shade-tolerant collectors?

Welcome to forum Bernard.

In general, solar electric panels do not like shading. As you have seen/read, any shading can easily stop a panel from generating any useful amount of power.

The best answer, is to install panels with no or a minimum of shading. Especially between ~9am and 3pm when you have the strongest sun.

For basic shading issues... Years ago we had one person here that mounted all is panels in "landscape" (on their "sides") in the same orientation. For his panels, the two parallel cells strings ran lengthwise down the panel. When he would get sticky snow, it would only cover the bottom string of cells, and his array would still provide 1/2 current until the rest of the snow melted.

There are two major types of charge controllers. The simpiler PWM type (pulse width modulation) controller (less expensive).

These controllers the solar array Vmp voltage needs to be matched to the battery bank. If you have a 12 volt battery bank, then (typically) you would need 1x Vmp~18 volt panel string, then put multiple panels in parallel. If one panel was shaded, the other panels would produce full power. The bypass diodes are mostly irrelevant in this configuration.

Another type of charge controller is the MPPT type (maximum power point tracking). You could put the same 1x panel Vmp~18 volt in series, then parallel them--And get the same result as the PWM controller.

Or you can put, for example, 4x 18 Volt Vmp panels in series with a 12-48 volt battery bank. If one cell/panel gets blocked, then that cell/panel goes "high resistance" (no current wants to flow through a "dark cell"). Obviously, we need current to flow through a dark panel to get current/energy from the other series panels (plus, too high of voltage can ruin the non-conducting cell). So bypass diodes around a "group" of cells will let the current go "around" the dark cells--Generally, (if I recall correctly), there are 2 to 3 bypass diodes per group of cells (roughly 9-10 volt maximum drop or so).

So, even with a bypass diode, you still lose a lot of voltage becasue of the dark cell(s). Power = Voltage * Current -- so if you drop 1/3 to 1/2 of the panel voltage, then you drop (roughly) 1/3 to 1/2 of the power from that panel/string.

And if you have several strings in parallel--Then the "low voltage"/"dark" string may drop out from producing any useful current at all in the presence of the other strings that are not shaded.

Which is better with shading problems, MPPT or PWM? It is usually not that simple. Usually PWM controllers are used on smaller solar arrays/systems and MPPT are used on larger systems. Rarely, do we get to make a choice on best output.

For Grid Tied systems (not off grid), there are "micro inverter" type systems--These put one AC inverter per solar panel--So, that a shaded panel only affects its own output. Central inverters have the same issues as large MPPT controllers. A single shaded panel can take out an entire "string" of solar panels until the shade "goes away".

-Bill