How to design a simple yet powerful electrical system for your van or skoolie.
The system outlined is centered around one 200Ah AGM battery which can be charged by solar, DC-DC, or shore power. Any of these components can easily be swapped depending on your budget and power requirements.
Electrical parts list
Step 1: Batteries & Daily Usage
Deciding how many amp hours (Ah) your house battery needs is step one in van electrical system design. Ah is the amount of energy charge in a battery that will flow (power your electrical components) for one hour. List all of the 12 volt electrical components you plan on using daily along with time, setting, and current draw. The current draw measured in amps should be listed in the part specifications. A separate list for 120v daily usage will also need to be made. Then multiple current draw, setting when applicable, and time (in hours) to calculate expected daily power usage for that electrical component. A few assumptions will have to be made to complete the list, for example, the compressor on your fridge will run more in the summer then then winter or which fan setting you will use most often.
12 Volt DC Daily Usage Table
It's important to understand that different battery types (lithium, AGM, and flooded) allow for different usable amounts of the listed Ah. In short, you can expect over 80% usable Ah from lithium while AGM and flooded are closer to 50%. It might seem like lithium is the obvious choice but the high cost is something that needs to be taken into consideration. I chose a Renogy 200ah battery because of the price point, AGM's are sealed (no venting of harmful battery fumes), and have longer life span then flooded. If you decide you want to upgrade from AGM to lithium down the road, it would be an easy swap.
Now you need to factor in how many days you plan on staying in one spot and what type of battery you selected.
3 days camping (not moving) * daily power usage / battery type 0.5 (AGM)
(3days*50dailypower)/0.5AGM = 300Ah
Before you purchase the battery bank or become overwhelmed by the potential cost and size, factoring in items like DC-DC charging and shore power can cut the house battery size down by 1/3 and in some cases up to a 1/2. Factoring in the Renogy 60 amp DC-DC charger and shore power, I opted for downsizing the house battery by 1/3.
Battery selection: Renogy 200 Ah AGM
(Factoring in AGM's approximate 50% usable Ah rating)
Step 2: Solar
Considerations when selecting solar panels.
Daily power usage
Expected sun for your area
I calculated my daily power usage to be between 50 and 70 amps. Then plugged my daily power usage into a solar panel calculation (outlined below) suggesting I should use 300 watts of solar.
Now that you know your expected daily power usage, you need to factor in peak sun hours for the area that you'll be spending the most time. Peak sun hours are when sunlight in a specific area reaches an average of 1000 watts per square meter, this is considered ideal solar charging conditions. Because I knew I would be traveling all across the United States, I factored in 4.61 of peak sun hours per day. 4.61 hours is listed as middle of the ranking in states vs peak sun hours. Turbine Generator made an easy reference table from collected data that ranks states vs peak sun hours.
One Renogy 100 watt solar panel can produce 5,5 amps per hour under ideal conditions. Because I installed three 100 watt panels and factored in 4.61 peak sun hours I can expect 76 amps of charge during ideal conditions.
5.5 amps * 4.61 = 25.35 amp per one panel under ideal conditions
25.35 * 3 solar panels = 76 amps
Before you order your solar panels measure the area on your roof to determine if they will fit. It's important to remember the charging capability of your solar panels can vary depending on weather, shade, season, and location. The calculation is an approximation for gauging your solar needs.
Step 3: Inverter
Size your inverter from the 120v AC daily usage table made in step 1. Having more electrical components run on 12v DC the better, as it takes a noticeable amount of power just to turn the inverter on.
120 Volt AC Daily Usage Table
I chose a 1000w inverter from Renogy. This will give me room to charge battery powered tools or run other miscellaneous 120 AC electrical components.
Step 4: DC-DC Charger
There are two considerations to keep in mind when sizing the DC-DC, also know B2B and alternator charging.
Maximum recommended charge current for the house battery
Renogy specifics a max charge current of 60 amps for their 200 Ah AGM battery. The alternator in the skoolie can output 145 amps. Knowing the skoolie draws between 50 and 80 amps under normal driving conditions, I'm comfortable selecting the Renogy 60 amp DC-DC.
Step 5: Shore Power
I consider shore power to be a bonus option for the electrical system. The goal is to size the house battery, solar, and DC-DC to match your off grid needs. If your budget allows for shore power, it offers a nice backup plan.
AGM batteries should charge at 20% of the rated capacity when using shore power.
200 Ah * 0.2 = 40 amps charger is the maximum recommended size.
I chose a 30 amp Samlex charger