This is an old revision of the document!
Note: this information should be regarded as experimental. It is being tested by secessus.
This article describes a small, simple, space-efficient, and inexpensive solar configuration that may be of use to cardwellers or minimalist vandwellers.
Most of the RV world is familiar with deep-cycle 12v systems; these are intended to store power for use overnight. If most power is only needed in the daytime then deep-cycle batteries are not required.
Instead of deep-cycling, the starter battery is non-cycled1) as described below. It can also be shallow-cycled.2)
Non-cycling is the use of solar power only when the battery is fully charged.
The LVR is the point at which the controller turns the LOADs back on. If running small loads (charging phones, LED lights) the setpoint may be set fairly low (like 13.0v). This will allow loads to be run as soon as possible.
If running larger loads (fans, laptop chargers) the setpoint should be set higher (like 13.5v - 14.0v). This is because the panel will be able to make more power closer to Vmp. Consider the popular Renogy 100w panel that puts out about 5.29A. At the lower LVR the panel3) will make 68.77W. At the higher LVRs the panel will make 71.42-74.06W
Note: running a small MPPT charge controller would make this immaterial, as the controller would run the panel at max power (Vmp) at 18.9v.
Shallow-cycling is a more aggressive approach, allowing for a bit of power after sundown. It is most suitable for starter batteries with removable cell caps.
The charging setpoint is set somewhat higher, ~14.4v. This will result in minor outgassing and a bit more power (76.18W using the panel data above). Battery watering is mandatory.
Starter batteries are designed for about 15% depth of discharge4). We can set the Low Voltage Disconnect to 12.5-12.6v as a floor. In a typical starter battery this could be 5Ah of power usable at night, enough to run an LED light for hours as well as run a small fan all night. All device charging should happen in daylight when power is relatively plentiful.
No-cyling never discharges the battery below 100% state of charge. Looked at another way, no-cycling keeps your starter battery charged all the time.
Because of this, no reduction in the ~36 month average longevity5) is expected.