What are (equivalent) Watt Peak Hours?

Equivalent Watt Peak Hours, or eWPH, is the metric that allows us to compare 2 solar panel installations of different sizes. It is defined as daily production (kWh) / Installation capacity (Wp) and has 'hours' as unit.

To express it in words: the eWPH is how long it would take to generate as much electricity as you do in 1 day, but if your installation worked continuously at maximum capacity. In the winter this will be low, typically less than 1 hour eWPH, but in summer this might get up to 7-8 hours, maybe.

We can compare a large installation of 30 panels with a smaller one of 8 panels and still say something about the efficiency of both. E.g. if the 30 panel installation gets an eWPH of 2 hours on the same day its neighbour with 8 panels gets a score of 3 eWPH, then the smaller installation was more efficient, did more with what it had.