The Importance of Power Supplies

Reading this recent post about Google's initiative to encourage PC makers to install more efficient power supplies, reminded me of a 2002 study commissioned by NRDC. Back in 2002, about 500M power supplies were sold in the U.S. annually, and about 6% of all electricity consumed in the U.S. flowed through power supplies. I haven't run across updated data and I will assume that the results of the 2002 study are still reasonable.

Energy-efficient power supplies, as we will see later, already exists and can be deployed by electronics manufacturers. Doing so would lead to about 15-20% savings in KWH consumed, or a savings of about 1% (from 6% to 5%) of the total electricity consumed in the U.S.

The 1 percentage point translates to about 24B tons of reduced CO2 emissions! Electronic products usually have three operating modes: active usage, standby, and sleep. The active mode accounts for a vast majority of electricity consumption:

With all the past attention given to standby energy losses ("leaking electricity", "vampires"), the above numbers justify the recent emphasis on power supplies that are efficient in active mode. The graph below illustrates what happens for an average PC, Monitor, and (analog) TV:

Drilling-down further and using numbers for PC's, Monitors, analog TV's, power supplies that are energy-efficient while electronic equipment are in active mode are paticularly attractive. Given that there are about 2 Billion power supplies sold each year, it becomes clear why power supplies are increasingly becoming an important issue among environmentalists. In the U.S. alone, the power supply market is about $4B/year and growing at 10% annually.

In the context of electronic equipment, power supplies take electricity (usually 110 Volts, AC) and converts it to a lower DC voltage. Linear power supplies are used mostly for low wattage products (15 watts or less), switching power supplies are more commonly found in higher wattage products like desktop computers, TV's and microwaves.


Energy efficiency of a power supply is measured by taking the ratio of output to input power:

Data from the 2002 NRDC study gives the following "typical" efficiency ranges (low, high) for when devices are operating in active-mode:

The more energy efficient switching power supplies range from 50% to 90% efficiency when devices/products are operating. While the data is about 5 years old, the 2002 NRDC study contains detailed efficiency and consumption numbers for a wide variety of electronic products:

Our measurements of a variety of electronic products yielded a wide range of efficiency levels for external power supplies. Efficiencies were usually higher with the original factory power supply provided with the unit than with after-market, “universal” adapters. It is simply easier to optimize a power supply for energy efficiency when it is intended to operate at a single voltage and relatively high load (see part load efficiency discussion below). Note that standby power consumption varied from a low of (less than) 0.01 watts to a high of nearly 2 watts, while active mode efficiencies ranged from as low as 20% to more than 90%.

PC's and Servers
What Google is proposing is to standardize PC power supplies from the current multiple voltages (+12v, -12v, 5v, and 3.3v) to a single voltage (12v). Google-designed power supplies are reported to achieve active mode efficiencies of 90%. Interestingly, Jeff Atwood graphs the efficiency of two very different power supplies:


and he notes that the more efficient power supply has peak efficiency at around 250 watts. Most home PC's barely consume 200 watts -- under full load! Google's proposal becomes even more interesting if power supplies can achieve 90% operating efficiency for a typical home PC user.

In order to start seeing efficient power supplies in home PC's and laptops leading PC manufacturers need to choose to install them. Google has chosen to bypass the server manufacturers and design their own power supplies. Here lies the quandry: the people who end up paying the electric bill (the consumers) are not the ones deciding what power supply goes into their PC's.


Consumers will start requesting energy-efficient power supplies and the OEM's will eventually relent and start transitioning to more efficient designs. There is already reason to be optimistic. As the NYTimes article notes, there is an initiative underway ("80 plus") which aims to encourage computer makers to start installing more efficient power supplies.

In the Data Center front, changes are coming at a faster rate, and multiple designs (including the use of shipping containers) are being proposed:


With power accounting for 40% of costs in a typical Data Center, energy innovations will emerge quickly. Hopefully some of the ideas will be applicable to the broader consumer market.

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