text: The most fundamental formula for Joule heating is the generalized power equation:
  where
  *  is the power (energy per unit time) converted from electrical energy to thermal energy,
  *  is the current travelling through the resistor or other element,
  *  is the voltage drop across the element.
  The explanation of this formula () is:
  Assuming the element behaves as a perfect resistor and that the power is completely converted into heat, the formula can be re-written by substituting Ohm's law, , into the generalized power equation:
  where R is the resistance.
  Voltage can be increased in DC circuits by connecting batteries or solar panels in series.