Are batteries in servers a good idea?
There are some definite advantages in Google's approach:
- No need to pay for UPS systems (saves CapEx dollars)
- Eliminates two conversion stages found in a traditional AC double-conversion UPS
- Reduces dedicated floor space/real estate commonly devoted to UPS/battery rooms
- Localizes fault domains for a failed server to just one server
- Scales linearly with the number of servers deployed
All of these add up to a solution that works just as well for one server as it does for one thousand servers. Coupled with Google's efforts to increase energy efficiency through founding and support for the Climate Savers Computing Initiative (CSCI) and its target of 92% power supply efficiency, this solution appears to be very efficient.
However, there are some down sides to Google's approach:
- A lot of batteries to wire up and monitor
- Increased air impedance from blocking airflow
- Lower battery reliability with increased ambient temperatures
- Higher environmental impact due to increased battery materials
- Individual server supplies are exposed to a higher level of power transients and harmonics
- Potential phase imbalances and stranded power in data centers
Issue #1 is self-obvious. Issue #2 can be seen from this picture from Green Data Center Blog; the physical mass of the batteries blocks a good portion of the air space in front of the server, which increases the resistance and in turn requires more fan power to move the same amount of air.
Issues #3 and #4 are somewhat related. Google, Microsoft, and other leading internet companies have advocated moving the ambient temperatures of data centers to higher temperatures, with some advising 35°C, 40°C, or even occasionally 50°C ambient temperatures. There are clear savings to be had here, but it may run counter to the battery approach used by Google. Assuming the Google batteries are conventional lead-acid batteries, a common rule is that the useful life of batteries drops by ~50% for every 10°C above 25°C ambient temperatures. Thus, a 4-year battery would only be good for ~2 years in a 35°C environment. In comparison, conventional UPS batteries are often rated for 10, 15, or 20 years. When consolidated in a UPS battery cabinet, the batteries can be protected from the higher ambient temperatures through localized cooling (batteries dissipate almost no heat) for increased life.
Lots of little batteries like Google uses results in more materials usage compared to the use of larger batteries. Couple that with reduced battery life at higher temperatures, and the result is not as good as it first seems. According to http://www.batterycouncil.org/LeadAcidBatteries/BatteryRecycling/tabid/71/Default.aspx, more than 97% of lead from lead-acid batteries is recycled, but this also states that 60-80% the lead and plastic of new batteries is recycled material. Looking at this last stat a different way, 20-40% of lead-acid battery materials are not recycled. Thus, even if Google performs 100% battery recycling, using lots of new batteries still results in the use of a lot of new materials.
I'll address issues #5 and #6 in a future post.
--kb
A nit, if I may:
ReplyDelete"more than 97% of lead from lead-acid batteries is recycled, but this also states that 60-80% the lead and plastic of new batteries is recycled material. "
That means that either:
1. some of the lead salvaged from old batteries go into something other than batteries
2. more new batteries are being made than old batteries are being retired.
'Looking at this last stat a different way, 20-40% of lead-acid battery materials are not recycled.'
nah- the stats you posted show no such thing.
'Thus, even if Google performs 100% battery recycling, using lots of new batteries still results in the use of a lot of new materials.'
As long as they get recycled at eol, no problem.
Regards
Jay
Jay,
ReplyDeleteFair point. Even if 20-40% of battery materials are new, that doesn't necessarily the older materials are necessarily not recycled for other uses, albeit lower ones on the scale of usable products.
I would like to share few ideas.
ReplyDeleteIdeas to help prolong the life of your battery:
* Clean the terminals of your battery with a soft dry cloth.
* Avoid charging for extended periods of time.
* Charging must be done at room temperature.
* Don’t hit the battery hard with anything as it may result in damaging the cells.
* Always use recommended charger or adapter for charging.
* Keep the battery away from heat sources as this will result in the discharging of the battery even though it is not in use.