Shifting to Cleaner Hours: How Time-of-Use Meets Carbon Intensity

Utilities are pushing customers toward Time-of-Use (TOU) pricing, where electricity costs vary by hour. At the same time, carbon-conscious consumers are learning about grid intensity — how clean or dirty the electricity is at any given hour.

But here’s the puzzle: TOU pricing and carbon intensity don’t always line up. In some hours, electricity is cheap but dirty; in others, it’s expensive but clean. This article explains the overlap, the mismatch, and how you can win on both fronts.

Why This Matters

Money vs Carbon: Aiming only for the cheapest hours may not reduce emissions.
Behavior Change: Smarter scheduling = lower bills and lower CO₂.
System Impact: Collective shifts can flatten demand curves and cut fossil fuel reliance.

What Is TOU Pricing?

Time-of-Use pricing divides the day into blocks:

Peak: Highest demand, highest price.
Off-Peak: Lowest demand, lowest price.
Mid-Peak: In between.

Utilities design TOU to encourage customers to spread demand and avoid system overloads.

What Is Carbon Intensity?

Carbon intensity is the grams of CO₂ emitted per kWh supplied on the grid. It depends on:

Fuel mix (coal, gas, nuclear, renewables)
Imports/exports with neighboring grids
Daily and seasonal generation patterns

Unlike TOU, intensity is about emissions, not cost.

Where They Align

Solar-heavy grids: Midday = both cheap and clean.
Wind-heavy grids: Overnight = both cheap and clean.
Coal-heavy grids: Peak = expensive and dirty.

In these cases, TOU and carbon intensity complement each other.

Where They Clash

California (CAISO)
- Midday is very clean (solar), but TOU may mark it as mid-peak pricing, not off-peak.
- Evening (6–9pm) is dirtiest and most expensive.
UK
- Overnight can be clean due to wind, but TOU may still charge “cheap” rates earlier in the night when fossil plants are running.

Result: if you follow TOU blindly, you may save money but increase emissions.

How to Balance Both

Check Live Intensity → use our Home Energy Calculator.
Overlay TOU Schedule → compare your utility’s rate chart with clean hours.
Pick the Overlap → target the cheapest and cleanest hours.
Use Automation → smart plugs, EVSE scheduling, appliance timers.
Prioritize Carbon When You Can → if the cost difference is small, choose the cleaner hours.

Case Study: EV Charging

Option 1: Charge at 10pm (cheap TOU, dirty grid) → 25 kg CO₂
Option 2: Charge at 2am (slightly higher TOU, cleaner wind) → 12 kg CO₂
Option 3: Charge at noon (solar surplus, mid-price) → 8 kg CO₂

The right answer depends on your goals. If you value both, the sweet spot is the overlap.

Action Plan

Get your TOU schedule from your utility.
Compare it daily with live intensity.
Shift flexible loads: laundry, EV charging, water heating.
Advocate for carbon-aware tariffs that align cost and carbon.

Frequently Asked Questions

Q: Why don’t utilities align TOU with carbon intensity?
A: TOU is designed around demand and grid stress, not emissions. Aligning both requires policy changes and advanced forecasting.

Q: What if my utility doesn’t have TOU pricing?
A: You can still follow carbon intensity