Solar chargers - any good?

[markharf]

There are good ones for cars--I carry mine wherever I go, charge it a couple of times a year, use it about the same number of times, never lets me down. There are also cheap ones for cars.

There are good ones for phones, tablets and laptops. I've started carrying one to charge my ancient iPhone now that its battery is almost kaput. Holds a charge for months of inactivity, lightweight and compact, will charge a solid state tablet or laptop with ease.

There MUST be good ones for motorcycles (sez I). But they won't be cheap: why would they be?

Mark