Most people think that solar panels need charge controllers for "£££" but most of the time you dont if you use DC to DC. All you need is a Buck Converter.

( famous last words)
You need a fuse, in and output sides, a diode to stop reverse charge and a buck converter that  will take the panels voltage and current (watts) and work within the range of the power and also your output.

A buck converter works buy lowering the voltage in doing so raise the current. a boost does the opposite.

lets say you bought a 250w solar panel for £30, its VOC is around 38 and the MPP is around 32.
the current about 8.33 amps

we want to charge a 12v battery.
we cannot do this with a £4 eBay special, as they just don't work. but with the buck we can 🙂

you need to set the voltage for the output and you can also adjust the current ( CV CC buck converters)

Nature well physics work in lowering the panels voltage while keeping the current high, in fact panels tend to make current from sun light and how bright it is the higher the current. as you have a set output voltage, the panel will set itself to the higher voltage and  sit there, The current will change up to your set points.

if you have 32v and 6amps from solar, (192watts) when you buck down, to say 13.6v,  your output current will be around 14.2 amps.

The other things that you will want is a power meter to see how much power you're making from solar and is charging the battery.

WE do make kits and items as well as ready made solutions to get you going, if you want a fully, part, plug and play or all bells and whistles we have you covered.