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swimfeeders
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08-06-2018, 04:24 PM
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Re: Wind Farms.

Hi

The figures are just not stacking up for tidal, which is why the Swansea Bay Tidal Lagoon is on hold.
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09-06-2018, 02:47 AM
42

Re: Wind Farms.

Originally Posted by Besoeker ->
You need something to get the variability of the source to match the on-demand expectation. Usually, that is "spinning reserve" from fossils.
That's partly true but spinning reserve can also be things like aluminium smelters and other plant that can have their power cut off instantly without damaging them. I mention aluminium smelters because they are heavy users of electricity but can survive for a number of hours without power.

The spinning reserve is not to cover demand expectations because that is pretty predictable, the spinning reserve is to cover the sudden failure of the largest piece of running generating equipment which is usually coal fired but in the UK could be nuclear.

In NSW the coal fired plant can cover this failure instantly for about a minute by losing boiler pressure which gives the Hydro plant time to start opening the dam gates to pick up load; then the coal fired plant has time to grind more coal to increase the generation on a more permanent basis. In the meantime the power control system monitors frequency and if necessary might drop off the odd aluminium smelter for a little while (frequency is the all important indicator of system health).

Originally Posted by Besoeker ->
A couple of points if I may.
Not every household is suitable for off-grid autonomy. Think of flats/apartment dwellings.

Storage technologies isn't just batteries. Hydro generation uses all that water behind the dam as storage. Ultracapacitors are a fairly recent development. Then there are energy storage flywheel systems. But so far, hydro is the only one at utility level. Itaipu, Three Gorges come to mind.
The only practical way you can store electricity is batteries and pumped hydro. In the former case the Tesla battery in SA is doing its job but it has a limited life (charge cycles) so its use is only for emergencies. Pumped hydro is used a lot - this is where water is pumped back up hill at night to storage to be released during the day to cover the peak demand periods. (Snowy and Shoalhaven schemes in NSW as examples)

About 85% of the energy used to pump the water to storage is recovered which may sound wasteful. However it often means the difference between keeping a piece of coal fired plant working overnight or having to "bank" it. Keeping the coal fired generator running means that a massive amount of oil or gas is saved by not having to revive it the following morning. It is not altruism that makes off peak power a fraction the cost of peak power.

Flywheels can be dodgy things. In the 1960s when I was an apprentice for GPO Telephones a continuity set was sometimes used at remote trunk route repeaters to provide power in an outage/emergency. Basically a motor and generator on a single shaft with a massive flywheel (and I mean massive - sometimes there might also be a DC motor which could run off batteries).

The AC motor normally drove the device and the generator provided power to the repeater station but if the mains failed the momentum of the flywheel kept the generator going for a considerable time.

This method was abandoned after one of the bearings seized and the momentum of the flywheel ripped the shaft from its mounts, burst through the side of the building and took the whole contraption for a journey of several miles across the Kent countryside.

Fortunately no one was killed or hurt and damage was confined to a large number of dry stone walls but the system was abandoned. As an aside it was lucky the machine wasn't spinning in the other direction because it would have destroyed the repeater station - there was little redundancy in those days.
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15-06-2018, 12:48 AM
43

Re: Wind Farms.

phew just got here from down udder - this is the latest from OZ

https://www.theguardian.com/environm...14&CMP=ema_632
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15-06-2018, 11:45 AM
44

Re: Wind Farms.

Originally Posted by gumbud ->
phew just got here from down udder - this is the latest from OZ

https://www.theguardian.com/environm...14&CMP=ema_632
Oh dear. You have the Grauniad down under too? I'd have thought the Aussies wouldn't put up with its bias.
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Besoeker
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15-06-2018, 03:10 PM
45

Re: Wind Farms.

Originally Posted by Bruce ->
That's partly true but spinning reserve can also be things like aluminium smelters and other plant that can have their power cut off instantly without damaging them. I mention aluminium smelters because they are heavy users of electricity but can survive for a number of hours without power.
Besoeker here.
That's load shedding rather than reserve.

Originally Posted by Bruce ->
The spinning reserve is not to cover demand expectations because that is pretty predictable, the spinning reserve is to cover the sudden failure of the largest piece of running generating equipment which is usually coal fired but in the UK could be nuclear.
It's needed to cover the variability of most renewable sources like wind, solar, and wave energy. There was a paper a while ago from Katholieke Universiteit, Leuven that suggested that, because of variability, such sources could not be more than 19% of the total supply. Beyond that, the required spinning reserve would use more energy than the renewable sources could provide.

Originally Posted by Bruce ->
In NSW the coal fired plant can cover this failure instantly for about a minute by losing boiler pressure which gives the Hydro plant time to start opening the dam gates to pick up load; then the coal fired plant has time to grind more coal to increase the generation on a more permanent basis. In the meantime the power control system monitors frequency and if necessary might drop off the odd aluminium smelter for a little while (frequency is the all important indicator of system health).
In UK, frequency varies very little. Currently it is 49.937Hz.
In general, the power quality is fairly good but getting worse because of hamonics.


Originally Posted by Bruce ->
The only practical way you can store electricity is batteries and pumped hydro. In the former case the Tesla battery in SA is doing its job but it has a limited life (charge cycles) so its use is only for emergencies. Pumped hydro is used a lot - this is where water is pumped back up hill at night to storage to be released during the day to cover the peak demand periods. (Snowy and Shoalhaven schemes in NSW as examples)
Dams like The three Gorges and Itaipu store energy very effectively - all that water behind the dam. But it needs the right topography. Norway is, as far as I know, the only country in Europe where Hydro is the major player. Wales has Dinorwig as pumped hydro and that is around 2GW for five hours then needs seven hours to recharge.


Originally Posted by Bruce ->
Flywheels can be dodgy things.
A company based at Capenhurst made a fairly good fist of it. They had some installed in a New York transit system for example. They were driven up to speed by VSDs. The test bed had a 1500 Vdc ultra low ripple source and a chopper to regulate the output from them.
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