SRP E-27 Demand Charges Explained

On SRP's E-27 Customer Generation Price Plan, the demand line is often the charge people misunderstand. It is not “how many kWh you used this month.” It is the highest thirty-minute on-peak power draw in the billing cycle, then priced through progressive $/kW tiers that change by season.

This page was rebuilt from SRP's E-27 tariff in the 2025/2026 ratebook (published 2026-04-27) and matches the math in the SRP E-27 bill calculator. It covers E-27 only. Other SRP plans can measure or price demand differently. Confirm the plan name on your bill.

E-27 is limited to residential customers with on-site generation who do not buy all of their energy from SRP. The ratebook states the plan will be eliminated as of the November 2029 billing cycle, with remaining customers moved to E-16. See the peak hours guide for the schedule context that sits next to these demand rules.

What E-27 is measuring

The ratebook's determination-of-demand rule is specific: billing demand is the maximum thirty-minute integrated kW demand occurring during the on-peak periods of the billing cycle, as measured by the meter. A single stacked half-hour during on-peak can set the demand charge for that whole cycle even if every other day was quiet.

Kilowatt-hours still matter for the separate energy charges. Demand is the intensity spike, not the monthly energy total.

Which hours can set demand?

Only on-peak intervals count. Off-peak use—including weekends and the six E-27 holidays—does not set this billing demand. The clocks themselves are seasonal:

Full holiday dates and schedule detail live on the restored SRP E-27 peak hours guide. Winter demand can be set by a morning spike, not only a late-afternoon one.

Progressive demand tiers, not one flat $/kW

Older summaries often quoted one summer dollars-per-kW number. E-27 does not work that way. After the meter records on-peak demand, the tariff prices it in three slices with different rates by billing season:

Worked July–August examples using those tiers (demand charge only, before energy, service charge, taxes, or riders):

• 5 kW → 3 × $11.90 + 2 × $19.97 = $75.64
• 8 kW → 3 × $11.90 + 5 × $19.97 = $135.55
• 10 kW → 3 × $11.90 + 7 × $19.97 = $175.49
• The same 8 kW in a winter billing cycle is about $49.89 under winter tiers—not the July–August total.

A flat “8 × $14.50 = $116” shortcut is not the E-27 tariff math. Your meter and bill remain authoritative.

Why stacking loads matters more than average use

Because only the worst on-peak half-hour sets demand, overlapping large draws is expensive even if monthly kWh look ordinary. Common stackers:

• Central AC compressor starts while other large loads are already on
• Pool pump plus dryer, oven, or well pump in the same half-hour
• Level 2 EV charging during on-peak windows
• Late-day solar fade while cooling load stays high (customer-generation homes still see grid demand when generation drops)

Practical mitigations are about coincidence, not perfection: finish flexible loads before the summer 2 p.m. window or after 8 p.m., avoid morning and evening winter peaks when possible, stagger heat-producing appliances, and pre-cool only within safe comfort limits. Equipment-level timing estimates: pool pump calculator, EV charging calculator.

What a lower peak can change (estimate only)

If a July–August cycle would have billed 8 kW and behavior or equipment reduces the measured on-peak maximum by 3 kW to 5 kW, the progressive demand charge alone changes by about $59.91 for that cycle in this tariff math. That is not a promised household savings figure. Actual results depend on your true interval demand, season, riders, and whether the lower peak holds for the whole billing cycle.

Use the SRP E-27 bill calculator to vary demand, season, and usage mix. Results are estimates of core E-27 charges, not a complete SRP bill.

What this page is not claiming

• It does not apply automatically to every SRP residential plan—only E-27 as published in the linked ratebook.
• It does not guarantee battery, thermostat, or solar savings percentages.
• It does not replace your bill, meter data, or SRP account tools.
• Energy charges, service-charge tiers ($20 / $30 / $40), taxes, and adjustors are separate lines.

Frequently asked questions

How does E-27 measure demand?

Billing demand is the maximum thirty-minute integrated kilowatt demand during on-peak periods in the billing cycle, as measured by the meter. It is not a kilowatt-hour energy total and is not averaged across the whole month.

Is the E-27 demand charge one flat dollars-per-kW rate?

No. Demand is priced in progressive tiers for the first 3 kW, the next 7 kW, and all additional kW, with different tier prices by billing season.

Do E-27 demand charges use the same peak hours all year?

No. From May 1 through October 31, on-peak hours are 2 p.m. to 8 p.m. weekdays excluding holidays. From November 1 through April 30, on-peak hours are 5 a.m. to 9 a.m. and 5 p.m. to 9 p.m. weekdays excluding holidays. Only those on-peak intervals set billing demand.

Source notes

• SRP ratebook with temporary FPPAM (E-27 section) — on-peak definitions, determination of demand, progressive per-kW tables, seasons, service charges. Published 2026-04-27.
• Site constants SRP_RATES.e27 and calculateE27DemandCharge — verified against that ratebook for calculator use (2026-07-27).
• Companion schedule article: SRP E-27 peak hours guide.

Source set reviewed 2026-07-27. Temporary May–October 2026 fuel and purchased-power adjustments can change summer energy prices; demand tier totals above are the ratebook totals used by this site. Your SRP bill controls.