Carbon · grid intensity

The same kilowatt-hour is not the same carbon

Grid intensity moves by 87% across a day. For an aeroponic nursery, the schedule of the fog pump is a bigger lever than the efficiency of the pump.

ZERO CARBON VERIFY · ESTABLISHMENT NOTE · 6 MIN READ

Every footprint calculation multiplies kilowatt-hours by a grid factor. Almost every calculation uses an annual average. That single choice hides the largest controllable variable in the whole system.

The spread is not small

On a grid with a large solar share, the marginal intensity at 2am is roughly a third of what it is at 6pm. A nursery that irrigates at night and one that irrigates in the evening can have identical equipment and identical consumption, and footprints that differ by 20% or more.

Period	kgCO₂e / kWh	What is on the margin
00–06	0.31	Baseload: nuclear, hydro, coal
06–09	0.38	Ramp-up, gas peaking
09–17	0.45	Solar at peak, gas balancing
17–21	0.58	Evening peak, gas and imports
21–24	0.41	Wind and hydro returning

Those numbers are illustrative but the shape is real. The evening peak is where the carbon is, and the evening peak is usually when lighting, pumping and cooling all run at once.

Why annual averages are still used

Because they are free. An annual figure comes with the bill; an hourly figure requires either hourly metering or a published marginal-intensity series joined to your load profile. Most sustainability teams do not have the second thing, so they use the first.

An annual average is not wrong, it is incomplete. It answers “what did this consume” and not “when did it consume it”, and only the second question has an operational answer.

What changes when you measure by hour

Scheduling becomes a real decision. Moving a pump from 18:00 to 02:00 is free and can cut the electricity footprint by a fifth.
Efficiency investments get re-ranked. A more efficient pump running at the evening peak may lose to the same pump on a timer.
The claim becomes auditable. “We shifted load” is checkable against a meter; “we are efficient” is not.
Storage starts to compete. A battery that shifts consumption out of the peak is a carbon asset, not just a resilience cost.

What we ask for

Grade A needs 15-minute intervals for twelve months. Grade B needs hourly. Below that the answer is a daily or monthly shape, and the reported uncertainty widens accordingly — we state the interval in the statement rather than pretending the precision is uniform.

The uncomfortable implication

If the schedule is the biggest lever, then a farm can cut its footprint without buying anything. That is good for the farm and awkward for anyone selling efficiency hardware — which is one reason hourly data is not yet standard: the people paying for the measurement rarely want the answer it produces.

We verify what the meter says. If the honest answer is that the equipment was fine and the schedule was not, the statement says so.

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This note describes our method and commercial position. It is not a verification statement and carries no assurance. Under the two-track plan the certification conclusion is signed by a licensed partner; this site issues the method, the evidence grades and the register.