SMA inverters & generators [RE-wrenches]

[Drake Chamberlin]

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At 02:56 PM 6/3/2008, you wrote:
>have two larger PV systems with backup generators. Generators are 30kw and
>500kw respectively, holding up all loads (no critical load breakout). I was
>told by SMA not to allow the inverters to see generator power in the event
>of a grid power failure (but I am curious to understand synch if its
>practical without frying the inverters)

It seems to me that it should be possible to supplement the load of 
backup generators with grid tie inverters, although I've not heard of 
it being done before with direct grid tie inverters.

A control system would be needed that would monitor actual loads.  So 
long as the loads were considerably larger than inverter output, the 
generator should be able to hold up the mini grid to keep the 
inverters on line.  When the load dropped, inverters could be shed.  .

A control system can be built with existing electronics and current 
transducers to measure the load and shed the inverter(s).  I would 
like to work with any EEs that wanted to put together a proto 
type.  I have further details and ideas.

The generators would need to put out very clean power.  A possible 
option to this would be to have inverters that could work with a 
wider frequency window when the utility grid is down.  The 4248 Sunny 
Island has a sensor that changes frequency parameters when the 
generator is running.  This would require working with inverter 
manufacturers who would likely need to get this option through 
U.L.  That is where it might get sticky. Does any one know how clean 
the output of various generators is?

I don't think supporting a generator in this way would require any 
new inventions.  Trace did something similar many years ago.

Drake


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