Phoenix SRP E-27 Rate Plan Explained for Solar Homeowners

I built Grid Getter because of this plan, and the story behind Grid Getter started with my own SRP E-27 bill. I'm an SRP solar customer on E-27, and after my first summer bill, where a single afternoon of running 2 ACs, and the oven at the same time (we just needed that sourdough bread) cost me over $130 in demand charges alone, I started digging into how the billing actually worked. What I found was a rate structure that punishes you for things you can't see happening in real time. So I built the tool I wished I had.

If you've gone solar in the Phoenix metro and SRP is your utility, you're likely on the E-27 plan. It replaced E-26 as SRP's standard offering for solar customers, and unlike the flat-rate plans most homeowners had before they installed panels, E-27 charges you two completely different ways: once for the energy you consume, and again for the rate at which you consume it.

That second charge is what catches people off guard. You can be conservative with your usage all month and still get hit with a demand charge that wipes out your solar savings.

One thing to know upfront: SRP has announced that E-27 will be eliminated as of the November 2029 billing cycle. Customers still on it at that point will be moved to the E-16 plan. For now the rates and structure below apply, but it's worth keeping an eye on what E-16 looks like if you're planning long-term battery strategy.

What Is the E-27 Plan?

Every month your E-27 bill has three parts:

• A fixed service charge (amount depends on your home's electrical service size and if it's single vs multifamily)
• A per-kWh energy charge that varies by season and time of use
• A per-kW demand charge based on your peak grid draw during on-peak hours

Your solar salesperson likly showed you how low the per-kWh is! Only a few cents! Hopefully they also shared the demand charge. That's the killer one.

E-27 Rate Schedule Breakdown

All rates below are from the official SRP E-27 Ratebook effective November 2025. SRP divides the year into three billing seasons, each with its own on-peak window and rate structure.

On-peak hours (weekdays only, excluding SRP holidays):

• Summer (May–Oct): 2 PM – 8 PM
• Winter (Nov–Apr): 5 AM – 9 AM and 5 PM – 9 PM

All on-peak windows fall during times when solar panels produce little to no energy (before sunrise and after sunset for winter, during the early evening), which makes demand charges particularly hard to offset with solar alone. Weekends and SRP-designated holidays are off-peak, which is a meaningful advantage if you time your heavy loads accordingly.

Monthly service charge

Your service charge depends on your dwelling type and electrical service size:

Tier	Applies to	Monthly
Tier 1	Apartments, condos, multifamily units (0–225 amp)	$20.00
Tier 2	Single-family homes (0–225 amp)	$30.00
Tier 3	Any residence over 225 amp service	$40.00

Demand charges (tiered by kW)

The billing demand is the maximum 30-minute integrated kW demand during on-peak periods in the billing cycle — one bad half-hour sets your charge for the whole month.

Summer (May, Jun, Sep, Oct):

Tier	Rate
First 3 kW	$9.85/kW
Next 7 kW	$16.32/kW
Additional kW	$29.26/kW

Summer Peak (Jul–Aug):

Tier	Rate
First 3 kW	$11.98/kW
Next 7 kW	$20.05/kW
Additional kW	$36.13/kW

Winter (Nov–Apr):

Tier	Rate
First 3 kW	$5.01/kW
Next 7 kW	$7.10/kW
Additional kW	$11.08/kW

The tiering means every additional kW of peak demand costs you more than the last. A 3 kW peak in July costs $36. A 10 kW peak costs $176. That escalation is why demand management matters.

Energy rates

Per-kWh rates from the November 2025 effective schedule:

Summer (May, Jun, Sep, Oct):

Period	Rate/kWh
On-peak	$0.0662
Off-peak	$0.0560

Summer Peak (Jul–Aug):

Period	Rate/kWh
On-peak	$0.0823
Off-peak	$0.0613

Winter (Nov–Apr):

Period	Rate/kWh
On-peak	$0.0673
Off-peak	$0.0634

The per-kWh rates are relatively modest compared to flat-rate plans. The demand charge is where the real cost lives on E-27.

Export credits

E-27 handles exports on a net kWh basis within each billing cycle, tracked separately by time-of-use period. SRP subtracts the kWh you deliver to the grid from the kWh you take from the grid for each billing cycle. If that calculation is net positive, you pay for the net kWh under the plan. If it's net negative, SRP credits the net kWh at the retail per-kWh price for that same time-of-use period.

The practical takeaway: exported solar can offset energy charges, but it does not make the demand charge go away, and excess generation in one time-of-use period is tracked separately from another. That's why timing still matters so much on E-27.

On my own bill, what pushed me to add a Powerwall was realizing that daytime overproduction wasn't solving the expensive part of the plan: late-day on-peak usage and demand spikes. Store what you generate during the day and use it during on-peak hours, and you can reduce both your billed kWh in that period and the grid draw that sets your demand charge.

How the Demand Charge Calculation Actually Works

This is where most E-27 customers get confused, because the billing method is less intuitive than it looks.

SRP doesn't charge you based on your total energy use during on-peak hours. They charge you based on your highest average kW reading across a fixed 30-minute interval during on-peak hours in the billing month. These intervals are aligned to the hour — :00 to :30 and :30 to :00. That one worst half-hour becomes your billable demand in kW.

Here's what that means practically. Say you have a 4-ton AC unit (roughly 4–5 kW depending on efficiency), a pool pump (1.5 kW), and your oven preheating (3.5 kW). If those run simultaneously one afternoon during on-peak hours, you're pulling around 10 kW from the grid. Even if that happens only once all month, that single interval sets your billable demand for the entire billing period.

At the tiered summer peak rates, a 10 kW peak demand in July costs you $176.29 in demand charges alone, before any energy charges. In a mild month where your Powerwall handles most of it, you might get that number down to 3–4 kW. That's $176.29 vs. $35.94 to $55.99 in demand charges for the same month.

The calculation resets every month, which is actually in your favor. A bad January doesn't carry forward.

That means you can reduce your demand charge starting next bill. I recommend you start now to build the habit.

How to Lower Your E-27 Demand Charge

The basics: stagger and pre-cool

Two things you can do today without any equipment. First, stop running your dishwasher, dryer, and oven simultaneously at 6 PM, sequence them instead, and ideally across separate 30-minute measurement intervals. The actual energy used is the same; the peak draw is not. Second, in summer, pre-cool your house before on-peak starts. Set your thermostat to drop to 76°F or lower before the on-peak window opens. The thermal mass of the building holds the temperature for a while, so your AC works less hard during the hours that actually set your demand charge.

Use Powerwall Time-Based Control as a starting point

Tesla's built-in Time-Based Control mode discharges the battery during your utility's peak hours. For E-27, you'd configure it to discharge during the summer on-peak window. This offsets some of your grid draw, which reduces your measured demand.

The catch is that Time-Based Control is reactive. It discharges on a schedule without knowing in real time how hard your grid connection is working. It reduces demand but doesn't target your demand ceiling.

Enable DemandGuard for active grid-draw capping

This is the feature I built because Time-Based Control wasn't enough for my own bill.

DemandGuard monitors your actual grid draw in real time and adjusts Powerwall output to keep you under a target demand threshold. Set your ceiling at 3 kW, and it holds the Powerwall in reserve specifically to shave spikes rather than just running a discharge schedule.

Because SRP bills based on your single worst 30-minute interval, even one unguarded spike during on-peak hours affects your charge for the whole month. DemandGuard keeps those intervals in check consistently, not just when the battery happens to be discharging.

Check your demand number weekly during summer

Your SRP account shows your month-to-date demand figure. If it's already at 8 kW by the 10th of the month, you know to be especially careful for the next three weeks. If you don't look, you find out when the bill arrives — and by then the damage from that one bad interval (see the demand math above) is already locked in.

How Grid Getter Handles E-27

I built Grid Getter with E-27 baked in because it's the plan I'm on and the plan every SRP solar customer either has or is getting. The E-27 rate schedule, on-peak windows, seasonal transitions, and tiered demand structure are all preconfigured. Connect your Powerwall, and Grid Getter already knows how SRP is going to bill you.

On E-27, timing your battery discharge and capping peak grid draw both depend on the same two inputs: knowing when SRP's billing intervals run and how much you're currently pulling from the grid.

Grid Getter's DemandGuard syncs with SRP's 30-minute metering intervals and manages your Powerwall output in real time against a demand target you set. You pick your ceiling, and Grid Getter keeps your measured demand under that number throughout each billing period. It also handles seasonal transitions automatically, switching its behavior when SRP's on-peak window shifts in November and May.

Setup is quick — enter your Tesla account email, authorize the connection, and Grid Getter loads the E-27 plan automatically.

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Start here: Log into your SRP account and pull your demand charge from last month's bill. It's listed separately from your energy charges. That number is your billable demand in kW. Use it as your baseline. That's what demand is currently costing you, and it's the number to bring down.