Yes, by a small amount, unless you live in the arctic circle or something.
But does that mean they’re worth it? Probably not. There’s the financial cost as well as the weight. Plus potentially eating into head room. Plus it’s another thing to potentially go wrong.
I certainly see the use case for campervans - a large flat roof is ideal, and being able to park for a couple of days and charge a leisure battery without flattening your main battery or running an engine seems perfect.
But for a passenger car, the use seems more limited.