Renewable Energy
They measure the size of a system, not how much energy it delivers. 1 GW = 1,000 MW = 1,000,000 kW, and the "p" in kWp stands for "peak": the maximum output panels reach under ideal conditions.
Example: a home rooftop is around 5 kWp; a 1 MW project is roughly 200 of those homes put together.