Power shares

[Carpenterjoe]

Yes, and we already have a suitable site and power station in NZ that could give us very similar results at a much cheaper price.

Tokaanu power station was originally designed to able to be used as pumped storage between Rotoaira and Taupo. However it never received consent to use a suitable operating range at Rotoaira which was limited to 30 cm, instead of the 1 m it needed.

The station exists, both lakes are already there. All it needs is for the machines to be retrofitted and get resource consent (good luck with that one) and IWI approval (not a chance in Hades). Total plant cost around $120 M.

Thanks Jantar

[kiora]

And then build in for more extreme weather events?
"Actually, the main capacity that's gone out in Texas is not the wind, it's actually some of the natural gas plants that were also not ready for the super cold temperatures," Gates says.
https://finance.yahoo.com/news/bill-...002303596.html

[Snoopy]

As for Onslow being modelled for wind farms being either on or off, that is not the way it has been modelled either. Rather it is assuming that the wind has a load factor of 35 -40%, and the model applied a random walk around that number.

Replace that "hours" with "hours to days". The duration of wind depends on the type of weather patterns prevailing at the time.

An anticyclone will mean very light, or even no wind, but with a possibility of sea breezes for wind farms close to the coast. Sea breezes are rather unpredictable, as they can be forecast as to whether or not they will happen, but not the direction, actual strength, or distance of fetch inland. Anticyclones typically take 3 days or more to pass over.

A cold front will be preceded by building Nor-westerlies for 1 to 3 days before it hits, but as it passes over the wind will drop and back to the Sou-west before picking up again. Then wind speed will fall away as the pressure builds. It is this change as the front passes that is when wind changes are measured in hours rather than days.

A warm front will be preceded by very light winds from almost any direction except NW, and veer towards a more northerly influence after it passes. This process also takes 2 or 3 days

Then there are occluded fronts, stationary fronts, tropical storms, polar vortices etc all with differing characteristics regarding wind strength and duration.

Add all these together and it means forecasting wind generation on very long time scales is quite easy, but shorter durations are very prone to error. It is common to see the wind forecast to the market to be out by well over 100 MW, and even 200 MW discrepancies are not unusual. The worst I have seen was a 390 MW error, and our installed capacity for wind at that time was 679 MW.

I have been thinking about my secondary school physics lessons. Kinetic energy IIRC was calculated using the formula 1/2mv^2, and analogous formula for kinetic rotational energy was 1/2Iω^2, where 'I' is the moment of inertia of the rotating object (the windmill hub and blades in this case) and ω (omega) is the rotational speed.

I have seen windmills gently touched by the wind and they spin in a kind of slow serenity. I have also seen them whipping along with vigour, like the driving wheels of a steam locomotive under full steam. It is the latter situation where these wind farms reach their generating capacity. The rotational kinetic energy formula shows that when a windmill increases speed tenfold, as they might do between light and full operation, the energy produced increases one hundred fold. While that is not literally on and off, in a practical sense it pretty much is. A 150MW windfarm at full load will be producing just over 12MW at light load.

Given this, Jantar's Anticyclone scenario, -based on light wind or sea breezes over two to three days - doesn't sound too difficult to pair up with complimentary hydro operations.

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.

What say you Jantar?

Cannot these 'shorter duration wind energy forecasting errors' be relatively easily accommodated?

SNOOPY

[Jantar]

..
What say you Jantar?

Cannot these 'shorter duration wind energy forecasting errors' be relatively easily accommodated?

SNOOPY

Yes, they sometimes can be, but that generally only happens when the company that owns the wind farm also owns the hydro storage. That way they can adjust their offers to suit. That is why White Hill and Manapouri is a good mix. Waipori and Mahinerangi also matched each other before Tilt split from Trustpower.

The commerce commission would have serious words with any companies that decided to share their trading strategies, even if it was for a good cause like storing wind energy behind dams.

[Snow Leopard]

I have been thinking about my secondary school physics lessons. Kinetic energy IIRC was calculated using the formula 1/2mv^2, and analogous formula for kinetic rotational energy was 1/2Iω^2, where 'I' is the moment of inertia of the rotating object (the windmill hub and blades in this case) and ω (omega) is the rotational speed.

I have seen windmills gently touched by the wind and they spin in a kind of slow serenity. I have also seen them whipping along with vigour, like the driving wheels of a steam locomotive under full steam. It is the latter situation where these wind farms reach their generating capacity. The rotational kinetic energy formula shows that when a windmill increases speed tenfold, as they might do between light and full operation, the energy produced increases one hundred fold. While that is not literally on and off, in a practical sense it pretty much is. A 150MW windfarm at full load will be producing just over 12MW at light load....

This is a massive misunderstanding of the generation of electrical power by a windmill and the relationship to the rotation speed of the blades.

Unfortunately the truth is somewhat complicated !

What is essentially true is that the greater the wind speed the more power can be generated, upto certain limits.

[Snoopy]

This is a massive misunderstanding of the generation of electrical power by a windmill and the relationship to the rotation speed of the blades.

Unfortunately the truth is somewhat complicated !

What is essentially true is that the greater the wind speed the more power can be generated, up to certain limits.

Really? Well the basic physics on rotational kinetic energy calculated using the formula 1/2 x Iω^2 is correct. As you hint at, converting that kinetic energy to electrical energy may be a bit more complex. I would imagine that power surges as a result of suddenly fluctuating wind conditions would need to be dealt with, as an example. But the issue here is not the technical details on how wind turbines make power. The issue is how that power is fed into the wider power grid extracting the most possible energy from the wind while keeping reserves elsewhere in the system as high as required.

In this context your statement that:

"the greater the wind speed the more power can be generated, up to certain limits."

while it might ring true, is not actually that useful.

I started out claiming that wind energy was either 'on' or 'off', even though I knew that was a simplification of the real situation. Jantar then informed me that the

"wind has a load factor of 35 -40%, and the model applied a random walk around that number."

But I think it is clear that these 35 -40%, figures are part of a whole year expected energy delivery perspective. Shorter term wind fluctuations require complementary hydro 'batteries' to be operated over hours or days. And during such periods, I expect the windfarms are operating far above their 35-40% 'average' contribution figure for short periods of time. Provided that time is short enough, even a hydro battery of limited capacity (like a few days) and a responsive enough activation/deactivation cycle could be useful to bracket with a wind farm to achieve optimal energy extraction from both. I contend that a few hours or peak wind generation could substitute for a hydro station with a holding tank of a few days. Your negative reaction to my post would suggest you don't believe this is so, and you may be right. However your statement:

"the greater the wind speed the more power can be generated, up to certain limits."

does not add enough knowledge to resolve the situation.

SNOOPY

[Jantar]

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.

Your high school physics would aslo tell you that P=FV. Or Power is Force times Velocity. So the ^2 relationship still holds as when the wind speeds up both the velocity and the force increase. As the turbine approaches the upper limit of its design wind speed, the pitch becomes fine enough that there is actually no force on the blades and the wind turbine slows down or even stops, so there is no generation at very high wind speeds.

[Jantar]

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.

Your high school physics would aslo tell you that P=FV. Or Power is Force times Velocity. So the ^2 relationship still holds as when the wind speeds up both the velocity and the force increase. As the turbine approaches the upper limit of its design wind speed, the pitch becomes fine enough that there is actually no force on the blades and the wind turbine slows down or even stops, so there is no generation at very high wind speeds.

[Snow Leopard]

I never said that the formula for kinetic energy was incorrect.

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 relationalship 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.


The power in the wind is proportional to the cube it's speed. Double the speed and the power increases eight-fold.

If a wind turbine can match its speed of rotation to the wind speed then when the wind speed doubles, it would spin twice as fast and be able to generate eight times more power.


What the heck is wrong with this website these days? It is basically unusable.

[Jaa]

Can't we just get the wind turbines up on some foils?