The difference between a kilowatt (kW) and kilowatt-hour (kWh) is the
most misunderstood topic of understanding electricity and how we
measure power and consumption/production. Both concepts are
referenced when talking about a photovoltaic solar system and important
to understand before buying a solar PV system. kW measure power, it
represents the actual electrical size of an electrical component, and kWh
measures consumption/production of an electrical component such as a
Photovoltaic system. kWh is what specific sized photovoltaic system will produce over a
given amount of time. To help make more sense of this let me use the
light bulb as an example. If a household light bulb is rated at 100 watts,
which describes the power it draws instantaneously, and you leave that 100-watt bulb on for one hour it will have consumed 100 watts
continuously for an hour or as it is called, 100 watt/hrs. Now if that
same light is on for 10 hours the bulb will use 1000 watt/hrs. (100 watt/
hrs. x 10) or converted to kilo (meaning 1000) it used 1 kWh. So now if
you buy a 10 kW sized system (about 30 solar PV panels) it is also
called a 10,000 watt system and if it is directed south at an optimum
angle to the sun in Colorado I can calculate that in one year that system
will produce 14,333 kWh of electricity. Now the system size (kW)
never changes, it is always a 10 kW system on this particular roof, but as
solar radiation varies from year to year and the equipment ages, the
production or kWh will vary each year.