Words of Wisdom: I'm not sure people always grasp the concept of “minimum” either; they tend to think it means “all that you really need” when it fact it means “the least you can get away with provided everything else goes right”. After all, the sun does not shine brightly every day. – Cariboocoot1)
[Note: a gentle introduction to solar is also available]
Solar (photovoltaic or PV) power is an excellent fit for 'dwellers and especially for boondockers. It is silent, nearly maintenance-free, and requires no infrastructure or grid. Downsides include expense, bulky panels, and the requirement for access to direct/unshaded sunlight.
Broadly speaking, solar power systems consist of panels to collect energy, house batteries to store energy, and charge controllers to regulate how those batteries get/stay charged.
Under normal use solar setups charge fully during the daytime and discharge at night; the lowest State of Charge will likely be just before sunrise. On a properly-sized deep cycle system the bank will have used no more than 50% of its capacity at this point. Then the sun comes up and charging begins again. 'Dwellers running small solar setups (or experiencing poor insolation or heavy loads) may have to ration their use of solar power.
The most difficult part of a solar power system (other than paying for it!) is sizing it correctly for your needs.
Maybe not. If any of these conditions are met you probably don't need solar:
When you use power from your system can be as important as how much power you use.
There are times (bulk, early absorption) when the system is struggling to charge the lead-chemistry bank; loads should be minimized during these periods.
At other times like late absorption and float the system will have surplus capacity that can be used to run loads.
Solar sizing has been moved to its own page.
Most house banks and accessories are nominal 12v.
Reasons to go 12v:
Reasons to go 24v (or higher):
Weather and shading have serious effects on solar output.
Cloud cover can have paradoxical effects:
Rainy weather causes a drop in current due to the cloud cover effect. An upside is it can wash dust off panels.
Dusty or snowy weather can cause a loss of output due to physical presence on the panels.
Panels yield the most power in cold temperatures. Since panels are dark and get very hot in the sun they are generally raised rather than directly mounted; this allows air circulation/cooling underneath.
[based on this reddit post]
There are a few issues to consider:
hot panels re-radiate heat onto the roof of the van. “On my white van (even with a 5” airgap) it is hotter in the shade under the panels than on the roof in direct sunlight.“ - secessus
Mounting hard panels to a rack increases airflow (thereby reducing heat-related power losses), reduces heat transfer, and minimizes the number of holes in the van roof.
Mounting hard panels directly to the roof still allows some airgap (the depth of the frame) and the roof corrugations will allow some airflow in the direction of the “valleys”. Taller Z-brackets may give a bit more airgap.
Mounting flex panels to the roof allows some airflow in the corrugations but no airgap. Good news: panel derating won't be so bad because the heat is conducted to your van roof. Which is bad news if it's already hot in your van.
Portable panels allow the vehicle to be in shade and panels in the sun. Also can be tilted for maximal yield.
Opinion: Bonus rant on panel/controller selection.