Hi Folks, I'm afraid that I have to take exception to the statement that
grid tie systems are 90% efficient. They are not. While it's true that the
inverters may be 90% efficient or better, they are but one component in the
system, and their losses must be multiplied by all the other losses in the
system. For example, the California Energy Commission has done extensive
research on this topic, and they rate most PV modules at 88% efficient.
When you factor in other system losses, such as wiring, dirt accumulation,
etc... the efficiency can drop as low as 67%. While I don't think this
number is typical, an overall system efficiency of 78-80% is more realistic.
For more information on how they estimated these losses, go to:
Shortcut to: http://abcsolar.com/pdf/2001-09-04_500-01-020.pdf