ERCOT 4CP Season (June–September): Scheduling Flower-Room Lights Around 3–6 PM Peaks

How 4CP billing works on Texas TDUs

In ERCOT, transmission costs for many large commercial customers are allocated using four coincident peak (4CP) billing. ERCOT identifies the four highest system demand intervals from June through September. The TDU averages your facility's demand during those four intervals and uses that kW value as your transmission billing determinant for the next calendar year [oncor-tariff] [kilowattlogic-4cp].

Oncor's tariff describes transmission service billed on "4CP kW" updated each January 1 based on the prior summer [oncor-tariff]. Retail electric providers pass the charge through on most commercial contracts.

ERCOT set a record peak near 91,308 MW on July 22, 2026 during a heat wave [ercot-peak-2026]. System peaks often land between 3 p.m. and 6 p.m. on weekdays when commercial cooling load is maximum. That window overlaps default light-on times if staff pick convenient afternoon schedules.

Why flower rooms are 4CP magnets

Indoor cultivation stacks high, flat load for twelve hours. When lights-on aligns with ERCOT's hottest afternoon:

1. Lighting contactors close at full wattage
2. HVAC compressors start immediately to hold setpoint
3. Dehumidifiers ramp latent load from transpiration

Each alone is manageable. Together they can set both monthly TDU demand and contribute to your 4CP average.

Unlike demand charges billed on your own monthly peak, 4CP uses ERCOT system peaks. You cannot control when the system peaks, but you can control whether your load is high when it does.

Scheduling tactics that preserve yield

Stagger rooms by 45 to 90 minutes. Three 100 kW flower rooms starting together create a 300 kW step. Offsetting start times spreads HVAC ramp while keeping each room's photoperiod intact.

Default lights-on after 7 p.m. or before noon. Late-evening schedules move peak kW away from office cooling overlap. Morning schedules push HVAC load into hours when system demand is often lower, but summer morning humidity may increase dehumidifier duty. Model both.

Pre-cool 30 minutes before lights-on. Drop room dry-bulb temperature before contactors close so compressors do not spike simultaneously with lighting.

Curtail nonessential load during watch days. When ERCOT publishes high system demand forecasts above prior peaks, trim veg room supplemental lighting or postpone CIP cycles.

Use EMS alarms. Set text alerts when facility demand exceeds a threshold during June through September weekdays.

Strategy	4CP benefit	Operational cost
Stagger rooms	High	Minor staff scheduling
Evening photoperiod	High	Possible HVAC night noise
Pre-cool	Medium	Extra kWh before peak window
Curtailment on watch days	Medium	Requires monitoring

PUCT 12CP proposal: plan for both rules

The Public Utility Commission of Texas has proposed shifting from four to twelve coincident peaks for transmission allocation by December 31, 2026 [puc-12cp-proposal]. More peaks dilute the impact of any single interval but increase the number of hours you must treat as risky.

Until a final rule takes effect, operate under 4CP rules and treat 12CP as a reason to build flexible scheduling now rather than locking rigid afternoon light times into automation.

Worked example: Oncor primary service grow

Assume your 4CP average was 220 kW in 2025 because lights-on at 2 p.m. stacked with HVAC. Oncor transmission charge might be roughly $2 to $4 per 4CP kW-month depending on tariff year (verify section 6.1.1.1) [oncor-tariff]:

• At $3/kW-month × 220 kW ≈ $660/month transmission ≈ $7,920/year

Shift schedules to cut 4CP average to 160 kW:

• Same rate ≈ $480/month ≈ $5,760/year

Savings ≈ $2,160/year from timing alone, before energy or distribution demand effects.

These dollars pass through your REP contract. Lower 4CP also helps if you negotiate supply based on load factor.

Integration with HB 46 buildouts

New Texas Compassionate Use facilities energizing in 2026 should program stagger logic before first harvest. Retrofitting schedules in a running facility requires change-control with quality teams. Greenfield is cheaper.

Document the chosen photoperiod clock in SOPs so maintenance staff do not "fix" timers back to afternoon defaults.

Monitoring checklist for June through September

• Subscribe to ERCOT demand notices or use a REP portal with system load charts [texas-4cp-guide]
• Export weekly interval data; mark top ten facility peaks
• Compare facility peak timestamps to ERCOT peak announcements
• Review REP bill for 4CP kW value each January
• Update light schedules if last summer's 4CP exceeded model

CenterPoint and AEP Texas: same ERCOT peaks

This article uses Oncor examples [oncor-tariff]. Houston CenterPoint and AEP Texas customers face the same ERCOT system peak definitions for 4CP [kilowattlogic-4cp]. TDU tariff sections differ on dollar per kW but timing strategy is identical.

REP contract language checklist

Before signing a Texas REP contract, read:

1. TDU pass-through section for transmission 4CP
2. Whether distribution demand is bundled or pass-through
3. Early termination if 4CP year exceeds budget

Texas cultivation energy page links territory-specific notes.

PUCT 12CP transition planning

PUCT proposed twelve coincident peaks instead of four by December 31, 2026 [puc-12cp-proposal]. More peaks mean more hours where load matters, but each peak contributes less individually. Build flexible EMS schedules now rather than hard-coding 2 p.m. lights-on.

Heat wave operations playbook

When ERCOT issues conservation appeals during record peaks like July 22, 2026 [ercot-peak-2026]:

• Delay veg room optional lighting
• Pause CO2 enrichment blowers briefly if GMP allows
• Pre-cool before peak window
• Monitor REP portal for real-time prices if on index

Document SOP deviations for quality review.

Comparing 4CP savings to battery peak shave

Batteries can shave 15-minute peaks but require capital and interconnection study. Staggering rooms costs software and discipline. Run both models if 4CP kW exceeds 250 kW [oncor-tariff].

TCUP and HB 46 new builds

New Texas Compassionate Use facilities from HB 46 should program stagger at commissioning [texas-hb-46 article]. Retrofit harder than greenfield.

Training staff on timer changes

Quality teams often resist schedule shifts. Document VPD and leaf temperature data from pilot rooms to justify permanent timer offset after 4CP season ends [oncor-tariff].

Interval meter required reading

Without interval data you cannot prove which adjustment lowered 4CP kW. Oncor and REPs provide 15-minute downloads on many commercial accounts [oncor-tariff].

Post-season review in October

Each October, download final 4CP kW assigned for next calendar year from TDU bill or REP portal [oncor-tariff]. Compare to model. If within 5 percent, keep schedule; if not, adjust timers before next June.

4CP season is a twelve-month bill set in four fifteen-minute windows. Flower-room scheduling is the lowest-cost lever Texas cultivators have. Treat peak avoidance as standard operating procedure June through September, the same way you treat IPM checks during flower.

How to read 4CP kW on your Oncor or REP bill

Transmission service for many large Texas commercial accounts bills on four coincident peak kW updated each January 1 based on the prior June through September system peaks [oncor-tariff] [kilowattlogic-4cp]. Your REP pass-through line may label it "4CP," "TCOS," or "Transmission Cost Recovery."

Pull January and February bills after 4CP season ends. Compare the assigned kW to your facility's top ten interval peaks from last summer. If the bill shows 210 kW 4CP but your highest facility peak was 175 kW, ERCOT system peaks likely occurred when your load was elevated relative to other hours you thought were higher locally.

Bill line	What it reflects	Your lever
Distribution demand kW	Your monthly peak	Stagger, pre-cool
4CP transmission kW	Avg load at four ERCOT system peaks	Avoid 3-6 PM overlap
Energy kWh	Total usage	LED, schedule

ERCOT set a record peak near 91,308 MW on July 22, 2026 during a heat wave [ercot-peak-2026]. System peaks often land between 3 p.m. and 6 p.m. when commercial cooling stacks with industrial load. Flower rooms on 12/12 photoperiod that flip lights on at 2 p.m. by habit contribute full lighting plus HVAC ramp into that window.

The PUCT has proposed moving from four to twelve coincident peaks by December 31, 2026 [puc-12cp-proposal]. Until a final rule takes effect, four intervals still set the charge. Build flexible EMS schedules now rather than hard-coding afternoon light-on times that staff reset after every harvest crew change.

CenterPoint Houston and AEP Texas customers face the same ERCOT system peak definitions for 4CP allocation [kilowattlogic-4cp]. TDU tariff sections differ on dollars per kW but timing strategy is identical: stagger rooms 45 to 90 minutes, pre-cool before lights-on, and monitor system demand June through September [oncor-tariff]. Pair 4CP avoidance with demand charge management on the TDU distribution side.

Each October, download final 4CP kW assigned for the next calendar year from the TDU bill or REP portal [oncor-tariff]. Compare to your model. If within five percent, keep the schedule; if not, adjust timers before next June. Without interval data you cannot prove which adjustment lowered 4CP kW [oncor-tariff]. Oncor and REPs provide fifteen-minute downloads on many commercial accounts.