Re: Government offer of *feed-in tariff of 60 cents per kilowatt hour (kWh)*

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Sylvia Else wrote:
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Thanks Sylvia,

Has anyone actually crunched the numbers to prove this is viable even with
 the limited inefficiencies, and there is a *net gain* in power?

Or is it just a political stunt to get more people to take up solar photovoltaic
cells,
 i.e. get on the green bandwagon, save the planet, stimulate the economy etc...

Will the net gain be a benefit to only the immediate neighbors who are there to
consume
It , or is of benefit to everyone on the grid?

Also, what if there is *excess* power produced by streets of houses with
solar photovoltaic cells, where is all that *surplus* energy stored??




Re: Government offer of *feed-in tariff of 60 cents per kilowatt hour (kWh)*


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I'm sure there's a net gain. Not only is the power produced by the PV
cells being consumed in the neighbourhood, but the grid losses, such as
they are, are obviated because that power doesn't have to pass over the
grid.

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photovoltaic cells,
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to consume
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Now you get in the murky area of the definition of benefit. The total
power available is increased, at the instant it's produced, but except
in very unusual circumstances, it's not power that would otherwise have
been unavailable (which would have let to power cuts). All the PV cells
are doing is reducing the production of power by the existing generation
plant with the highest marginal cost (typically gas or oil). The only
benefit is the elimination of the CO2 that would have been produced by
that other plant. Whether that elimination is a real benefit is a
separate argument.

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Well, that won't happen. Even in a green politician's wildest dreams,
there's simply not going to be anything like enough PV output from
domestic rooftops to meet the entire power load during the day.

That aside, where is surplus energy stored? For the most part, we have
no practical way of storing energy on this sort of scale. There is a
small capacity to pump water from the lower side of hydroelectric plants
to the high side, and the energy, or most of it anyway, can later be
recovered by operating the hydroplant. Of course, this presupposes that
the hydro plant doesn't have enough reserve to have operated anyway.

This scheme is used, as are some compressed air storage systems, but
they are limited by the need to have suitable places to build them.
There are a few other mechanisms, but none have a major impact. But
these schemes would never be used to store the energy produced by PV
cells. It wouldn't be economically worthwile. Where they are used, it's
to store energy produced cheaply overnight from coal or nuclear so that
it can be used during the day, where other sources (gas, oil) are more
expensive.

Sylvia

Re: Government offer of *feed-in tariff of 60 cents per kilowatt hour (kWh)*


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"reducing the production of power"

Interesting you say that as I have wondered about the "mechanism" to gauge
 the amount of power that is required to maintain all the houses/factories at a
particular time of day etc.

Is there some kind of dynamic sensing device that knows if there is a reduced
load
and therefore less coal/gas is burned?
Then if the demand is increased, does the "mechanism" sense this instantaneously
and say "x tonne" of additional coal is shovelled into the furnaces to generate
more electricity?



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It'll never meet the demands of industry, there is no way you can power
an aluminium plant with PV, that's for sure!


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I've heard about storing the access energy into the batteries of electric cars
that are plugged into the grid , that of course is some time into the future (
if it ever eventuates)





Re: Government offer of *feed-in tariff of 60 cents per kilowatt hour (kWh)*


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a particular time of day etc.
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load
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The entire network is the sensing device. The more current is drawn, the
more torque is required to keep the generators rotating at their nominal
rate. Any tendency for the rotational rate (or equivalently, mains
frequency) to change is detected by the generator control mechanism, and
inputs (steam, gas, whatever) changed accordingly.

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instantaneously
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generate more electricity?

In the very short term, it's the rotational energy of the generator that
changes.

In practice, specific generators are tasked with maintaining the
frequency by changing their power output, and their owners get paid a
premium for doing it.

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if it ever eventuates)

Seems highly improbable to me. At the times when the stored energy is
needed, daytime, the cars are more likely to be being driven, or at
least not plugged in. In any case, a car owner is likely to want his
battery charged against need, and not come out of his house to discover
the the car's unusable because of a preceding high power demand. The
whole "using car batteries" concept is being pushed by the PV/Wind
brigade, in an attempt to address the inherent limitations of a system
that produces power when it can, not when it's needed.

Sylvia.

Re: Government offer of *feed-in tariff of 60 cents per kilowatt hour (kWh)*



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a particular time of day etc.
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load
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thermal plants (gas, coal, nuclear etc) can't respond fast enough to
track to diurnal load variations, other types or plants ( hydro, compressed air,
and
internal combustion) can respond more quickly.

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instantaneously
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generate more electricity?

AIUI power load equates to drag on the generator rotor which if it
exceeds the input torque reduces the frequency of the mains supply.

that can measured and used to close the feedback loop

the one time I got to play with a 3kVA portable generator
I plugged a 2.4kW heater into it and watched it respond
the motor slowed a little and the mechanical govenor in
the crank-case moved a linkage which opened the throttle
to compensate. (my impression was it got louder but not
noticeably slower)

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for sure! they need 24 hour power for a start...

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if it ever eventuates)…

This is what all the different electricity supply tariff rates are
about. Excess power (mostly) generated by thermal plants sold off
cheap because they can't turn the boiler off and back on overnight
(or during other periods of low demand).



Re: Government offer of *feed-in tariff of 60 cents per kilowatthour (kWh)*



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a particular time of day etc.
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load
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air, and
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instantaneously
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generate more electricity?
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cars
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( if it ever eventuates)…
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Currently, there arnt any efficient ways of storing electricity.
All the known methods require turning the electriciy into something
else , storing the something else, and then reconverting the something
else back into electricity.
At every conversion phase, you lose some of the electricity.
Hydro dams are the best so far, but they are only around 70%
efficient.
So storing electricity only makes sense when the electricity to be
stored is coming from a very low cost power source like a coal fired
power station.


Re: Government offer of *feed-in tariff of 60 cents per kilowatt hour (kWh)*



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yup.


Doesn't matter in terms of the user receiving the feedin rate.  The
metering is at your point of connection.  What losses there are
between you and the "consumer" of your fed-in energy isn't *your*
issue.  And if you analyse the situation, you will realise that your
feedin will *reduce* the overall grid losses, as your neighbours'
power consumption will no longer ALL be generated afar, and the
consequent transmission/distribution losses will be slightly lower.
 
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Yes.  Useful in that what nett you feed back into the grid means less
grid power from the usual sources being consumed by other grid
connectees.
 
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Don't matter.  You aren't pumping it back to the power station.
 
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yup.


Forget the efficiencies.  They are confusing your thinking (?).

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photovoltaic cells,
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The cost of grid electricity incorporates the cost of capital
infrastructure.  Plant needs to be sized to meet peak load.   If they
(the generating body) can get away with less plant because some of
that peak load can be avoided through whatever mechanisim, they save
big bucks.  Off-peak tariffs are one way they try to "peak-lop" by
encouraging consumers to shift discretionary load to off-peak periods.
But the peak is still daytime due to industry/commerce/airconditioning
and that is when solar will provide its greatest potential
contribution.

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consume
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It's a benefit to:

(a) you, in a smaller bill and a warm fuzzy feeling re (b)

(b) the environment, in less fossil fuel being consumed overall (*)

(c) the generating authority, by way of reduced capital servicing
costs.

(d) the environmental polluters in China who are producing the
overwhelming majority of domestic panels sold in Australia.

Which of those matters most to you is up to you.

(*) this ignores the environmental cost of photovoltaic panel
production.  Arguments rage as to the "payback" or breakeven period,
with claims as high as 20 years or as few as 3 years.

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It isn't stored.  It offsets the amount generated at the power
stations on the grid.  The grid connected loads (consumers) will only
consume what they consume.  In the extreme (aka hypothetical) scenario
where feedin consumers are able to contribute more than the remaining
consumers are consuming, the power stations shut down and your excess
isn't going anywhere.  You can *only* feed in to the grid what is
being elsewhere consumed from it, no more.  So in that extreme
scenario, you are unable to feed in all that you are generating in
excess of your own requirement.  Do not fear, it will never happen in
your lifetime.

The biggest risk factor in establishing a solar photovoltaic
capability on your premises is that the feedin tariff isn't a fixed
multiple of the consumption tariff - rather it is a fixed figure.
Governments may choose to vary it in sympathy with the rises in the
consumption tariff, but I've not seen much evidence of sympathy from
goverments over a long period.  And any "carbon tax" or similar WILL
jack the consumption tariff skywards, so the relative savings may well
disappear over a short period and fail to justify the capital outlay.

Re: Government offer of *feed-in tariff of 60 cents per kilowatt hour (kWh)*



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Except that it doesn't do that, because the infrastructure still has to
exist to supply power when the PV cells aren't. Today in Sydney was a
nice example of how PV cells can fail even to offset airconditioning
loads. It reached 40 degrees where I live, but was still overcast for
much of the day.

Sylvia.

Re: Government offer of *feed-in tariff of 60 cents per kilowatt hour (kWh)*


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If you would have solar power on your roof you would have noticed that even with
cloud cover the power output is quite strong. 50% output is easily reached on my
system, even without direct sunlight but obviously depending on the extend of
the cloud cover. In heavy rain it's down to 10%. The diffusion of light also
makes PV systems less directional. Just my observations.

Tony

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