How many solar panels

I always thought that any shade on one panel would replicate that shade spot and solar decrease in all panels if strung together.

No Crusier. The cells on a panel are usually wired as two strings of 18 cells. Shading one cell in a string will affect that whole string, but not the other string which is wired in parallel with the affected one. Likewise, other panels wired in parallel will not be affected by their neighbours, apart from possibly a little leakage. The diodes Boobook recommends are to prevent that leakage.

Cheers

John

Cruiser, further to what John is saying, your thought about the shading can occur, particularly when Panels are wired in series. Partial shading can reduce the whole output of several panels. But most solar panels have "bypass" diodes in their terminal block these days when you buy them to prevent this.

Bypass when they are in series, blocking when they are in parallel to stop the leakage.

Thanks heaps guys for your thoughts. I like the idea of having the portable panel, but most of our trips we are usually driving somewhere during the day stopping at night. I'm leaning toward putting the whole four up top. The blocking diodes are now my problem. Some info I've researched supports what Bookbook says while others say that as long as the charge controller has a blocking diode, that will suffice. Apparently the inefficiencies caused by having blocking diodes between the panels is worse than the loss caused by not having them. I'm not so sure, as what Bookbook says makes sense to me. So a little more research into how much loss the blocking diodes can cause as to how much they can save is now on my to do.
Thanks again for your input, much appreciated.

Tomtrish,

Yes many websites will refer to a blocking diode not being necessary when you have a controller, and that they lead to a loss. Both of these are true. However the statement about the controller negating the need for the blocking diode is only in the case where you have one solar panel ( or several in series).

With respect to the losses, if you use a schottkey diode, you will lose about 0.4V, that is about 4 watts per panel or 16 watts in total out of your 300W

Consider that you have 4 panels in parallel and no blocking diodes. If one or two panels are shaded, then they act as a load and consume much of the current from the, working panels. ( just like a single panel draws current from the battery without a controller). A blocking diode in series with each panel stops this reverse current flow. The cost of 16 watts during full sunlight is far less than you could expect with some panels acting as a load, under partial shade conditions, when you can lease afford losses. Also it is possible that the reverse current could damage your shaded panels, ( but unlikely).

If your panels are identical, right next to each other, and will never be shaded then you could get away without them.