Solar power question

**Bushmiller** · 29th September 2019, 01:04 AM

Originally Posted by NCArcher

Lets get a couple of things sorted out here. There is no 'reverse flow' or 'having to generate a larger voltage to be able to overcome the line voltage' it doesn't work like that. The grid is just a network of wires that distributes electricity to where it is needed. One thing to remember, there is no storage (apart from SAs battery) the power stations basically generate power on an as needed basis. There are very sophisticated distribution control centers that work out where the power is needed and how much at any time. The generators in a power station are constantly altering their output to match the required load. Although there are safety interlocks to prevent it, a blackout can be caused by one generator going down, due to a fault or failure, when the other generators see that loss of power to the grid they ramp up very quickly to try and get the power back up to the required level. The sudden surge can cause a generator to trip on over load and then you have an even bigger hole in the power requirements, so the remaining generators ramp up and so on and so on. Although that has nothing to do with solar power on houses it sort of explains what is happening with the grid. When you turn on an appliance, current flows through either an element or a coil and heats it or makes it spin. In Australia that current flow reverses 50 times a second so reverse flow is not a thing. When you feed power into the grid you are adding current flow not changing the voltage. The voltage is set and the control systems work very hard to keep it where it is.The voltage will vary by relatively small amounts but if it goes outside certain limits it will cause protection systems to trip and shut everything down.
I'm not sure how solar systems cost the generators more money but i suspect it's more political than operational. The generators sell electricity at a regular rate and then an exorbitant peak rate. I suspect the solar input is cutting into the peak rate revenue but that's just a guess.

Thanks Tony

I probably should have gone into those aspects but did not. Besides which you have explained it better than I would.

The advent of increased solar power (and wind power) has changed the dynamic of how the traditional thermal power stations operate. Until now the periods of high demand have been winter and summer. Winter used to be the high point but in recent years, thanks to increased air conditioning, summer is the highest point. On a day to day basis night time was a period of low demand and low prices. As solar generation increases, the day time prices are not so high or so volatile and night time prices are higher than they used to be. As a consumer you are used to a fixed price for your electricity, but the wholesale market has a constantly varying cost apart from fixed contracts. The wholesale cost varies every five minutes and this is dictated by a complicated bidding process submitted in advance of the day. Overall these are the average prices for this year to date across the Eastern states.

QLD 7.2c
NSW 8.5c
VIC 12.3c
SA 10.5c

For some reason I don't have the figures for Tassy, but they too are part of the grid (there is a DC link under Bass Straight) and I would guess will be similar to SA and VIC.

I expect most of us are paying around 28c/KWH for our power and a little less for off peak water heating. Only a few years ago the average wholesale prices were around 5/6c. Although retail prices have increased they are probably less than the wholesale increases proportionately. I would also guess that much of the increased power bills are down to increased usage. (I have just donned my flak jacket on that one!). It is true to say that the wholesale prices of just a few years go were unsustainable. There was one year that every QLD generator forecast a loss.

Tony mentioned the exorbitant peak rates. They can be: up to $14/KWH!! However, this is rare and increasingly so. When it happens, it lasts for five minutes. What is more frequent is when the cost goes to - $1/KWH . Yes, that is a negative figure. Actually what we see at work is a MW cost, so -$1000 and between the two units that is a cost to us of $800,000 per hour. Of course we commence reducing load, but that takes time: It is not quite like braking in your car. To reduce load in a controlled fashion may take hours. Normally, the price reverts to normality way before we have to go too far as the Gas Turbine stations can just switch off. I mention this purely to highlight that the generators do not have the cushy position many parties out there assume.

Regards
Paul

**NCArcher** · 29th September 2019, 08:44 AM

Originally Posted by Bushmiller

For some reason I don't have the figures for Tassy, but they too are part of the grid (there is a DC link under Bass Straight) and I would guess will be similar to SA and VIC.

The Tassie link was cut a couple of years ago. I can't remember how it happened but it was almost impossible to hire a decent sized diesel generator for about 3 months as they were all shipped to tassie to make a massive diesel generator power station while the cable was repaired. Tassies power consumption is tiny. There are only 500k people in Tas.

**Bushmiller** · 29th September 2019, 09:12 AM

Tony

The link was indeed broken and I can't remember the details of how either. It has been repaired for some time now and it appears on our maps of the grid along with the other states. I don't know why it was not in the list of average prices. It is less than SA but still significant. It was constructed to insulate Tasmania against a drought as a large proportion of their power is Hydro. When the line broke they had been freely selling off their power to the mainland and the dams were low. Consequently they were up a creek and no paddle.

It took months to repair the line during which time there was, as you say, a very good market in diesel generators.

Regards
Paul

**pintek** · 29th September 2019, 05:22 PM

Originally Posted by Bushmiller

'as you say, a very good market in diesel generators.'

I believe the diesel generator market was propped up further in the summer after Hazelwood closed the doors when the AEMO contracted a hire company to install them at the old Morwell power station for grid top up. Same year they requested some industrial plants to close over the summer period to reduce load requirements. Crazy stuff. I wonder if it will take a system black for people to see the fragility being forced into the grid.

**RossM** · 3rd October 2019, 11:47 AM

Originally Posted by Bushmiller

Tony mentioned the exorbitant peak rates. They can be: up to $14/KWH!! However, this is rare and increasingly so.

The park spot price actually has a cap - it's set at $12,500/MWh ($12.50/KWh) This is less rare than you may think, as it can be invoked by the market operator at any time to force load shedding during peak demand.

This link has a full run-down on the grid and it's operation

**Bushmiller** · 7th October 2019, 02:06 PM

Originally Posted by RossM

The park spot price actually has a cap - it's set at $12,500/MWh ($12.50/KWh) This is less rare than you may think, as it can be invoked by the market operator at any time to force load shedding during peak demand.

This link has a full run-down on the grid and it's operation

Ross

That is a good link and goes a long way to explaining some of the intricacies of electrical generation as it exists on the eastern seaboard. It is however a little out of date (2010) and some aspects have been revised. Load shedding does not occur because the price has gone high. It occurs because there is insufficient generation capacity to support a stable system. The market operator, AEMO, can invoke load shedding if they feel the stability of the system is being compromised or likely to be compromised, but they don't do this by raising the cost. The cost varies by the bidding process in which the generators participate. Load shedding varies from state to state. The first to go in the southern states are the industrial consumers, but in QLD industry is preserved and it is the domestic element that is the first to be shed.

I thought you may be interested to see some snapshots of the variance in power generation. These prices and loadings occured on Saturday 5/10/2019.

0700hrs. At this time in the morning Solar is active.Tasmania being a colder climate looks as though it has similar generation demands to SA. Tasmania is actually closer to half that of SA when the latter state wakes up and switches on their air conditioners!

Spot price 0700hrs 5 Oct 2019[43445].PNG

0701hrs. Solar is really kicking in and the price has gone negative. Just one minute later (remember it is adjusted every five minutes)

Spot price 0701hrs 5 Oct 2019[43446].PNG

1249hrs.

Spot price 1249hrs 5 Oct 2019[43447].PNG

1817hrs. Completely different scenario. The solar is pretty much out of the equation and prices are higher everywhere.

Spot price 1817hrs 5 Oct 2019[43448].PNG

I have to reiterate that this is just a fairly random series of snapshots, on a weekend and in Spring. I have shown them only to show the range of prices and how quickly at times the price can fall. I should also point out that this is not the only products for which generators are paid so it is by no means the whole story. Also most thermal generators have some fixed contracts with large consumers so not all electricity is sold on the spot market. The above should only be seen as a guide to market trends.

The prices above are for MWs so divide by 1000 and you have the Kwh price you see on your domestic bills.

The picture would be very different today, being a week day with industry in full swing and a very hot day as well (33degs C here by 1100hrs. Almost 37degs C at 1300hrs ).

Yesterday we spent hours with the price at $0.00! I met a man on Saturday evening who commented on how expensive solar power was making our electricity. There is an element of that from the early days where incentives were offered to establish solar power (primarily rooftop solar PV), but as you can see that is being significantly counteracted with the effect on traditional thermal generators at certain times. I would have liked to have shown him those snapshots above.

It is a complex issue and very easy for interested parties with agendas to cherry pick.

This is another link that may be of interest to the solar watchers:

Australian Photovoltaic Institute • APVI Solar Maps

This is the AEMO website which is live and everybody can see an instantaneous spot price.

Access the latest news, perspectives and backgrounders on energy here. – Australian Energy Market Operator

A moment ago just for information:

NSW: $53
QLD: $0
VIC: $92
SA: $ -292 (yeah, negative)
TAS: $97
WA: $27 (Not on our grid and 3 hours behind)

Regards
Paul

**forrestmount** · 7th October 2019, 06:58 PM

Not sure if I should post a response on this topic as I am not an expert in power distribution, but I was told by friends who are in the industry the single biggest issue solar power presents to the network is when a large cloud coverage takes out a lot of houses feeding power into the grid without warning for short periods of time. This scenario rings true to me.

Sent from my iPad using Tapatalk Pro

**Bushmiller** · 7th October 2019, 08:19 PM

forrestmount

There is always a "rolling reserve" in the system to take up any shortfall (at least mostly). Generators place their bids in price bands so they are mostly not at full load. It is difficult to imagine cloud cover "suddenly" materialising. Cloud moves across the sky in a controlled manner. I would need to hear corroboration of that type of scenario. My gut feeling is that it is anecdotal and no different to any sudden demand. People tend to imagine how the system works rather than knowing. See NCArcher's earlier post on the way electricity feeds along the lines. (Post #12).

It is important to remember that electricity is not stored. Whatever is generated is used. The voltage needs to be regulated so machinery and equipment is not damaged. Electrical protections are in place so the systems do not destroy themselves. This is what happened in the SA storms when the power lines blew down. The interconnector from Victoria shut itself down so it was not overloaded and in doing so contributed to the problem short term. Without that protection serious damage may have occurred that kept it out of service for weeks rather than hours.

Regards
Paul

rrich · 8th October 2019, 02:48 PM

Ah yes! Mr. Kirchhoff and his laws rear their ugly heads again. Anyone who has studied electronics has suffered through the chapter on Kirchhoff's Laws.

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