Smart thermostats make for smarter grids

Untitled by johnwilson1969
Untitled by johnwilson1969

We have been discussing off and on how smart power meters (see Smart metering data storage appetite) and intelligent sensors (see the Sensor cloud comes home) such as smart thermostats generate copious amounts of data.  Sensors and meters such as these are used in a new power distribution network called the smart grid.

But recently there was a report in Technology Review of how smart thermostats can “communicate” with power companies to determine current energy costs and then alter temperature settings to reduce power use.

Power companies give discounts to those customers who install the smart thermostats in the hope that such devices will lower peak power use.  If this happens they will save significant investments in new power generation and power lines to satisfy the ever-growing peak power level. This probably works best in summer with A/C equipment which is a prime user of electricity during peak consumption periods. The story goes on to say that these smart thermostats have been used in a small test bed but are about to be rolled out on a wider basis.

Power thrashing?!

One serious concern brought up in the article is that when such devices are rolled out on a large scale there is a high chance of power thrashing.

As smart thermostats reduce home power consumption in volume, they may end up driving the cost of power down low enough such that the thermostats, on the next cycle, will start to consume more power, leading to power thrashing.

If this happens on a big enough region, such oscillations of power use may lead to an even higher peak than what was in place prior to the smart grid.  And if the thermostats have been in place for a while and succeeded in reducing peak power capabilities, such thrashing may lead to a smart grid crash or congestion collapse.

Thrashing prevention on the power grid

There are three ways to prevent power thrashing:

  • Increase the amount of peak power to handle the worst case regional energy working set.
  • Decrease the power consumption of the largest power users.
  • Decrease the number of consumers.

It would seem the first solution defeats the purpose of the smarter grid.  I believe the second approach can best be implemented by having even more smart appliances which can reduce power consumption on demand.  As for the third approach, this may be infeasible, as you cannot just drop power to consumers without some serious consequences.

Dumb grid solutions

We have for a couple of years now received a discount on our power bill by having a special device attached to our A/C unit that reduces our power consumption on one day a year. It’s not quite as intelligent as the smart thermostats discussed above but it does the job (at least once/year).  Such devices, used on a large scale could provide the capabilities of the smart thermostat but eliminate the potential for thrashing and large power oscillations.


So the smart grid is coming but the smarter it gets the more care we need to take in implementing it.


Smart metering’s data storage appetite

European smart meter in use (from (cc)
European smart meter in use (from (cc)

A couple of years back I was talking with a storage person from PG&E and he was concerned about the storage performance aspects of installing smart meters in California.  I saw a website devoted to another electric company in California installing 1.4M smart meters that send information every 15min to the electric company.  Given that this must be only some small portion of California this represents  ~134M electricity recording transactions per day and seems entirely doable. But even at only 128 bytes per transaction, ~17GB a day of electric metering data is ingested for this company’s service area. Naturally, this power company wants to extend smart metering to gas usage as well which should not quite double the data load.

According to US census data there were ~129M households in 2008.  At that same 15 minute interval, smart metering for the whole US would generate 12B transactions a day and at 128 bytes per transaction, would represent ~ 1.5TB/day.  Of course thats only households and only electricity usage.

That same census website indicates there were 7.7M businesses in the US in 2007.  To smart meter these businesses at the same interval would take an additional ~740M transactions a day or ~95GB of data. But fifteen minute intervals may be too long for some companies (and their power suppliers), so maybe it should  be dropped to every minute for businesses.  At one minute intervals, businesses would add 1.4TB of electricity metering data to the household 1.5TB data or a total of ~3TB of data/day.

Storage multiplication tables:

  • That 3TB of day must be backed up so that’s at least another 3TB of day of backup load (deduplication notwithstanding).
  • That 3TB of data must be processed offline as well as online, so that’s another 3TB a day of data copies.
  • That 3TB of data is probably considered part of the power company’s critical infrastructure and as such, must be mirrored to some other data center which is another 3TB a day of mirrored data.

So with this relatively “small” base data load of 3TB a day we are creating an additional 9TB/day of copies.  Over the course of a year this 12TB/day generates ~4.4PB of data.  A study done by StorageTek in the late ’90s showed that on average data was copied 6 times, so the 3 copies above may be conservative.  If the study results held true today for metering data, it would generate ~7.7PB/year.

To paraphrase Senator E. Dirksena petabyte here, a petabyte there and pretty soon your talking real storage.

In prior posts we discussed the 1.5PB of data generated by CERN each year, the expectations for the world to generate an exabyte (XB) a day of data in 2009 and  NSA’s need to capture and analyze a yottabyte (YB) a year of voice data by 2015.  Here we show how another 4-8PB of storage could be created each year just by rolling out smart electricity metering to US businesses and homes.

As more and more aspects of home and business become digitized more data is created each day and it all must be stored someplace – data storage.  Other technology arenas may also benefit from this digitization of life, leisure, and economy but today we would contend that  storage benefits most from this trend. We must defer for now discussions as to why storage benefits more than other technological domains to some future post.