It's happening, the power grid is changing. - Page 1
Forum section: electronics / general

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: April 20, 2016, 12:33:39 pm
content: An interesting thing here I stumbled across yesterday: The National Grid in the UK are inviting tenders for projects which can supply between 1 and 50 MW into the grid in sub 1s response times. It is interesting to see this becoming a thing now as we reduce the amount of large steam driven rotating machinery for generation.I wonder if this reduction in system inertia is also from the demand side? i.e. fewer directly connected large synchronous motors, instead most stuff nowadays is inverter driven so presumably wouldn't contribute to the general rotating mass of the system in the same way?http://www2.nationalgrid.com/Enhanced-Frequency-Response.aspxCopied and pasted:BackgroundThe changing generation mix in GB is reducing the contribution that synchronous generation makesto the energy market, which in turn is reducing the level of system inertia, particularly on low demanddays. Lower system inertia affects the ability of the System Operator (SO) to manage the systemfrequency within normal operating limits. This in turn will drive the procurement of larger volumes ofthe existing frequency response products. NGET is therefore investigating alternative solutions, oneof which is the creation of an enhanced frequency response service. The aim of this service will be toimprove management of system frequency pre-fault, i.e. to maintain the system frequency closer to50Hz under normal operation, however performance in post-fault conditions is also of interest.NGET believes that the most appropriate way to develop this new service is to run a tender for fouryear contracts for enhanced frequency response capability. This will give NGET experience inintegrating enhanced frequency response into the suite of system management options, as well asproviding a competitive route to market for new technologies. Whilst a number of the energy storagesolutions currently available have the ability to provide frequency response in these enhancedtimescales, NGET welcomes the participation of any technology types which can meet the requiredparameters. Provision of additional services such as reactive power will also be taken intoconsideration.Ultimately, it is NGET’s aim to create a sustainable tendered market for the provision of enhancedfrequency response services from all technologies, work which is being progressed through theSMART Frequency Control project1. This would ensure that there is a route to market for bothexisting and new providers, regardless of technology type, and also would realise the benefits ofcompetition in the procurement of these services.

author: tggzzz
author_rank: Super Contributor
timestamp: April 20, 2016, 12:52:48 pm
content: Oh, that is interesting.The sub-second response time means that hydro won't be sufficient; IIRC that takes 20s to reach full power.Is there any indication how long this has supply power? If only 20s, then I suspect flywheels or compressed gas might work.

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: April 20, 2016, 01:16:44 pm
content: "Our initial analysis indicated that a battery with a 45 minute duration (minimum operational state ofcharge to maximum operational state of charge) based on current frequency data and possibly onethat minimizes or at least meets the 95% availability. However, this is currently under review, andwe will be giving more guidance on the minimum duration required shortly. The maximum durationthat we would value from an EFR service is 30 minutes, any ability of the assets to deliver energybeyond this timeframe has no additional value to NGET, however it is up to Applicants to size theenergy capacity of their assets (where necessary)."So maximum 30 mins. They've stated battery here but elsewhere in the documentation they are very keen to stress they are completely agnostic about what technology is used. In fact I read just now that they've received tenders so far from 68 projects, 60 of which have qualified to tender of 1.3GW in total, of which 880MW is battery based. It doesn't say what other ideas people have come up with.As you've stated, they already have frequency response arrangements in place with things like pumped hydro and diesels that can pick up in high 10's of seconds to low number minutes.

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: April 20, 2016, 01:22:05 pm
content: It is also interesting to think that once there is a decent install base of electric vehicles, this service could be provided by a vehicle fleet operator if the chargers were bi-directional and say 10% of the battery charge was made available to use.

author: coppice
author_rank: Super Contributor
timestamp: April 20, 2016, 01:25:49 pm
content: Quote from: DenzilPenberthy on April 20, 2016, 01:16:44 pmBattery based might mean nothing more than having a minute or two of battery capacity while they get something else on line. UPSes are often described as battery based when they have a few minutes of battery, and a diesel generating set.

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: April 20, 2016, 01:44:29 pm
content: Quote from: coppice on April 20, 2016, 01:25:49 pmGood point, I hadn't thought of that.Another interesting thing to note is that these projects are required to be symmetrical, i.e. act as a power sink in the event of an over frequency event

author: Delta
author_rank: Super Contributor
timestamp: April 20, 2016, 02:19:05 pm
content: This is very interesting indeed!To the shed! Time to dig out some old car batteries, flywheels and hydraulic cylinders! O0

author: stmdude
author_rank: Frequent Contributor
timestamp: April 20, 2016, 07:42:57 pm
content: Quote from: DenzilPenberthy on April 20, 2016, 01:16:44 pmI've seen a diesel start within 1/50th of a second for emergency power on a cell-tower. Explosive charges in the cylinder(s) will make them start in a real hurry.Probably doesn't scale with the size of diesels needed for more than a couple of KW.

author: station240
author_rank: Unknown
timestamp: April 20, 2016, 10:27:58 pm
content: I'd imagine battery and super capacitor based systems would do this easily enough.Perhaps also flywheel based generators.

author: Delta
author_rank: Super Contributor
timestamp: April 20, 2016, 10:51:47 pm
content: I don't think the technological task is particularly difficult. For exampleA series string of around 1000 12v lead acid batteries to give a DC bus voltage above the 15.5kV P-P voltage of the three phase 11kV MV net, being continuously float charged from the grid, whilst trickling a little bit through an inverter back to the grid. That inverter could be cranked up to max chat in a few cycles!Making it economically plausible (ie profitable) is the challenge.I'm off to price up 12v LA batteries...

author: Someone
author_rank: Super Contributor
timestamp: April 21, 2016, 12:49:36 am
content: Quote from: station240 on April 20, 2016, 10:27:58 pmMicroinverters coupled to super capacitors would be a very interesting way to deliver on this tender, while still utilising the inverters during normal operations. A controller that maintains a minimum charge in the capacitor and dumps excess power to the grid, then on demand can draw down on the capacitor storage. If consumers could access the variable market pricing there would be plenty of people doing this sort of thing already, but the current level of investment needed to access the market is a huge problem.

author: johansen
author_rank: Super Contributor
timestamp: April 21, 2016, 05:18:24 am
content: what i'm concerned about is the wet dream of using everyone's hybrid car battery as a free energy sink/source.There's no way you are going to get paid fair market value for the inevitable KWH per dollar cost of a battery (lead acid is something like 30 cents per kwh, minimum, under ideal conditions and faithful maintenance, 20 percent depth of discharge, etc) lithium ion is higher; allegedly lithium iron phosphate has reached parity with lead acid.. that is if it can really can deliver 3000 charge cycles at 80 percent depth of discharge, and at the end of 3000 charge cycles, the amp hour capacity is still 80% of new. (anyone have any data on this?)also why does anyone need a power grid that keeps the frequency within .1Hz?

author: MrSlack
author_rank: Frequent Contributor
timestamp: April 21, 2016, 06:26:15 am
content: Sticking the crazy Victorian lunatic hat on for a second, screw supercapacitors and battery banks. What I want is giant several hundred-ton flywheels all across the country. Think of them as massive capacitors except with AC in and AC out as you can have AC drive and standard generators. Sync them to spin slightly above a multiple of 50Hz and then when there is a grid demand switch them in at 50.5Hz and switch them back out when the energy spike is handled and the other plants have come online at 49.5Hz. Plus the linear decrease in frequency as energy is used means they can easily be used to sync phase with a control loop. They can initially have energy injected via solar, gas, steam, diesel, tread wheels (only joking) or from a quiet spot on the grid.Now I'm going to find that elephant I was going to electrocute while wildly firing my blunderbusts into the air and observing my pocket watch through the fluff of my neckbeard.

author: tggzzz
author_rank: Super Contributor
timestamp: April 21, 2016, 07:13:35 am
content: Quote from: MrSlack on April 21, 2016, 06:26:15 amIn the 70s/80s my father briefly surveyed energy storage for the CEGB/CERL. His focus was, IIRC, on medium-scale storage to see if there were alternatives to Dinorwig which was just coming online. Flywheels would not have been able to store "interesting" amounts of energy, but maybe the definition of "interesting" has changed - hence my question about how long any new scheme would have to store power.One of the problems with flywheels is their failure mechanisms, particularly what happens when bearings disintegrate - something that is more likely to happen if you start extracting power within a second. If bearings disintegrate then the resulting damage willnotbe confined to the site, since the flywheel will carve a path across the countryside as its power is dissipated. Such behaviour is deprecated by safety inspectors!ISTR seeing a picture the result when that happened to a turbine - there was a neat hole in the building's wall, just like in old cartoons!

author: MrSlack
author_rank: Frequent Contributor
timestamp: April 21, 2016, 07:36:52 am
content: Interesting stuff. The failure mode was what was interesting to me... I could imagine a 500 tonne steel cylinder steamrolling a small village!More sensibly I envisaged a horizontal disk dug deep into the ground. Although that may just result in an earthquake machine

author: BillyD
author_rank: Regular Contributor
timestamp: April 21, 2016, 08:04:40 am
content: Quote from: MrSlack on April 21, 2016, 07:36:52 amI wonder how much consideration would you have to give to aligning the wheel with the axis of rotation of the earth. A horizontally spinning disk will attempt to invert itself by 360 degrees once per day as the earth rotates, so there would be strain on the bearings to counteract this. Not to mention slowing down the earths rotation, oh the humanity....

author: MrSlack
author_rank: Frequent Contributor
timestamp: April 21, 2016, 08:06:37 am
content: I think I might actually be an evil James Bond villain in the making. One beeeeeelion dollars or I will stop the Earth spinning and move to my space station on the moon.

author: MrSlack
author_rank: Frequent Contributor
timestamp: April 21, 2016, 08:44:08 am
content: What about lots of smaller flywheels. Thousands of them?

author: Kilrah
author_rank: Unknown
timestamp: April 21, 2016, 09:04:38 am
content: Then the cost of multiplying the auxiliary equipment likely exceeds the savings from the smaller flywheels...Envoyé de mon SM-G930F en utilisant Tapatalk

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: April 21, 2016, 09:14:32 am
content: I was wondering last night about flywheels too. I don't think even compressed gas or diesel engines with explosive charges in (I'll have to look that up, not heard of this before) would be any good. I can't see any way of spinning up an alternator of 1 to 50 MW size to synchronous speed in sub 500ms without destroying it. Unless it was kept spinning all the time which would be very energy and maintenance inefficient.I wonder if hydrogen fuel cells would be able to deliver power in that sort of response time? I've heard about some pilot projects generating H2 from excess wind energy and feeding it into the gas grid. Maybe store a bit of it and feed it into some shipping container sized fuel cells?As I was thinking about flywheels I was picturing a landscape like the days of town gas here in the UK when 'gasometers' were a common sight in every town. Will we see large structures like this dotted about the place filled with spinning concrete blocks?https://en.wikipedia.org/wiki/Gas_holderAlso as regards the need to maintain the system at precisely 50.000Hz - There are reasons for this but the real reason is that the frequency is driven by the balance of supply and demand. If there is excess power being fed in to the grid, everything speeds up and the system frequency increases. Conversely if there is more demand than supply, the frequency drops as the (traditionally synchronous) generators bog down and slow under the increased load. If the frequency falls too far from 50Hz, the generators which are still supplying power will start to trip out as they are overloaded which then puts more load on the remaining ones and can cause a cascading failure of the whole grid.

author: coppice
author_rank: Super Contributor
timestamp: April 21, 2016, 10:10:10 am
content: Quote from: stmdude on April 20, 2016, 07:42:57 pmStarting piston engines with explosive charges is nothing new, but I've never heard of them starting, running up to speed, stabilising, and being ready to go on line in anything like 1/50th of a second. You can't even get a high output from a piston engine until it has warmed through.

author: Delta
author_rank: Super Contributor
timestamp: April 21, 2016, 11:28:36 am
content: I've worked at sea on Class 3 Dynamically Positioned vessels, where standby engines (4.3MW each) were kept pre-heated to 60C, with an external pre-lube pump running all the time. With compressed air starters, these would be on line and on load in less than 10 seconds. Not quite what's needed here, but impressive non the less. (It didn't stop the idiot DPOs from wanting to run every available engine all the time with 15% load on the poor coking up blighters though)

author: Someone
author_rank: Super Contributor
timestamp: April 21, 2016, 11:33:01 am
content: Quote from: coppice on April 21, 2016, 10:10:10 amDiesel backup has been around a long long time, and is well proven for response within seconds:https://en.wikipedia.org/wiki/Diesel_rotary_uninterruptible_power_supplyIn general a fast starting Diesel backup scales up to MW sizes and can be assisted in starting with compressed air. They form the essential safety systems of power stations.

author: tggzzz
author_rank: Super Contributor
timestamp: April 21, 2016, 11:48:49 am
content: Quote from: Someone on April 21, 2016, 11:33:01 amIn the UK the power source of last resort, i.e. "black start" if the entire network is down, is pumped hydro.

author: Spikee
author_rank: Frequent Contributor
timestamp: April 21, 2016, 12:28:25 pm
content: have a giant elevated reservoir and pump water in it when having excess electricity supply. Quite cheap and gravity is pretty fast.

author: Delta
author_rank: Super Contributor
timestamp: April 21, 2016, 12:42:06 pm
content: Quote from: Spikee on April 21, 2016, 12:28:25 pmThat's called pumped hydro is is already in use, however the response times are far too slow for this specific application.

author: Ian.M
author_rank: Super Contributor
timestamp: April 21, 2016, 02:56:51 pm
content: https://en.wikipedia.org/wiki/Dinorwig_Power_Station75 seconds from stationary or 16 seconds from spinning synchronised 'motoring' standby.The water in the penstocks has significant inertia, and valves take finite time to open.The flywheel idea is more promising, but it cannot be kept at a rotational speed equivalent to 50.5Hz then cut in as required, as it will take time of up to 1/freq_diff to synchronise before it can be cut onto the grid. That could easily be 0.7 seconds (grid dropped to 49.8Hz). It also wouldn't be able to accept excess power from the grid during a sudden demand drop. More promising would be to interpose a differential gear, with the flywheel and generator on either side of it and the main shaft normally locked. Add a torque converter and reduction gear running off the flywheel to drive the main shaft in either direction and you could pick up the load or accept power as quick as you could release a brake band and slam in a clutch. However the mechanical complexity and maintenance requirements would be severe.I suspect that the only commercially viable solutions will be electronic ones using storage batteries or supercaps. Reversible high voltage DC<>AC inverters are a well understood and mature technology that's already on the grid (seehttps://en.wikipedia.org/wiki/HVDC_Cross-Channel), just build one with a storage bank instead of a link cable and updated control systems to handle cutting in in one cycle.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 21, 2016, 07:39:42 pm
content: The fly-wheel could use a slowly electronic rotating field instead of a fixed DC field. So the mechanics would provide something like 45 - 55 Hz and the electronics would compensate for the +-5 Hz only. This works reasonably well with some windmills and the electronic DC/AC converter only needs to work on a faction (e.g. 10%) of the power of the whole setup.For generators and motors the efficiency gets better and specific costs usually go down when they get larger - so there is an incentive to make rotating machines relatively large, though it still small enough to allow transport. So it likely won't be a 500 tons fly-wheel, but also not many 0.5 ton ones. For a flywheel there is also given size / speed relationship. So they would run to fast (thus no easy generator / motor and more bearing problems) if too small.One big candidate for this might be battery storage at those windmills that already use electronic DC/AC converts and larger solar power installations - though likely not much solar in England.

author: Someone
author_rank: Super Contributor
timestamp: April 21, 2016, 10:32:05 pm
content: Quote from: tggzzz on April 21, 2016, 11:48:49 amThese examples are not black start resources, they are immediate ride through and backup to provide uninterruptible power for life critical systems (such as the safety systems of power stations) and flywheel + diesel is a very mature and scalable technology. As above hydro can provide massive energy storage but comes on slower than the tender requires, so it could be a component of a bid but there still remains the need for an extremely fast dispatchable generator to ride through until the slower generators come on (hydro and open cycle gas turbines would be currently called "fast" and have similar dispatch speeds of many seconds but less than a minute).

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: April 22, 2016, 09:54:31 am
content: Quote from: Someone on April 21, 2016, 10:32:05 pm"The Cruachan Power Station (also known as the Cruachan Dam) is a pumped-storage hydroelectric power station in Argyll and Bute, Scotland. It is one of only four pumped storage power stations in the UK, and is capable of providing a black start capability to the National Grid.""Another important feature of Dinorwig [pumped hydro site] is that it has been designed to assist restarting the National Grid on the occasion of a complete power failure (a black start). It includes diesel generators and large batteries which would allow the plant to restart even in the event of a complete shutdown of the grid (Dinorwig is not unique in this respect as some fossil-fuel plants are also able to self-start)."...

author: Someone
author_rank: Super Contributor
timestamp: April 23, 2016, 08:29:56 am
content: Quote from: DenzilPenberthy on April 22, 2016, 09:54:31 amYes, thats a black start resource. We've been talking about fast starting Diesels generators for riding out interruptions and providing a fast energy supply, often coupled to flywheels to provide immediate (cycle by cycle) availability.

author: ConKbot
author_rank: Super Contributor
timestamp: April 24, 2016, 10:55:28 pm
content: Quote from: DenzilPenberthy on April 22, 2016, 09:54:31 amBlack-start isnt relevant to this fast transient capable grid improvement though. Black-start is for re-starting the grid after grid-wide outages. I.e. everything has gone black. You start the diesel backup generator at the hydro station, open up the sluices, provide excitation for the generators, provide power to a coal/NG/nuclear power station which provides base load, start getting other power stations online and re-synchronized while re-connecting load. Hydro power (pumped or standard) is generally a good starting point for a black-start capable power station, no multi megawatt cooling pumps and air blowers, etc. And since you're just changing a valve to adjust flow to a turbine, and don't have an equilibrium to manage, or massive amounts of water to heat or cool (nuclear/coal/nat-gas steam plants) they can be pretty responsive too, but black-start doesn't imply fast transient response, and fast transient response doesn't imply black-startOn the grid transient handling issue. Obviously for a grid-scale thing you need big things where scaling them up provides economy and doesn't cause safety issues (like storing all the energy in a massive flywheel) I wonder if flow-battery technology has improved enough to be useful for something grid-scale, without using chemicals conceived by satan himself. Or for hydro-electric power, if it would be possible to use smaller, faster-responding turbines and a different intake design to improve transient response. I.e. a dam with 30 2 MW turbines intead of 4 15MW turbines, even if they were grouped together to keep from increasing the amount of support equipment excessively.