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

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.

photovoltaic cells,

to consume

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.

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

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.

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.

Don't matter. You aren't pumping it back to the power station.

yup.

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

photovoltaic cells,

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.

consume

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.

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.

"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?

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

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)?

a particular time of day etc.

load

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.

instantaneously

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.

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.

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.

a particular time of day etc.

load

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.

instantaneously

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)

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

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).

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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

a particular time of day etc.

load

air, and

instantaneously

generate more electricity?

cars

( if it ever eventuates)?

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.