For my camper vanelectric conversion, I wanted to have an entirely solar off-grid solution. To live for days or weeks in the woods, I could not rely upon shore power. But I’d never wired anything before, and knew nothing about batteries or power consumption.
Solar Off-Grid Electricity Needs
Electricity needs will differ wildly from person to person. I know some vandwellers who have nothing more than a portable solar battery for charging their cell-phone. I am a computer programmer by trade, and part of my goal was to be able to work from anywhere without concern for power. Though I splurged extensively on the electrical system, it’s something that can cost as much or as little as you want.
The first thing I did was to consider which devices I would be running, and how often:
I’ve intentionally over-estimated much of these needs, because the goal is to get an upper bound of my usage. Next, I considered how I’d use the van. My goal, I decided, was to be able to go on a 4-day weekend trip and not worry if there was no sunshine to power the solar panels.
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If you’re comfortable with volts, amps, and watts you can skip this section. If you’re a novice to electrical engineering, “watts” are probably the easiest unit to understand. A watt is the measurement of the amount of power consumed… in effect, your “fuel.” Sometimes we speak in terms of watt-hours (Wh), or “how many watts were consumed in an hour.”
As a simple example, the iStatMenus application on my MacBook Pro currently tells me that the power adapter is providing about 50 watts. Assuming consistent usage, this implies 50 Wh, or 50 watts consumed per hour.
Where things get confusing for novices is that many devices and batteries will provide their specifications in terms of volts and amps instead of watts. You can simply multiply volts by amps to calculate watts, though. For example, if you take a look at most wall-outlet chargers, you’ll find the volt and amp rating on the back. A USB 3.0 port might say that it’s rated for 5V and 2A, which tells us that it’s maximum is 10 watts (5V * 2A). The actual consumption will based upon the needs of the device. If your laptop is out of battery and you plug it in, it may approach the maximum while it charges. But if it’s fully charged and hibernating, it might only use a few watts. If you’re curious, this is because the power source (battery) will still provide roughly the same number of volts (5 in our example), but the device itself will “request” fewer amps from the circuit.
To really wrap your head around all this, and estimate your own needs, I highly recommend buying something like the Kill-A-Watt. This simple device sits between the outlet and your device to monitor everything on your behalf. I bought one during my initial planning and enjoyed testing devices around the house to understand how it all fit together.
Finally, a note about AC/DC (alternating current and direct current). A battery provides DC, but home outlets are all AC. Without getting into the history and reasoning for this, it is important to know that converting the output of the battery from DC to AC will require an inverter and will cause you to lose somewhere around 20% of your electricity in the conversion process. In the end, I actually managed to wire the entire van using DC (even the computer), though I keep and inverter around for those rare cases I need to plug a standard appliance in.
A high-capacity alternator, to produce more electricity while driving.
An inverter, giving me a standard AC plug next to the driver’s seat.
Upfitter switches, allowing me to connect the van’s batteries to other things.
Still, there are many reasons not to use the in-car battery for vanlife living, the most obvious of which being the risk of draining it and preventing the car from starting. Another is that car batteries are charged by the alternator, meaning it requires burning gasoline to charge. Personally, even two car batteries would not be enough for my stated needs. The car-system instead provides something important for me: a secondary way to charge my living-system.
I ended up wiring the upfitter switches from the van into my living-system’s battery. This means I can just flip some switches on the dashboard while driving and it will recharge the battery, if need be.
Choosing a Battery
As I mentioned, the goal was to go for a 4-day weekend without fear of losing power. I put the upper-bound of my consumption around 2,000 watts per day (2 kW), though in reality this was a pretty big overestimate (it’s been closer to 1 kW at the most). So I decided to buy a ~8 kW battery. I bought my battery from Lithionics, a custom-made battery company specializing in just this sort of application. They are pricey, but very high quality. Their lithium-ion batteries (unlike lead-acid batteries in cars) are safer, lighter weight, last longer, and charge faster. They also have built-in circuit called a battery-management system which protects the battery and maximizes life. Here’s the massive, ~120lbs battery placed in the van:
Understanding Solar Off the Grid
Next, I had to consider how I’d charge the battery. Again, because electricity was my big splurge, I fit as many solar panels on the roof as I could. I ended up with 3x 170W panels, for a maximum potential of 510W.
The reality is that solar panels will practically never reach their theoretical potential. I’ll get into the specifics of how charging and wiring works in a subsequent post, but for now I’ll just mention that the panels realistically provide about 50-75% of their rated value for 6 hours per day. If I make sure to park in the sun, and conditions are reasonable, I can replenish about 2 kW per day. Given that my actual daily usage is somewhere between 1/2 and 1/4 of that, and that even poor conditions will yield some charge, it means that I need to explicitly recharge roughly 1 day for every 3 I am in sub-optimal conditions (i.e., parked in the redwoods underneath a dense canopy). I can go about 7 days without recharging the battery, but then it’d take a few days to fully recharge.
Part List / Costs
Let me say once more: I splurged on electrical. Keeping that in mind, here’s a rough sketch of the major electronic parts (battery and solar components, skipping details like wiring for now):
Overall, I budgeted about $10,000 for my electrical system, once you factor in the wiring and smaller parts (switches, outlets, etc.)
This post is just a sketch of how I thought about the electricity problem. In the next post, I’ll look at the reality of how my system came together. I’ll share exactly how I safely mounted the solar panels, chose the remaining parts, wired up a complex circuit, cut down my power usage even further, and ultimately figured out how to run the whole thing on DC (even the computer). In the mean time, check out the rest of the build posts here.
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