Power is measured in kilowatts (KW) and is the instantaneous demand for electricity. For example, a small heater will typically consume 2.4 KW. Your wiring, Grid, batteries and inverters must be capable of supplying this instantaneous power demand.
Energy is the total of Power over time and the usual unit is Kilowatt Hours KWh. The heater will use 2.4KWh in one hour, 57.6KWh in a day and 21 MWh (megawatt hours) in a year. A typical Pooled Energy customer uses 10-20MWh a year total.