Hello Tobias and welcome to the community!
I'm very happy to hear that you'll be coming to Ireland soon and would be happy to advise you with this. Bye laws in the country do vary and different beaches may have certain regulations. However, generally barbecues are permitted on Ireland's beaches, as they are contained. Non-contained fires are not permitted.
Before going planning this, I would suggest getting in touch with the local council for wherever you'll be visiting - they would be able to provide more definitive advice on this matter. You can find all Irish local authorities here
I hope this information proves useful and, most of all, I hope you have a fantastic stay in Ireland!
All the best,