mauried:
Solar panels are really only good for directly charging batteries where the solar panel voltage is higher than the battery voltage thats being charged.
Solar panels dont work well with switching converters especially in low light, as switching converters need something that approaches a voltage source when they start, and solar panels dont behave like this.
What usually happens is that as the solar panel voltage rises as the light intensity rises, eventually the switching converter will try and start and will try and draw current from the panel , which cant deliver enough so the panel voltage collapses, and the switching converter then goes into an unstable state where it may sit there drawing current but not switching, ie it wont start.
The simplest solution is usually the best, ie use the solar panels to directly charge a battery via a blocking diode, and then run everything else off that battery.
Thanks. A thought occurred to me based on this. Would it be possible to design a circuit that would basically have three states:
One, if the power put out by the panel fell below a certain threshold, say at night, the time from just before to just after sunrise and sunset, and during heavy cloud cover, it would basically shut off, except the part that monitored the current light level, which would use minimal current drawn from the battery otherwise being charged, and of course block the panel from drawing on the battery.
Two, if the power was above another, higher threshold, when there was direct sunlight hitting the panel, the circuit directed the output to the battery, either directly or via some charging circuitry.
And three, if the power was between these two states, such as during light cloud cover, or in the hour or so after sunrise and before sunset (beyond the few minutes after sunrise or before sunset), it would also charge the battery, via charging circuitry, but initially draw upon it to sort of "prime the pump" to get the charging circuitry started, sort of like how a car starts up, drawing on its battery before charging it.
Did I just describe how an MPPT circuit works? I mean, surely it's possible to design a circuit that could take advantage of those times when some solar energy was available, but far from maximal, and also prevent the panel and circuit from draining the battery when there was basically no usable solar energy available.