What Is 24/7 Carbon-Free Energy? – Hourly Matching Explained
"100% renewable" is one of the slipperiest claims in corporate energy. One company that makes it buys enough solar certificates each year to equal its total use, even though its servers still pull grid power at midnight from whatever plants are running. Another tries to make sure clean power is being produced near its facilities every single hour. The second approach has a name, and it's changing how big buyers sign energy deals. What is 24/7 carbon-free energy, and how does hourly matching work?
24/7 carbon-free energy (CFE) means matching every hour of a facility's electricity use with carbon-free generation on the same grid, instead of matching total use once a year. Under traditional annual matching, a buyer can claim 100% renewable power by purchasing enough certificates over twelve months, even if much of the night is served by fossil plants.
Hourly matching compares consumption and clean supply hour by hour, so surplus solar at noon can't cover a shortfall at 2 a.m. Results are expressed as a CFE score, the percentage of hours of use met by clean power. It's harder and costlier than annual matching, but it pushes buyers toward resources that produce around the clock.
How Is Hourly Matching Different From Annual Matching?
Hourly matching checks clean supply against demand in each hour, while annual matching only checks the yearly totals. That sounds like a technicality. It isn't, because solar and wind don't produce on the same schedule a data center consumes.
A simplified, made-up case makes the point. A data center draws a flat 10 MW, or 240 MWh a day. It contracts a solar farm that produces 240 MWh on a typical day, all of it in daylight. We'll use six-hour blocks to keep it readable:
| Time block | Load (MWh) | Solar (MWh) | Matched (MWh) |
|---|---|---|---|
| Midnight to 6 a.m. | 60 | 0 | 0 |
| 6 a.m. to noon | 60 | 80 | 60 |
| Noon to 6 p.m. | 60 | 140 | 60 |
| 6 p.m. to midnight | 60 | 20 | 20 |
| Total | 240 | 240 | 140 |
By annual-style accounting, solar equals load, so the buyer claims 100%. By time-matched accounting, only 140 of 240 MWh were actually covered: 140 ÷ 240 ≈ 58%. The other 100 MWh of midday surplus went to the grid, and the night was served by whatever else was running. Real hourly accounting slices the day into 24 pieces instead of four, but the result looks similar.
Why Did Companies Start Moving to 24/7 Carbon-Free Energy?
Companies moved toward 24/7 carbon-free energy because annual matching had a blind spot. It encouraged buying the cheapest certificates, usually from solar or wind in places with plenty already, without guaranteeing that fossil generation would fall during the hours the buyer actually used power.
Google became the best-known champion. It set a goal of running on 24/7 carbon-free energy by 2030, and its explanation of the shift from annual to hourly matching reported that its operations were 67% matched on an hourly basis in 2020, even though it had matched 100% of its annual use with renewable purchases for years. That gap is the whole story in one number.
Other buyers, utilities and governments joined the push, and a United Nations-backed 24/7 Carbon-Free Energy Compact launched in 2021 to promote the idea. Hourly matching is a better measure of real impact, in my view, though it isn't the only thing that matters. Where and when a new plant is built also changes how much fossil generation it actually displaces.
How Is a CFE Score Calculated?
A CFE score is calculated by adding up, for every hour of the year, the smaller of two numbers: the facility's consumption and the carbon-free supply credited to it. Divide that total by annual consumption and you get a percentage.
- For each hour, take the clean energy credited to the buyer, from contracted plants plus, in some methods, the carbon-free share of the local grid.
- Cap it at that hour's consumption. Surplus in one hour doesn't carry to the next.
- Sum the matched energy over all 8,760 hours.
- Divide by total consumption.
Using the daily example above, a facility repeating that pattern all year would score about 58% from solar alone. Adding wind that blows mostly at night, or a battery that shifts some of the noon surplus into the evening, raises the score. Each extra point usually costs more than the last, because the hardest hours to fill are long calm, cloudy stretches.
What Resources Fill the Hard Hours?
The hard hours get filled by clean resources that produce at night and in bad weather, or by shifting energy and demand in time. A strong 24/7 portfolio usually mixes several:
- Wind: Often stronger at night and in winter in many regions, complementing solar.
- Battery storage: Moves midday solar into the evening peak; covers hours, not days.
- Firm clean power: Hydro, nuclear and geothermal produce around the clock and fill the gaps renewables leave.
- Clean dispatchable fuels: Renewable natural gas or, eventually, clean hydrogen in generators that run only when needed.
- Load flexibility: Shifting flexible computing work toward hours and locations with more clean power.
Location matters as much as technology. A data center on a grid already rich in hydro or nuclear starts with a high score. One on a coal-heavy grid starts low and has to contract much more.
How Are Hourly Clean Energy Claims Tracked?
Hourly claims are tracked with time-stamped certificates, sometimes called granular certificates or time-based energy attribute certificates (T-EACs). A traditional renewable energy certificate (REC) represents one MWh of clean generation sometime during a period, often a month or a year. A granular certificate records the hour it was produced, so it can be matched to consumption in that same hour.
Some certificate registries in North America and Europe have built systems to issue hourly records, and standards groups have worked on common formats. Coverage is still uneven. In many regions, buyers rely on meter data from their contracted plants and their own facilities to calculate hourly matching themselves.
What Does Hourly Matching Mean for On-Site Power?
Hourly matching changes how on-site power looks on paper. A facility running on its own gas generators scores close to zero on carbon-free energy in every hour they run, no matter how many annual certificates it buys elsewhere. Under annual accounting, those certificates could hide that.
That pushes on-site designs in a few directions. Solar and batteries inside the fence raise the score during the day and into the evening. Generators fueled with renewable natural gas, or some day clean hydrogen, can count during the hours they run if the fuel's attributes are properly tracked. And a site connected to a clean grid can lean on that grid in hours when its own resources fall short.
For remote and off-grid sites, the lesson is simple: the hours a generator runs are the hours to work on. Cutting generator run time with storage and renewables does more for an hourly score than any amount of distant certificates.
What Are the Limits of 24/7 Carbon-Free Energy?
The main limits are cost, availability and accounting rules that don't require it. Building a portfolio that reaches 90% or more hourly matching can take overbuilt renewables, storage and firm resources that cost more than a simple annual deal. Smaller buyers often lack the scale to sign such contracts at all.
There's also a reporting gap. The Greenhouse Gas (GHG) Protocol's Scope 2 Guidance, the standard most companies follow for reporting electricity emissions, accepts annual certificates in its market-based method. So hourly matching is a voluntary step beyond the rules. If you're sorting out how hourly claims fit into overall data center emissions reporting, that difference is the first thing to understand.
Finally, grids have boundaries. A clean megawatt-hour in one region doesn't help a data center on a congested grid hundreds of miles away, which is why serious 24/7 programs match within the same grid region.
24/7 Carbon Free Energy Puts Every Hour on the Scoreboard
What is 24/7 carbon free energy? It's a higher bar for clean power claims: matching consumption with carbon-free supply on the same grid every hour, not just adding up annual totals. The difference can be large, as the 58% example and Google's own 67% figure show.
Hourly matching pushes buyers toward wind, storage and firm clean power that cover the night, and it rewards siting on cleaner grids. It also costs more and remains voluntary under today's main reporting standard.
The most useful first step costs almost nothing: take a year of your facility's interval meter data and your contracted plants' output, and calculate your current hourly CFE score. The uncovered hours will jump off the page, and their pattern (nights, winter, calm weeks) tells you what kind of clean power to shop for next.