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What exactly is the difference between 'generating a voltage' 'generating a current' and 'generating power'? Are all these terms linked in some way? And for which situations do I use each term?

For example, do we say a solar panel generates power or voltage when radiated by sunlight?

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Three scenarios spring to mind: -

  • Voltage is generated by "a process" and the connected load takes a current as per ohms law. That current and that voltage implies a power as in volts x amps. This is the normally referred to as power generation but power is only generated if a load is connected.

  • There are other "processes" that generate a current (as in a photo-diode detector) but these tend to be used into short circuits (as per a trans-resistance amplifier) so there's not really a voltage or power involved.

  • Some "processes" directly generate "power" as in the far field of a transmitting antenna or the light emitted from a lamp or LED.

do we say a solar panel generates power or voltage when radiated by sunlight?

It cannot generate power without a load but it can generate a voltage and that can produce current into the connected load.

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  • \$\begingroup\$ Oh okay. So if I were to just leave a solar panel in the sun, does it collect all that sunlight and store energy in the form of voltage inside it? Essentially asking if the solar panel becomes a battery. \$\endgroup\$ – noorav Jul 19 '20 at 14:10
  • \$\begingroup\$ No, it doesn't store energy. \$\endgroup\$ – Andy aka Jul 19 '20 at 14:16
  • \$\begingroup\$ Oh okay. So how does a solar panel (kept in the sun) behave when it is not connected to any load? Does it just sit there getting hotter due to all the photonic energy? \$\endgroup\$ – noorav Jul 19 '20 at 17:34
  • \$\begingroup\$ Yes it does just that. \$\endgroup\$ – Andy aka Jul 19 '20 at 17:58
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All three terms are likely to be used interchangeably when talking casually.

However, if we want to be precise, then there is a very clear difference between them.

We can theoretically generate a voltage, or a current, using no power, or in practice very little power to cover the losses. It's quite easy to generate a high voltage, and as long as no current has to flow, it doesn't need much power. We could maybe generate 1 kV, or 1 MV, using the same small amount of power. You can get a large current flowing at very low voltage, some motherboards generate over 100 A for the CPU at very low voltages, without using much power, while superconductors can circulate a current indefinitely.

To generate power however, requires power. If you want to generate 1 kW of electrical power, whether that's 10 V at 100 A, or 100 V at 10 A, then you need at least 1 kW of some other form of power to do it. It might be mechanical power from a engine or water turbine, it might be solar power incident on a solar panel.

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