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Cornered! Power v energy. Get it right!
Cornered! Power v energy. Get it right! | Power v energy. Get it right! |
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| Written by Stuart Corner | |
| Tuesday, 20 February 2007 | |
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The units of electrical power are the watt, kilowatt, megawatt and gigawatt. The units of electrical energy are watt hour, kilowatt hour etc. Thus a 100 watt light bulb will consume 1 kilowatt hour of electrical energy every 10 hours. A generating station with a 1 Megawatt output will produced 24 Megawatt hours of electrical energy if running at full power for a day. So to AMD's press release, headed "AMD reveals scope of annual US data centre energy consumption: 45 billion kWh, at cost of nearly $US3 billion." That makes perfect sense, but it then goes on to say "the study found that in 2005, in the US alone, data centres and their associated infrastructure consumed five million kW of energy, the equivalent of five 1,000 MW power plants." That's a very far cry from 45 billion! What the release meant was that "data centres and their associated infrastructure consumed energy at the rate of five million kW PER HOUR, which would require the entire output of five 1,000 MW power plants." Multiply five million by 24 (hours in day) and 365 (days in a year) and you get pretty close to that 45 billion KwH figure. The release then went on to say: "The study found that in 2005, total data centre electricity consumption in the US, including servers, cooling and auxiliary equipment, was approximately 45 billion kWh...with total data centre power and electricity consumption for the world estimated to cost $7.2 billion annually. The report also examines the growth in electricity demands since the year 2000, concluding that over the last five years server energy use has doubled." So here we go from talking about 'electricity' to 'power and electricity' and then 'energy'. What does it mean? Well data centres don't cook with gas and although they do use diesel for backup, I suspect that all these references are to 'electrical energy' ie 'electricity'. A little intellectual rigour in the use of scientific concepts and terminology would go a long way.{moscomment}
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