kW stands for kilowatt, or 1,000 watts. It is a measure of power. Your LG solar power system is rated according to the number of watts it can produce each hour. For example 12 x 260Watt panels will make up a 3,120 kW system. Normally you would then also use a 3 kW inverter with this system to convert the panel’s direct current (DC) voltage to 240V AC.
kW/h stands for kilowatt hour. It is a measure of energy. If you use a 1 kW electric pool pump for one hour, it will consume 1 kW/h of energy. Or if you use 20 x 50W down lights for an hour they will consume 1kW/h. Usually your electricity bill is billed in units of kW/h.