance, if your daily power usage is 1200Wh, your daily amp-hour requirement is 100Ah (1200Wh / 12V).

To ensure you can recharge your batteries fully each day, you need enough solar panel capacity to produce the required amp-hours. Consider factors like sunlight hours and panel efficiency.

On average, a 100W solar panel produces around 30Ah per day. Thus, to generate 100Ah daily, you would need approximately 300W of solar panels (100Ah / 30Ah per 100W panel).

Factors to Consider

• Sunlight Hours: Your location and the time of year affect how much sunlight your panels receive.
• Panel Efficiency: Higher efficiency panels generate more power per square foot.
• Battery Type: Different batteries (lead-acid vs. lithium) have varying charging efficiencies.

Easy Solar Setup for RVs

The easiest way to get started is a plug-and-play solar suitcase with a charge controller attached like:

Renogy 100 Watt 12 Volt Portable Solar Panel with Waterproof 20A Charger

Check Price at Amazon

These portable kits connect directly to your RV batteries using alligator clips or ring terminals. The charge controller prevents overcharging.

Just set up the panels in the sun pointing south and connect them to your batteries’ positive and negative terminals. It’s a simple solution to keep batteries topped up while camping.

If you would rather install a solar panel on the roof of your camper, consider buying a solar kit that includes everything you need. Like this kit by a company called Topsolar:

Topsolar Solar Panel Kit 100 Watt 12 Volt Monocrystalline

Check Price at Amazon

It can seem like a daunting task at first, but it’s relatively easy to set up a more permanent panel with a kit like this. Here is a quick guide:

1. Mount the Solar Panel:
   • Select an optimal location on your RV roof that receives maximum sunlight.
   • Secure the solar panel to the roof using screws or adhesive, following the solar kit manufacturer’s instructions.
   • Attach the solar panel to the mount, ensuring it’s stable and secure.
2. Connect the Solar Panel to the Charge Controller:
   • Locate the positive and negative output terminals on the solar panel.
   • Use the provided wiring to connect these terminals to the corresponding input terminals on the solar charge controller. Red is positive, black is negative.
   • Ensure all connections are tight and secure to prevent any power loss.
3. Connect the Charge Controller to the RV Battery:
   • Identify the battery terminals on the charge controller.
   • Use the provided wiring to connect the positive terminal on the charge controller to the positive terminal on the RV battery.
   • Similarly, connect the negative terminal on the charge controller to the negative terminal on the RV battery.
   • Double-check all connections to ensure there are no loose wires.
4. Verify Connections and Power On:
   • Ensure all connections are correct and secure.
   • Turn on the solar charge controller. It should display the charging status. Most turn on automatically when a solar panel or battery is connected.
   • Monitor the controller to ensure it is correctly charging the RV battery.

Tips:

• Safety First: Always work with the RV battery disconnected initially to avoid any accidental shorts or sparks. It’s also a good idea to cover the panel during the installation if done outside during the day.
• Cable Management: Use cable ties or clips to keep wiring neat and secure.
• Controller Settings: Adjust the charge controller settings according to your battery type (e.g., lead-acid, AGM, or lithium) for optimal charging performance. The manual included with the kit/charge controller will guide you through this.

These are two ways to get started. If you want larger setups, consider leaving a comment and I can help you further.

How Much Electricity Will A 100W Panel Generate?

To give you an idea of how much power a 100W solar panel can generate under different conditions, here are some rough estimates:

• Sunny summer day: A 100W panel can generate around 30-40Ah per day, assuming 6-8 hours of direct sunlight.
• Cloudy summer day: On a cloudy day, expect around 10-20Ah per day, as the panel will only receive diffused light.
• Sunny winter day: In winter, the sun is lower in the sky and days are shorter, so a 100W panel might generate 20-30Ah per day with 4-6 hours of direct sunlight.
• Cloudy winter day: On a cloudy winter day, you may only get 5-10Ah per day due to the limited sunlight and cloud cover.

Keep in mind that these are rough estimates, and actual output will vary based on your location, weather patterns, and panel orientation. To maximize solar charging, adjust your panels to face the sun directly and park in open areas without shade.

If you find that a single 100W panel isn’t sufficient for your needs, consider adding additional panels or upgrading to a larger wattage panel to increase your daily power generation.

You can also combine solar charging with other methods, like running a generator or plugging into shore power when available, to keep your batteries topped up in all conditions.

Dealing With Cloudy Days

When sizing your solar panel system, it’s also wise to add a buffer for cloudy or overcast days that provide less peak sunlight.

While the calculations aim to fully recharge batteries in one sunny day, on cloudy days you may only get 30-50% of that production. Plan for a few extra solar panels than the minimum size, or incorporate alternate charging like a portable generator, to cover periods of low sunlight.

Another strategy for cloudy days is to oversize your battery bank beyond your anticipated daily usage. With a larger amp-hour capacity, your batteries can better ride out those low solar charging days without dipping dangerously low on state of charge. This provides more flexibility in your solar system sizing.

Extending Battery Life

In addition to solar charging, you can reduce battery draw with efficiency steps:

• Upgrade to LED lights: Longer lasting and up to 90% more efficient
• Upgrade to lithium batteries: Higher charging efficiency than lead-acid
• Add a generator or inverter: For periodically charging batteries from shorepower

Using Your RV’s AC Outlets

The solar setup mentioned charges your RV’s 12V DC battery system, not the 120V AC outlets. To run AC outlets and appliances, you need:

1. Inverter: Converts 12V DC battery power to 120V AC. A 1000W-2000W pure sine wave inverter like this one by Renogy (click to view on Amazon) can run most outlets except large AC units.
2. Charge Controller Bypass: An inline switch to disconnect from the converter when plugging into inverter power.

For seamless AC power access, consider a solar generator which integrates an inverter, lithium battery, and solar charge controller in one unit. Top models include:

• Bluetti EB3A (268Wh, 600W inverter)
• EcoFlow Delta 2 Solar Generator (1024Wh, 1800W inverter)
• Jackery Explorer 2000 Solar Generator (2160Wh, 2200W inverter)

These rechargeable from solar allow you to run AC appliances and electronics by plugging directly into your RV’s AC outlets using adapters. It’s an all-in-one power system for off-grid camping.

With the right solar charging setup tailored to your RV’s battery bank and power needs, you can go boondocking for weeks without depleting your batteries. Start small with a portable 100W solar kit and upgrade as needed.

Conclusion

In conclusion, properly sizing your RV’s solar panel setup is crucial for maintaining battery charge while boondocking and dry camping.

By understanding your battery capacity, calculating your daily power usage, and choosing a solar panel wattage that can replenish that usage in a day of sun, you can create a reliable off-grid power system.

Remember to account for the differences between lead-acid and lithium batteries, and consider oversizing your solar array or battery bank to handle cloudy days. Portable solar kits offer an easy entry point, while solar generators provide a simple all-in-one solution for powering AC appliances.

With the right solar setup, you can enjoy the freedom of RV camping without worrying about dead batteries. Assess your power needs, start small, and upgrade as you gain experience. Happy boondocking!

Related Articles for Further Reading

• Renogy Lithium Vs Battle Born Batteries, Review & Comparison: A detailed comparison of two popular RV battery options. This can help you understand which battery might work best for your needs.
• Best 10W Solar Panels For Charging 12V Batteries 2024: A guide on small solar panels that are perfect for topping up smaller batteries or supplementing larger setups.
• How To Use Solar Panels With A Prewired Furrion Solar Port: Instructions for integrating solar panels with RVs prewired for solar, useful for many modern RVs.
• How To Connect A Zamp/SAE Solar Panel To A Goal Zero Yeti: A detailed guide on connecting specific solar panels to popular portable power stations, which can be part of your solar setup.
• How To Connect Two Renogy Solar Panels Together: Learn how to properly connect multiple solar panels to increase your system’s capacity.