irish passport holder

Yes. 

Yes, but before Brexit it was never enforced. Irish, being in EU MAY still be ignored but I wouldn’t chance going over the 183 days as then considered  Tax resident . This may change with the Etias scheme, only in that all passports will be electronically checked .

The answer is yes and no 

as an Eu passport holder you should  report report your presence at 90 days but it’s never been checked on

So you could stay for 89 days then leave for one day and return so it’s  the rolling 180 days which doesn’t apply 

No, Irish passport holders can stay for 180 days, actually I think it's 183 days in a calendar year. It's 90 days for non EU passport holders. 

Stay 183 and pay Tax

But you must register at 90 days.

You cannot (legally) stay over 90 days in a single visit, unless registered.

From the Irish Consulate website ..

Staying for longer than three months

All EU citizens who want to stay in Spain for more than three months have to register in person at the Oficina de Extranjeros (Foreigners Office), which is normally part of the town hall (Ayuntamiento), or at designated police stations.

You will be issued a Certificate of Registration with your name, address, nationality, identity number (NIE) and date of registration. The certificate serves as confirmation that you have registered, but is not recognised by the local authorities as a valid form of identification and you are not obliged to keep the certificate with you.

Spain - Department of Foreign Affairs (dfa.ie)

Follow the links to "additional information".

Thanks for your input Will but as always these things are confusing. 

I just Googled it again and it clearly states that an Irish passport holder may stay 180 days and after that if you don't register you could be fined and pay tax. 

I do still have doubts though because Ireland is not in Schengen so I'm going to dig a bit deeper.  I'll vlet you know what I find.

The web link that I provided is from the ROI Dept of Foreign Affairs.

If you find a more authoritative source, please let us know.  

There is a difference between Registration and Residency (and this is often misunderstood or conveniently ignored). If you stay over 180 (182 ?) days, you can be deemed Resident and subject to all the taxes/back-taxes that Spain can apply. The link that I provided is talking about Registration - a different status, applicable at 90 days.

FWIW, when I applied for Residency in 2018 (a Brit, pre-Brexit), there was a tick-box on the form for Registration and a different one for Residency.

That's very helpful Will, thank you. I went on line again & a company called Balcells (legal eagles) have good information on the different options 

 When we first arrived in Spain we were advised to get a Certificado de Registro de Ciudadano de la Unión which we did. It's a green paper containing our NIE, address etc. It differs from a normal NIE paper (white) & we got it from the Police. Its very straightforward to get if you are an EU citizen & you can apply for it when you are in Spain but again only if you are a EU Citizen. Otherwise you must apply in your country of residence.

The requirements are clearly set out in their website balcellsgroup.com

You can then proceed to get your residency card (TIE) which allows you to stay in Spain as an EU citizen  legally and permanently.  We don't require that as we only want to stay here twice a year for longer than 90 days legally. 

It means we can stay in Spain for 183 days without becoming a resident. We hold Irish passports.