The day-ahead market price (PZU) published by OPCOM. This is not the price on your bill: it is the wholesale price, which reaches consumers later through supplier tariffs, taxes and grid fees.
Bars are the price for each hour, the line is demand. Price usually climbs with demand, and midday hours are cheaper because solar covers part of it.
If you can move a laundry cycle, an EV charge or a water heater, these are the hours to pick. Cheap and clean do not always coincide: nights are cheap, middays are clean.
The hours with the lowest market price.
The hours with the least CO₂ per kilowatt-hour.