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Feeding solar power back into municipal grid: Issues and finger-pointing - Page 3

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Posted by Home Guy on April 4, 2011, 1:16 pm
 
"trader4@optonline.net" wrote:


Under the terms of the Ontario Microfit program, you (the home owner)
with a (typical) 3kw to 6kw solar array, will be paid 80 cents /kwh for
20 years.  The going rate for buying electricity in this market at the
residential level is (when you factor in all the various transmission
and delivery costs) about 15 cents / kwh.

You are paid 80 cents / kwh for *any* electricity leaving your array (a
billing meter is installed right after your invertors).  It doesn't
matter if your own home (AC unit, etc) will suck 100% of that solar
energy with none of it going back into the grid.  In fact, it's probable
that on that hot summer day that your home will still be pulling energy
from the municipal grid - just not as much because of the contribution
from your own panels.


There has been some mention of a PF (power factor) issue when it comes
to these panels.

But still - you can't push more electricity onto a network than the load
is asking for (given that your invertors are functioning correctly I
guess).

Posted by hubops on April 4, 2011, 8:09 pm
 



I guess  ,    not.



Posted by daestrom on April 6, 2011, 11:19 pm
 On 4/4/2011 9:16 AM, Home Guy wrote:

One issue that utilities worry about is the available fault current.
The breaker main in a typical home might be able to safely interrupt as
much as 10 kA.  The current of a dead short in your home is a function
of the sources feeding it.  If the total is less than 10 kA, the breaker
opens and everyone's safe.  If the sources could feed more than 10 kA,
the breaker may fuse/melt and the fault will continue to draw current
and your house burns down.

So when adding new sub-station equipment and generating units, they have
to calculate the available fault currents and make sure it's still under
the breaker/protection equipment capabilities.


All that being said, I can't honestly think a small grid-tie PV
installation would make enough of a difference to be a problem.  Worst
case is your neighbor has a fault and the combined current from the
utility and your PV setup exceeds his breaker's interrupting capacity.

But a good EE could sharpen his pencil once and do the calcs and
probably find there is a wide margin between what the pole transformer
can supply to a fault and what your PV system would supply.  They're
probably just to worried about their liability to bother.

daestrom
P.S.  Maybe if every household in a whole development had such a
microFIT installation?  I'd have to see the numbers though to believe it.

Posted by m II on April 6, 2011, 11:31 pm
 

One issue that utilities worry about is the available fault current.
The breaker main in a typical home might be able to safely interrupt as
much as 10 kA.  The current of a dead short in your home is a function
of the sources feeding it.  If the total is less than 10 kA, the breaker
opens and everyone's safe.  If the sources could feed more than 10 kA,
the breaker may fuse/melt and the fault will continue to draw current
and your house burns down.

So when adding new sub-station equipment and generating units, they have
to calculate the available fault currents and make sure it's still under
the breaker/protection equipment capabilities.


All that being said, I can't honestly think a small grid-tie PV
installation would make enough of a difference to be a problem.  Worst
case is your neighbor has a fault and the combined current from the
utility and your PV setup exceeds his breaker's interrupting capacity.

But a good EE could sharpen his pencil once and do the calcs and
probably find there is a wide margin between what the pole transformer
can supply to a fault and what your PV system would supply.  They're
probably just to worried about their liability to bother.

daestrom
P.S.  Maybe if every household in a whole development had such a
microFIT installation?  I'd have to see the numbers though to believe it.


-----------------

The fault capacity of a household main breaker or fuses is not an issue,
unless very old technology, like you.
One hundred feet of twisted triplex supply cable limits faults to well
within the fault tolerances.

On a commercial installation or multiple dwelling installation this can be a
problem with main breakers / meters bolted to a huge supply bus or less than
10 feet of conductors but the fault capability spec. requirements are
typically increased to accommodate the huge fault levels available.


mike


Posted by daestrom on April 8, 2011, 10:49 pm
 On 4/6/2011 19:31 PM, m II wrote:

Got some numbers/calculations to support that?  Is that including the
next door neighbors with their PV installation?

daestrom

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