Pls excuse the snip.Originally Posted by pollenface
That is what the "blocking diode" is for, to prevent reverse current flow when the sun isn't shining.
Also, a PWM Reg will reduce the effective rating of the panel by about 1/4 to a 1/3rd.
Panel direct to battery is very common in many standby applications.
For example there are no regs on all of the small maintenance charging panels you see for vehicles that you sit on the dash and plug into the ciggy lighter
It is also why most Panels under 20 watts come with alligator clips and not MC style solar connectors.
The battery voltage on my boat sits at approx 12.8 off charge and rises to 12.9 when the panel is in full sun.
Effectively the battery is appearing as a huge capacitive load to the panel and in practical use the system will perform better than a PWM reg system with the non-regulated panel output running close the the max power knee of the performance curve IE max current output so almost like it has an invisible MPPT Reg.
BUT... the Panel output has to be such that the load of the fully charged battery still draws a current flow so as long as you don't put too large a panel in place and the panel has a blocking diode it should have no noticeable adverse effect to the battery life.
I do, however, totally agree that a panel without a blocking diode won't work as desired and once you get up in solar panel power to battery capacity past a certain point you have to use a Reg.
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