Chris Green wrote:
For charging a 12 volt (or maybe 24v or 36v) battery look for an MPPT
charger to run from the solar panel[s]. This maximises the output from
the solar panels by optimising the load it applies and also makes the
conversion down from the (approx.) 30 volts to what's needed to charge
a 12v battery as efficient as possible.

What kind of solar are we talking about? A small panel, or a roof array?

For a small panel a MPPT can be used to charge a 12V battery (for example
lead acid) so you have a constant supply, and then you can run regular 12V
accessories off it - for example many AA battery chargers come with a 12V
power brick.

You can also get MPPTs that directly charge lithium ion, but it seems NiMH
isn't a common output.

You may be able to run a 12V NiMH charger directly from the MPPT without a
lead acid buffer, but the NiMH charger probably won't like it's power coming
and going (it'll forget how much charge it's just put in for example).

Search ebay for 'MPPT' for some examples (noting that you might not want to
order the ones shipping from China at this point)

Theo