A solar panel does not power anything directly. It refills the battery that does, and the useful question is never “how many watts is the panel” but “how many watt-hours a day will it actually put back”.
Those are very different numbers. A panel’s rating is measured under standard test conditions: full perpendicular sun, a specified spectrum and a cool cell. A panel lying flat on a roof in Britain in October meets none of those. Plan on a fraction of the badge figure, assume less in winter, and treat anything better as a good day.
This matters most for exactly the cooking on this page. An electric hob or a grill can spend several hundred watt-hours on one meal, and a modest panel may not replace that inside a day at this latitude. Solar makes a battery last longer. It rarely makes a battery unnecessary.
Angle and shade do more than size. A panel tilted toward the sun substantially outperforms a larger one lying flat, and a single shaded section can cost far more output than its area suggests. A folding panel you can prop and move is worth more in practice than a bigger fixed one, which is the opposite of what the price comparison suggests.
Check the connector matches your power station before buying, and check the input voltage range it will accept. This is the most common mismatch of the two.