Monday, February 20, 2006

Units - warning, tecchy ahead

One thing that really bugs me in sci-tech reporting is units.
Units are what distinguishes hard science from stamp collecting. Is it 127 metres away or 0.127 kilometres away? what's the difference, is that the same distance and who cares anyway? Well, in the real world, bridges collapse, cars explode and airplanes fall out of the sky so yes, its extremely important.
When the information overload is kicking in, credibility is established or destroyed based on an incredibly fine margin, units quickly mark an amateur from a possible expert. Take this story on the Snowy scheme in The Australian, how can i take this reporter seriously when they think electricity is traded in MW/h ? If they can't get the unit of electricity correct, what credibility do they bring to other multiple facets of the discussion? Environment, economics, tradgedy of the commons, water rights, farming, tourism, electricity market operations, future eating etc etc are all part of the problem and these guys can't even dig around and find the correct units for electricity consumption? Good grief.

BTW the standard unit for energy is the Joule (J). A kilojoule is 1000 Joules. A Watt (W) is a rate of energy delivery/consumption of 1 J per second. A unit of electricity you purchase at your house is 1 kWh (NB 1 kW for 1 hour is = 1000 J/s x 3600 s = 3600, 000 J or 3.6 MJ). It's a far more user-friendly unit for day to day use, but remember, it's just joules at the end of the day.
Electricity is traded in the market in chunks of 1000 kWh = 1 MWh. This collapses down to 3, 600,000,000 J or 3.6 GJ so you can see that they are trading units of energy - as they have to.
Purchasing the right to pull off the grid 3.5 MW is a different question because it is a rate of extraction (think of your water supply: quantity vs delivery rate) and is a problem for your distribution network. A unit of MW/h is ludicrous, it says that you are accelerating the rate at which you are pulling energy off the grid...

Yes, i understand this may seem pedantic, but science and engineering hinge on precisely defining the terms and units that are at work. If the newspaper can't hire people with the smarts/training to write these stories, maybe it should contract them out to people that can.

Update 23/2/06: *ahem*, i dropped a factor of 1000 from the calculation for 1 kWh. A little embarrassing during a rant on units and inaccuracies in newspapers...


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