Updated on May 25th, 2025

We’ve been a part of several van build forums and Facebook groups for the last few years, and one thing has become abundantly clear. Building an off-grid electrical system is where most people struggle with their DIY van builds.

In this post, we will start by explaining the basics of setting up an off-grid electrical system. Then, in the second part, we will walk you through our system and the decisions we made for our Promaster campervan build.

In the interest of transparency, please be aware that the following may contain affiliate links and any purchases made through such links may result in a small commission for us at no cost to you.   We appreciate you shopping from these links!

The Three Parts of an Off-Grid System

An off-grid system will consist of three separate parts:

1. A storage system, i.e. batteries, where you can collect power and use it when you need it.
2. An input system: how you’ll get power into your storage system.
3. An output system: how you will use all that power you’ve stored up!

Storage System

The storage system is batteries. Batteries are the heart of your system and allow you to have electricity when the sun is down, or the engine is off.

Sizing a Battery Bank

To know how to size your battery bank, and many other components of your system, you’ll need to do a little legwork to figure out how much power you will be using. When you live in a house or apartment, it’s easy to forget about some of the power draws since electricity is just a flip of a switch. But when you start having to create and store your own power, it becomes a lot more important to think about things like, how much power does it take to charge my phone overnight?

There are several online calculators to help you figure out your usage, but many of them will calculate your monthly or yearly usage. We recommend figuring out your daily usage. Jackery, a portable power station company, has a great article that breaks down in depth how to calculate your 24-hour usage.

We also recommend using a electricity usage monitor, to see what your average daily usage is on items like laptops, cellphones, and small appliances while you are still in your house or current living situation. An average daily usage over a week or so is a great number to use for those items. We were surprised when we used one prior to moving on to the boat in 2020. Andy’s laptop used a lot more power than the “average” laptop estimates online. We found it super helpful in coming up with our numbers.

12 Volt vs 24 Volt Batteries

Off-grid electrical batteries, no matter their chemistry, come in several voltages. The most common are 12, 24 and 48 volt. We are not going to go into 48-volt here, as those are typically used in much larger systems than you would need in a van or boat.

12-volt is the native voltage for many items you’ll install in your van, like water pumps, LED lights, fans, etc. This is the main advantage of 12-volt batteries because you will not need any additional items like step-down transformers to run these crucial pieces of your system.

The advantage of 24-volt is the higher voltage so you can use smaller (and less expensive) wires. Also, many of the higher power inverters (like those larger than 3000W) are 24-volt.

There isn’t really a difference in cost, weight, or footprint between 12-volt and 24-volt when you break it down to per usable Watt-Hour.

Types of Batteries

Two major battery types are used in off-grid systems: Lead Acid and Lithium.

Lead Acid

Lead comes in several formats: flooded, AGM, and sealed lead acid. For the purposes of most van builds you would most likely want to use AGM or sealed if you decide to go the lead acid route. Flooded lead acid batteries vent hydrogen gas and require a good deal of secondary work to make them safe in confined living spaces.

The only real pro of Lead Acid over Lithium is that they are significantly less expensive upfront than Lithium. However, this gap is closing every day.

Lithium Iron Phosphate

For the purposes of this article we will only be talking about the LiFePo4 batteries. Other Lithium options are more expensive and have safety concerns when used for this purpose, so we cannot recommend their usage.

LiFePo4 batteries are lighter, smaller, and have much longer service life than lead-acid batteries. They also are able to be discharged significantly lower without harming the batteries. Lead Acid should only be discharged to around 50-60%, while LiFePo4 batteries can be discharged to pretty much 0% without issue.

As an example if you were to put a 100A-Hr AGM next to a 100A-Hr LiFePo4 battery, the AGM would be larger, heavier, and would have about 50A-Hr of usable power, while the LiFePo4 battery would be smaller, lighter, and have about 95A-Hr of usable power.

If you can swing the upfront cost, we highly recommend going with Lithium Iron Phosphate over lead acid.

Output System

Output is the fun part of electrical. It’s how you are going to use the electricity that you have produced and then stored. Most builds will have both an AC and DC output, but we know a few people who have gone DC only but it can make life a challenge!

DC Output System

DC or direct current is the 12 or 24 v system that comes directly from your batteries. In most vans or RVs fans, lights, refrigerators, cigarette style chargers and water pumps usually run off the DC system and in some cases air conditioners can also run off DC power.

In its simplest set-up, DC will run from the batteries to a fuse box, and from the fuse box to the items it powers.

AC Output System

AC or Alternating Current is the 110V part of your system. Alternating current is used by most standard household appliances, computers, some air conditioners. Think anything that has a standard two or three-pronged plug.

In order to take the DC power being put out by your batteries, you need to convert it into AC power through an Inverter.

Inverters come in a variety of sizes but the most common in vans are 1500, 2000, or 3000 watt. This is another place where it’s a good idea to estimate your usage BEFORE you purchase your inverter.

Planning a fully electric galley? You’ll probably need something 2000w or larger. Need to just charge your laptop occassionally? You might be able to get away with something smaller. It’s pretty easy to figure out. Just take a peak at the owners manual for your electric appliances and you’ll need to size based on the maximum watts they draw.

Input System

Now that we’ve talked about all the fun ways we are going to use the electricity we are storing in our batteries, we have to talk about how to get the power into the batteries or input.

There are four major ways to input power to your batteries.

Solar

Solar is the most preferred option for off-grid electrical systems. It is silent and able to create power both on the move and while stationary. The only downsides are, that it requires a lot of space, mainly on the roof, and that if you have a few cloudy or shaded days in a row you likely will not keep up with your usage.

Solar requires a few pieces of equipment:

• Solar Panels–The arrays that harness the sun to make power.
• Solar Charge Controllers–Take the power coming in from the panels and safely put that power into the batteries.

Engine Charging

Engine charging uses an alternator to use your vans engine to create power that can be stored in batteries. There are two main ways to accomplish this:

1. Second Designated Alternator: This requires attaching a second alternator to your engine that creates power only for your house batteries in the van. It requires a mount and the additional cost of a second alternator/ regulator.
2. Battery to Battery Charging: This uses the van’s existing alternator and diverts some of the power going to the van battery to the house battery bank. This requires a battery to battery charger.

In most of our off-grid electrical setups, we’ve gone with the battery-to-battery charging option. In our current van we would have explored the second alternator if the Promaster had the mount for a second alternator, but it does not.

Shore Power

Shore power is essentially plugging into the grid temporarily. It is used in campgrounds or while mouchdocking at friends or family. It requires access to a power source outside of the van, so technically its not “off-grid” but having multiple ways to charge is so important that we are including it here.

When you plug into shore power, you’ll need a battery charger that will convert the 120v coming from a house or campground to 12v/24v to be stored in the batteries. In some cases, it can be used directly by your 120v system, depending on your setup.

Shore power requires an input plug and a battery charger.

Generators

Generators are like shore power’s loud and smelly cousin. It requires all the same pieces as shore power would. Instead of plugging into the power grid at a campground or house, you plug into the generator, which uses gasoline or diesel to create the power. Generators can be both portable or built-in, but regardless even after the cost of installing the system you’ll still be paying fuel to run it.

It’s also important to note that many campgrounds have limitations on generators, and when out boondocking most of your neighbors will be hoping you only use your generator sparingly.

Our Promaster Van Electrical System Components

Below are the components that we have used in our Promaster build. You may notice a theme that most of the components are from Victron. We have used other options in the past with mixed but mostly awful results. We would recommend any of the products below after years of using them in all four of our off-grid set-ups. If you are looking to save money on your build, buying cheap components is not where to do it. We would recommend doing a smaller battery bank, a smaller invertor, or smaller solar array over choosing most of the non-victron parts.

To maintain our running budget for these posts, the prices below are what we paid in April/May 2024.

Previous Costs: 17,481.51

• 3 300A-Hr Epoch 12v Batteries $0–We will be sharing these batteries with the boat so we did not include them in our budget.
• 2 100A-hr WattCycle 12v Batteries $309.89–These will be the backup for the boat or van.
• Victron 2000VA Inverter $978
• 3 250watt Rich Solar Panels $615.57
• Victron 100v 50amp Solar Charge Controller: $184.00
• Victron 12/12 50A Battery to Battery Charger $328.10
• Victron Battery Monitor $159
• Bluesea Systems Battery Switch $42.48
• Misc Wire and Plugs and Fuses: $482.74

New Costs: $3099.78

TOTAL RUNNING COST: $20,581.29

Check out our other Van Build Posts here!