Who owns and maintains a stand-alone power system?

It depends on the delivery model, and the distinction matters for both regulatory and commercial reasons.

Under a distributor-led model, the DNSP owns, installs, operates and maintains the SAPS as a network asset, and the customer continues to be supplied and billed as a network customer. Essential Energy, for example, installs, owns, maintains and operates its SAPS at no additional charge to eligible customers. Eligibility is typically limited to existing connections with an established retail account, not greenfield sites or new developments.

Under a customer-owned model, which is how most telecommunications, mining, rail and water SAPS are procured, the asset owner owns the system and maintains it directly or under a service agreement.

Valen supplies into both. What changes between them is not the hardware but the documentation, the monitoring architecture and the maintenance regime, because a network asset carries obligations a private asset does not.