If I can talk to someone and tell him that a new power plant inaugurated by Prime Minister will produce $60$ megawatts per hour, will it be true to use $\mathrm{MW}$ unit for Power?
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5$\begingroup$ What do you mean by $60\,\mathrm{MW}$ per hour? $\mathrm{W}$ itself means energy produced or consumed per unit time. $\endgroup$– SchrodingersCatCommented Nov 24, 2015 at 7:35
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$\begingroup$ i think that staement is false because MW is not basic Unit .. am i thinking right ?? $\endgroup$– M Abid MajeedCommented Nov 24, 2015 at 8:21
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1$\begingroup$ 60MW per hour could be the rate of change of power generation. If you started with the plant generating no power and it took an hour to get the power up to 60MW then the rate of change of power generation would be 60MW/Hr. $\endgroup$– John RennieCommented Nov 24, 2015 at 8:32
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3 Answers
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You're right that the unit "megawatt" is abbreviated MW.
However, as Aniket comments, watt itself means "energy per unit time", so saying that the power plant produces 60 MW per hour doesn't make sense.
In your comment, you question whether MW is a "basic unit". I'm not exactly sure what you mean by this, but the SI unit of power is watt, so if you want to express your statement in SI units, you should say
- "The power plant produces energy at a rate of 60 millon watt",
but either of the following statements are equally true:
- "The power plant produces energy at a rate of 60 MW".
- "The power plant produces energy at a rate of 60 megajoules per second".
- "The power plant produces energy at a rate of 80461.3 British horsepower".
- "The power plant produces energy at a rate of 44 million foot-pounds-force per second".
Being an astronomer I was brainwashed to cgs units, so I'd go for
- "The power plant produces energy at a rate of roughly $10^{15}\,\mathrm{erg}\,\mathrm{s}^{-1}$".
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1$\begingroup$ What's that in Kessel Runs? $\endgroup$ Commented Nov 24, 2015 at 13:29
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$\begingroup$ I think your examples could be improved by amending each to read, "plant produces energy at a rate of" $\endgroup$– DJohnMCommented Nov 24, 2015 at 16:23
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$\mathrm{Watt}$ (or Joule per second or $\mathrm{J/s}$) is the SI unit of power. So megawatt is a valid unit of power (expressing power with order of magnitude $10^6$) and is used mainly in commercial statements.
Definition: Power means the quantity of energy consumed or produced per unit time.
So $\mathrm{MW/hr}$ actually makes no sense since it expresses the quantity of energy consumed or produced per unit time per unit time i.e. the quantity of energy consumed or produced per unit time squared. In other words it refers to the rate of change in power generation.
answered Nov 24, 2015 at 8:29
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Notice, the unit of power is $~\mathrm{J/s}$ or $~\mathrm{W(Watt)}$.
The unit $~\mathrm{MW}$ indicates the energy (in $~\mathrm{mega\ joules}$) produced by power-plant per unit time (in $~\mathrm{seconds}$)
The unit $~\mathrm{60 \ MW\ per \ hour}$ doesn't represent a physical quantity.
answered Nov 24, 2015 at 8:26
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$\begingroup$ Yes, it's a bit like (litres per second) per hour. $\endgroup$– Dr ChuckCommented Nov 24, 2015 at 8:29
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$\begingroup$ here can i use statement something like this : 60 / 60*60*3600 KW/h $\endgroup$ Commented Nov 24, 2015 at 8:36
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$\begingroup$ No, not really. As the unit $KW/h$ makes no sense $\endgroup$ Commented Nov 24, 2015 at 8:40
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1$\begingroup$ To be excessively pedantic $\frac{kW}{h}$ could represent the derivative of the output power curve. $\endgroup$ Commented Nov 24, 2015 at 13:30
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$\begingroup$ So acceleration is not a physical quantity? $\endgroup$– jinaweeCommented Nov 25, 2015 at 20:02