Your dream is to run on solar energy, but where do you start?  Do you cram as many solar panels as will fit on top of the rig, or set up a portable solar panel to plug into a port on the side?  Sizing a system that is appropriate for your rig is as individual as choosing the color of your custom countertops.  There is no one-size-fits-all; it’s a ”just right” fit for you, your lifestyle, and when and where you plan to travel.

You’ve spent months, maybe even years, poring over every last detail of the structure, layout, woodwork, flooring, paint, and decorative touches that’ll make your new RV conversion truly feel like a one-of-a-kind build just for you! 

You want to take your rig off-grid, but the idea of listening to a gas-powered generator chug along while stargazing from your rooftop deck certainly doesn't sound appealing. Not to mention hauling around gallons of gasoline to run it, and what your neighbors will think as your exhaust drifts over to their campsite.  And, you certainly didn’t spend all of this time and money on your new baby to cram it in cheek-to-jowl in an RV park! 

Perhaps you prefer to spend your winters in the desert and your summers by the ocean.  Or maybe hitting the slopes in the winter is your thing.  Wherever that happy place is for you, it’s likely far away from power lines. 

We’ve been living, traveling, and working from the road with solar power for over 13 years now…and teaching thousands of others how to do it for themselves.  We’ve been all over North America during that time, but just happened to be pulling into our former “home town” in the Blue Ridge Mountains of North Carolina for a couple of weeks when our friend Jacob reached out with some solar questions. “I just converted a bus for my parents so that they can retire and travel to music festivals. Now, I am ready to add solar and have some questions.”

His parents wanted a system large enough to meet their energy needs, with some extra cushion in the “solar budget” in case they ended up using more power down the road than they had initially planned.  They also wanted to build in enough flexibility so that they could recharge their batteries in three different ways: solar power, engine power, and with shore power as a backup.  To see this process in action, check out our installation video. Scroll to the end of this article to view a video on this installation.

What Appliances Can I Run in My Off-Grid RV?

First, let’s take a look at what they wanted to run.  Since their bus was intended for short camping trips and music festivals, the number of appliances was significantly fewer than for someone using the bus for full-time living. However, we built in plenty of room for expansion should they want to scale things up or down the road.  Determine your own energy needs and organize your solar build!

Below are the appliances that they wanted to power off-grid:

(Watt Hours = Watts x Hours)

Which Solar Components Do I Need to Run My Appliances? 

Next, we’ll examine the solar components required for installation, taking into account this load assessment. The table above suggests that the system needs to be able to collect, store, and deliver an average of 1,500 Wh per day, with a maximum AC load of 1,800W, if both the hair dryer and laptop are running simultaneously. 

Average Daily Solar Hours:  How to Choose the Right Solar Panel Wattage

Unless you’re parked on the equator, the number of hours of sunlight varies throughout the seasons; we’ll be using an average of five hours of solar gain per day, which is a conservative average for the southeastern USA from springtime through fall.  Find your daily average in the USA, or in other countries.

Using our comprehensive Solar System Sizing Worksheet, it appears that a single Renogy 320W solar panel may be sufficient to meet their needs.  But they’re likely to see only about 85% of that power output under the best of conditions, so to power their daily energy needs, they’ll need more than one.  They chose to install two 320W panels, but they could have opted for four 100W panels or two 200W panels to reach their minimum solar array size wattage.

The two 320W panels, connected in parallel, provide a maximum of 640W.  Assuming 85% efficiency means they can count on 544W of solar power, assuming five hours of good solar gain per day.  Again, planning for potential future expansion is a good idea, especially for those rainy days when solar gain is hard to achieve. If you plan to travel to places with a lot of shade, Renogy ShadowFlux panels are a great option, as they are designed to handle partial shading from trees, power lines, and rooftop equipment.

Keeping an additional portable 400W foldable panel on hand is also very helpful.  It can be placed in the sun on an extension cord while your rig is parked in the shade, or during the late fall, winter, or early spring when the sun angle is low, or to augment your solar surface area on a cloudy day.  Truly, it’s a helpful tool for any time of year!

We chose a parallel connection for two main reasons:

1. The wire length between the solar panels and the solar component cabinet is short, so that we won’t have much transmission loss.
2. This bus is mostly going to be used on the East Coast, and that means trees and trees mean shade. 

Parallel connections tend to work better in shade because if one panel is shaded, the other can still produce power.  In a series connection, if one solar panel fails due to shade, they all fail.  Renogy offers various panel styles designed to withstand shading conditions. 

Each panel has an output of 37.9V and 8.5A; when the two are connected in parallel, the maximum output is 37.9V and 17A. This information will help us determine the size of the charger controller.

Selecting a Charge Controller to Handle the Power Input

Based on the specifications from the solar array (37.9V and 17A), they chose a charger controller that can handle the input parameters while also fitting into the allocated space for the solar components.  The 50A DC to DC Charger with MPPT is a powerful space-saver, as it serves double duty.  It will regulate both the solar input and boost the battery bank with an engine charge while driving – a win-win!

With a maximum input of 750W, this compact yet powerful charge controller enhances system flexibility.  If it is cloudy for a few days or they’re parked under trees, they can charge up their house batteries while driving from one place to the next. The MPPT technology will utilize the higher voltage of these 320W solar panels to provide a significant boost to the charging current.  Tip: It’s essential to give this component ample breathing room so it functions properly and doesn’t overheat.

Additionally, when the battery bank is fully charged, the solar input will trickle-charge the starting batteries, ensuring they are ready to crank the engine whenever needed.  This is an excellent feature for use in a boondocking situation or when the bus will be spending some time in winter storage.  No more jump-starting dead batteries!

Which Off-Grid Batteries Offer the Best Power for Their Size?

Based on the initial energy use assessment of 1,500 watt-hours (kWh) per day, they needed a battery bank that could deliver enough power without exceeding the safe depth of discharge (DOD).  Using lead-acid batteries (at a 50% DOD) would have required them to install 3000 Wh of batteries, because, with this chemistry, they could only safely use half of the battery capacity.  However, with Lithium Iron Phosphate batteries (at an 80% DOD), they only needed 1,875 Wh.  So, instead of three heavy and very large lead-acid batteries, two small yet powerful LiFePO4 batteries did the trick!

They chose to install three DuoHeat 100Ah Mini-Core LiFePO4 Batteries to power the living area in the bus when off-grid.  That extra battery is simply insurance for those days when the sun doesn’t shine for several days and they aren’t driving. These small, lightweight, and powerful batteries can handle a wide array of temperatures because they are self-heating. They can be installed inside the living area and won’t need to be removed from the bus during winter storage because they can handle some pretty cold temps (down to -4 degrees F in storage)! 

With an 80% DOD, these batteries will safely deliver over 3kWh per cycle.  Again, they’ve built enough flexibility into the battery bank that, if needed, they can use more power without dipping too low. See our video review of the DuoHeat 100Ah Mini-Core LiFePO4 Battery for more details!

How Do I Run Household (AC) Appliances in My Off-Grid RV?

Obviously, this bus didn’t come with a traditional RV converter that would allow them to charge auxiliary batteries and run household appliances while plugged into shore power, so they chose to install a 2000W Renogy Inverter Charger to do double duty.  With this 2-in-1 component, they’ll be able to run household AC appliances while off-grid AND charge up the house batteries when plugged into shore power. Another win, win!

With the automatic transfer switch, this unit safely switches between power in and power out.  And, if they ever want to run a coffee maker, an Instant Pot, or even a hair dryer occasionally, a 2000W inverter will do the job.  However, it’s essential to note that the inverter can safely handle any one of these appliances individually, but not all together. The great news is that if you overload an inverter, it will simply beep and shut itself off, rather than causing damage to the component or your appliances.

What’s the Best Way to Monitor My Off-Grid Solar-Powered System for My Conversion?

To monitor the battery's charging status and electrical load, we’ve installed the Battery Shunt 300 between the negative battery terminal and the negative busbar.  The shunt will connect wirelessly to the Renogy ONE Core Monitor, which displays the status of all system components in a convenient touchscreen format.  They mounted this just above the solar cabinet in a clear and easy-to-read location.

Installation Considerations

Here are some things to keep in mind, in addition to what you’ll find in each of the component installation manuals: 

• Always disconnect any power supply from solar panels or shore power while installing solar components.
• All of the components give off heat while doing their jobs, so be sure to plan out not only the size of the components, but also the free space they need around them for ventilation.
• Fuses and breakers need to be appropriately sized and placed between components, see wiring diagram below.
• Short wire runs increase efficiency.  We were lucky that the location of the solar cabinet and the bus starting batteries were so close together.  This saved money on the wire length and decreased transmission loss.
• Grounding the DC to DC Charger.  Experience has taught us that it’s best to ground the DC to DC Charger directly to the common ground on the starting battery, in addition to the common negative busbar. 
• The Inverter Charger needs to be grounded to the vehicle chassis in addition to the common negative busbar.
• Many vehicles have no AC power distribution panel.  When installing the AC power output from the Inverter Charger, it’s recommended to install an AC breaker panel to provide additional protection for the AC outlets. 
• It’s also a good idea to install a DC distribution panel for all DC appliances, such as cell phones, so that they will be protected with an appropriately sized fuse as well.

Ready to dive into your own project?  With the right-sized solar panels and components, you’ll be prepared to power up your own conversion adventures and hit the open road.  The “Fest Bus" has been happily rolling along – and their solar-powered system is providing all the power that they need to enjoy some summertime music festivals in the southeast!