Power shares

[Snoopy]

The puff that is supplying that 30-40% load factor sounds more like my 'locomotive breath' scenario. It strikes me that if a warm or cold front takes 2-3 days to pass over then those windmills will not be running 'flat chat' for 2-3 days. It seems to me as though this 30-40 percent 'average' is more likely made up of a few hours at 100% but most of the spinning time spent at maybe 10 or 20% energy generating capacity (remember when the wind speed halves from peak, then the energy generating capacity if a windmill falls to just one quarter of peak). Thus modelling wind energy based on 30-40% capacity does not mean the wind farm is producing maximum energy 30 to 40 percent of the time. Maximum energy production might only occur just 10% of the time and with a wind energy generation model that applies a random walk around that peak, you could still get to that 30-40% load factor. If the true peak is relatively short in duration, it should be possible to accommodate that with a hydro-reservoir with a storage capacity of just a few hours.

After doing some more reading, it strikes me that I am looking at integrating wind farms into the wider power grid the wrong way. I had assumed that when a front passes through, all the wind turbines in a particular location will behave in roughly the same way. Hence my concentration on what is happening to individual turbines. However, on reading page 160 of the reference below a different picture emerges.

https://www.wind-energy-the-facts.or...s/chapter2.pdf

Variations within the Minute

"The fast variations (seconds to minute) of aggregated wind power output (as a consequence of turbulence or transient events) are quite small, due to the aggregation of wind turbines and wind farms, and hardly impact the system."

This is telling me that those fast acting 'gust spikes' I was concerned with are not an issue, because the same 'gust spikes' are not acting on every windmill in a windfarm at the same time.

Variations within the Hour

"The most significant variations arise from the passage of storm fronts, when wind turbines reach their storm limit (cut-out wind speed) and shut down rapidly from full to zero power. However, due to the averaging effect across a wind farm, the overall power output takes several minutes to reduce to zero. And in general, this is only significant in relatively small geographical areas, since in larger areas it takes hours for the wind power capacity to cease during a storm. For example, in Denmark – a small geographical area – on 8 January 2005, during one of the biggest storms for decades, it took six hours for the installed wind power in the West Denmark area to drop from 2000 to 200 MW (5 MW/minute)."

'The passage of a storm front can be predicted and technical solutions are available to reduce the steep gradient, such as the provision of wind turbines with storm control."

From what I can figure out from this power station map:

https://ens.dk/sites/ens.dk/files/An...201907_eng.pdf

the wind power in 'West Denmark' gets around 50% of their wind power from the offshore 'Horns Rev I II and III' wind power stations. These three are all located over a 50km stretch of ocean. So even in a severe storm, these windmills took several hours to shut down. The New Zealand wind farms are generally not as far spread out as this. But this is telling me that in the New Zealand situation, we might expect the full ramp up or ramp down of a distributed windfarm system will take a matter of hours, not minutes, even in the most severe weather situations. In this context, matching a southern windfarm portfolio, spread out more than 100Km across the lower South Island :

1/ Mahinerangi Wind farm (Mercury Energy 36MW)
2/ Mt Stewart Wind farm (Pioneer Energy 7.65MW)
3/ Flat Hill Wind farm at Bluff (Pioneer Energy 6.8MW)
4/ White Hill Wind farm (Meridain owned) 58MW

with a storage lake system of modest capacity, like Contact's Roxburgh and Clyde dams, looks do-able.

SNOOPY

[Jantar]

...

1/ Mahinerangi Wind farm (Mercury Energy 36MW)
2/ Mt Stewart Wind farm (Pioneer Energy 7.65MW)
3/ Flat Hill Wind farm at Bluff (Pioneer Energy 6.8MW)
4/ White Hill Wind farm (Meridain owned) 58MW

with a storage lake system of modest capacity, like Contact's Roxburgh and Clyde dams, looks do-able.

SNOOPY

Snoopy, The largest swing I have seen in NZ is 350 MW in 30 mins. Typical swings nationwide are 50 to 100 MW per hr.

The issue with assuming that Contact's dams can buffer the swings in those South Island Wind farms is that Contact does not own them, and does not have access to their offers until after the event. Therfore there is no incentive for Contact to carry sufficient plant, and operate inefficiently, to buffer those swings.

The market will not compensate Contact for carrying additional plant and leaving room in their head ponds. Nor are the owners of the wind farms going to. Therfore it simply won't happen.

[Snoopy]

Snoopy, The largest swing I have seen in NZ is 350 MW in 30 mins. Typical swings nationwide are 50 to 100 MW per hr.

For a big swing I guess the only solution is a big reservoir (even if that 'reservoir' is firing up[ a Rankine unit). But for smaller swings, surely a reservoir of a few days should allow such an industry player to participate?

The issue with assuming that Contact's dams can buffer the swings in those South Island Wind farms is that Contact does not own them, and does not have access to their offers until after the event. Therefore there is no incentive for Contact to carry sufficient plant, and operate inefficiently, to buffer those swings.

The market will not compensate Contact for carrying additional plant and leaving room in their head ponds. Nor are the owners of the wind farms going to. Therefore it simply won't happen.

I don't understand why ownership of windfarms is an issue. Whoever owns a windfarm knows they can't store the energy they generate. They have to feed it into the grid. Everyone knows the likely amount of power to be offered to the market because they know the size of the installed wind turbines. There are weather forecasts that allow you to predict the wind to some extent. And when those forecasts are wrong, there is enough time to bring in alternative generation. So if I was sitting on the Clyde/Roxborough hydro battery, subject to minimum run of the river restrictions of course, I would be turning the hydro turbines off as the front came through. I would do this because I would know that any water saved could be sold at a higher price in times of low wind. There is my profit incentive. I don't need to 'own' a wind farm to profit in this way.

So what am I missing? Or would it just be easier if I came down to start my new job as 'Grand Poohbah Controller' of the Clyde river hydro battery next week?

SNOOPY

[Snow Leopard]

Snoopy, The largest swing I have seen in NZ is 350 MW in 30 mins....

I presume that the grid survived that, how?

Was their a frequency drop?
Did they shed load?

[Snoopy]

The kinetic energy of a moving system is the 'stored' energy that was applied to that system to accelerate it to it's current speed.
That kinetic energy indeed increases with the square of the speed.

But that has absolutely zero relationship to the power produced by a wind turbine.

Recovering the kinetic energy of a system to produce electrical power is achieved by the system slowing down.

Yes, but I consider that the kinetic energy that can be taken out of the system, might have some correlation with the kinetic energy put into the system in the first place? I can think of a couple of reasons why the correlation might break down though.

1/ If the rotating part of the wind turbine acts as a flywheel, then it can store kinetic energy for short periods. However, the spinning turbine blades taper at the tips and have most of their mass concentrated at the hub. This is for structural design reasons, but is the exact opposite of what you want from a flywheel. In an effective flywheel mass should be concentrated at the outer radius of the blade. Given these blades are designed to be responsive to wind changes, I very much doubt that they were designed with any flywheel effect in mind.

2/ It should be possible to store some of the mechanical energy, once it has been converted to electrical energy in capacitors. You could certainly smooth the electrical output in one sense by doing that. The problem is when you eventually release the electrical energy from the capacitors into the system, that in itself is likely to cause a disruptive spike in power. So I am not sure how practical such a storage system would be. As a third alternative, you could certainly 'spread the load' by having a battery storage system on site. But that would be a very expensive addition to the whole system.

I imagine then the point you are making Snow Leopard is the average output over a whole field of turbines is not representative of the energy spikes that might be generated by one particular turbine?

SNOOPY

[Jantar]

...

So what am I missing? Or would it just be easier if I came down to start my new job as 'Grand Poohbah Controller' of the Clyde river hydro battery next week?

SNOOPY

They have a vacancy right now. There is a 6 month training period before you go solo as a Dispatch/Trader. The trading side only takes a couple of weeks to learn, its the Hydrological management that thakes the longest.

[Jantar]

Duplicate post

[Snoopy]

They have a vacancy right now. There is a 6 month training period before you go solo as a Dispatch/Trader. The trading side only takes a couple of weeks to learn, its the Hydrological management that takes the longest.

This is an insult. The Grand Poohbah does not need to be trained. The Grand Poohbah has already been trained, - by you Jantar. My world war one flying ace alter ego will be firing up the Sopwith Camel and we will be flying in on Monday to start. And yes I will be bringing my bucket to sort out any incidental 'hydrological management' issues'. See you soon.

SNOOPY

[Tomtom]

Probably not as widely appreciated is that a national grid actually has a level of capacitance that acts as a reactive balancing componet simply owing to the scale of the system. However, as there are much bigger fish out there than you and your kettle, so they also have capacitance banks. If the public had their cups of tea interrupted every time there was a short on the grid electricity would never have taken off.

What's always been more interesting to me is that there are other utility type businesses don't have a spot-price system or distribution grid. Data (mobile and ISPs) has a grid but no spot pricing, water has no grid or spot pricing, road usage has a grid but no spot pricing etc.

[Snoopy]

Snoopy, your comment "... the basic physics on rotational kinetic energy calculated using the formula 1/2 x Iω^2 is correct" is spot on, but the wind turbines do not spin faster as the wind blows harder. Instead they change the pitch of the blades to get more force from the wind without changing speed.

So as the wind slows down, the angle of the wind turbine blades pitch more against the wind. That means a lesser amount of wind creates the same force on the blades so we get the same power but -just as importantly- the same power frequency (so appliances designed to run at AC 50Hz will continue to run properly).

SNOOPY