I don't think you'll find a working solution like that. Output from solar panels requires careful handling if it's 240v AC, bear in mind that the output from a solar panel would be dc natively. The important figure is still the amperage, a trickle charge requires very little, fractions of an amp. The fact that you essentially only need 12-14v dc at tiny amperage would mean a solar panel large enough to deliver 240v with the associated translation to AC would be a terrible and unwieldy solution.
I thought there might be a solution that fits on the dashboard and plugs into the lighter socket but I've not looked for one.
I don't think you'll find a working solution like that. Output from solar panels requires careful handling if it's 240v AC, bear in mind that the output from a solar panel would be dc natively. The important figure is still the amperage, a trickle charge requires very little, fractions of an amp. The fact that you essentially only need 12-14v dc at tiny amperage would mean a solar panel large enough to deliver 240v with the associated translation to AC would be a terrible and unwieldy solution.
I thought there might be a solution that fits on the dashboard and plugs into the lighter socket but I've not looked for one.