FuelCell Energy SureSource 4000, 3.7 MW (discontinued)
FuelCell Energy's discontinued 3.7 MW high-efficiency carbonate plant, with roughly three units ever built
FuelCell Energy SureSource 4000, 3.7 MW (discontinued) is one of 12 fuel cells tracked in the SecondWatt catalogue, each with specifications, lead times and indicative secondary-market pricing.
FuelCell Energy SureSource 4000 dossier: 3.7 MW rather than 4 MW, roughly 60% electrical efficiency, discontinued status, known fleet and inspection guidance.
The SureSource 4000 is a discontinued 3.7 MW combined heat and power carbonate plant, and both the name and the implied rating in the backlog need correcting. It was never a 4 MW machine: the Connecticut Siting Council petition for the Danbury installation describes a 3.7 megawatt combined heat and power fuel cell facility, and the Groton Naval Submarine Base installation is two SureSource 4000 plants with a total output of 7.4 MW, which is 3.7 MW each. The distinguishing specification is efficiency. FuelCell Energy described the Triangle Street plant as achieving approximately 60 percent electrical efficiency when it began commercial operation in April 2020, which is materially above the 50% published for the current 1.25 and 2.5 MW systems and is the highest figure the manufacturer has published for a carbonate product. It is gone from the catalogue. The current carbonate platform page lists only the 1500 and 3000 systems, the Block System range runs 1.25, 2.5 and 12.5 MW, and no 4000-series product appears in the March 2026 corporate presentation or any Block System material. No formal discontinuation notice was ever published. The total known installed population is roughly three units and 11.1 MW across Danbury and Groton, which is far too small to support a secondary market and arguably too small to justify a live product page rather than a legacy fleet-support entry.
Why it matters
This entry is a discipline test for the catalogue. A product with three units built, no successor at its rating, no discontinuation notice and a headline efficiency figure that beats everything still sold is exactly the record that gets published as if it were current. Marking it explicitly no longer offered is more useful to a buyer than leaving the status implicit.
Who buys it
Only the operators of the existing Danbury and Groton installations, who need service and module exchange rather than new equipment. There is no buyer profile beyond that fleet, and any prospective purchaser at this rating is directed to the 2.5 MW or 12.5 MW Block Systems instead.
Role in the data center
None current. The installed units serve a municipal site and a naval base as baseload combined heat and power rather than data center supply.
Key specifications
| Rated output | 3,700 kW |
|---|---|
| Rating corroboration | 2 units totalling 7.4 MW at Groton |
| Electrical efficiency | approximately 60 % |
| Technology | Molten carbonate, internally reforming |
| Production status | Discontinued; absent from the current platform page |
| Successor at this rating | None; nearest are the 2.5 MW and 12.5 MW Blocks |
| Danbury commercial operation | 2020-04-21 |
| Known installed population | about 3 units, 11.1 MW |
| Module design life | 5-year target cell design life (legacy) |
| System design life | 25 to 30 years |
| Product warranty | 15 months after shipment or 12 months after acceptance |
| Datasheet availability | No public datasheet was ever published |
Technical summary
Rated output: 3,700 kW, not 4,000 as the name implies Electrical efficiency: approximately 60%, the highest FuelCell Energy has published for carbonate Technology: molten carbonate, internally reforming, roughly 650 degrees C class Configuration: combined heat and power Production status: discontinued with no successor at 3.7 MW; no formal notice published Known installed base: about 3 units and 11.1 MW total Danbury, Connecticut: 1 unit, commercial operation from 2020-04-21, manufacturer-owned Groton Naval Submarine Base: 2 units totalling 7.4 MW Module design life: 5-year target cell design life on legacy modules System design life: 25 to 30 years, so balance of plant far outlives the stacks
Pricing and availability
Trend: up Lead time, new: Not offered.
Lifecycle and maintenance
Carbonate systems are designed around a 25 to 30 year system life with stack modules replaced inside it, at a 5-year target cell design life on legacy modules and 7 years on current production. The manufacturer publishes a 10% to 15% decrease in power and efficiency across the life of a module, and the legacy 3000 datasheet expressed the same thing as an efficiency band falling from 49% to 44% LHV. Balance of plant therefore outlives three to five module generations, which is why value concentrates in module age rather than plant age. Long-term service agreements run up to 20 years and include module exchange, and the agreement permits a new or a used replacement module.
Common failure points
- Stack module end of life — Modules carry a 5-year legacy or 7-year current target cell design life and then need a maker exchange
- Electrolyte loss — Molten carbonate is lost over long exposure through volatilization of alkali chlorides
- Service agreement transferability — Without a transferable agreement the asset cannot be exchanged, serviced or warranted by anyone
- Sulfur and halide contamination — Testing at 5 ppm H2S produced rapid power loss, and organic sulfides and halides remain unsolved
- Second-life modules — The maker may fit a new or used replacement module, so a refurbished plant can hold aged stacks
- Long start-up — A cold unit is not a same-day restart and no published start duration exists
Procurement channels
None. The platform is not offered new, no dealer stocks it, and the only route to service on an existing unit is the manufacturer's long-term service agreement.
Regional notes
Both known installations are in Connecticut, at Danbury and at the Groton Naval Submarine Base, reflecting the manufacturer's home-state procurement base.