The independent system (SEI) is composed of the unbound system (Sistema Eléctrico Não Vinculado, SENV), which operates under free market conditions (i.e. most of this power is finally sold to the customers who switch out of the regulated system), and the special regime system (Produtores em regime especial, PRE), in which generation by co-generation plants, mini-hydro plants, and other renewable energies such as wind power plants is supplied to REN at regulated tariffs.
Sõltumatu süsteem (SEI) koosneb sidumata süsteemist (Sistema Eléctrico Não Vinculado, SENV), mis tegutseb vabaturu tingimuste alusel (st enamus sellest elektrienergiast müüakse lõpuks tarbijatele, kes lahkuvad reguleeritud süsteemist), ja erirežiimiga süsteemist (Produtores em regime especial, PRE), kus küttejaamade, väikeste hüdroelektrijaamade ja muid taastuvaid energiaallikaid, nagu tuuleenergiat, tootvate elektrijaamade toodang tarnitakse RENi reguleeritud tariifide alusel.