How the fleet gets called
Enrollment is simpler than the name suggests. When you sign up, you let the utility send a signal to your battery's software on days it expects a tight evening. Your battery, which normally fills from your rooftop solar during the day, holds that charge and then discharges during the peak window, roughly 4 to 7 pm for APS and a similar late-afternoon block for SRP, though the exact hours depend on your rate plan. Your house runs partly off the battery, so it pulls less from the grid at the worst moment.
Multiply that by thousands of homes and you get relief that shows up right when the desert needs it. The timing is the whole point. Solar output falls off a cliff as the sun drops behind the mountains, but the heat, and the cooling load it drives, stays high deep into the evening. A battery fleet covers exactly that gap, which is why both utilities would rather pay for it than fire up an expensive peaking plant or buy power on a strained market.
What you sign up for, and what it pays
SRP and APS take different paths to the same place. SRP has leaned on an upfront incentive, a one-time payment on the order of a few hundred dollars per kilowatt-hour of usable battery capacity and capped per home at last public report, in exchange for letting SRP dispatch the battery on peak events. APS has leaned more on ongoing enrollment, with a bill credit or incentive for keeping your battery available during called events. Both reserve a limited number of events per season and limit how deeply they draw your battery, so you keep a reserve for your own outages.
The honest part: the dollar figures move, and the fine print matters more than the headline number. Whether the math works for you depends on which battery you own, whether it sits on the approved equipment list, your rate plan, and how often you would have cycled the battery anyway. Read the current terms on the program page before you count on a payment, because the incentive levels and the approved hardware have both changed before and will again.
Who runs it, and who answers to whom
This is where Arizona gets its own flavor. APS is an investor-owned utility, so its programs, rates, and cost recovery run through the Arizona Corporation Commission, the elected five-member body that regulates private utilities in the state. When APS wants to expand a battery program or recover its cost, it files at the ACC, and those filings are public and searchable by docket on the commission's eDocket site.
Salt River Project is a different animal. It is a public power utility, a political subdivision governed by its own elected board, and it is not regulated by the Corporation Commission. SRP's board sets its prices and approves its programs in its own public meetings. So if you are an SRP customer hunting for the paper trail, the ACC docket will not help you; the SRP board agenda and the program page will. It is a small distinction that trips up a lot of valley residents who assume one agency watches both utilities.
Worth watching this month
1. Watch the APS and SRP residential battery program pages for the 2027 summer enrollment windows, which typically open months ahead of the June peak season and can close once a cap is reached.
2. Check whether your battery model is still on each utility's approved equipment list, since those lists get revised and a drop can quietly end your eligibility.
3. On the Arizona Corporation Commission's eDocket site, watch for any new APS filing touching residential storage or demand response, which would flag a change in the credit or in cost recovery (this one actually matters; most ACC filings are routine).
4. Follow the SRP board's public meeting agendas for any vote on battery incentive levels, since SRP changes these at the board, not at the ACC.
5. Keep an eye on the monsoon and heat outlook heading into next summer, because the number and depth of peak events, and therefore how often your battery gets called, tends to track the heat.