I know large solar panels generate more energy than is needed to manufacture them, but what about small portable solar chargers for mobile phone or radio? I've read somewhere that their efficiency is much lower than that of the large panels. Wouldn't you be better off just using 'traditional' rechargable batteries?
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It's quite a hard question to answer objectively, because you don't know how much these panels will be used. They may be left out in bright sunshine all day in which case they will likely generate more energy than was used to manufacture them over their lifespan, or they may stay locked in a cupboard on all but a couple of days a year. Their efficiency will depend much more on the construction technique and technology used as well, so it's hard to give a certain objective answer here.
However, the advantage with these panels is less about the energy you can make back, and much more about the convenience of harvesting power without batteries in the wilderness, or trickle charging without having to change rechargeable batteries. Up to a certain point, yes you may well be better using rechargeable batteries - but what happens after that? If I'm on a journey through wilderness for a few weeks in a hot climate, does it make more sense to take a few ten's of AAs with me, or a simple solar panel and a bunch of connectors?
These sorts of panels may well not make their energy consumption back over the course of their lifetime, but you could postulate a sensible argument that that's not their aim. Their aim is to provide a convenient source of continuous power in sunlight when few other sources are available.
