Windmill Vs Grid Stability?

As someone who actually commissions wind farms the answer is quite simple, put simply the capacity of a wind farm (or any other form of small generation) is quite small compared to the capacity of the bulk of the rest of the generation (coal, gas, hydro, nuclear, etc) so large variations in a small generation site don't really effect the overall grid much. No matter how many wind farms (or solar for that matter) you put on the grid the percentage generation will always be small compared to other (more stable) forms of generation.

There are special cases, such as Hawaii, where a really large proportion of their generation is wind. In cases like this there is a regulation issue, but I think they combat it with energy storage and generators. I don't know much more about this particular site because I have not been asked to commission there. You could try an internet search.

Utilities are well aware of this intermittent behaviour of renewable sources like wind and solar and are working on mass scale storage of electricity. In fact, this storage field is widely researched world over today. Batteries, pumped storage, ultracapacitors, compressed gas etc. are actively being tried for storing electricity when the sun shines or wind blows.

N T Nair, EKL

Actually it's a case of too much of a good thing. It's not so much the intermittent nature of the wind at the low end of the scale, it's when the wind is blowing nice and hard and the wind farm is running at full capacity. Under that scenario the utility has to back down its conventional generation in order to absorb all that "free" energy flowing into the grid.

The problem arises when a stronger gust of wind sweeps through the area and causes all those wind machines to reach their operating limit and simultaneously start shutting down to prevent overspeeding, with the resultant loss of generation which the utility now has to instantaneously supply. That's where the stability/system security problem arises, as large chunks of generation suddenly disappear and reappear on the grid. Granted that's what "spinning reserve" is for, but those governors may not be able to respond fast enough or properly to those changes...and somebody has to pay the fuel cost for keeping everything spinning.

Hi RamConsult, I have been off line since this post so lost the thread, - what I wanted to say is there are many solutions to that problem, but I will wait for the update notice to refind the thread as many may have been advanced (or not :) Cheers, Geoff Thomas

Note that how quickly (load or) generation change srongly affect how easy they are on the grid.

Current construction windmills use rectified power to drive inverters which feed the grid. Two system benefits are that the stored energy of rotating parts can be robbed (like a boiler) in the short term and the inverter has much more responsive control than if it had the prime mover's inertia dominating phase control.

The (excellent!) discussion so far has all but explicitly stated one of the trade-offs: a "thou shalt" in the form of contributions to the grid renewable energy due to legislated targets on the one hand and "thou shalt not" in the form of grid instability on the other.

It has not factored in "curtailment." When the utility simply cannot use the energy, thank you very much, Power Purchase Agreements typically include giving them the option of throttling back -- or cutting off completely -- the power that the turbines generate.

Thanks to all...

Why can't we control some selected load during wind speed reduces?

Since, in my home state TamilNadu, India has wind farm's capacity of ~5000MW where total installed capacity is ~14000 MW . So to solve problem scheduled black out is being implemented. So instead of completely shut down whole unit we can shut down particular loads.

Is it practically viable?

Certainly this is theoretically viable, but practically viable is very hard to say. Particularly by people not in your community.

The difficult part is getting people to agree which electrical services are vital so power must be present 24/7, which services have a vital time window for power to be present, which services are simply convenient to have power or which services are a pure luxury item that people can do without until more power is readily available.

Wind,solar,tidal etc are not 100% reliable,they can reduce intensity or fail at any time.

Somebody said if you have wind power you should also have quick start diesel power rated 100% of wind power.

This is an article I wrote in 2007, and I live in Australia, so mention local references, but I think it really opens up this discussion in a good way, - due to local politics, I called it "Base Load, Capacity and Cost." I hope moderators let it through although I apologise for the great length, - but then it opens some doors.. One of the difficulties that Wind generated power has faced is the charge of not being Base Load, it is easy to see that the wind does not blow all the time, whereas there is always a need for electricity. Proponents of wind argue correctly that the wind generated power displaces coal generated power and that the modern grid could handle as much as 30+% wind input with not much difficulty. Those who find it impossible to imagine giving up their coal would like to say. "We don't consider Global Warming important enough to have extra capacity that does not contribute to providing base load to our overloaded systems." But they know that wouldn't be a good look so they talk about capacity factors and the high cost of wind. Well, lets look at it, a wind farm costs about $1.50 to $2.00 per installed watt, a Coal fired plant around $1.20 to $1.40. Then the coal fired plant has to bring enormous quantities of coal in every day and all day to throw down the hungry mouths of the boilers, and a whole team of guys to maintain and supervise etc. And yes there are a swag of subsidies from the taxpayer that reduce that cost, - but they don't really reduce it, only spread it around and disguise the real cost. So what the baseload guys say then is that a wind farm only averages 30% of it's capacity, actually most are between 35 and 45% but it is true, the wind farm produces on the average wind speed not the maximum. However if you look at conventional power stations, they supply a very changeable load, Cooktown for instance uses up to 20 Megawatts per hour at Peak time but only 4 megawatts in the middle of the night, and most residential, small business and office customers the same, so those conventional power stations would also be lucky to average 30% as well, - same would be the case for nuclear. There is a certain remnant of thinking left over from the earlier technology, coal powered stations that required a day to warm up, so could not just increase production, as actually can modern powdered coal stations, gas powered stations, geothermal powered stations, and increasingly, Solar thermal powered stations, - which store steam pressure for night use as well. In those days you had what is called "spinning reserve" where the coal station had to run at a high level to have capacity at peak times, hence the great desire for electricity retail utilities to encourage "off peak' power usage, now really no longer required but no one in that area wants to really inform people of this change as it would then also inform them that all the old arguments are gone as well, and the rationalisation for allowing such gross polluters as the Latrobe valley, Loyang etc, monstrosities to continue on their planet dissing way. However economics will drive this now the electricity industry is becoming de-regulated, - the powers that be have only a very limited time before the people really understand the situation. What should actually be talked of is not base load, but total load, but as several states in Australia no longer have the capacity to provide the full load if it is a really hot or really cold day, that is a tabu subject, - not for us fortunately, as our thinking goes further than the next election.. - as it must, as we love our children. It is also a very true argument that wind power or solar electric power, both being dependant on the variabilities of nature, can not be guaranteed to prop up the total power demand by themselves as the wind may not be blowing at that time so now we are talking about "virtual" power stations, able to call on a mixture of sources from a wide area and the range of these is increasing daily because the technology is there and idealistic and forward thinking people are just going for it, Mr Howard and his ilk notwithstanding. Also being implemented overseas is the high voltage DC networks, which have only negligible losses, as opposed to the transmission losses of the Australian current network of 41%, needing therefore 41% more coal burned. An important component of this mixture is Geothermal, - see the geothermal display, enough geothermal power to supply Australia for 7,500 years at current usage, and able to react very quickly to changes in demand, It is not as cheap as wind, and it's long term economic viability is better served by not draining each thermal reservoir of all it's heat at once, (then you have to drill new wells all the time) as it takes quite a while to recharge, but to share the load as we will still require electricity/energy in 7,500 years time, - barely an eyeblink in terms of our planets' history or even the history of human beings. Let us not make the same short sighted decisions as "we" made with the treasure of oil and look like making with coal and nuclear, to use everything as if there were no tomorrow, because tomorrow always comes. Various total load contributors now look good, - each of them tends to think they have to do the whole job because of the conservative criticisms they face, but we can stand back and assess for ourselves as we sensibly look at the situation. An overview: this will be presented in a workshop on Sunday. * Interesting work is being done on tidal energy production, there are several places in Australia that have huge tidal resources, - and availability can be guaranteed thousands of years ahead, - hey that is real base load! (Although not 24 hours per day) * Wave power is looking very positive, although most development is focusing on de-salination, the high pressure water can easily be made to generate electricity and then when the wind starts blowing that energy can be diverted to make up the water. * Gasification and Digester technology is developing apace, - Sweden is already moving to generate all it's energy needs from it's copious forests, - 10 years they reckon, we could at this moment generate an enormous amount from our cities' huge waste stream, and as it is storable gas, - can be used when required, is part of total load! Although this technology is already developed, there are some new developments that incline more to a wider production from these resources such as Plasma Arc reforming, Critical water pressure, Terra preta etc, these will extend our flexibility and efficiency. As in the article above, Wind power companies are starting to think storage, eg the one in northern Germany using an old salt mine to store compressed air, the other to produce hydrogen, and of course there have been amazing developments in battery technology, - the Redox concept, where the power is stored in the fluid, so you can have absolutely huge batteries, Super capacitors, highly energy dense and able to respond virtually instantaneously, huge flywheels, Lithium batteries, Silver batteries, all sorts, and also Fuel cells, - even a charcoal powered fuel cell, - all these technologies, although sometimes specific in a particular place, - easy to integrate into our Virtual Power Station, even to the new trend of folk with Solar Electric panels on the roof of their houses also having batteries to store the power and sell it to the grid at peak times when they can get a better price for it, potentially all those somewhat independent households supporting the communities' needs at the right time. This Virtual System need not be centralised, - it takes the power from wherever it is, integrates it into the whole, if one element fails here or there no big drama, lots of smaller sources can easily make up for a bigger source, although extreme shortages are dealt with by capacitor banks, part of the conditioning system, (Electronic Shock Absorber or (ESA) that gives enough time to isolate a problem, cascading failures are prevented, huge power failures as we have seen with older centralised systems can be eliminated - by the non centralised virtual concept.

Cheers, Geoff Thomas, Advanced Wind Technologies, Australia.

Thanks... It is useful article. but I need some clarification

What do you exactly mean by this statement: the modern grid could handle as much as 30+% wind input with not much difficulty.

Kind Regards, Mansoor

Hi Mansoor, sorry for any ambiguity, I meant that if the grid is supplying say 100 megawatts, and the 30 megawatt wind farm connected to that grid, goes from a situation of no wind to rapidly increasing wind, so that over a shortish period of time, say 5 minutes, it is adding to the grid it's full potential output of 30 megawatts, - which the grid will see as a negative load, modern power stations such as gas powered or powdered coal fired generators can be quickly turned down and just as quickly turned up, as they do at Peak periods, all the time. One wonders just how much variation in demand when millions of people watching the Simpsons or such all get up at the ads and turn on the kettle for a cup of tea.. probably more almost instant demand than all the wind turbines in America, and the grid copes fine with that. Actually the variance at Peak is much higher, in my state of Queensland for instance at the non peak time demand will be at 20 to 30% of network capacity whilst at Peak time it may reach 110%, necessitating in some load shedding, running generators over spec. turning on old oil fired plants or importing from another state. For the old style coal fired plants of course, which took a day to turn up, they go to a mode called spinning reserve, presumably the field coils receive lower stimulation in their gen-sets. Also it may be a problem for Nuclear plants as I have been told they can not turn down or are very reluctant so to do. In the long term, "flow" style or other batteries may prove economical with further development and Geothermal "Hot dry rocks" is also reasonably quick to turn up and down. Hope that was the ambiguity resolved? Cheers, Geoff.

Thanks I understood :-)... Could you say that is there any 'standards' are available for installed capacity of wind farms. I mean x= installed capacity of wind farms / overall installed capacity . So is there any international standards for 'x' ?

Kind Regards,

Mansoor

Hi Mansoor, I have not come across any accepted worldwide standards, - in the old days we talked about 20%, and the odd engineer seized upon it as a life-belt, but those days are gone, new technology, not old tried and true, will set, and constantly increase, the ratio of wind farm and overall installed capacity, - Denmark is a good example with the whole country, - consisting of very high concentrations in particular areas, dealing with this issue positively. I suspect that renewable energy, being a negative load, will eventually be incorporated into the grid to the same level of penetration as Peak Power usage, the greatest positive load, - after all why not? and there will be a lot more tools and technology becoming available to grid managers and workers, - hopefully they will become informed and able to use them, as such occurs. Cheers, Geoff.

Denmark exports excess for storage in countries around them I believe - and pays a premium when it is returned.

Grid size would be as important as anything in determining how much wind power can be fed in.

There are some good articles available on the net about BPA in the US northwest and how they try to mix the wind power with hydro and control the scenario. Apparently it is a wild ride for grid managers and dam operators - sometimes the wind farms are simply told to pack it up and shut down supply - I have also read where there is a negative price for wind power fed in if it is in excess of what the grid wants.