183 days

There is no 90 in 180 or restrictions on EU members. However, if he stays more than 183 days he becomes a tax resident in Spain regardless of whether he is registered or not. To stay over the 90 days he should register on the Non Spanish EU citizens residing in Spain as a non resident up to 183 days. Once they go over that they become fiscal residents.

Now, in the real world, there are no checks made on EU citizens entering Spain therefore the only way he would be caught would be if he registered his stay or was asked for proof of flights. That ain't gonna happen and didn't happen to the Brits when we were in the EU. It's only now passports are being stamped that a check can be made.

Officially, no he can't stay more than 183 days in any one calendar year. Realistically he can do what he wants unless he gets picked up for an offence. 

Even as an Irish passport holder your friend is limited to 90 days (not 183) before he has to sign on the foreigners register at the National Police station. Failing to do that means he has overstayed.

Details here:

https://administracion.gob.es/pag_Home/en/Tu-espacio-europeo/derechos-obligaciones/ciudadanos/residencia/obtencion-residencia/inscribirte-residente.html

Steve 

The acquisition of Irish passports by Brits really only gives them the opportunity to live here under the radar, illegally in other words.

Just like the Brit's without Irish passports. Spanish border staff don't check but will stamp your UK passport. Both Irish & UK passport holders are illegal over 90 days but the Spanish aren't too bothered.

Once (if ever) EES is up & running then both passport holders will find it more difficult.

So if he as been here 8 months he’s in trouble.

UNLESS he left Spain for 1 day and then came back again. If so, his number of days starts again, whether it is 90 or 183 etc

If he's here for longer than 183 days in one calendar year then he would be classed as a tax paying resident regardless of how many visits or breaks in between. 

Before 2021 I knew many British people who came to Spain for several months, typically from mid-September, and went back in May.  They were usually retirees who owned or rented properties in Orihuela Costa. No one bothered them and they never had any problems travelling back, by road, air or ferry. Obviously for British passport holders that has changed now but I suspect for Southern Irish passport holders the same situation exists. As long as they are not running any business in Spain then I don't think the Spanish authorities are interested.  

 Going forward I'm not sure if EES will change that, it remains to be seen how it tracks non-Schengen EU citizens.   

Rgds,

Aitch.