Active Power CleanSource HD flywheel UPS, 675 kW
Active Power's battery-free flywheel UPS at 675 kW, still built in Austin under Piller ownership since 2016
This model is part of SecondWatt’s ups system research catalogue. Specifications and price observations are included where supported by sources. Equipment availability and commercial terms require confirmation.
Active Power CleanSource HD dossier: 675 kW battery-free flywheel UPS at 7,700 rpm and 10.2 MJ, 15 s ride-through, and bearing service intervals.
CleanSource HD is a battery-free flywheel UPS rated 675 kW and 750 kVA at 480 V on the UL datasheet, or 625 kW at 380, 400 and 415 V on the CE version. An integrated steel flywheel spinning at 7,700 rpm stores 10.2 MJ and delivers 15 seconds at full load, 20 at 75%, 29 at 50% and 56 at 25%. Efficiency runs 96.5% at half load and up to 98% at full, output regulation holds within 1%, and up to seven systems parallel for 4,725 kW. The whole package occupies 35 square feet across two cabinets and weighs 10,971 lb.
Active Power was established in 1996 and listed on NASDAQ in 2000, but in November 2016 the business and assets were acquired by Piller Power Systems and merged into the Piller division, with Langley Holdings plc as ultimate parent. Active Power Inc. survives as an operating entity and brand, manufactures in a 135,000 square foot ISO 9001:2015 plant in Austin with capacity above 300 MW of flywheel UPS a year, and runs its own 24/7 US service organisation. Piller and Active Power should be treated as one supplier group.
The line is not a legacy holdout. In June 2025 more than 200 CleanSource battery-free UPS units built in Austin shipped for a 75 MW data center expansion in Mantsala, Finland, described as one of Europe's largest, and the parent's 2025 annual report records a much larger follow-on US order for delivery in the current year.
Why it matters
The economic case is the absence of a consumable. Active Power markets 20 or more years with no battery changes against VRLA replacement every three to five years and lithium or nickel-zinc every ten, and quotes battery UPS efficiency at 96% or lower against its own 98%. Against a battery plant that has to be bought three or four times over a twenty-year life, the flywheel's higher first cost is the whole argument.
Who buys it
Data center and industrial operators who want backup energy with no battery replacement cycle, no battery room cooling load and no lithium fire code exposure, and who already run fast-start generators. The design is only valid where the genset is proven, because ride-through is 15 seconds at full load rather than minutes.
Role in the data center
Battery-free ride-through between a utility failure and a fast-start generator, sized in 675 kW increments and paralleled to 4,725 kW. It sits on the critical bus in 35 square feet across two cabinets, with no battery room, no lead-acid recycling stream and no dedicated battery cooling behind it.
Key specifications
| Rating (UL, 60 Hz) | 675 kW / 750 kVA at 480 V |
|---|---|
| Rating (CE, 50 Hz) | 625 at 380/400/415 V kW |
| Efficiency | 96.5 at 50% load, up to 98 at full load % |
| Flywheel | 7,700 rpm storing 10.2 MJ |
| Ride-through | 15 s at 100%, 20 s at 75%, 29 s at 50%, 56 s at 25% load |
| Bearing type | Precision ceramic ball bearing in a field-replaceable cartridge |
| Dimensions | 80 H x 132.0 W x 39 D (2,032 x 3,353 x 991 mm) in |
| Weight | 10,971 (4,976 kg) lb |
| Heat rejection at full load | 19.10 kW / 65,210 BTU/hr |
| Parallel capability | up to 7 systems for 4,725 kW |
| Standards | UL 1778 listed, cUL CAN/CSA 22.2 No. 107.1, FCC Class A, EN 62040-2 |
| Design life and maintenance | 20-year design life; annual check plus a bearing change every third year |
| Ambient range | 32-104 (0-40 degrees C) degrees F |
| Manufacturing | Austin TX, 135,000 sq ft, ISO 9001:2015, above 300 MW per year |
Technical summary
Rating (60 Hz, UL): 675 kW maximum, 750 kVA maximum, 480 V. Rating (50 Hz, CE): 625 kW at 380, 400 or 415 V. Input: 480 VAC three-phase, three-wire plus ground; 60 Hz; range +10% to -15%. Output: 480 VAC three-phase; voltage regulation within 1%; mains-synchronized. Efficiency: 96.5% at 50% load, up to 98% at 100%; above 96% at 40% load. Flywheel: integrated steel rotor at 7,700 rpm storing 10.2 MJ. Ride-through: 15 s at 100%, 20 s at 75%, 29 s at 50%, 56 s at 25% load. Bearings: precision ceramic ball bearings in a field-replaceable cartridge. Physical: 80 x 132.0 x 39 in (2,032 x 3,353 x 991 mm); 10,971 lb; 35 sq ft over two cabinets. Standards and life: UL 1778 listed, cUL CAN/CSA 22.2 No. 107.1, FCC Class A; 20-year design life.
Major variations
Two builds of the HD: a UL version at 675 kW and 750 kVA on 480 V, 60 Hz, and a CE version at 625 kW on 380, 400 or 415 V, 50 Hz. Alongside it sit the CleanSource PLUS SMS and MMS at 333 to 2,667 kW, which run 10,000 rpm and 6.2 MJ against the HD's 7,700 rpm and 10.2 MJ, take a bearing change every fourth year rather than every third, and are the units covered by the July 2025 OSHPD pre-approval OSP-0829. An OEM rental fleet exists in POWERHOUSE and containerized configurations. Up to seven HD systems parallel to 4,725 kW.
Configurations and options
Two builds carry different ratings and different listings: the UL machine is 675 kW and 750 kVA at 480 V, 60 Hz, and the CE machine is 625 kW at 380, 400 or 415 V, 50 Hz. Beyond that the configurable items are the parallel count, up to seven systems for 4,725 kW, and the service package, since the ceramic bearing cartridge is a field-replaceable consumable on a three-year interval and is the recurring spend on the machine. Seismic is not a catalogue option: the family product guide says consult factory, and the July 2025 OSHPD pre-approval OSP-0829 covers CleanSource PLUS SMS and MMS rather than the HD, so a seismic project needs written factory confirmation. Active Power also runs an OEM rental fleet in POWERHOUSE and containerized forms, which is where ex-fleet units originate.
Compatibility and dependencies
This is a complete UPS rather than an energy store, taking 480 VAC three-phase, three-wire plus ground at 60 Hz and returning the same, mains-synchronized, within 1% regulation. What it depends on is the generator: ride-through is 15 seconds at full load, 29 seconds at half, so the standby set start time and the transfer scheme are part of the specification rather than a downstream detail. In exchange it needs no battery room, no battery ventilation and no spill containment. The room does have to take 19.10 kW, or 65,210 BTU/hr, of rejected heat at full load and hold 0-40 deg C. Physically it is two cabinets across 35 sq ft, 132.0 in wide and 80 in tall, at 10,971 lb, so floor loading and the rigging path are gating items long before the electrical tie-in.
Pricing and availability
Trend: rising Langley Holdings, which has owned Piller since 2005 and Active Power since November 2016, reported in its 2025 annual report, announced 6 February 2026, that Power Solutions division revenue reached 793m euro with 1,952m euro of orders on hand at year end and capacity for the largest behind-the-meter data center power equipment sold out for 2026 and nearly all of 2027. Active Power shipped more than 200 CleanSource units for a 75 MW expansion in Mantsala, Finland in June 2025. Lead time, used or refurbished: No used or refurbished unit listed as of August 2026. Warranty, used: 1-year typical from refurbishment dealers.
Lifecycle and maintenance
Active Power builds the CleanSource HD to a 20-year design life with no stored-energy replacement, which is the whole economic case against a battery plant: no VRLA change at three to five years and no lithium or nickel-zinc change at ten. The consumable is the bearing. The HD runs precision ceramic ball bearings in a field-replaceable cartridge, with one non-invasive annual check and a cartridge change every third year; the sibling CleanSource PLUS MMS goes to every fourth year. Active Power publishes no MTBF figure for the HD and no IEC 62040-3 classification. US service runs from Austin, Texas and international service through Piller subsidiaries and service centres, so parts risk is low relative to a discontinued line.
Thermal and emissions profile
Flywheel and rotary UPS produce no combustion emissions and carry no battery at all, which removes the category's largest environmental liability: no lead-acid recycling stream, no lithium fire code, and what Piller describes as no environmental disposal concerns at end of life. The second-order saving is cooling. Batteries need a controlled room at 25 degrees C or lower to reach rated life, while VYCON states the VDC needs no cooling and Piller states air conditioning is not required for POWERBRIDGE. Active Power rates CleanSource HD to 104 degrees F (40 degrees C) at 96.5% efficiency on half load and up to 98% at full load, so the parasitic cooling load a battery room imposes never appears.
Common failure points
- Ceramic ball bearing cartridge — A missed cartridge change lets the bearing wear until the rotor is lost
- Flywheel and integrated motor-generator — The steel rotor turns at 7,700 rpm inside the motor-generator, so a rotor event is terminal rather than repairable
- Standby generator dependency — Ride-through is 15 seconds at full load, so a slow or unproven genset leaves the load exposed
- Ambient and storage exposure — The unit is rated 0-40 degrees C and a decommissioned machine may have been stored outside that window
- Seismic representation — The July 2025 OSHPD pre-approval OSP-0829 covers CleanSource PLUS SMS and MMS rather than the HD
- Heat rejection at the room — Full-load heat rejection is 19.10 kW or 65,210 BTU/hr and a retrofitted room may not carry it
Inspection checklist
Read the bearing service log first; Active Power specifies a ceramic cartridge change every third year on the HD. Confirm run hours and discharge count rather than calendar age. Verify the nameplate against the UL datasheet at 675 kW and 750 kVA on 480 V, 10.2 MJ at 7,700 rpm and 15 seconds at full load; the 6.2 MJ figure on the marketing page belongs to CleanSource PLUS MMS. Check the parallel count against seven systems and 4,725 kW rather than the 5,400 kW claim on the product page. Establish the storage temperature history against the 0-40 degrees C rating. Require written factory confirmation before treating the HD as seismically pre-approved, because OSP-0829 covers CleanSource PLUS. Confirm the room can reject 19.10 kW at full load, and verify the genset start time the 15-second ride-through depends on.
Procurement channels
New units and service direct from Active Power in Austin, with international coverage through the Piller network across 50 or more countries. Active Power Rentals offers standalone POWERHOUSE and containerized systems from one month upward with turnkey installation and commissioning, and an OEM rental fleet is the most likely origin of any future ex-fleet secondary units.
Regional notes
UL 675 kW builds at 480 V, 60 Hz for North America and CE 625 kW builds at 380, 400 or 415 V for 50 Hz markets. US customers are served from Austin, Texas, where the line is built in a 135,000 square foot ISO 9001:2015 plant, and international customers through Piller subsidiaries and service centres across more than 50 countries.