Energy is the ability to do work, while power is the rate at which work is done.
Power is a time average of energy (energy per unit time). 1 kW is energy 1 kWh is power Steve Spence Subscribe to the Renewable Energy Newsletter & Discussion Boards. Read about Sustainable Technology: http://www.green-trust.org [EMAIL PROTECTED] ----- Original Message ----- From: "Darryl McMahon" <[EMAIL PROTECTED]> To: <biofuel@yahoogroups.com> Sent: Thursday, May 01, 2003 7:56 PM Subject: Voltage (was: RE: [biofuel] World's first hydrogen service station opens in Iceland) > Sorry to quibble, but voltage is potential difference, which implies a capacity to > do work but it is not energy. When current is flowing (amps), work is being done, > and that is energy. Volts x amps = watts. Energy is measured in watts, not volts. > > So, let's consider the power equation, P=EI, > where P = power (in watts), > E = voltage (in volts), and > I = current (in amps) > > Power (energy) is measured in watts, but E is potential difference (or > electromotive force) and is measured in volts. There is no power (energy) until > there is current (amps). > > Voltage is not energy, and that is what P=EI says. Voltage x current = energy. > > Darryl McMahon > > "kirk" <[EMAIL PROTECTED]> wrote: > > > but voltage is not energy > > ------------------ > > P=EI > > > > That says it is. > > > > Kirk > > > > -----Original Message----- > > From: Darryl McMahon [mailto:[EMAIL PROTECTED] > > Sent: Thursday, May 01, 2003 3:38 PM > > To: biofuel@yahoogroups.com > > Subject: Re: [biofuel] World's first hydrogen service station opens in > > Iceland > > > > > > When charging a deep-cycle battery, it does not take any more energy (in > > watt- hours) to put in the tenth kilowatt-hour than it did to put in the > > first kilowatt- hour (assuming at capacity somewhat larger than 10 kWh). > > It may take a higher voltage (potential difference) to continue the > > charging as the battery becomes charged, but voltage is not energy. > > > > (There is an exception at end of charge for certain chemistries, where > > more energy is used to put in the last few percent of the full charge, but > > this is no longer charging, but overcharging, sometimes referred to as > > equalization. A smart charger reduces charging current accordingly in > > this situation.) > > > > When you are putting a gas into a pressurized vessel, it does take higher > > pressure to overcome the rising pressure in the vessel. It is the work > > required to create the higher pressure that takes more energy. > > > > Darryl McMahon > > > > Icarus Solem <[EMAIL PROTECTED]> wrote: > > > > > Hello, > > > > > > It seems that the same is true for charging a battery system, only in > > > this case you are working against the electric potential of the battery > > > cell, instead of the mechanical potential of the pressurized system. If > > > a hydrogen tank is initially empty, it takes more energy per unit to > > > fill it as the pressure rises. The same is true for a deep-cycle > > > battery system - as you run the electrochemical reation to charge the > > > battery, you have to input more energy to run the reaction uphill? I'm > > > guessing that these efficiencies can all be improved - just as the > > > efficiency of biomass to ethanol conversion has increased over the > > > years. > > > > > > Cheers, Karus > > > > > > On Wed, 30 Apr 2003, martin wrote: > > > > > > > An electrochemical reaction where the desired product has to be forced > > > > out at a relatively high pressure requires more energy to push the > > > > reaction over equilibrium. > > > > > > > > kirk wrote: > > > > > > > > >I'm not aware of any change in potential with pressure. You have any > > > > data to > > > > >the contrary? > > > > >Kirk > > > > > > > > > >-----Original Message----- > > > > >From: martin [mailto:[EMAIL PROTECTED] > > > > >Sent: Tuesday, April 29, 2003 9:29 PM > > > > >To: biofuel@yahoogroups.com > > > > >Subject: Re: [biofuel] World's first hydrogen service station opens > > > > >in Iceland > > > > > > > > > > > > > > >Down goes efficiency. > > > > > > > > > >kirk wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > --- > > > > Martin Klingensmith > > > > http://nnytech.net/ > > > > http://infoarchive.net/ > > > > > > Biofuel at Journey to Forever: > http://journeytoforever.org/biofuel.html > > Biofuels list archives: > http://archive.nnytech.net/ > > Please do NOT send Unsubscribe messages to the list address. > To unsubscribe, send an email to: > [EMAIL PROTECTED] > > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ > > > ------------------------ Yahoo! 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