Simple System to Charge Batteries

What you need to do is figure out how much energy per day you are using--And plan a system to support that.

More or less, if you are using Flooded cell Lead Acid Battery every day (charge during the day, discharge at night)... Then I would suggest you only use 1/4 of the stored energy in the battery (more or less, there is not enough hours of sun in a day to recharge an FLA battery from 50% to > 90% state of charge in one day--Typically it takes 2 days "worth of time on charge" to fully recharge.

Another rule of thumb is I would suggest for 10%-13% (or so) rate of charge for full time off grid batteries that are used every day.

So... Just some numbers to start with... Say your van has an 80 AH @ 12 volt battery (probably not a deep cycle battery--So discharging to 85% or 75% State of Charge is about the maximum amount you want to do anyway... Discharging a standard car battery to 50% state of charge (or lower), it will probably last a few months to a year in typical use.

So, if you are just charging 1x "van battery" every day (discharge to 75% SoC)--The calculations would look like:

• 12 volts * 80 AH * 0.25 discharge (to 75% SoC) = 240 Watt*Hours per day
• 80 AH * 0.25 discharge = 20 AH per day of usage

Assuming a fixed array in Omaha Nebraska, facing south:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Omaha
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 49° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.35	3.66	4.41	4.72	5.05	5.44
Jul	Aug	Sep	Oct	Nov	Dec
5.56	5.34	5.20	4.45	3.40	3.09

Lets say you want to (on average) use this system though December:

• 240 WH per day * 1/0.52 off grid system eff * 1/3.09 hours of sun per day = 150 Watt solar panel/array minimum

For a small system (single battery), a 150 Watt panel + PWM (inexpensive) solar charge controller could work OK--During winter, you would need to run a small genset or your van to make up for bad weather.

If you were going to use a larger battery (or charge multiple batteries), then a larger array (200 Watt or more), you may want to look at larger solar panels (>200 Watts) that have Vmp~30 volts or higher and an MPPT charge controller (cheaper panels, more expensive MPPT charge controllers).

Some other suggestions:

1. alligator clamps do not work well for charging/heavy DC loads (higher currents). Using connections with bolts/nuts/wingnuts or actual DC connectors is much more reliable.
2. If you are disconnecting and moving batteries around, you want to disconnect the solar panel first, then the solar charge controller (switches, breakers, etc.). And when reconnecting, connect the battery first and the solar panels second--Doing it backwards, it is possible to "confuse" the solar charge controller or even (possibly) damage the charge controller.

https://www.amazon.com/s?k=battery+terminals&ref=nb_sb_noss (an example of many types of battery terminals)
https://www.amazon.com/UTSAUTO-Thickened-Terminal-Positive-Connectors/dp/B0787NPBFN (an example of wingnuts+battery terminals)

Without knowing more about your batteries, plans for use (1x battery runs a week between charging, or you recharge it daily, etc.) and how many batteries and their AH capacity, and other details, it is sort of difficult to give you a detailed answer.

-Bill