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Feeding solar power back into municipal grid: Issues and finger-pointing - Page 37

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Posted by trader4@optonline.net on April 17, 2011, 3:19 pm
On Apr 15, 7:46pm, "k...@att.bizzzzzzzzzzzz"

Ok, subsitute the words "gets wasted and performs no useful
work".  That is what you are saying.

That sure must be news to all the power companies that are paying
people for having PV arrays generate power to the grid.

Actually, they do turn very slightly faster when supplied by a
slightly higher
voltage.   Heres' a good reference that covers HVAC compressors:


Take a look at the graph, which shows slip, which is the variation
shaft speed and the sychronous magnetic field which is determined by
line freq.  It shows that slip is also a function of voltage, that
when voltage
increases, RPMs increase slightly.

Agreed.  At higher voltage they do burn a tiny bit brighter. And that
would appear to be an example of what you could consider
wasted energy.  Unless you want to factor in that in winter at
least, in some cases, it adds to the available heat.

Because 240V is out of the range of operation for a 120V
AC motor.  Stick to the case at hand.  We're talking about
running an AC motor at 120V or 121V.  I say running it
at 121V means the current will be slightly less, resulting
in the motor operating at the same HP output, but at
slightly higher voltage and slightly lower current.  And/or
part of the voltage increase will result in more power
being delivered by the motor to the AC comptressor.
You say what?  The motor justs takes that extra volt and
turns it into pure heat?   How does it know to do that?

Well they do consume power in relation to their voltage
and current.  Take a look at these formulas:

Look at the one "To find horsepower."  Clearly I can get the same
HP output by raising the voltage slightly while the current gets
reduced.  Also take a look at the previous graph, which clearly
shows that full load current DECREASES if you increase
voltage slightly.

Again, you'd think that if most or all of that net energy that is put
onto the grid
by PV arrays is being wasted, we'd have heard about it from someone
before this.

Posted by g on April 13, 2011, 2:59 am
On 12/04/2011 16:50, Home Guy wrote:

The inverter must ensure that it transforms the DC from PV to the
frequency and voltage of the grid. To ensure flow of current into the
grid the voltage must be attempted to be raised. Because there are
losses between the inverter and the grid, the voltage will be higher
than the grid.

Fairly good analogy, and due to internal resistance in the pipe then
that must be overcome by having a higher pressure. Don't forget that
somewhere someone else has to reduce the water flow into the pipe system
in order to avoid pressure buildup. Because the water in the pipe system
is used up as it is supplied, at the same rate.

  See the pipe analogy above, the power lines from the inverter has some
resistance, which results in a voltage drop. Therefore the voltage
measured at the inverter will be slightly higher than measured a
distance away.

Why? take a hypothetical grid with 1 megawatt consumption. Generating
machinery produce that energy at a set voltage. Mr Homeowner connects to
the grid with a 10kW PV array. If no power utility adjustment took place
then the overall voltage of the grid will increase. OK for small
fluctuations, but if enough PV arrays came online, somewhere energy
production has to decrease or bad things will happen due to high grid

You cannot unless your local load is zero. You must subtract the local
load from the generated PV array power if the house load is lower. If
the house load is higher than the PV array output then you will use all
the PV array power with the difference supplied from the grid.

Correct, due to a slightly raised voltage if there is a voltage drop
between the inverter and the grid. (There is some drop)

Not possible, the current is controlled by the internal resistance in
the lamp. They will draw a current by the formula volt/resistance.
So when the PV array produces current, grid current is reduced.

The voltage increase you will see at the output of the inverter is very
small, but it does depend on the cables used.

An example: I have a 300 feet underground cable to the nearest utility
transformer and a 100A service panel.

If I max out the power, I will have a voltage drop over the cable of
about 6 Volts. Much higher than normal households.

When your PV array is producing full power, and your house load matches
that, then the voltage difference between the grid and inverter is zero.

at any other house load, current will flow in the power utility lines,
and the inverter voltage increase is a function of the loss in those

Posted by hubops on April 4, 2011, 8:07 pm

  I believe that 10 kw is the maximum size for micro-fit pricing,
in Ontario.   per property.
 .. now available for roof-top only  -  formerly rural free standing
tracking were elegible. ?
Each individual property/service  will have specific limitations -
  .. there's old crappy services out there !  fer shur.
but  -  BIG but  -  I would demand hard facts from my distribution
company - about any specific "grid"  limits  -  that would be
restrictive to a 10 kw solar  ...
 Don't let them snow-job you  -  by saying they have to now plan for
all your neighbours installing  10 kw solar ...
  My understanding  is that these micro solar will be connected
through their own meter ?  so the property owner will not be able to
affect the "sales" by adjusting his demand....  

Posted by Home Guy on April 5, 2011, 1:37 pm
 hubops@cccanoemail.com wrote:

Correct.  Anything over 10 kw falls into a different program - called
"Fit".  But given the geographic area of Ontario (mostly above 42
degrees latitude) you'd need a pretty big house with no tree shading to
generate anything close to 10 kw.

The microfit program really only started in late 2009.  Up until some
point in 2010, you got 80 cents / kwh regardless if it was roof-top or
ground mounted (basically the early program documentation wasn't clear
enough or didn't differentiate between the two styles).  It was only by
mid 2010 that they announced a different price rate for ground mounted
panels - I think it's 60-odd cents.  Anyone that already had
ground-mounted was grandfathered in at the roof-top rate (80 cents).

It's a scam, really.  The local and regional electricity providers (we
generally call the electricity service the "hydro" service, because
historically Ontario's electricity was first generated by hydro-electric
facilities in Niagara falls) does not really want to see these solar
panels on residential rooftops - I suppose they don't need the hassle of
new sources for problems with the grid, power-factor issues,
competition, etc.  

When you get denied to connect your panels to the grid, it's not really
based on the wiring between your house and your distribution transformer
(nobody comes out to look at that).  The denial is based on the capacity
or condition of the regional substation serving your corner of the city
- something for which I can't really imagine how it's involved in the
transmission of the energy your panels are going to put into the grid.  

The fact is that unless you turn off your AC unit on the sunniest /
hottest days of the summer, the energy your panels are putting out will
be 100% consumed by your own home's load, with none of it going out to
the grid.  But you'll still get paid 80 cents / kwh because the payment
meter is placed right after the invertor output before it goes anywhere

You're sort of correct.

Yes, the panels have their own meter.  But nothing the owner can do with
his home's load will affect billing or revenue from the panels - because
he's paid for any and all kw being generated by the panels - even if
none of those kw are technically leaving his own home.

Posted by daestrom on April 6, 2011, 11:26 pm
 On 4/5/2011 9:37 AM, Home Guy wrote:

As I said in another post, one concern is how much fault current can be
drawn from the system.  If there is a largish substation and several PV
generators on it, then the total current feeding into a fault *could* be

If that fault happens to be in someone's home and it exceeds the
*interrupting* capacity of their main breaker, the breaker may not be
able to isolate the fault and their house burns down.

It would seem to me that it would take a large number of PV
installations to really raise the possible fault current very much
though.  Maybe they just don't want to pay an engineer to figure it out.

P.S.  Note that the available fault current has nothing to do with the
circuit breaker's trip setting and only loosely related to the
individual inverter output capability.

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