A watt (W) is a instantaneous measurement of power. A kilowatt (kW) is a thousand watts. Electrical power is a rate that signifies the relations of voltage to current. A watt is equal to the voltage multiplied by the current of a system at a given point.
A watt-hour (Wh) is a cumulative mesurement of energy. A kilowatt-hour (kWh) is a thousand watt-hours. If a 1 kW generator runs for 2 hours it produces 2 kilowatt-hours of energy. (kW x hours of operation = kWh.) The kilowatt hour is the unit of measurement that most utility companies use to bill there customers.
To use an analogy, we can think of electricity like beer. If we think of beer flowing from a keg, the volume of beer would be like the current and the pressure in the line would be like the voltage. If we fill glasses from the tap for an hour, the number of pints would be like kilowatt-hours per hour and our utility bill would be like the tab at the end of the night. If we pump the keg it's like increasing the voltage and if we get a bigger tap it's like increasing the current- either way we're increasing the amount of beer that can be poured- similar to how wattage increases when voltage or current increases. Right now I'm working on a video that demonstrates this analogy- I think it's gonna take at least three kegs to prove my point. Stay tuned.
The quote you have is a little misleading. It doesn't say if the 550,000 kWh is produced per day, week, month or year. If we ignore all inefficiencies in a system, a 400kW array in the sun for 5 equivalent sun hours a day will produce 2000 kWh per day, 60,000 kWh per month and 720,000 kWh per year. With some reduction to the sun hours and some reductions due to inefficiency in the system, it would make sense that an array that size could produce that amount of electrical energy in a year.
Check out the Photovoltaics: Design & Install Manual. It's a good source of info:
http://store.altenergystore.com/Books-Workshops-Videos/Solar-Electric-and-Passive-Solar/Photovoltaics-Design-Install-Manual/p481/Wikipedia has good entries on Watts, Energy, Power and other basic electrical definitions.
http://en.wikipedia.org/
