Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!

 


Forgot your password?
Close
typodupeerror
×
Power Australia

A Tesla Big Battery Is Getting Sued Over Power Grid Failures In Australia (vice.com) 123

Posted by BeauHD from the broken-promises dept.
Tesla's Big Battery, located in southern Australia, just got hit with a federal lawsuit for failing to provide the crucial grid support it once promised it could. Motherboard reports: Built by Tesla in 2017, the 150-megawatt battery supplies 189 megawatt-hours of storage and was designed to support the grid when it becomes overloaded. Now operated by French renewable energy producer Neoen, it supplies storage for the adjacent Hornsdale wind farm, using clean energy to fill gaps that coal power leaves behind. It made waves at the time of its construction for being the largest lithium-ion battery in the world -- though it's now been superseded by another Tesla battery, the 300-megawatt Victorian Big Battery, also in Australia, which caught fire in July. On Wednesday, the Australian Energy Regulator (AER), the body that oversees the country's wholesale electricity and gas markets, announced it had filed a federal lawsuit against the Hornsdale Power Reserve (HPR) -- the energy storage system that owns the Tesla battery -- for failing to provide "frequency control ancillary services" numerous times over the course of four months in the summer and fall of 2019. In other words, the battery was supposed to supply grid backup when a primary power source, like a coal plant, fails.

The HPR's alleged pattern of failures was first brought to light during a disruption to a nearby coal plant in 2019, according to the regulator. When the nearby Queensland's Kogan Creek power station tripped on October 9, 2019, the HPR was called on to offer grid backup, having made offers to the Australian Energy Market Operator (AEMO) to do so. But the power reserve failed to provide the level of grid support that AEMO expected, and, in fact, was never able to do so in the first place, the lawsuit alleges, despite making money off of offering them. Though HPR did step in eventually, and no outages were recorded, the incident spurred investigation into a number of similar failures over the course of July to November 2019. The reserve's failure to support the grid in the way it promised created "a risk to power system security and stability," a press release on the lawsuit says.
This discussion has been archived. No new comments can be posted.

A Tesla Big Battery Is Getting Sued Over Power Grid Failures In Australia More

A Tesla Big Battery Is Getting Sued Over Power Grid Failures In Australia

Comments Filter:

  • "Nearby" (Score:5, Insightful)

    by dohzer ( 867770 ) on Monday September 27, 2021 @08:08PM (#61839473)

    When the nearby Queensland's Kogan Creek power station tripped...

    Only a bit over 1,650 km from the HPR by road.

    • Re: "Nearby" (Score:4, Insightful)

      by crispi ( 131688 ) on Monday September 27, 2021 @08:13PM (#61839485)

      Ppl have no clue of the scale of Australia.

      • Re: "Nearby" (Score:5, Funny)

        by PPH ( 736903 ) on Monday September 27, 2021 @08:44PM (#61839601)

        Australia is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to Australia.

        • "Australia is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to Canadians."

          FTFY

          • Re: "Nearby" (Score:5, Funny)

            by ArmoredDragon ( 3450605 ) on Monday September 27, 2021 @10:45PM (#61839813)

            Well Canada is different. When we Americans banished them north of the wall for refusing to stand up to their king, they got angry and 95% of the wildlings moved within 150 miles of the US border, and have lived there ever since. The rest of Canada is unpopulated except by the remaining 5%, which are white walkers, weights, sasquatchs, children of the forest, and undead polar bears. So basically nothing is out there, and if you're part of the living, nothing of any significance is very far away from you.

        • Well,
          a friend of mine was flying from Sydney to Frankfurt Germany.
          He said: literally half the flight time was over the continent of Australia (ofc. that was a bit exagerated, but close).

      • Re: (Score:2)

        by Targon ( 17348 )
        The same can be said of the USA, or Canada. People from Europe just can't understand the scope of how big other countries really are besides Russia and China. Here in the USA, you can go for over 300 miles to get across an individual state. California and Texas are beyond the comprehension of those people, and Australia is far larger.

    • Maybe they mean the coal mine was near to the coal powered power station, which makes a lot more sense?

    • Re: (Score:2)

      by Ronin441 ( 89631 )
      Motherboard also say "four months in the summer and fall". But the interval in question is actually July to November, which is winter and spring.

    • It effectively is nearby as far as the power grid is concerned. The HPR has provided FCAS for tripped Queensland based power plants numerous times in the past, so much so that local Queensland gas plants complained that they were being undercut interstate by a service they specifically were designed to offer in a co-located fashion.

    • Only a bit over 1,650 km from the HPR by road.

      For those accustomed to non-metric units, that's 1.17 Texases or 1.45 Frances, as measured by the east-west drive on I-10 across the state and the north-south drive from Calais to Spain, respectively. Australia is HUGE.

  • Tesla? (Score:5, Insightful)

    by HanzoSpam ( 713251 ) on Monday September 27, 2021 @08:14PM (#61839489)

    It looks like they're suing the company managing the battery. I don't see where Tesla, or the battery itself, are even involved.

    • Re:Tesla? (Score:5, Insightful)

      by fahrbot-bot ( 874524 ) on Monday September 27, 2021 @08:26PM (#61839545)

      It looks like they're suing the company managing the battery. I don't see where Tesla, or the battery itself, are even involved.

      Yup, but ABC and Vice (and /.) putting "Tesla" in the headline catches more eyes than some company no one has ever heard of ...

    • Re: (Score:2, Informative)

      by GigaplexNZ ( 1233886 )
      While true, they're suing over the technical failures of the Tesla hardware.

      • Re:Tesla? (Score:5, Interesting)

        by im_thatoneguy ( 819432 ) on Monday September 27, 2021 @09:27PM (#61839685)

        Not necessarily. They're suing because Horndale was being paid to be available 24/7 for outages. But sometimes they weren't available when they were under contract to be ready.

        That doesn't mean the hardware failed since it's a managed product. If you have a battery backup on the grid you can also use that to buy power during low prices and resell during high prices. Horndale may have discharged a lot of power for profit and simply been empty.

        That would be a very valid lawsuit to file. If you're being paid to be a standby reserve but you apparently were double-dipping by also playing the energy markets then you deserve to be sued.

        If I deposit my money in a bank account and you charge me $50/year for a checking account, my expectation is that I can write a check at any moment and it'll be cashed. If you then though take my money and buy bitcoin and when I look to withdraw discover that you don't have the liquidity to cash a check then I'm going to sue because you failed to live up to the service I paid you for. That doesn't mean though that the ATM is broken.

        • Re:Tesla? (Score:5, Informative)

          by Bandraginus ( 901166 ) on Tuesday September 28, 2021 @12:52AM (#61839995)

          That doesn't mean the hardware failed since it's a managed product. If you have a battery backup on the grid you can also use that to buy power during low prices and resell during high prices. Horndale may have discharged a lot of power for profit and simply been empty.

          That would be a very valid lawsuit to file. If you're being paid to be a standby reserve but you apparently were double-dipping by also playing the energy markets then you deserve to be sued.

          Of the original 100MW/129MWh capacity of the battery, 70MW/10MWh are dedicated for providing the FCAS function in TFA. 30MW/119MWh can freely participate in the open market for price arbitrage.

          Its obligations are quite clearly spelled out here [arena.gov.au].

          The article says that HPR did step in and provide FCAS duties, just not at the capacity expected by AEMO. The article doesn't really say why.

          That said, here's another take on it [reneweconomy.com.au]. That article says that coal fired power plants constantly fail to meet their FCAS duties, but are rarely fined. Not sure why HPR is being held to a higher standard.

          • Re:Tesla? (Score:5, Informative)

            by sxpert ( 139117 ) on Tuesday September 28, 2021 @01:03AM (#61840017)

            simple... it's a political stance, the regulator does not appear to be particularly independent from the coal-corrupted government

            • They did resist the construction pretty aggressively. The remembered quote is have the biggest battery. Have the biggest banana. It makes no difference.

              • No they didn't. They resisted changing the entire FCAS market market by including an additional 6 second market to the existing 60 second and 5 minute market. They never opposed the construction of the battery or its participation. And after they saw what the battery was capable of they added a whole new market segment for it.

            • Re: (Score:3, Insightful)

              by thegarbz ( 1787294 )

              simple... it's a political stance, the regulator does not appear to be particularly independent from the coal-corrupted government

              Not a political stance at all, it's a simple contractual stance. The requirement for FCAS includes not only what you do, but how quickly when bidding for the contract. If you breach the contract expect to end up in court. It's not rocket surgery. Neoen bid on an FCAS contract they couldn't deliver fast enough and got a financial advantage over a competitor. The regulator dragging them to court is the system working perfectly as intended.

              When you're an anti-government crazyperson everything looks like a cons

          • Re:Tesla? (Score:5, Informative)

            by ScienceBard ( 4995157 ) on Tuesday September 28, 2021 @03:37AM (#61840261)

            Of the original 100MW/129MWh capacity of the battery, 70MW/10MWh are dedicated for providing the FCAS function in TFA. 30MW/119MWh can freely participate in the open market for price arbitrage.

            Its obligations are quite clearly spelled out here [arena.gov.au].

            The article says that HPR did step in and provide FCAS duties, just not at the capacity expected by AEMO. The article doesn't really say why.

            That said, here's another take on it [reneweconomy.com.au]. That article says that coal fired power plants constantly fail to meet their FCAS duties, but are rarely fined. Not sure why HPR is being held to a higher standard.

            I've got some experience on the US side of this. A certain amount of play is built into the system just given that statistically a certain amount of traditional generation is expected to have mechanical failure. If a coal plant bid in to provide a service and had a pipe rupture and force it offline, that is highly unlikely to be a malicious or negligent act, it's just something that happens. I wouldn't expect the regulator to fine someone for that. On the other hand, if I found out you had a coal plant bid into the market to provide a service at 100MW while at the same time the plant was derated to 50MW for planned maintenance, I as the regulator would come back and fine you severely.

            What this sounds like is the operator wasn't managing the battery responsibly. If I had to guess, I'd assume they were missing some obvious "you should have known about this" loss or capacity limitation. Back of the envelope I've been advised to guess about 15% round trip loss for a battery of that type (that's for the battery and all the intervening equipment between it and the grid). So could be they were bidding in the service without accounting for their losses, which would limit the extent of service they could provide below the maximum. Another reasonable guess would be some kind of charge/discharge rate limitation that wasn't accounted for. Given Australia is stupid hot for a lot of the year, it wouldn't surprise me at all if there was a set of engineering numbers for derating the system at a certain temperature that were ignored, and instead some optimized or baseline value was used in the software doing their calculations. Which given the speed at which they installed the thing I'd expect there were a lot of white collar workers scrambling to figure out how to integrate it into software and such.

            Folks are very caught up on the cost and physical difficulty of integrating batteries, but honestly the back end of managing the minutia of batteries in software/modeling space is pretty intense too. They introduce a LOT more computational complexity and data to manage to these systems, and cause some pretty severe statistically abnormal behaviors when you get a lot of them into energy models. The traditional generating system wasn't just built the way it was for cost reasons, it was also vastly easier to manage. Batteries are very challenging from a computational perspective, even more so than things like rooftop solar.

          • Re: (Score:2)

            by tlhIngan ( 30335 )

            Of the original 100MW/129MWh capacity of the battery, 70MW/10MWh are dedicated for providing the FCAS function in TFA. 30MW/119MWh can freely participate in the open market for price arbitrage.

            Wouldn't be the first time people were "playing the market" by being a bit fast and loose and hoping no one notices. You may have 30MW available to play in the market, but eventually people will try 36MW, maybe 40MW, and then more. After all, if you're not actually called on for all 70MW, no harm, no foul, right?

            It wo

            • Re: (Score:2)

              by catprog ( 849688 )

              Except what actually happened is their was a setting that meant they delivered 15MW(I think) instead of the 30MW they were supposed to . This setting is now fixed.

              (I.e the setting meant they only took the grid to 49.6Hz instead of 50Hz)

      • No they aren't. They are suing over contractual failures of the operator. The hardware works just fine and is doing precisely what it was designed to do.

        I drive a Renault Clio. It can go 180km/h down the autobahn. If I tell you I can drive you from Hamburg to Berlin in 1.5 hours and it turns out I can't it's not the fault of the Clio for not being able to do 200km/h, it's my fault for offering you something I couldn't deliver with the hardware I have.

        The suit here is because Neoen is offering on the market

    • The other thing is that a lot of Australian infrastructure work is surrounded by shady business dealings and corruption at many levels. On the surface, this sounds like the HPR suing the AER for failing to provide a service, but there could be a lot more to it than that, someone didn't get paid enough, or it was felt that someone else got paid too much, or someone got a contract they shouldn't have and this is payback, or who knows what.

      It's also a fairly risky tactic, because you never know what will tur

  • What are they alleging? (Score:3)

    by sanosuke001 ( 640243 ) on Monday September 27, 2021 @08:21PM (#61839519)

    So, HPR "failed" to provide grid support but "HPR did step in eventually, and no outages were recorded". So, what are they alleging? How did they fail? I read TFS and skimmed the top of TFA and nothing of substance was found...

    • Re:What are they alleging? (Score:4, Informative)

      by Synonymous Cowered ( 6159202 ) on Monday September 27, 2021 @08:38PM (#61839583)

      I'm not entirely certain either, but the summary says:
      "for failing to provide "frequency control ancillary services" numerous times over the course of four months"

      From my (admittedly lacking) knowledge of power generation, when there is an oversupply of power, the frequency of the supplied power goes up. When there is an undersupply, the frequency goes down. Ideally, the frequency should remain fixed (60hz in the US, and I believe other countries tend to use either 50 or 60hz). Many devices can handle some slight variation from this, but too much variation can cause a issues.

      I think what I might be getting from the article is that the battery failing to do its intended job of keeping the frequency constant. So maybe there wasn't enough variation to cause a blackout, but it was enough to cause issues?

      (I now prepare for someone with a much better understanding of the matter to smack me down for my primitive understanding)

      • Re:What are they alleging? (Score:5, Informative)

        by sfcat ( 872532 ) on Monday September 27, 2021 @09:16PM (#61839657)
        You got it mostly right. There are just an issues you didn't discuss. This battery has a discharge rate it needs to be able to maintain to do the job of controlling/supporting the frequency of the grid. That discharge rate is usually a function over the amount of charge the battery has (but can also be dependent upon other factors). It seems that the financial agreements assumed a constant minimum rate of discharge. At different levels of charge, the battery isn't able to supply this minimum level of discharge. This makes the battery discharge longer but at a lower rate of delivering power at different points as the battery discharges (assuming some capacity hasn't already been lost). The problem is that the marketing of the battery stated ideals and when the financial agreements were drawn up, they stated that the ideal rates were the promised rates of constant delivery. So in financial agreements when you under-perform to what is promised penalties kick in. The operation hasn't been paying said penalties possibly because they don't agree with the interpretation of the financial agreement, or possibly because they don't have the funds to do so. Either way the problem was business people not understanding the physics of what was being sold combined with the overselling of the battery system's capabilities. Once again, over promise, under deliver. Pretty standard for battery technology. Anyone who is surprised is naive.

        • Once again, over promise, under deliver. Pretty standard for battery technology. Anyone who is surprised is naive.

          So guys are like batteries.

        • overselling of the battery system's capabilities

          Considering this was only supposedly a problem for a 4 month period, 2 years ago and 2 years after it went into service this smells a lot more like someone at Hornsdale figured that they could reduce their reserve % for higher profit trading on the energy market rather than overselling the capabilities.

          If it had failed to meet the contract since installation then you could say it was oversold. But it would be really weird that there was only a brief period years after it began operation and years prior to

          • Re: (Score:2)

            by ytene ( 4376651 )
            And it’s even harder to believe that the buyer of an installation this big, this complex and this dependent on new designs would not have insisted on rigorous testing at the point it was commissioned and paid for. You simply don’t hand over tens of millions of dollars for something that doesn’t work.

            • Re: (Score:3)

              by Luckyo ( 1726890 )

              Oh you sweet summer child.

          • Re: (Score:2)

            by AmiMoJo ( 196126 )

            It might not just be that period when it failed, that might simply be the period they have fully documented for the purposes of the lawsuit.

      • I'm no engineer. Nor operator. But lets talk about generating AC power from a hydroelectric dam. Watch this video to see what it takes to sync up to the grid: https://www.youtube.com/watch?... [youtube.com]

        The hertz (frequency) is dictated by the propeller SPEED. And then the phase (sync) needs to be inline with the grid.

        Bringing it back to Tesla, batteries store power in DC, not AC. So you need equipment that will turn the DC power into AC. Enter the inverter. Big inverter. Just like your car's or UPS on a computer data

        • Inverters are basically able to sync to a grid instantly (or within a cycle, so a fraction of a second) and for a battery like this one it would be synced permanently. The issue here wasn't that they didn't sync it's that they didn't provide the service in the time required. The FCAS market basically says that bidders for services need to list the time and capability to correct frequency deviations. That means as the frequency drops they need to pump power into the grid, as frequency rises they need to suck

    • In IT terms: HPR sold a premium 24/7 'on call' service to the government but the government discovered that numerous times when they tried calling to get support there was nobody on-call to answer the phone between July 2019 and November 2019.

      Hornsdale needed to track when the battery was and wasn't available to provide service and only bill for the time when they could actually provide service.

    • How did they fail?

      FCAS contracts are time dependent. Stepping in "eventually" is a breach of contract. To control frequency on the network you bid on the market not only how much capacity you can provide, but also how quickly.

      If you need to get to the airport as fast as possible, the Taxi says you can be there in 10min, your Uber driver says 5min, you'd be quite pissed if it took the Uber driver 15min to show up.

    • They are alleging that capacity was advertised by HRP as being available and said capacity was not available and HRP could not deliver the capacity that they advertised at that time.

      Breach of contract or fraudulent advertising by HRP. Could have been disastrous, but it wasn't.

      Oh and Tesla, so clicky.

  • In the hands of a French enterprise, a company formerly owned by elon musk's baby, Tesla, failed to provide the level of grid support that AEMO expected.

    I'm reminded of a cartoon a decade or three ago, lampooning the Kennedy's dog for being in the neighbor's trash cans.

  • Who writes this junk?

    • Same morons who put "you" in every headline that has absolutely nothing to do with "you."

      Like, "now you can do X with your Y." What if *I* and two thirds of the people who read it don't have a Y and wouldn't dream of doing X?

    • Re: (Score:2, Insightful)

      by sfcat ( 872532 )
      No but Tesla's customer is. And they are being sued because a Tesla product isn't living up to Tesla's marketing promises. I know in retail this is assumed but in industry, this will only lead to lawsuits. That's why industrial minimums actually happen in practice because people don't like to be sued. This makes buying a Telsa battery in the future such an attractive business proposition. I assume after this lawsuit is finished, Neoen will sue Tesla for damages due to breach of contract (unless they fo
      • You assume it is the battery. Neoen may have over sold capacity, or sold too much capacity at night for profit and did not have enough left over for contactual obligations. Or many other things.

        It amazes me how "the battery" is the headline on Slashdot. Here is a article that is non slashdot mangled.

        https://www.queenslandcountryl... [queensland...ife.com.au]

      • So so many Luckyo's around here. (Score:1)

        by Anonymous Coward

        "Who writes such junk posts?"

        The answer would be you.

        It alleges that during this time, the “droop” setting for the Hornsdale battery had been adjusted by a “firmware” update from 1.7 per cent – the minimum allowable droop setting for any battery providing contingency FCAS – to 3.7%.

        You think it's Tesla's fault the settings were wrong? Maybe have someone competent update the settings next time, and learn how to run your equipment properly.

        So so many Luckyo's around here.

  • No info in the the article whether the battery operator provided what they promised or whether what the government asked for was reasonable and expected. Itâ(TM)s a shame that the article doesnâ(TM)t even mention the mere existence of the important question of which side might be right. Hopefully the media and Slashdot will post a follow up story on the case or on an investigation into that (which side seems to be correct).

  • Context Seems Relevant... (Score:5, Informative)

    by ytene ( 4376651 ) on Monday September 27, 2021 @11:31PM (#61839905)
    It's the last link in the above article that provides the most interesting background to this story. For ease of access that's the link to RenewEconomy.com.au, here [reneweconomy.com.au].

    A few elements taken from the RenewEconomy article:-

    Hornsdale - the 315MW wind farm with the "Tesla Battery" in South Australia, is now owned by Neoen, a French company.

    After building the Hornsdale battery solution, AEMO, the Australian Energy Market Operator, were so happy with the solution that they contracted Neoen to build the Victoria Big Battery at Geelong, which will have twice the generating capacity and roughly 225% of the battery storage once complete.

    The Hornsdale battery is also seen by market observers as bringing the Australian gas cartel to heel [reneweconomy.com.au], as there is evidence that the gas-based generators had bumped charges ten-fold and that the Hornsdale battery was denying the incumbents of the ability to charge extortionate fees. For example, those incumbents were charging AEMO up to AUS$7 million a day to provide contingency for planned maintenance, by charging between $11,500-$14,000/MW for contingency, Hornsdale offered the same service for $270/MW, less than 2% of the price bid by the gas cartel.

    Earlier in 2021, a major incident caused by the loss of the main links between New South Wales and Queensland, praised the response of the Hornsdale battery while being devastating in criticism of legacy coal and gas generators.

    Perhaps most telling of all, senior electrical engineers contacted by the author of the RenewEconomy piece made a telling observation: “We seem to be in an environment where we blame renewables and inverter technologies for not being perfect, while at the same time turning a blind eye to the imperfections of legacy kit,” one engineer said, on condition of anonymity, adding that it seemed to be a “misrepresentation” and a “politicisation” of the issue.

    In short, whilst there was undeniably an issue, it does look from the material made available that not only were the issues with the Hornsdale battery less than those seen from coal and gas providers, not only did the coal and gas providers escape sanction while Hornsdale was singled out for sanction, not only did the same regulator now taking Hornsdale to court happen to be singing their praises earlier this year... but - also earlier this year - the same entity contracted for an even bigger battery solution that Hornsdale. Which rather begs the question: if things were working so well for the "Tesla battery" earlier this year, what has changed that means that they are not working now? It seems unlikely that it was the Tesla battery" at fault here.

    I understand that the writers over at Vice need source material to generate clicks. I understand that "Tesla" evokes a polarizing response that in turn generates page clicks and therefore ad revenue, but maybe we're also getting to the point where this sort of "journalism" (from Vice) really shouldn't get the oxygen of free publicity that being linked by Slashdot will generate.

    Nothing to see here. Move along, move along.

    • not only did the coal and gas providers escape sanction while Hornsdale was singled out for sanction, not only did the same regulator now taking Hornsdale to court happen to be singing their praises earlier this year... but - also earlier this year - the same entity contracted for an even bigger battery solution that Hornsdale

      You seem to be criticising the regulator without understanding what it is they regulate. There's nothing to sanction coal and gas providers for until they fail to meet their obligations contractually. For one coal providers don't provide FCAS, they operate a different market and that market contract does not guarantee 100% uptime, incidentally this is why the FCAS market exists in the first place. In the FCAS market you not only mention what you do but how quickly you can do it. Gas companies are universall

  • The irony of this, is that today (28th September) is the 5th anniversary of why the Big Battery exists in the first place. The whole of the state of South Australia, due to a massive storm front, was without power for 8 hours, some parts of the state didn't get power restored for days afterwards. It was surreal. Here's a link to the ABC Australia article about it. https://www.abc.net.au/news/20... [abc.net.au]

    • Re: (Score:2)

      by Targon ( 17348 )
      There are pieces of this that are not being talked about. How much of this comes, not from the "Big Battery" having a problem, but from other things such as the power delivery FROM the Big Battery to the grid? The battery itself is probably not at fault, but people in operations may have been slow to respond when something like a circuit breaker tripped and needed to be reset. Here in the USA, many of us are no stranger to the idea that you have the power company, you have the homes, but then, you ha

  • The headline on this post seems a bit misleading. It is HPR, the company that manages the power reserve which is getting sued, for not providing power. It is not clear that this has anything to do with Tesla, or the technology.

  • People have no idea how big Australia is.

    • land area of australia: 2.97M sq mi.
      land area of Europe: 3.93M sq mi
      land area of USA: 3.8M sq mi
      land area of Russia: 6.61M sq mi.
      land area of Canada: 3.86M sq mi.
      land area of China: 3.71M sq mi.

      • Ironically after your post people outside of America still have no idea how bit Australia is, and the sad part is that people inside America don't even know where Australia is.

  • Signed,

    Battery

Slashdot Top Deals

In the long run, every program becomes rococco, and then rubble. -- Alan Perlis

Close