As a 2026 rule of thumb, a typical domestic solar system lands somewhere around €1,300–€2,000 per kWp installed before the grant, with clear scale economics — small systems sit nearer the top of that band and larger systems nearer the bottom, because the fixed costs (scaffolding, labour, paperwork, the inverter) spread over more panels. A flat €1,800 SEAI grant then comes off that. So a small 4 kWp panels-only system works out roughly €7,000–8,000 before the grant, around €5,000–6,000 after it at the cheaper end; bigger systems cost more in absolute terms but less per kWp.
A battery adds roughly €350–€600 per usable kWh on top, so a 5 kWh battery typically adds something in the region of €2,000–3,000, and a hot-water diverter adds a few hundred euro. Those are pre-grant figures (the €1,800 grant is a single flat amount, it doesn't scale with the battery or diverter). Real quotes vary a lot with roof complexity, panel and battery choice, and how busy installers are — so treat these as a sanity-check band, not a fixed price.
The single best protection against overpaying is to get three like-for-like quotes and compare them on the same spec: same kWp, same usable battery kWh, same panel and inverter tier. A quote that's wildly above this band for a standard roof deserves questions; one that's suspiciously below it deserves them too (check the panel/inverter brands and that it's a registered installer). The grant drops to €1,500 from January 2027, so a 2026 completion is worth €300 more.