Off-Grid Travel — Setting Up A Solar System

When you’re living out of a vehicle, or even just traveling out of one, power quickly becomes a big concern. You need it for lights, to charge your various devices, to run your coffee maker and other appliances, and possibly even to store your food if you’ve got an electric refrigerator. You could do what many RV owners do: rely on campgrounds with electrical hookups plus a couple of car batteries to get you from one campground to the next. But, those campgrounds are pricey and often amount to glorified parking lots. Wouldn’t it be better if you had the freedom to camp anywhere, without having to worry about finding somewhere to plug in?

That’s exactly what we’re going to be covering in this article: off-grid power on the road. There are two major methods for doing this: with a portable gas generator, or with solar. Gas generators have long been the preferred method, as they provide a large amount of power reliably. However, they’re also fairly expensive, cumbersome, noisy, and obviously require that you bring along fuel. Luckily, major advances in solar technology over the past decade have made it very practical to use solar energy as your sole source of electricity on the road.

The Goal

Whenever you’re starting a new project, it’s always important to clearly define your goal. This is never more true than when you’re going to be relying on the outcome for your personal well being. So, first, we’re going to discuss what the average overland traveler wants and needs for power. The most obvious first requirement is lighting.

Luckily, efficient LED lighting is pretty ubiquitous these days. It’ll probably take less than 50 watts to completely light up your vehicle with 12V LED lighting. Most modern televisions will use a similar amount of energy.

Next up, you’re going to want to be able to run at least a few basic appliances. For us here at Hackaday, a coffee maker is at the top of that list. Unfortunately, coffee makers use a lot of power — a Keurig can use up to 1500 watts while heating up. Other appliances use similarly high amounts of power. A microwave will use roughly 1200 watts while running, and a toaster oven uses even more.

Characterizing Your Needs

This chart, provided by WAGAN, lists some common appliances and their power consumption (though TV power consumption has been dramatically reduced in recent years)
This chart, provided by WAGAN, lists some common appliances and their power consumption (though TV power consumption has been dramatically reduced in recent years)

Then there are the really high energy consumption appliances, such as air conditioners and heaters. Both of these require a lot of power to run, and also need to be run for long periods of time. While it is technically possible to run both from a solar setup, it would require a massive investment in solar panels and batteries for storage. In that case, a generator would be more cost-effective.

So, for the sake of brevity, let’s say you’ve decided to forego the air conditioner (or will only use it when you have access to shore power). The heater, water heater, and refrigerator will all be run off of propane. That leaves you with a setup that will only be consuming ~100 watts most of the time, and occasionally will peak close to 2,000 watts when the appliances are in use. Now let’s talk about what you’ll need to buy to make that happen.

The Equipment

There are four main components that are going to be going into your solar system: a converter, an inverter, batteries, and the solar panels themselves. Virtually all RVs (and vehicles in general) are set up to run 12V DC electricity. This is so they can be run directly from something like a standard car battery. Most of your appliances and other household devices, however, are powered by the 120V AC you generally get from your wall outlets.


This is where the inverter comes into play. It takes 12V DC from your batteries and turns it into 120V AC, so that you can run all of your normal household devices. That said, the process isn’t perfectly efficient, which means you should try to use the 12V system as much as you can (for instance, for the LED lighting). Inverters will also consume some power even when nothing is being run through them, so it’s best to shut them off completely when not in use.

As we covered in the last section, you’ll probably want an inverter capable of 1,500 to 2,000 watts of continuous output. Not all inverter output is the same even though the power ratings may match. Pure Sine Wave inverters are more expensive, but provide power that is much closer to “real” AC power available from an outlet. Some appliances will have problems running off of the less expensive Modified Square Wave inverters (and could possibly even be damaged). If you’re not sure which you’ll need, it’s probably best to spend a little more on a Pure Sine Wave model.


The opposite of an inverter is a converter — it turns 120V AC into 12V DC. These are necessary for charging your batteries from shore power (a mains outlet), and for running your 12V system from shore power. Virtually all RVs will have a converter already built into the electrical system, but you’ll need to purchase one if you don’t already have one and want the option to charge your batteries from an outlet.

Solar Panels

With the solar panels themselves, you’re really only limited by how much space you have available and how much money you have. The more watts you can afford (and fit onto your rig), the better. While some panels are slightly more efficient than others, they’re all pretty close to each other right now. Which means it’s mostly about how many square feet you have available and how much money you’re willing to spend. Most people will need 150 watts at a minimum, with something like 600 watts being ideal.

Earthroamer, a leader in off-grid expedition vehicles, provides a 3,000 watt solar panel array on their XV-LTS model.
Earthroamer, a leader in off-grid expedition vehicles, provides a 1,200 watt solar panel array on their XV-LTS model.

How much you’ll actually need is pretty difficult to guess, however. A 150 watt panel, for example, will only actually provide 150 watts under perfect conditions (clear day, sun directly overhead, etc.). In general though, you can probably expect to actually get 1/3 to 1/2 of the rated watts during daylight hours on average. This will obviously vary based on weather conditions, time of year, and how you position the panels. You’ll also need a solar charger to go with the panels, but these are inexpensive and are generally just matched to the wattage of your solar array.


Finally, you’re going to need batteries with which to store all of this power. All of this equipment was designed specifically to run off of standard 12V car batteries, but they aren’t actually the most ideal battery for the application. Car batteries are meant to provide a huge amount of starting amperage (to start your car’s engine), and aren’t meant for the kind of long slow drain you want for a solar setup. There are batteries designed specifically for solar setups, but a solution that’s both ideal and economical is to use golf cart batteries.

Golf cart batteries are mass produced and optimized for deep cycle use.
Golf cart batteries are mass produced and optimized for deep cycle use.

Golf cart batteries are good at storing a lot of energy and are generally inexpensive. However, most come in 6V instead of 12V. That means that you’ll need at least two wired in series to get to 12V (multiple pairs can be wired in parallel). You’ll want to choose the number of batteries based on your expected usage. A good rule of thumb is to have enough to run your system for a day or two without recharging, which should be enough to carry you through situations where your solar panels aren’t outputting much power (in bad weather, for instance).

The Setup

There are three ways to charge the batteries on this system:

  1. With the solar panels, which will always be happening passively when there is enough sunlight to generate some current.
  2. From your vehicle’s alternator, which you only want happening when the vehicle is actually running (to avoid draining your car battery).
  3. With shore power, which is ideal for quickly charging the batteries when you’ve got access to mains electricity.

Charging your batteries with the solar panels will happen completely in the background. Your solar charger should always been connected to the batteries, that way you’ll be gathering and storing energy anytime there is sunlight. If your batteries are already full, the solar charger will simply keep them topped off with a trickle.

Taking advantage of your car’s alternator to charge the batteries is similarly simple. If your vehicle is wired to pull a trailer, then you’ve already got what you need. Just connect a plug with 12V and ground wired up, and have those wires run into your battery bank. Whenever the vehicle is running, some power from the alternator will be used to charge your batteries. For most vehicles, this won’t be a huge amount of power, but it’s good to take advantage of everything you have available.


Using shore power gets a little more complicated, because it’s easy to create a loop that will run your charge/discharge system constantly. The converter will take mains electricity (120V AC “shore” power), and convert it into 12V DC to charge the batteries and run your 12V electronics. However, if your inverter is connected, it’s going to attempt to turn that right back into 120V AC. Furthermore, if the inverter output isn’t isolated from your shore power circuit, you’re going to create a loop where the inverter then feeds the converter, and the converter feeds the inverter. This is a never-ending loop that will, at best, drain your batteries, and at worst could damage your equipment.

This means that your entire system essentially needs to have two “modes” — one for when you’re connected to shore power, and one for when you’re not. When you’re connected to shore power, that should feed directly into your vehicle’s 120V system (to power your appliances) and into the converter to charge your batteries and run the 12V system. When you’re disconnected from shore power, the inverter should be reintroduced (and the converter disconnected), and your 120V system should be run from that.

You can handle that kind of circuit setup in one of three ways: manually (physically unplugging the inverter when you plug into shore power), with a switch, or with a relay. Manually is, obviously, the cheapest and simplest, but you carry the risk of forgetting to do it. And, depending on where your equipment is stored, it might be difficult to physically get to. A switch is a good option for solving the latter problem, but you still have to remember to flip it when you connect or disconnect from shore power. A relay solves both problems, and requires no effort on your part, but you’ll need the electrical know-how to wire it up (which shouldn’t be a problem for Hackaday readers).

A complete mobile system overview [Image Source: Living In My Car]
A complete mobile system overview [Image Source: Living In My Car]
No matter which option you choose, what’s important is that the inverter and converter should never be running at the same time. When you’re connected to shore power, the inverter should be disconnected and the converter connected, and your 120V circuit should be connected directly to shore power. When you’re disconnected from shore power, the inverter should be connected and the converter disconnected, and your 120V circuit should be connected to the inverter’s output.

On the subject of output, we’ve already mentioned that you’re going to have two primary circuits: a 12V circuit and a 120V circuit. The 12V circuit will be connected directly to the batteries, and will feed anything that runs on 12V (LED lights, water pumps, heater igniters, etc). This circuit can use inexpensive fuse blocks designed for cars or RVs. Keep in mind that wire gauge is important here, especially if you’re going to be running a lot on the 12V circuit, so choose your wire size appropriately for the amperage and wire length.

The 120V circuit will be connected to the inverter’s output (and switched to mains when you’re on shore power). This will power any of your household type devices. The inverter itself will have it’s own fuses, but keep in mind that those won’t be part of the circuit when you’re on shore power. So, it’s prudent to fuse the entire circuit after the point where it switches to mains electricity.

The Execution

As described, this system is designed to be as passive as possible. If everything is set up properly, you shouldn’t have to do anything other than use your appliances and devices like you would expect. That’s especially true if you used a relay for switching to shore power. In that case, the only thing you have to do is plug your rig into a mains outlet if it’s available. Everything else should be humming along happily in the background.

That said, there are a few things you should pay attention to and check from time to time. The first seems obvious, but just be conscious of your energy usage. For example, there is no sense in brewing an entire pot of coffee if you’re only going to drink one cup. You should learn very quickly what uses a lot of power, and what you want to prioritize.

Next is basic maintenance. This kind of system actually requires very little maintenance, but it’s a good idea to occasionally monitor your batteries to make sure they’re healthy. Basically, just take a look and see if they seem to be charging and discharging consistently and predictably. You should also take the time to clean your solar panels every now and then, to make sure you’re getting as much power as you can out of them.

Finally, periodically check your wiring to make sure it’s all secure. We’re going to assume you, as a Hackaday reader, know how to properly set up wiring, but when it’s being jostled on the road it’s possible for things to come lose. The last thing you want is a fire caused by a short somewhere.

Other than that, the most important thing you can do is enjoy the freedom of off-grid travel! We’ve even covered how to build your own travel trailer if you’re itching to get on the road. Have any tips of your own, or cool stories about your travels? Be sure to share them in the comments below!

137 thoughts on “Off-Grid Travel — Setting Up A Solar System

      1. Gas powered fridges are good for regular use, they just don’t come with all the bells and whistles and you have to keep the burner area clean. This last issue can be a bit of a problem, because the air intake attracts spiders like crazy and the webs can choke off the flow of air. And yes they are pricy, but so are PV’s in the sort of acreage I see on the RV in the photo.

          1. Yyyyno… even a large family don’t really make enough waste to boil a couple of pots of water a week on the methane. Only worth thinking about if you’ve got a larger than pet collection amount of livestock.

          1. All the RV ones I have owned, the combustion chamber was external to the cabin. But in any case even for the indoor ones, its not a big flame and as I wrote above, you’ve got to keep the intake clean.

          2. The box isn’t sealed. Unless you put a lot of work into that.
            The fridge combustion path is external to that box. Unless you did a kludge install.
            Due to stove burners inside that “box”, standard setup for such “boxes” is a CO and LP detector. Low oxygen is also popular, particularly if you worked on that seal job.
            A LP fridge is the least of your concerns.

          3. Dax If the instalation is done after the book With air in and out it’s no problem. It is 10thousands of RV’s who use propane. But it hav to be done properly.
            Tor H

        1. A 3-way fridge is the least electrically-efficient fridge option. If you are actually off-grid, then planning for the most electrically-efficient setup helps keep you there, and the most electrically-efficient fridges are DC or AC/DC using a sealed compressor like the Sawafuji Swing (Engel) or Danfoss/Secop (Nova Kool, etc.). For example, a 4.5 cu ft Nova Kool R4500 uses a max of 4.4A@12VDC compared to a similarly-sized Norcold 3-way that uses a max of 16.2A@12VDC.

          1. Yeah but if you’re mobile, I think the energy density of propane makes a 3-way fridge worth the difference. In practice they run off mains when you’re docked, gas when you’re parked somewhere with no power, and 12V when you’re moving (because you have to shut the gas off when you’re driving, for safety). Overall I bet it uses less battery than the fridges you mention.

            If you’re talking about a static setup for a house, you’re very probably right. Well, depending on if you get propane delivered.

      1. The only reason (if you have propane burners) is for convenience. Although, in my particular case my propane system isn’t in use, as I wasn’t able to find a horizontal propane tank for a reasonable price.

    1. Depends what you choose to spend – as of late 2016, you can get a good-quality 160W solar panel for US$200, and you’ll need a solar charge controller (quality controller maybe US$450, cheap $100), and some wiring and panel mounts, but you already have battery banks on off-grid campers and RVs. That’s continuous, silent energy as long as the sun is shining, which is usually when I choose to go camping.

      Here’s my RV solar setup:

          1. Solar panels might not need refilling but solar batteries need replacing and aren’t cheap. When putting together a first solar setup most people tend to make calculations based on published equipment specs and ideal performance figures without fully understanding how dramatically real world usage will impact these figures and lead to unexpected system costs after the initial investment. Lead acid batteries are a perfect example. A decent sized battery bank might run you $500 to $1000 to get the reserve power necessary to see you thru inclement weather, occasionally heavy use, etc. For that size investment you’ll obviously want to get as much life out of your battery bank as possible, say 5 years. Unfortunately the expected life of even deep cycle lead acid batteries starts to rapidly fall any time you discharge below 60% capacity. If you want to use the full capacity of your battery bank by regularly “deep cycling” below 10-20% then he might be replacing batteries annually. If you want several years of battery life with the same usable amp/hour capacity then that means only using 30 to 40% of your bank’s capacity and going with a much larger battery bank ($$$)

    1. If electrical energy is the concern then a propane stove (or white gas, or alcohol) can boil water.

      Though that means you need to top up on propane, (or white gas, or alcohol) in order to boil water… granted a little bit of white gas goes a long way in a stove, and chemical energy (fuel) is usually much more energy dense than batteries.

      You can even get a Moka pot and do something more than instant coffee…

          1. AND your camper will smell like gasoline while you’re cooking. Here’s another way of looking at it: if you use a white gas powered stove, your engine will run on that, so you always have some reserve fuel supply. I’ve run my generator off of white gas just so it wouldn’t smell so bad. Ran just as well as on gasoline, but of course white gas is more expensive.

            Also, if your vehicle engine is diesel, stoves jetted for kerosene will work on diesel fuel.

    2. That is if you don’t really like coffee!!!
      But following your thought, you can always pour your heated water over fresh hand ground coffee and voila, good tasting coffee. About that same time (else the grinding.)
      Never understood instant coffee, else no grind to toss away.

        1. Heh, Walmart cheap coffee is nasty, either in that GreatValue white label or that Hills Bros, not sure if that’s a house brand, it’s turned up elsewhere…. but the NoName is actually fairly good… as good as mass market brands anyway.

    3. BTW, I found the holy grail earlier this year, (and a splinter of the true cross a couple of years ago) a 300W 2 mug coffee maker, okay it calls itself a 4 cupper, but who really drinks out of those thimbles. Anyway that be grail because there’s any number of cheap inverters or power packs you can run it off.

      The splinter I guess is a nice 450W power pack with about half a kilowatt hour of batt in it, maybe more, haven’t really ran it dead. it’s the size of an overstuffed briefcase, but slots nicely under a seat.

      With that and that, I’m good for first coffee of the day before the fire’s on at least 3 mornings in a row.

      However, for neat, get one of those k cup holders on amazon that you juszt pour boiling water through and a refillable K-cup… and then you can zap your water, electrocute it with jumper cables or fry it with the solar mirror tile ray of death.

    4. Or you could burn your rubbish and some sticks in a kelly kettle to heat water for nothing.
      Oh and why take a microwave and a television, surely these are the kind of things you want to get away from in your earth roamer?

    5. No, that is not true. The transformer and magnetron have losses between 20%and 40%. The most efficient way is an electric kettle or immersion heater. Any heat generated by the element has no other way to go than into the water.

      1. I think people think microwaves are faster because they make coffee quicker than waiting for a kettle to boil. But that’s because most kettles have a few cups’ worth of water in them, that ends up heated and cooled down again half a dozen times before it’s drunk. Where with a microwave you just put a mug in.

  1. Unless that truck is driving around from the power produced by the solar panels it’s not “off grid”. Since clearly it isn’t why not just run that 6 litre diesel for 54 seconds, take 130 amps off the genny and charge your battery bank?

    1. A generator (or car engine) is most certainly off the grid, if a generator isn’t “off the grid” that by that logic solar, wind, hydro etc are not either. Its certainly not “green”, but neither is it connected to the grid in any way.

      1. I consider “off the grid” to be a viable lifestyle after the Zombie Apocalypse. You have to be fully self sufficient, not just pop down to the local Rotten Robbies for a fill up and some Doritos. Otherwise it’s [marketing]off the grid[/marketing].

      2. Just my opinion, but by Finns standard walmart is off grid, they have solar panels. By my standard off grid means that you don’t connect to the grid at all, driving a truck to a connected garage and filling it with fuel is a connection and therefore not off grid, watching television is a grid connection, as is a mobile phone.
        there is way more to being off grid than not directly paying for electricity,
        in the same way there is more to being a hippy than going to Goa for Christmas.

        1. Well yes, but mobile off-grid is basically impossible. A vehicle big enough to live in, needs a huge amount of energy to go anywhere. And there’s no portable, independent source of energy that you could carry. So if it’s going to move, it needs fuel. Off-grid houses are different, and of course possible since it’s been done.

          Getting the living part independent is a fair accomplishment, even if the thing still needs chemical fuel to move. Carrying all your daily energy with you gives a lot of independence, if the grid went off in my house I’d be sat shivering in the dark. Well actually I’d probably go to bed.

    2. Full disclosure: I used to work for Earthroamer.

      They’re designed to do just that. Ideally, you can park it and be able to use everything from solar only. But, if you’re a heavy power user then running the engine is perfectly fine to charge up the batteries. The engine is actually really efficient (I think less than a gallon an hour).

      1. Whenever I’ve calculated the cost of electricity, (which costs me about $0.12/kw-hr on the grid), it has come to at least $1.00/kw-hr. This is from either a vehicle engine or a petrofuel-powered engine-driven generator. How this comes out to “actually really efficient” is a mystery to me.

        1. Last time I brained that I was at 50 cents, but that was mid tange home use genny, not vehicle motor.

          But anyway “really efficient” is gonna be a lie with a motor that only gets a third of the energy input at the shaft and then blows another two fifths of it using a vehicle alt.

          1. You can get special heavy-duty alternators, meant for things like caravans and boats, for supplying living needs. I dunno if they’re more efficient, but I’d guess “yes”, since they’re designed for just that purpose, rather than just providing the energy to work headlights, windscreen wipers, and starting the engine.

            I’m surprised an alternator is only 60% efficient though. Motors / generators are generally around 90%.

      1. because 130 A for 54 seconds (0.9 minutes, or .015 hours) comes to less than 2 A-hr. And you’re not going to get 130 A, because for the first few minutes, much is going back to the vehicle battery to replenish the charge from starting that behemoth.

    3. Great piece of math there. 2 amp hours ~130/60 (rounding 54 seconds up to a full minute.)
      About an iPhone’s worth of power.

      For charge times:

      The maximum recommended rate is C/5 (a charge rate in amps of one-fifth the overall battery capacity in amp-hours), but only when the cells are between 10 and 85 percent state of charge (SOC). After the cells reach 85 percent SOC, then a C/10 is the maximum. After cells reach 95 percent SOC, between C/20 and C/15 is recommended.

      The reason for the maximums is heat. Higher amperage means more heat, particularly when the cells are getting fully recharged. Thermal cycling wears the plates and sloughs off material.

      Which means the comment: “its fine to run your engine to charge the batteries” is naive at best. You’ll have to run it for hours to get back to full SOC. multiplying the cost of fuel estimates and oh by the way running a diesel at less than full load is a recipe for shortening your engine’s life too.


          1. Displacement is measured in Metres
            Time is measured in Seconds
            Volume is measured in Litres
            Current is measured in Amperes

            Why for the love of little ducklings is there a need to bodge a new term when one exists that is well established and in common use?

    4. Are you referring to using the truck engine and alternator to draw 130 amps and charge the battery bank? You really don’t want to do this to often. Alternators are not really designed to run “wide open” for any length of time. An alternator might be rated at 130 amps but drawing this maximum output rating is very hard on them. Manufacturers even recommend using a separate charger to build up the charge level on a severely discharged starter battery before installing it back in the the vehicle because of the extended heavy current draw on the alternator from trying to bring up the charge level on a dead battery can lead to failure.

    1. The main drawback there is that the engine is way too large to just function as a generator; a scaled down, dedicated engine for the generator is considerably more efficient.

      Given the power demands of the A/C, I have to wonder if trying to make a propane-fired A/C would be a better option than running it off an electric motor.

      1. I fully agree. Here in NYC it’s common to see street vendors using little two strokes to power a couple lights… even the best generators (so called “inverter” generators, because they vary their speed and run an inverter instead of running at a constant 600rpm) can only throttle down to about 1/3rd or 1/4th power, which is still far more than you need to run a few lights. The generators are usually like 600W, so they still waste 100W running a couple LEDs.

        Other solutions would be getting several generators (200W, 400W, 800W, 1600W) and automatically dispatching them to meet the load (some really efficient apartment building water heaters do something similar), or a full hybrid system with batteries big enough that you’d need to run the truck engine for quite a while to charge them up from 50% (running at full alternator “load”)

        1. >”can only throttle down to about 1/3rd or 1/4th power”

          If that was the case, imagine a 250 HP car engine – it would redline on neutral if it wasn’t able to throttle down. Instead, that’s an idiosyncracy of small 2-stroke engines because they need to be running quite fast to keep the thing going.

        2. I live in NYC; boondocking in a skoolie. I have 400 W solar on my roof, a charge controller & just got 4 SLR155 AGM Solar batteries to designate as the battery bank. I need to get an inverter for the system. Still researching that. I’m reading a lot of knowledgeable posts here, and I’m still learning the system. I was thinking of connecting the bus alternator to the battery bank as an alternative charge source when the sun is low (most if NYC winter). any advice or recommendations for where to get a pro help me set it up? I don’t have a microwave, TV or any of that crap. I don’t have a fridge at the moment as it’s bloody cold enough to keep the milk from going bad…but looking into getting a 12V one for summer. I heat with a Lil buddy propane heater, windows cracked…but I’m planning to purchase a EPA cert woodburning stove as soon as poss.

      2. Maybe you just need more altgernators to get it higher up the efficiency curve :-P…

        Though of course you’d also need hefty batts connected with copper 2x4s to handle 1000s of amps at once, even if 10 min did get it fully charged.

      3. A modern engine will idle along quite happily sipping fuel and being better for the environment than anything 2-stroke. I think there was a story either on here or Jalopnik recently comparing emissions from a Ford Raptor to a leaf blower. The leaf blower was worse.

        The real problem is that most car & (consumer) truck engines are not designed with static running in mind.

        They will suffer if left idling for long periods. I used to work with cable jointers who would spend (on shifts) ~2 weeks sat in one place in a Transit van, splicing fibres in the back with the engine idling to keep the lights on. The van sounded like it was about to throw a rod, the guy said it always does that, and a quick thrash up & down the motorway would clear it all out again.

        Land Rover put special instructions in their service books for static running when powering things from the PTO, converting oil change intervals into hours running and such like. They also fitted vastly over-spec cooling systems.

    2. Oh always wondered about HO alternators, are they any more efficient? Just wondering since they’re often in the same size case as regular. … and regular ones are oft quoted being a sucktastic 60% eff or so.

      1. You’d need to store the gas…somehow. Compressing H2 and O2 mix is a guaranteed way of blowing yourself up. Separating them is difficult. Keeping them in bags under low pressure is inefficient and still dangerous…

    3. RV trailer batteries charging through the trailer harness amounts to almost nothing – because due to the wire sizes and the connector involved – it’s limited to about 5-8A. You’d need a trailer connector with jumper cable sized wire running the full length of the tow vehicle then then trough the trailer harness for your tow vehicle’s alternator to provide any useful charging to the battery – not even counting the voltage drop. Keep in mind vehicle alternators have a voltage sense wire going to the vehicle battery to insure alternator output voltage is high enough so that at the vehicle’s battery you’re regulated to ~14.8V charging. There is no such sense wire running back to your trailer – another reason you end up with 5-8A max – too much voltage drop. You could put in a second alternator under the tow vehicle’s hood for the RV with a sense wire back to the trailer battery to remove the voltage drop from the high current line to the RV.

      1. You’re correct about the limited current capacity of a 12V vehicle supplied power through the trailer harness and wiring. The resulting charging capability is effectively limited to around 100 watts due to the wire gauge and fuses. In order to get around this limitation in my own application I’ve considered running a 1000-1500W invertor off the tow vehicle battery/alternator and using the existing trailer wiring to pass 120V AC to the trailer convertor allowing for ~1000 watts of charging capacity. Obviously would require some minor rewiring on the trailer side but nothing substantial (most of the necessary wires are already ran).

    1. I second this – trying to represent a nearly-armored motorhome as “off the grid” or “earth friendly” or just about anything other than what it really is (a large, petrochemically-fueled villians’ lair for invading the peace and quiet of remote areas) is disingenuous at best. I’m sure that a satellite signal will reach the big-screen television just fine no matter the power source.

      1. The fact that it is often used in reference to people trying to live a more eco-friendly lifestyle does not change the definition of the term. “Off the grid” means exactly that, not being connected to the electrical grid. Period. Other than some trains and buses, you’d probably have a hard time finding a moving vehicle that is not off the grid.

        If the vehicle shown was a Prius with solar panels, it wouldn’t make it any more “off the grid” than the beast in the picture.

      2. ” (a large, petrochemically-fueled villians’ lair for invading the peace and quiet of remote areas) ”

        This guy gets it. :-D

        I was calling it a mad scientists truck, classically based on an old ambulance or schoolbus, but you can live in plus act as field ops center for whatever you’re hacking on this week, weather balloons, rocketry, tornado chasing, crypto critter investigation, dark sky astronomy… plus BOV and vacation wheels.

  2. Dammit Jim, I’m a hacker not a bottomless wallet….

    So don’t be afraid to rig your own convertor from old ATX PSUs, some can push quite a few amps, though you may want to hack the sensors, feedback or pot settings to give you more like 13.8 V if you want them to charge the house batts.

    Also investigate what you can do with the guts of an old UPS, might get inverter/convertor in one unit.

    I’m noodling around with kitting out a minivan with removable units. Got a whole windshield full of battery minder type solar panels, not a real lot of watts but gets you long evenings of LED lighting and phone and tablet use. Didn’t pay retail on those of course, they’re probably $20 a watt or something insane. Anyhoo this also gets a bed in the back and a rear, stand under hatch kitchen.

    1. I’d be really interested to see if a UPS could be hacked into a usable inverter for RVs. Even if you can only get say 600 watts out of it, that’s still useful for a ton of people. Might have to tinker with that idea myself…

        1. I have an old 1kW sinewave UPS, but unfortunately it had 24V batteries. And using a conventional 50Hz transformer, it is very heavy.
          But I would not fear, overloading it. The fridge uses 1kW only for 5s to start up. Even a coffeemaker uses the power only some minutes continously.

      1. When using a UPS as an inverter, be mindful of the load capacity of the UPS. It was probably not designed for continuous duty at anything even approaching it’s maximum output. After all, the engineers designing it knew how big the battery would be, and planned accordingly. If you’re not going to get more than 20 minutes of solid use from the battery, making it capable of running for 8 hours would just add unnecessary cost to the item.

        Running it at a reduced output level to overcome that causes it to run much less efficiently, so that may not be a good way to deal with it.

        1. I disagree. 20 minutes is pretty damn close to steady-state in my book. If you want to design something that will fail after an hour – or even eight hours – but still be good to go at 20 minutes, you’re going to have to design pretty carefully. It’s easier to design for continuous than to try to walk that kind of fine line. When you see circuits rated at a certain “peak” and another certain “continuous” output, the “peak” usually means something like “not more than one minute”.

          1. There are e.g. small kitchen appliances like hand-held blender or bread slicer which have often a rating of 2-20mins of continuous operation. But I don’t think you want to draw 1kW or more continuously out of a battery system. Fridge starting or a cup of coffee are short time peaks average draw is much less.

    1. What would be cool and possibly also neat, would be if you could rig your alternator and vehicle AC on a clutch and have them belted together to spin separate, then have a jack shaft you can hook up a foldaway savonius rotor to on a 20ft pole and have the breeze run AC for you.

    2. Some motorized appliances and yard equipment actually use DC motors with a bridge rectifier or simply 4 diodes to convert AC to pulsed DC.

      Which is more efficient? Converting 12VDC to 120VAC or 120VDC?

      1. While the motors are DC, the switches are not. I found this out the hard way one time when I was using a clothes iron as a test load for a 120V battery pack. Worked fine until the thermostat tried to turn the iron off, at which point the contacts turned into a solid lump of copper.
        Switches are designed to break a certain amount of current, and when you’re powering with AC, the current stops 120 times every second, which breaks the arc. With DC, the switch itself has to have a large enough gap when you open it to quench the arc.
        Furthermore, if the tool has a variable speed control, this will almost certainly not work on DC, and may be destroyed if you try.
        So don’t assume that since an AC appliance uses a DC motor, that it will operate on DC.

  3. An emergency 900w generator can be had for less than 100$ these days. Add to this a second alternator to the traction engine to recharge batteries and some solar panels to supplement power. With that said a 7KW lithium battery from a ford c-max or a fusion can be had rather cheaply. ~1000USD used, figuring out a proper charger for such a battery is the issue. Also chopped wave inverters are actually more efficient than pure sine wave inverters to the tune of 5-15% more efficient. I disagree that we should be using golf cart batteries. What we need is a proper charge controller for lithium. If done properly a lithium backed setup can be about the same price as a led acid battery setup and weigh allot less at 1/2 the space consumed.

    1. Yes, $1000 is cheap, compared to other sources for high-capacity Li-ion batteries. However, what I’m looking to improve on is a 100 A*hr (1.2 kW*hr) lead-acid. I’m not trying to run for a week without recharging, and don’t have $1000 to throw around for just one piece of the system. Your solution blows the budget with the first component.

      Also, I’m assuming by “7kW” you mean “7 kW*hr”, which is $143/kW*hr. I can get lead-acid for $73/kW*hr. So yes, in long-term cost Li-ion is probably cheaper due to longer life, it costs almost twice as much in initial cost. Half the space and 1/4 the weight also count for something, but not enough to make up for the initial cost.

  4. So this article starts talking about solar, but then promptly forgets about it and doesn’t even include solar in the system diagram?

    You’ll need a charge controller between the solar panels and the batteries. My favorite model for <500W systems (which I have the most experience with) is the EPSolar Tracer series. They can handle 150V panel strings and down convert them to the 12V or 24V of your battery pack. They're particularly nice because they speak MODBUS so you can mount a remote control head or plug it into a computer to monitor/change settings.

  5. Further to Mr Finnegan’s good comment.

    As a live aboard sailor I’d say the golf batteries and capacity as quoted in the article is vague and underestimated. Call it 200 amp hours a day power budget, you’d need 400 amp hours minimum battery capacity as you will destroy your lead acid batteries if you discharge below 50%. Better 600 amp hours so that’s 6 of them. At a guess that bus has got 500 watts of panels on top which will generate around 150 amp hours a day in a moderate climate /lattitude in summer so your still coming up short. AGM batteries would give both higher discharge levels and faster charge rates with commensurately higher spend on investment but smaller volume and weight to cart around and more discharge/charge cycles.

    If your interested, sailing yacht cruisers have been discussing and experimenting with the comprising configuration for decades. A good primer:

    1. The warnings about discharging lead-acids below 50% don’t hold up to math. One battery manufacturer that actually specified such things, rated their batteries at 100 cycles at full-discharge, or 200 cycles at 50% discharge. The graph was pretty linear from there. In my book, that works out to the same number of total lifetime kw*hr per battery, regardless of the discharge depth.

      1. Hmm, a distinct lack of source citation and some sophomoric math. It’s far from linear.

        Depth of discharge vs lifetime cycles
        Deep-cycle battery
        100%. 150–200 cycles
        50% 400–500 cycles
        30%. 1,000 and more cycles

        So if you want to buy new batteries every 6- 9 months and leave a trail of lead and acid and money in your wake go ahead and crush them regularly.

        Nice graphs here:

        1. Okay, we’ll use YOUR reference. See that scale on the left? It’s LOGARITHMIC. If you were to linearize that scale, you’d see a linear relationship between depth of discharge and number of cycles.

        2. Note in particular, they’re rating their battery at 250 cycles at 100% discharge, and 500 cycles at 50% discharge. At 25% discharge it’s more like 1100 cycles, so it DOES get better if you really, really underrate your capacity, but not by the drastic amount people claim it does.

  6. This article is pure crap, the image diagram doesnt make any sense for an min van guy!
    If you want to have more usable energy, start by consuming less: use gas for cooking instead of microwave, parking heater instead of electric boiler, etc…

    1. Don’t use AGM betteries unless you have a charge controller made specifically for them.

      AGM batteries use exactly the same chemistry as “sloshy” lead-acids. The only time lead-acids give off hydrogen is when they’re over-charged. When you overcharge standard lead-acids, they vent hydrogen, and you eventually have to top them off with water. When you overcharge AGM batteries, they DO produce hydrogen, they simply blow the vent fuse or crack the case, and they have no option for topping off the water.

      Standard lead-acids tolerate over-charge gracefully, AGMs don’t.

    2. Indeed. And if you’ve got the propane fridge you’ll want a CO monitor which will go off when the hydrogen off gassing happens, making the CO monitor much more useful as a discus as you pitch it in the middle of the night.

  7. I have a European camping trailer, complete with propane fridge, stove and heating system (also heating water for the sink and shower) a 12V system and a grid tie if needed.

    There is no safety conserns at all with the propane if it is correctly installed, heck I have lived in it for weeks in the winter (sub freezing temperatures) without grid tie.

    The fridge is triple powered propane/12V and 230V, the heating systen is propane/230V (although the circulation pump for the heating is 12V/230V)

    I am just changing the circulation pump for the heat for the first time, the radiators will heat up without it, but not as fast, and the trailer was built in the 70s to this specification.

    The only thing added since the 70s is the solar panels, the controller and 120Ah of fresh batterys, and I changed the lights to LED’s

    1. I live in Norway my wife and me have a Triple E Empress 1993. We can live in the mountain for almost a week without shorepower. All lights are 12v led, Heating are propane, fridge are propane, waterheater and stove are propane and yes we have the best we can get in alarm NX5 is it called. It take propane , narcosic, smoke, co, and many more. Coffie are made the old way on stove. Of course all the propane equipment are proper installert, with the proper air intakt and outled. The inverter is on only 300w, and thats plenty for our use. For tv and so..For charging cellphones and so I have mounted usb outled 5v. The batteries are 300ah AGM. Thea are charger is a 25a intelligent CeTec in 8 steps who take care of itself. When driving the alternator give food to the batteribank via a dcdc charger so the batteries get 14,4v all the time. On the top a 120w suncell. (This could be the triple)
      When we freecamp we want to live as normal as possible without shorepower.

  8. Mother Earth News and others have run adverts for 12volt everything, it and USB is the only global standard we have. Look at Japan with half and half, two grids! You can cool off with a 12volt heater fan, much more efficient than those cheap window fans with their induction heater-motors. There are 12volt video screens the size of desktop monitors, to use with a 12volt powered ATX supply to run a PC. No I didn’t leave out a zero. Come bar time there are 12volt blenders, smoothies too. Boiling water is a fuel job, make coffee with very hot but not boiling water poured over the original Melita filter cone weather at home or on the road for the best standard way of brewing. On the road truckers have used the exhaust header for foil wrapped cooking, X miles till done.
    So many things are available in the 12volt size that one could live at home with just 12volt power and gas. I have read in said zine about building on this design with downside that to be legal the house had to have a complete 100amp mains system as well even though the owner did not power it.

  9. “Using shore power gets a little more complicated, because it’s easy to create a loop that will run your charge/discharge system constantly. The converter will take mains electricity (120V AC “shore” power), and convert it into 12V DC to charge the batteries and run your 12V electronics. However, if your inverter is connected, it’s going to attempt to turn that right back into 120V AC. Furthermore, if the inverter output isn’t isolated from your shore power circuit, you’re going to create a loop where the inverter then feeds the converter, and the converter feeds the inverter. This is a never-ending loop that will, at best, drain your batteries, and at worst could damage your equipment.”

    I have a big issue with this section regarding “looping” anybody who wires a system that has the potential to introduce such a loop should NOT be attempting to wire anything up and has NO understanding of what they are doing. I’m all for people building their own stuff but please do at least a little bit of reasearch and build things that WILL be safe.
    If your system has the potential for such a loop the possibility of charge confusion will be the least of your problems – you will probably all ready be dead (or have killed somebody else) as you will have mains voltage on the pins of your power plug.

    Dangerous, illegal and just plain stupid.

    1. Of course there have to be disconnect switches or relays. Or a combined inverter charger like in an UPS. This makes most sense, as you need only one transformer (it can work in both directions) and a little more electronics.

  10. My experience with my solar setup (northern Europe not sunny California) is the rule of thumb is 1/10th the rating of the panel is what you’ll get, on average over any given 24 hour period for most of the year.

    Also, a single leaf falling on a single cell of one panel will drag that whole panel’s output down to fckall, and potentially your whole install if it’s not wired sensibly.

    Unfortunately I haven’t had time to write my junk up on my website or I’d whore the link here.

  11. Wow at that kind of return JohnU that almost seems not viable.

    Correct me if I’m wrong but if you had a 3kw system you can expect to get 300wh for the day?

    Here in Australia – in the vicinity of Canberra I get on average 3 x the array power i.e. 3kw system gives around 9kwh per day

    1. I think it is like 300W * 24hrs = 7,2kWh/day. I calculate with a factor of 5, like daily production in summer is like equivalent to 5hrs of peak, this would be 15kWh/day for a 3kW_p system. But probably not if it lies flat on the roof.

  12. What a fancy set up! Spendy too I’ll bet… If you’re ever really interested in this stuff take a look at what the vandwellers are doing. It doesn’t need to cost an arm & a leg to have lights, computer, phone & TV all run off solar in a van you’re traveling in & most it off 12v.

  13. As someone who’s been living mostly off solar power for the last 4 years in my motorhome, I find this article outdated. I converted to LiFePO4 batteries 3 years ago, and was not bleeding edge. Read Technomadia’s or my articles on them. When my propane fridge (which can run inefficiently with electric) dies, it will be replaced with a 12v compressor fridge. (They are optimized for efficiency rather than price.) Where practical, use 12v DC rather than 120v AC to avoid inverter inefficiency. Seasonally migrate rather than spending lots on heating for cooling.

    1. “Seasonally migrate rather than spending lots on heating for cooling.” While this is nice lifestyle, if you can afford it, it underlines the flimsy make-believe of ‘living off the grid.’ Like an infant, the umbilical cord might be cut but the dependency on mother remains total. This is particularly true with RV and other mobile living.

      1. WTF are you talking about? Okay, blarsblarson is probably retired, else he’d not be able to take his own advice. But how does this translate into “the flimsy make-believe of living off the grid”??? Many lifestyles work with seasonal moves – I know a guy who is a housepainter. He can’t work during the rain months here in Oregon, so he spends the other half his year in Thailand, living like a king for less than he possibly could here. Not exactly “off the grid”, but my point is that you are blind to any alternatives beyond the norm.

        I’d rather listen to someone who’s walked the walk, rather than ten people who can only talk the talk.

        1. IF your plan for living off the grid includes seasonal migrations in an RV to manage the costs of heating and cooling, you are depending on infrastructure which itself depends on the grid (and pipelines, and transportation networks, and supply chains) you simply cannot avoid. A Gypsy lifestyle may be far freer than a fixed one, but it is in no way a low-energy way of living.

          1. Not true. Seasonal migration may depend on infrastructure, but far less than living in a permanent house does. The savings in fuel costs from NOT needing heating or air conditioning doesn’t mean you are an island; it just means you don’t waste as much of your hard-earned money as people in fixed houses seem to find acceptable.

            Off-grid doesn’t mean “depends on nobody” – of COURSE everybody who drives anything but a 4WD requires roads, and even they depend on the availability of fuel and other consumables. Who said anything about that?

          2. One way or the other you depend on the grid, defined for the purpose of this argument as the whole energy infrastructure, (although it is still true if we limit it to electric power.) The reality is, at best you are only once removed in an RV when you are not directly connected. As well I’m also fairly certain heating costs of a home above the snowline insulated to R-100 standards uses less fuel to heat in a season than driving 1500 miles south (and back again.)

          3. Sorry, I never agreed to your definition of “the grid” to mean anything that depends on anything that depends on anything that depends on distributed AC power. Your argument is void. And NO, a single drive of even 1500 miles (which I don’t concede anyway) is NOT going to cost more in fuel than the heating for a small house for the whole winter. Do the math.

          4. First you can’t just ignore interdependencies because they do not fit into your ideological notions. Second, indeed one can do the math – I do not think you know what R-100 constrution implies as far as thermal management are concerned in a single-family dwelling.

      2. I never made any “totally off grid” claims, I said “mostly off solar”. I work seasonally, and live on less than what my mortgage payments were before. Some people telecommute from whereever they happen to be.

        1. I know you did not, and indeed one can live a mobile life inexpensively. My remark was aimed at broad claim of living mobile off-grid which was the thrust of the lead post and I was pointing out that migration to reduce heating/cooling costs cannot be reasonably called an off-grid strategy

  14. If you’re attempting large AC loads with an inverter in your RV/boat/whatever, keep the resulting 12V current in mind. For example consider running an 800W 120VAC microwave from an inverter. That inverter is going to draw 70A+ from the 12V battery factoring in the conversion efficiency. Plan on some seriously heavy gauge wire (think #1 or #2 gauge) or the inverter will shut down from voltage drop. Two high capacity 6v golf cart batteries in series can provide that for a while, but a single 12V battery will suffer an early demise under that punishment. If your wife really needs to blow dry her hair and make coffee off the inverter for 15 minutes/day you need to plan accordingly if you like wilderness camping . My setup kept both of us happy for years. It was also fun watching an occasional movie on inverter AC during wash out rainy days with the kids. You’d be surprised how helpful a 60W solar panel is on long sunny summer days.

  15. I have only a small setup for camping with tent and car, basically for running a 12V compressor fridge as I don’t like warm beer and rotten meat or rotten or UHT milk. For cooking the coffee or food I use butane. In no way the system could support electric heating.

  16. Incredible use of solar. I have 3 pieces of 4×6 feet solar panels installed on the roof of my house. During the summer it does store quite a lot of energy that can last for 2 nights. Definitely would love to have this in my RV.

  17. A critical part seems to be overlooked in this discussion, a battery isolator which is used when a vehicle battery and charging system is connected to a second “recreational battery” system. What can happen is the deep cycle battery in the rv gets discharged to its minimal level over the time the rig is parked and engine is off, the main battery used to start the engine will equalize charge with the deep cycle battery and probably result in the starting battery not having enough charge left to start the engine potentially leaving the campers stranded!! It (the isolator) also prevents the discharged deep cycle from the alternator being overloaded when trying to charge the discharged secondary battery at an excessive current and putting the alternator at high risk of failure.
    Also the cost argument is crazy cause nothing about camping in an RV is cheap EVER! and solar systems can be assembled for budget friendly prices with some careful shopping try Harbor freight for panels and consider batteries like Optima deep cycle batteries they are called Dry cell’s and have real impressive specifications and no acid to spill or water to add and handle deep discharges and fast charge rates that would trash any standard lead acid battery fast! And as far as CO and propane in a trailer NUTS use a CO detector, maintain your equipment and remember thousands of rv’s use propane fridges and furnaces every day and CO deaths are a rare thing, not impossible but still an acceptable risk. Solar systems should add to the flexibility and improve the usability of the RV, which any night I don’t have to park in a KOA and pay just cause I need the power to run my RV is a good reason to have the solar as an additional option for power. not having to hear a generator running and burning up fuel all night is another positive that solar can give. that is I want my modern appliances and don’t want to go without heat, warm food and safe storage of my groceries ! Camping may not be “roughing it” exactly but I refuse to “cave man ” it either!!

  18. I recently bought a 1973 Dodge Sportsman motorhome demolished it and built a tiny house on the motor homes frame. However, when I was tearing apart the motorhome, I wasn’t paying attention of how the electrical system hooked up and worked. For 6 months now, I’ve been trying to learn how to rehook it up and what parts go where and what hooks to what. Your article is very nice and helpful however I still don’t quite understand what parts need to be hooked to what! Would you be willing to send me something or a diagram showing me what wires go where and what hooks to what in order to make this system work. Unfortunately I don’t quite understand just from the picture above!
    Please and Thank you

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