Designing and installing a solar system is a fairly complex undertaking and requires a fair bit of knowledge in the realm of electricity. This post is NOT meant to be a how-to, as every situation is different and will require a unique solution. This video and article are here to explain the basics and share what we learned and how we did it. Please seek out a professional installer in your area if you are not 100% comfortable with all of the concepts of solar and electricity in general.
RV Electrical Basics
RVs generally have three electrical systems: Coach DC (Direct Current), House DC, and House AC(Alternating Current). Coach DC is just for the engine or tow vehicle and isn't a concern.
House DC runs things like lights, pumps (water and hydraulic), furnaces, and control panels. House AC is just like a regular house, running things like a microwave, coffee pot, air conditioners, TVs, and computers.
These two systems are linked by either a converter or an inverter. A converter takes AC power and converts it to DC power. This is to charge the batteries and provide DC power for loads when connected to an AC source like shore power or generator. An RV with only a converter cannot power AC appliances when not connected to a power source like shore power or generator. This is where an Inverter comes into play. An inverter takes DC power and converts it to AC power, allowing one to run AC appliances from the battery bank. An inverter is a crucial piece for anyone wanting to boondock and still enjoy the comforts of home. We cover our inverter install in a separate video here. Additionally, most higher-end inverters are also chargers.
On the surface, solar is fairly straightforward. Sunlight hitting a solar panel produces DC power. That DC power can vary greatly in voltage and amperage (depending on how they are wired) and that DC voltage needs to be converted (usually down) to match the RV, which is commonly 12 volts or 48 volts. This conversion is done by one or more solar controllers. Those controllers are configured for the type and capacity of the battery bank with the appropriate voltages for staged charging (bulk, absorption, and float).
The bottom line is that a solar system is simply a DC power source when the sun is out. That DC power source is used for charging the batteries and/or powering DC loads, just like the DC power from a converter or inverter/charger.
Before solar can be useful, it needs a place to store energy, so we need to figure out how much battery capacity we need. Again, this is not a how-to video/article, so I'm going to skip the math here. See the end of the article for some resources on all of the math behind this.
A good battery bank is the heart of any solar/boondocking system. See our battery monitoring video for more details on the types of batteries and their pros and cons. We chose Battle Born Lithium-Ion Batteries for a few reasons: Lithium-Ion is the best thing available right now, being that their rated capacity and real-life capacity are equal. They can be discharged 100% without damaging them. Additionally, Battle Born Batteries have a robust BMS (Battery Management System) built into each battery. This BMS keeps the cells balanced, protects the batteries from over-charging, over-heating, over-cooling, etc. We've been using Battle Born Batteries (3 of them) for about 2.5 years and they've been rock solid!
Since we want to run an air conditioner when boondocking, we really need all the battery power we can afford and fit into our RV. That's the bottom line for us. However, it also works out in math. Our main AC is 1600W and we want to run it for about 6 hours overnight (considering it cycles on and off). That's 9600Wh (Watt-hours). We chose to install ten 1200Wh (100Ah) batteries in series which yields 12,000Wh. Considering we also lose about 10% of power when inverting from DC to AC (the air conditioner is AC) and we will also need to run our computers, coffee pot, etc, we are sized about right. Sort of…
Ideally, when sizing a solar system you want to size it for two days of load for rainy/cloudy days. But, since we also have a generator, that can take up the slack on a rainy day. Also, twenty batteries are just not feasible fiscally nor physically.
The solar side of the equation needs to be sized for the battery bank. Generally speaking, you want to install as much solar as possible without overpowering your battery bank. If your batteries can handle 100 Amps of charging current, it makes no sense to install a solar system capable of providing 150 amps as the extra 50 would just be wasted.
Our battery bank (10 Battle Born 100Ah in parallel) can theoretically handle 1,000 watts of charge. I say “theoretically” because that much current would require some VERY thick cable and we don't have a charging source (solar or inverter/charger) capable of coming anywhere near that. Additionally, our wiring is designed for 400 amps maximum.
So, we need to size for that 400 Amp maximum. That isn't a problem. If we covered every inch of our roof with solar we'd come nowhere near that. So, for us, it's a matter of how many panels we can fit on the roof. That turns out to be about ten panels so I can leave some room to walk up there. See the video for how I figured this out using a drone and copy/paste.
Of course, I want each panel to produce as much as possible. When shopping for panels, I tried to find something new and cutting edge that would give us the most bang per panel. Turns out, there are none that really stand out and a 200 Watt panel is on the high end. Since we have friends (You Me & the RV, Runaway with the Clarks, Our Epic Field Trip) who all used hi-tech 200W panels and like them, I decided to go that route.
In regards to how I wired them, I'm not going to get into the weeds on the different configurations (all in series, a mix of series/parallel, etc). But, the gist of it is that I wanted as few controllers as possible. One controller would have been great, but I didn't find any controllers in the Victron lineup that could handle 2000 watts. So, I ended up with two strings of five panels in series (1000W each), and two Victron Smart 150/100 controllers.
The first number in that (150) is the maximum voltage. Each of the five panels can produce 24V so, wired in series, that's 120V. If you do the math at 10 Amps, you'll notice that equals 1200W which is more than the panels' rated 1000W. Solar panels have ratings for voltage and amperage, but also have ratings for open-circuit voltage and short circuit current. To be honest, I'm still not clear on what those are, but I do know those are the numbers to use for planning. In general, it's always best to plan for a larger than needed power when talking about wiring and components like controllers anyway.
The second number is output amperage. So, I need to take that 1200W and divide it by 12 (our battery voltage), and I get 100 (Watts Law). So, 150/100 is perfect for this situation.
Another note on the wiring of the panels: The higher the amperage, the bigger the wire. The bigger the wire, the more difficult it is to deal with. Voltage, on the other hand, can be very high and requires no increase in wire size. So, if I wired the panels in parallel, I'd be looking at around 24 volts at 48 Amps. If I did that, I'd need wiring capable of handling 50 Amps. Thick and bulky. Wiring the panels in series gives me a higher voltage (120V) but only 9.5A. Wiring in parallel, you add amps and voltage stays the same. Wiring in series, the voltage adds and amperage stays the same. This is why solar panels are usually wired in series.
Another critical part of all of this is how to wire everything together and not start a fire! Again, this is where knowledge of ohms law, watts law, and how to size wiring based on amperage comes into play and it could be a whole book covering that topic.
But, there are two basic rules to follow. Each circuit or run of wire needs to be sized for the amperage it will carry. And, each and every circuit needs to be protected with a fuse or breaker. That breaker or fuse should always be the weakest link in the circuit. Its whole purpose in life is to die so you don't die in a fiery inferno. Because, if the circuit has no breaker or the breaker is too large, the wire becomes the breaker by melting and catching stuff (your RV) on fire!
Note: The roof wiring needs to be “solar” wire which means it's designed to sit on your RV roof exposed to rain and UV light. Additionally, all roof connections need to be waterproof MC-4 connectors.
The End Result
Everything on the left side of the diagram (surge guard, ATS, Inverter, etc) was already in place and just needed some moving around. The same is true for the batteries…. Just move and add (see video). The shunt is also new but replaced the BMV-712 shunt we already had. See our RV Battery Monitoring video on that.
The upper right is all the new stuff, so I'll start on the roof and work my way down.
Side note: For wire sizing by amperage and length, there are lots of resources on the internet. I like this one from Blue Sea systems.
We have two strings of five panels each wired in series. Each string of panels, wired in series, can produce a maximum of 120V at 9.5Amps. The wiring of the panels, including down to the front bay is 10AWG (10 gauge). The cable runs from the panels to the front bay are straight through with no bus bars (no need since we are not wiring the strings together at all).
Once in the front bay, the positive leads from the panels go through two 15A breakers. I would have preferred 10A breakers, matching the amperage from the panels, but the 10AWG wiring can handle 15A at this distance just fine. Breakers protect wiring, so that's fine. From the breakers, the runs go to the PV side of the controllers, along with the negative directly from the panels. All of that wiring is 10AWG.
Coming out of the controllers, we're looking at a potential of 100A, so we need bigger wiring. Since we need less than a meter of wiring for this circuit (connecting to the DC bus bars directly below), we can go with 4AWG here. Just like the previous circuit, this one is protected with breakers but rated at 100A, then directly to the DC bus bars.
I like using breakers for this application instead of fuses because it also gives me a way to disconnect circuits.
Victron Smart Shunt
First off, a shunt is the ONLY way to get the true state of charge from a battery bank. The shunt sits between the negative side of the battery bank and EVERYTHING else. This means that NOTHING except the shunt should be connected to the battery bank's negative side. The best way to get everything off the batteries (RVs usually come with a spaghetti mess on the battery) is to use bus bars. The end result is that ALL DC current has to go through the shunt and can be monitored and metered. See our RV Battery Monitoring post for more details.
I replaced our Victron BMV-712 shunt for two reasons: First, I completely trashed it when using the ratchets to crank up the inverter to the ceiling (see video). Second, I wanted one that would “talk” to the solar controllers (see Interoperability below).
The Smart Shunt works just like the BMV-712 but has all of the smarts (and Bluetooth) built right into the shunt versus the display unit.
Interoperability and VE.Smart
When you have two solar controllers charging the same battery bank and supplying power to the same DC systems, they need to be able to coordinate with each other. This is why I picked Victron. The latest lineup of Victron products can use a VE.Smart network to communicate over Bluetooth with each other as well as the Smart Shunt. This allows the controllers to know about each other, working together, as well as the true voltage and state of charge. All wirelessly! I had enough wiring to do as it was!
So, what about charging from the Inverter? While we can leave the inverter on to charge also, I don't like that it's not part of the smart network, so I mostly leave it off and let solar charge the batteries. However, if we ever need to charge our battery bank faster, I can turn it on. Each controller can provide 100A (with 100% sun light), and the Inverter can provide another 125A (from shore or generator). This gives us up to 325Amps DC for charging. With 1000Ah of battery, that means we can charge our system from 0 to 100% in a little over 3 hours (1000 / 325).
Learn More About Solar and RV Electrical
If you saw our RV School video, you know I absolutely LOVE the NRVTA! Absolute top-notch facility and instructors! Well, they recently launched a solar course! I have not taken this course but, knowing the quality of instruction there, we have no reservations recommending it. The solar course preceded by the RV Fundamentals course (which I did take) will give you the mental tools you need to build your own solar system! All that stuff above about Ohms Law and Watts Law… they have you covered even if you can't spell it!
Another great resource I found is a book by Will Prowse called Mobile Solar Power Made Easy! Will also has an awesome YouTube channel: DIY Solar Power with Will Prowse. While I have a background in electronics from the Navy and feel very comfortable with RV electrical systems, I needed to fill in some knowledge gaps in how solar systems work. His channel and book were a tremendous resource.
- Inverter Project: youtu.be/1rPKWrXQYWA
- RV Battery Monitoring: youtu.be/3-xPCMgVdd4
- RV School (NRVTA): youtu.be/cTxJ23Zd27E
- RV Moochdocking: youtu.be/80ZucqclD80
— Roof —
- Hi-Tech 200W Solar Panels: changinglanesrv.com/solar-panels
- Solar Panel Z-Style Mounting Brackets: changinglanesrv.com/solar-mounting-brackets
- TEMCo 10 AWG/Gauge Solar Cable: amzn.to/3wLoa4K
- BougeRV 12 PCS Solar Connectors (MC-4): amzn.to/3BdXKfd
- Plastic Dustproof Waterproof IP65 Junction Box (roof): amzn.to/3kAcajU
- 10/2 AWG Duplex Tinned Marine Wire 30 Feet (roof to front bay): amzn.to/2VVO8pt
- RecPro 1021 Self-Leveling RV Sealant: amzn.to/3wHGSKF
- Waterproof NPT Cable Glands: amzn.to/2UgE226
- Plastic Chisel Scraper Remover Tool Kit: amzn.to/3l7fraG
— Front Bay —
- Battle Born 100Ah 12V LiFePO4 Deep Cycle Battery: changinglanesrv.com/bb-12v
- Victron SmartSolar MPPT 150/100 (what we used): changinglanesrv.com/victron-150-100-mppt-bb
- All Victron MPPT Solar Charge Controllers: changinglanesrv.com/victron-mppt
- Victron SmartShunt 500A: changinglanesrv.com/victron-smart-shunt
- DIN Rail Midnite Solar Circuit Breaker, 100A 150VDC: amzn.to/3hJKK9G
- DIN Rail PV Breaker – 15 Amp, 150 VDC: amzn.to/2URmkSz
- Midnite Solar-BBE (Breaker Box): amzn.to/3zbOh6G
- Blue Sea Systems 600A Bus Bar: amzn.to/3kxpUwa
— Cabling and Tools —
- 4/0 AWG Flexible Welding Cable (Inverter and Battery): amzn.to/3BdZ7uC
- 4/0 AWG Copper Terminal Lugs: amzn.to/3kupvdR
- 2/0 AWG Flexible Welding Cable (battery interconnects): amzn.to/2VIU9Wj
- 2/0 AWG Copper Terminal Lugs: amzn.to/3BoHWXt
- 4 AWG Flexible Welding Cable (controllers to batteries): amzn.to/3xIGAV3
- 4 AWG Copper Terminal Lugs: amzn.to/2VYBQgd
- 3/4″ Heat Shrink Tube Red/Black: amzn.to/3BgZ6G8
- 1/2″ Heat Shrink Tube Red/Black: amzn.to/3xSKRFu
- 16 Ton Hydraulic Wire Crimper Crimping Tool: amzn.to/3z8cQ4b
— Miscelaneous —
- Dremel 3000-2/28 Variable Speed Rotary Tool Kit: amzn.to/3zctPlQ
- Fluke 376FC True-RMS Clamp Meter with iFlex: amzn.to/3ij1cgg
- Wagner HT1000 Heat Gun: amzn.to/2Uet8dd
- Mobile Solar Power Made Easy! (book): amzn.to/3wVOARz
- DIY Solar Power with Will Prowse: www.youtube.com/user/errolprowse
- The Tall & Short Travelers: www.youtube.com/channel/UC6RhktSQsbWXV5-JTwyGmbw
- Our Epic Field Trip Solar Video: youtu.be/RwQlder8nwU
- You, Me & the RV Solar Video: youtu.be/8NxccaQ_Hmw
- BlueSea Systems Wire Chart: changinglanesrv.com/wire-chart
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