Google has joined Facebook's Open Compute Project and proposed a new design for server racks that could help cloud data centers cut their energy bills.

The OCP was started by Facebook six years ago as a way for end-user companies to get together and design their own data center equipment, free of the unneeded features that drive up costs for traditional vendor products.

Other big cloud providers such as Microsoft jumped on board, but Google, which is known for operating some of the world's most advanced data centers, stayed away. On Wednesday, at the OCP Summit in Silicon Valley, it said it has now joined.

Google's first contribution will be a new rack design that distributes power to servers at 48 volts, compared with the 12 volts that's common in most data centers. The increase will help to accommodate more powerful computing equipment. Google says the new design is more efficient than its old 12-volt system because it reduces electrical conversion losses by 30 percent.

Google says it's deployed thousands of the racks in its own data centers so the technology is ready for widespread use.

"The key thing that we figured out was, to get the efficiency in cost and power, you have to directly feed the 48 volts to the motherboard and convert it only in one step," Urs Holzle, the senior vice president in charge of Google's infrastructure, said at the OCP Summit. "So these workloads have only one AC-to-DC transformation step, and you step down the 48 volts -- for example, at the CPU -- to around 1 volt."

The higher voltage isn't the only change Google is pushing. The OCP's current rack design is too deep for the narrow aisles in Google's data centers, Holzle said, so Google's specification calls for a rack that's a bit shallower. He said standard server equipment still fits in the smaller racks.

Google and Facebook apparently worked on the design together, and Facebook may use the 48-volt racks in its own data centers, Holzle said. That would be an unusual level of cooperation between two companies that compete in other areas.

It's not clear why Google chose to join the OCP now, though if it wants the industry to rally behind a new power standard, the OCP is a good place to propagate it.

Google's membership makes Amazon the last of the four big hyperscale cloud providers that's not part of the OCP. Even Apple, which is known for being highly secretive, said it had joined the group last year.

Google has other OCP projects in mind as well."OCP is still light on software, and there's a lot more than could be standardized," Holzle said.

For example, it wants to develop an alternative to SNMP (Simple Network Management Protocol), which has been the standard for sharing operational data about equipment in data centers, such as temperatures and fan speeds.

"SNMP has been outdated for a while," Hozle said. "I think there's an opportunity to define standards in a way that will let every operator use the same one, and then every vendor to export their data in the right way."

He also mentioned hard disks as an area for improvement. Google submitted a paper at a Usenix conference last month that called on storage vendors to revamp spinning disk drives for use in cloud data centers.

"The basic idea is that large-scale operators don't care about individual disks, they care about thousands of discs that are tied together through a software system into a storage system," Holzle said.

"So there's lots of opportunities both in the physical form factor to save costs, and then in the overall architecture to save complexity."

The OCP Summit runs for two days. Intel, Microsoft and other companies are also submitting new specifications at the event.