Solar Power + House Battery Charging System + Starter Battery Charging for RV, Camper, and Van
It's time to upgrade the solar power and house battery charging system. Technology has improved since I first installed it and the charge controller I was using was designed for lead acid batteries, with too few settings for LiFePO4 batteries that I use now.
This article focuses on mobile solar power for RV, camper, van and trailer use.
Most of the electrical system components that I'll be recommending below are VICTRON brand. Their products might be a little more expensive than other brands, but it's totally worth it because the quality is exceptional, highly customizable but still simple to use, excellent bluetooth app, and the devices can all be setup in a network to communicate with each other.
SOLAR PANELS
Although the solar panels are arguably the most important part of the solar power system, they are also commodity items. Use whatever solar panels of good quality that fit your system needs. Choose name brands that have good reviews.
How Many Watts Of Solar Panels Do I Need?
Don't underestimate how weak solar panels actually are in real life application. A 100Ah 12.8V LiPO4 battery has an average of 1300Wh of energy (estimating about 13V average). That means it would take 100W panel 13 hours of direct sunlight to recharge, which isn't realistic. You'll rarely see the max wattage out of a panel, and in a static installation, only expect an average of 5 hours per day of full output. That means you need a minimum of 260W of solar to fully charge a 100Ah battery in 5 hours. Fully discharging the battery every day is too aggressive, because your max daily use should be limited to about 50%, such that you have capacity to compensate for days without sun. But when the battery does get discharged 100%, there needs to be enough solar to recharge it within a day. So to be conservative, you will need 300W of solar panel per 100Ah of 12.8V LiFeP04 battery.
3W of solar per 1Ah (13Wh) of 12.8V LiFeP04 battery.
For 100Ah 12.8V LiFePO4 = 300W of solar
For 200Ah 12.8V LiFePO4 = 600W of solar
For 300Ah 12.8V LiFePO4 = 900W of solar
For 400Ah 12.8V LiFePO4 = 1200W of solar
You can see how the limit for a camper van is about 300Ah up to 400Ah if you also have a DC-DC charger than can charge off the alternator.
The calculations above did not take into account the nominal load on the system while charging. If your load is pulling 5 to 10A, you will need 64 to 128W additional solar power capacity to cover the load in addition to charging the battery, else the charging will take longer.
Mobile Solar Panels
Any panels below 300W are designed more for mobile applications. These can be divided into rigid and flexible panels.
Rigid Mobile Solar Panels
Rigid panels have a glass face with aluminum frame. They are designed for a lifespan of 20-25 years (but will continue to work for much longer). I've used RENOGY brand 100W panels, and will now be upgrading to 175W panel because it fits perfectly within the width of the Sprinter van roof, without sticking out over the edge. 200W panels are only 8" wider, but that makes them stick out too far. Some people take 2X 200W panels and install them lengthwise on the roof, side by side and they don't hang over the edge. This is a good option if you have the open space for the 58" long panels.
If rigid solar panels fit on your mobile system, then use them instead of flexible solar panels. Rigid solar panels will outlast and outperform flexible panels. They also provide shade for the roof vs transmitting heat. They are easier to service vs glue down install.
Flexible Mobile Solar Panels
Flexible panels can conform to curved surfaces and are much lighter than rigid panels. The downside is that they have a shorter lifespan as low as 3-5 years. Advertising claims 10-20 year lifespans, but in reality they don't last that long. They also pass heat through to the mounted surface and they are difficult to remove when glued down. Read this article here for the opinion from a solar company who has to service installations using flexible panels. Only use flexible panels if you need the low profile, low weight, confirming to curved surface, and you are prepared to replace them more often.
Home or Commercial Solar Panels
Solar panels for home or commercial use are normally 300+W per panel. They are cheaper per W than the smaller mobile panels. There are many quality brands, like REC that manufacture panels for other brands like Panasonic.
Santan Solar sells a variety of new, scratch and dent, and used home/commercial solar panels for excellent prices.
SOLAR CHARGE CONTROLLER
I'll be using the VICTRON SmartSolar line of MPPT solar charge controllers. Although Victron is a high-end product, their solar charge controllers are very reasonably priced considering their capacity.
To figure out what size (voltage and amps) solar charge controller you need, they have a very useful calculator.
The controller voltage rating must be higher than the max PV (solar panel array) voltage. The interesting thing is that they recommend undersizing the current capacity of the controller by up to 130%. If you have 400 [rated] watts of solar panels charging a 12V system, the charge controller only needs to be 307W at 12V = 25.6A. The theory is that the panels never reach their max rating and a higher input current won't damage the controller.
MPPT solar controllers have the highest efficiency at an input voltage of about 1.5X the battery voltage. The advantage of using higher voltages is smaller gauge PV wire needed and less voltage loss and better performance in shade and cloudy situations that cause a significant voltage drop. For solar installations with long runs of wire, the higher transmission efficiency of the high voltages is greater than the slightly lower charging efficiency of the controller. Shooting for an input voltage of 2-3X the battery voltage is ideal.
On a typical camper van install:
There's usually a max of 400W created by 4 x 100W solar panels.
For a 12V system, these should be wired 2S2P, 2 in series and 2 in series (2 series pairs connected in parallel).
The output will be about 44V. PV max voltage @ min temperature = 51.6 V.
VICTRON recommends their SmartSolar MPPT 100/30, which only costs $128 (as of 2024) on Amazon. That is a very good price for such a feature rich controller.
The Bluetooth connectivity and the app are amazing. Also, the stored trends and instant readout options are very useful. Stored trends shows a history of all the data that you may want to see to determine what is going on with the system. The instant readout shows the important data for each Victron device from the home screen of the app without needing to connect directly to a specific device.
BATTERIES
Before buying LiFePO4 batteries, one of the most important factors to consider is whether the batteries will ever need to be charged in sub-freezing weather (they are not in a climate-controlled area). If yes, then you will need a heater to warm the batteries up well above freezing before they can be charged. Otherwise, if the batteries don't have a low-temperature protection, charging them below freezing will damage them. Even if they do have a low-temperature protection, but now heater, they can only be discharged below freezing, but not charged. That could lead to a situation where the weather stays too cold for too long to charge the batteries and they fully drain.
The following list of batteries focuses on low cost. There are plenty of more expensive, very high-quality battery brands out there, but it gets expensive fast when you have to buy several batteries. These batteries are a balance of quality vs cost, and usually, as long as the cells are good quality and the BMS is decent, the battery will last the same as the expensive brands.
Self-Heating LiFePO4 Batteries
Self-heating batteries are usually about $75 to $100 more than ones that only have a low temp cutoff, but the cost difference is worth it for 1-4 battery systems over trying to rig up a heater that may or may not work reliably. For a larger battery system, a heated enclosure will save money and protect the batteries better.
Low Temp Protected LiFePO4 Batteries (Not self-heating)
Low-temperature protected batteries prevent charging below freezing. They cost a little bit more than batteries that don't have this feature, but it's worth it to be safe. If your solar charger has a low temp cut off, that could be used instead, however, all other chargers also need to have a low temp cut-off.
This battery also has Bluetooth to monitor it. LiTime has good ratings and teardowns and tests can be seen on YT.
I posted this to show the a low cost battery with low temp cut-off I can find, but the quality is unknown, so do your research before buying. NOTE: It's not clear whether the low-temperature cutoff applies to charging or discharging.
I posted this to show the current lowest-cost battery with low temp cut-off I can find, but the quality is unknown, so do your research before buying. NOTE: It's not clear whether the low-temperature cutoff applies to charging or discharging.
LiFePO4 Batteries Without Low Temp Cutoff
LiFePO4 batteries without a low-temperature cutoff should only be charged in a climate-controlled area so that they are never exposed to freezing temperatures while charging.
REDODO batteries are well reviewed on YT with lots of tests and teardowns
LiTime has good ratings and teardowns and tests can be seen on YT.
These are well-reviewed batteries and should be reliable.
I haven't researched the quality of these yet. Do your research before purchasing.
DC-DC CHARGER (HOW TO CHARGE FROM ALTERNATOR)
To charge a LiFePO4 12V battery from the engine alternator, you need a 12V-12V DC-DC charge controller. The VICTRON Orion XS 50A is an excellent 12/12 Volt DC-DC charger. It has a 98.5% efficiency rating which allows it to be very small without a finned heatsink. It does not get hot like the previous generation 12-12V DC/DC chargers.
It has a 50A output, which is quite a lot for the size. If your alternator can output more (while still powering the vehicle electrical system), then another Orion XS can be setup in parallel for 100A output.
BATTERY CURRENT MONITOR (SHUNT)
A battery current monitor shunt is important for monitoring the state of charge of the battery bank. There are 2 main options for this from Victron.
The SmartShunt does not have a display (Bluetooth only) and needs to be configured and view data from the app.
Supposedly the bluetooth range of this device is quite short compared to the BMV-712
The BMV-712 has a remote display and Bluetooth. Settings can be configured from the display and also from the app over Bluetooth. Basic data can be viewed on the display, and more detailed data can be viewed on the app.
Supposedly the Bluetooth range on this device is much further.
It has an onboard alarm that can be set to alert about issues
It has an onboard relay that can trigger other devices.
Victron Energy SmartShunt 500 amp Battery Monitor
Victron Energy BMV-712 Smart Battery Monitor
HOW TO CHARGE THE STARTING BATTERY FROM THE HOUSE SOLAR PANELS (OR HOUSE BATTERIES)
Ok, so we're successfully keeping the house batteries charged up using the solar panels. Now how can the starting battery be kept charged when the RV van is sitting unused for some time, or to prevent accidentally discharging the battery.
The solution is a 12V to 12V DC-DC charger that goes from the house batteries to the starter battery. If there's already a 12V-12V DC-DC charger going from the engine alternator to the house batteries, your gonna need to make sure that both of these are not running at the same time to prevent a charge loop that can run down the batteries. The easiest way is to use the ignition signal to only turn on the DC-DC house battery charger and turn off the DC-DC starter battery charger when the engine is running.
The VICTRON Orion-Tr Smart 12/12-Volt 18 amp 220-Watt DC-DC Charger Isolated (Bluetooth) is a bit overkill for keeping the starter battery charged, but it's the smallest DC-DC charger that Victron offers, it will do the job very well, and it can be monitored over Bluetooth.
The wiring diagram below is for charging the house batteries. Reverse the wire connections for charging the starter battery. Connect S1 input to the ignition signal in a way that opens the circuit to prevent charging when the engine is running.
SYSTEM DISPLAY
Although there are dedicated displays sold by Victron to see the full status of the solar power system, the cheapest method is to use the free Victron Connect app. It can be used from your phone, but if you want to install a dedicated display use an old phone or a cheap Android device and install that permanently somewhere. The app has a setting that keeps it open all the time if needed.
INVERTER FOR DC to AC POWER
Use whatever inverter you want that fits your application. Be aware that the DC current draw of the inverter doesn't exceed the discharge rate of the batteries (nominally 1C, ie a 100A max draw from 100Ah battery), and that the DC power cables are sized appropriately for the current draw.
I learned the hard way that a microwave uses a lot more power than it's advertised power (output power). A 700W microwave can use up to 1200W. That means a 1000W inverter will not run a 700W microwave. The only microwave I
POWER DISTRIBUTION BLOCK (BUS BAR)
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The products shown here were purchased by me with the intent to use them. I did not receive any free items, and I am not being paid or compensated for this review. The video, description, and comments may contain affiliate links. If you click on a link, I may receive a commission. Money earned helps to support my channel and bring you more informative videos about engineering, crafting, and DIY
