A petawatt-hour (PWh) is a unit of energy equivalent to one quadrillion watt-hours. It measures the total amount of energy consumed or produced over time, where one watt-hour is the energy used by a device consuming one watt of power for one hour. This large unit is often used in discussions about energy generation and consumption on a national or global scale. To put it in perspective, a petawatt-hour is enough energy to power millions of homes for an entire year. It is commonly referenced in the context of renewable energy sources like solar power and wind energy, which are increasingly important in addressing global energy needs and reducing carbon emissions.