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.
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
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.
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.
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.
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 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).
There are three ways to charge the batteries on this system:
- With the solar panels, which will always be happening passively when there is enough sunlight to generate some current.
- From your vehicle’s alternator, which you only want happening when the vehicle is actually running (to avoid draining your car battery).
- 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]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.
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!