Energy Dome’s CO₂ Battery stores electricity by compressing carbon dioxide and retaining the heat produced during charging, then generates electricity later as the CO₂ expands through an expander or turbine. It is a grid-scale, long-duration storage system—not a carbon-capture plant. Energy Dome describes its product as suited to 8–24 hours of dispatchable capacity, but its published efficiency, cost and lifetime figures come from different company or project sources and should not be treated as one independently verified performance profile.
How does the CO₂ Battery work?
The system uses carbon dioxide as a recirculating working fluid in a closed thermomechanical cycle. During charging, electricity powers equipment that compresses the CO₂. Energy Dome says the gas is stored under pressure in liquid form, while heat created by compression is retained for use during discharge.
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When electricity is needed, the stored heat is returned to the process. The CO₂ evaporates and expands through an expander or turbine, which drives a generator. The CO₂ then returns to the dome or gasholder to be used again. In effect, the system converts electricity into stored pressure and heat, then converts those back into electricity. Energy Dome’s technology overview and 2026 brochure describe the cycle.
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The standalone configuration stores and reuses heat from charging. CO₂ Battery Plus instead integrates a co-located gas turbine and uses its waste heat rather than relying on heat stored during the battery’s charging cycle. Energy Dome says this configuration more than doubles peak output and can boost efficiency for gas-fired generation; those are company claims, not an independent comparison.
#1 Best Overall
- Double-Sided Battery Organizer: The Ontel Battery Daddy is a compact & portable way to organize, store and protect a boatload of batteries! Clear 'Easy View' cover lets you see everything at a glance and prevent any unwanted contact
- Maximize Battery Organization: Battery Daddy uses both sides to store up to 180 batteries of various sizes and types. This sleek, compact battery case holds 76 AA, 72 AAA, 8 9-Volt, 10 C, 12 Coin Cell and 8 D batteries (Batteries not included)
- Help Prevent Battery Drainage: Don't let loose batteries touch and drain other batteries. Stay organized and be prepared for power outages or battery-operated household items like remote controls, flashlights, toys and emergency gadgets
- Battery Tester Included: This battery storage case comes with a tester that can check whether your single-use or rechargeable batteries are still good. Align the battery's positive and negative ends on the tester to view the result on the indicator
- Durable and Portable Design: With a clear locking lid, secure latches, and a built-in carrying handle for easy portability and storage in many drawers, shelves or emergency kits. Great for professionals, technicians or anyone needing batteries on the go
Is the CO₂ Battery carbon capture?
No. The CO₂ is the working fluid in an energy-storage cycle: it is compressed, expanded, and recirculated. The described process does not permanently capture and store carbon emissions. The word “carbon” in the system’s name refers to the fluid, not to a carbon-removal function.
How long can it store energy, and what is its round-trip efficiency?
Energy Dome’s product page describes 8–24 hours of firm, dispatchable capacity. Round-trip efficiency is the share of charging electricity that the system returns as electricity after a full charge-and-discharge cycle; figures can differ with system boundaries and measurement method.
Rank #2
- Double-Sided Battery Organizer: The Ontel Battery Daddy is a compact & portable way to organize, store and protect a boatload of batteries! Clear 'Easy View' cover lets you see everything at a glance and prevent any unwanted contact.
- Sleek and Compact Design: Battery Daddy uses both sides to store up to 150 batteries of all types. Holds 58 AAs, 68 AAAs, (4) 9 Volt, 8 Cs, 8 Ds, & 8 Button Cells. Easily stores away in any drawer. Includes Battery Tester
- Find the Right Battery: Incorrect storage drains batteries. Stay organized and be prepared for power outages, new gifts, or any time you need to replace a dead battery. Built-in carrying handle lets you take it anywhere
- Battery Tester Included: Battery Daddy comes with a tester that can check whether your single-use or rechargable batteries are still good. Just align the negatives and positives of the batteries on the tester and you can see the result on the indicator
- Easy Storage: The compact size allows for storage in drawers and shelves along with your other supplies and household items. The portable design has a sturdy carrying handle and secure heavy-duty latches so you can easily transport
| Figure | Source and context | How to read it |
|---|---|---|
| 70%+ net AC-AC and MV-MV | Energy Dome’s 2026 brochure | Company-published efficiency figures using the stated AC-AC and MV-MV boundaries. The brochure says performance is third-party verified, but the reviewed excerpt does not name the verifier or include a test report. |
| 75% round-trip efficiency | European Commission CORDIS CO₂ Battery project factsheet; project record signed in 2023 | A project-record metric, not by itself independent validation of a commercial plant’s operating performance. |
Energy Dome also claims a lifetime of more than 30 years and no degradation on its product page and in its 2026 brochure. These remain company claims in the sources cited here. The figures should not be combined with the CORDIS project metric as if they were measurements from a single independently verified system.
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What does it cost?
The European Commission CORDIS project factsheet gives two capital-cost figures, each with a different basis. They are project-record figures rather than a like-for-like comparison with other storage technologies.
Rank #3
- Fireproof Explosion Proof Waterproof: Fireproof Battery Organizer Case is made of upgraded non-itchy silicone coated fiberglass that can withstand temperatures up to 2000. It's also highly water-resistant. And the special material has a certain explosion-proof performance, we design this Battery Organizer Box to minimize the hazards and losses caused by battery explosion
- Stores For More Type Batteries: It can hold 79*AA, 56*AAA, 8*C, 6*D, 9*9V, 30*Button type batteries( 3V lithium - CR 2032,CR 2016,CR 1632, CR 2025,LR44 etc.), total over 200 batteries. Keeping your batteries organized and helps extend the life of your batteries
- Safely Stores Batteries: Our fireproof battery organizer bag features a double zipper and durable handle to keep batteries from shock in the event that a defective battery were to swell, leak, or explode, our bag is designed to contain this and keep your family safe. This battery case neatly holds the batteries snugly in place within the foam pre-cut slots and keeps the contact ends from contacting each other, making it easy for you to find whatever battery
- Lightweight & Portable Battery Box Containers: You can not only hang the battery pouch on the wall, put it in a storage room or drawer and anywhere away from fire, but also take it with you on trips and to various outdoor activities. It is suitable for birthdays, New Year, Christmas, Valentine's Day, Mother's Day, Father's Day and many other holidays
- Please Note: BATTERIES NOT INCLUDED. YOHAWJER included a battery tester is suitable for all types of batteries with the organizer but Does NOT include any batteries. Super convenient for you to distinguish which batteries need to be recycled
| Capital-cost figure | Basis recorded by CORDIS |
|---|---|
| €183/kWh | First-of-a-kind CAPEX in the project record signed in 2023. |
| €103/kWh | Projected CAPEX at a production rate of 50 plants per year in the same 2023 project record; this is a scale scenario, not an observed cost for a fleet of plants. |
These figures alone do not establish a current installed price. Project size, scope, financing, location and the basis used to calculate cost all matter when comparing storage proposals.
How does it compare with lithium-ion or other storage?
The most useful starting distinction is duration: Energy Dome targets multi-hour grid storage and gives an 8–24-hour product range, rather than positioning the system as a small consumer battery. That does not establish that it is cheaper, more efficient, or better suited than lithium-ion, pumped hydro or another long-duration technology in every application.
Rank #4
- Portable battery storage box with battery tester
- Can hold 110 total batteries, including 36 AAA, 48 AA, 4 C, 4 D, 4 9V, 14 coin cells
- Carrying handle for easy portability; wall mountable
- Battery tester included; tests 1.5V and 9V batteries for usability
- Transparent cover allows you to see batteries without opening the lid
A fair comparison needs consistent figures for discharge duration, round-trip efficiency, installed cost and its cost basis, lifetime and degradation, siting constraints, materials and supply-chain exposure, dispatch profile, and project maturity. The cited material does not provide an independent, consistent dataset across these technologies, so it cannot support a universal winner. Energy Dome’s own comparison table against lithium-ion is a company comparison, not an independent apples-to-apples assessment.
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Where are Energy Dome’s projects?
Project announcements describe plans, contracts and expected dates; they are not proof that a plant has been commissioned. The dates below are the announcements’ stated expectations, not confirmation of present operating status.
Best Value
- Set of 4 - Two AA and Two AAA Battery Storage Boxes, Each Box Provides Storage for up to 48 Batteries – “Batteries Are Not Included”
- The Strong and Secure Locking Latch Design Keeps Batteries Neatly Organized and Safely Protected Inside the Storage Box.
- Includes Four Movable Dividers Per Box to Create Smaller Compartments - Also Great for Separating Live Batteries from Dead.
- Constructed from High Impact Plastic Material - Good for Storing and Organizing Your Batteries While Traveling or Camping Etc.
- Dimensions: AA Box, Length, 7 ½” X Width, 4 ¾” X Height, 1 ¼” - Dimensions: AAA Box, Length, 6” X Width, 4” X Height, 1”
| Location and announcement | What was announced | Status indicated by the source |
|---|---|---|
| Ottana, Sardinia — December 2024 | A 20 MW / 200 MWh plant designed for ten-hour discharge, with ENGIE contracted to optimize dispatch in Italian power markets. Energy Dome said it would own and operate the facility. | The announcement described the plant as nearing completion and gave a planned commissioning window. That forecast has passed, and the cited announcement does not establish whether the facility is operating now. Energy Dome/ENGIE announcement. |
| Global partnership — Google, July 2025 | Google announced a long-term partnership, an investment in Energy Dome, and plans to support multiple commercial projects globally. | A partnership announcement and development plan, not evidence that the planned projects have entered operation. Google announcement. |
| County Offaly, Ireland — June 2026 | A 23 MW / 200 MWh project near Rhode, with Lumcloon Energy as local development partner. The announcement says land, planning consent and grid connection were secured, and EirGrid awarded a ten-year capacity contract. | Expected online in 2028; prospective as of the June 2026 announcement. Project release. |
| Coronado Generating Station, Arizona — June 2026 | A planned 19 MW, ten-hour system. Energy Dome is to own and operate it; SRP is to dispatch its output under a 20-year tolling agreement. The announcement says Google will fund a portion through cost-sharing with SRP. | Expected online in 2029; proposed, not an operating result. SRP’s Chico Hunter said: “This project will enable SRP to test the real-world performance of Energy Dome’s technology in the Arizona climate.” Project release. |
What should a prospective buyer or grid planner verify?
For a utility, grid operator or large energy user, the technology is best assessed as infrastructure rather than as a consumer battery. Before using headline figures in a procurement or planning decision, ask for project-specific evidence that matches the intended site and contract.
Quick Recap
- Operating evidence: Request commissioning records or operating data for the relevant system configuration, not only an announced project schedule.
- Efficiency boundary: Confirm whether the quoted figure is net or gross, the AC or medium-voltage boundary used, and what auxiliary loads and operating conditions are included.
- Cost basis: Separate equipment and installation costs from project-specific costs, and distinguish a first-of-a-kind estimate from a projected manufacturing-scale scenario.
- Duty cycle and duration: Match the proposed charge and discharge profile to the service required, rather than comparing duration figures alone.
- Lifetime evidence: Ask what operating data supports lifetime and degradation claims and how those claims relate to maintenance, component replacement and warranty terms.
- Project readiness: Check local permitting, grid access, offtake or dispatch arrangements, and the current commissioning status of comparable installations.
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