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Google Challenge Results In Astoundingly Efficient Inverters 245

AmiMoJo writes: A few summers ago, Google and IEEE announced a one million dollar prize to build the most efficient and compact DC to AC inverter. It was called the Little Box Challenge, with the goal of a 2kW inverter with a power density greater than 50 Watts per cubic inch. Typical solar inverters have a density of about 5 W/cubic inch. Now the results are in, with the winners hitting 143 W/cubic inch using GaN transistors, and two other teams meeting Google's goal.
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Google Challenge Results In Astoundingly Efficient Inverters

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  • The world is a slightly better place.

  • Efficiency (Score:5, Insightful)

    by fyngyrz ( 762201 ) on Monday March 07, 2016 @10:40AM (#51652945) Homepage Journal

    Astoundingly Efficient Inverters

    This doesn't seem to be about efficiency at all, but rather about power density (how much power can be converted in a particular cubic volume.)

    Not that small isn't a worthy goal, but efficiency is important in any application where available power isn't both free and copiously oversupplied.

    • Re:Efficiency (Score:4, Insightful)

      by guruevi ( 827432 ) <evi AT evcircuits DOT com> on Monday March 07, 2016 @10:44AM (#51652983) Homepage

      Don't they go hand-in-hand though? You can only dissipate so much (waste) energy in a particular cubic volume. Decreasing the amount of waste energy increases the amount you can pack together. It wouldn't be a challenge if you're just looking for miniaturization.

      • Re:Efficiency (Score:4, Interesting)

        by DeathToBill ( 601486 ) on Monday March 07, 2016 @10:55AM (#51653049) Journal

        Maybe, though Hack-a-Day say it involves an "incredible thermal management solution," which doesn't sound like they've actually bumped the energy efficiency up that much.

        Why were Google so keen to have an inverter that maximises power density? Why not maximise energy efficiency?

        Ideally you'd like to minimise cost of energy. But I guess it's fairly difficult to construct a competition around this: It depends too much on production scale and the prevailing cost of electricity. But why power density as a substitute?

        • Re:Efficiency (Score:5, Interesting)

          by AmiMoJo ( 196126 ) <mojo@world3.nBLUEet minus berry> on Monday March 07, 2016 @01:13PM (#51653849) Homepage Journal

          Batteries. Current inverters are rather large compared the batteries that can provide their maximum output power.

          Electric vehicle charging would benefit from this. You want to be pushing 120kW+ DC into the battery. You can also go back the other way and run your house from the car battery to save money when your solar panels are not producing anything.

          • by Guspaz ( 556486 )

            The inverters used for 120 kW+ charging isn't in the car, it's in the charging stations. The only charging stations hitting 120 kW+ are Tesla's superchargers, which are pure DC as far as the car is concerned.

        • Re: (Score:3, Insightful)

          by Jim Sadler ( 3430529 )
          Wouldn't it be wonderful to do that energy conversion outside the home with a tiny box. Keep in mind that the more equipment inside a home the more power the home will consume. In hot weather a big box inside the home would add to the cooling energy load on the home. If installed outside the home a duct could, in cold weather, direct that excess heat from the converter to keep pipes warm or pumps from freezing up. Most people fail to realize that once power is sent down the power line t
        • Re:Efficiency (Score:5, Insightful)

          by torkus ( 1133985 ) on Monday March 07, 2016 @04:56PM (#51655239)

          Electrical Efficiency is loosely coupled to volumetric efficiency. We're talking about an inverter roughly the size of a fist that's outputting 2kW. Without very high efficiency your cooling solution would be larger than your inverter. A moderate size CPU cooler (sinking ~65w) is the size of this whole inverter.

          The rules require efficiency >95% which is typical for high efficiency inverter systems. At that, the primary benefit to higher efficiency is lowered cooling requirements (i.e. size) which is the primary goal of the competition.

          So the rules basically *do* set teams out to maximize efficiency. Having small, highly efficient inverters is useful is many applications (solar, vehicular, UPS, etc.)

          As for Google's exact benefit? I could see them running these in datacenters: deliver 450VDC rails to all your racks and power them off a hockey puck inverter or two. Simple to scale - add more battery, more racks with inverters as needed. Everything becomes modular.

          Beyond that, solar and larger UPS systems typically run at 450VDC - so this means you can also scale your UPS and solar installation in conjunction with your datacenter. Basically combine all the technologies together without requiring large monolithic components. Ok, TLDR my own post.

      • Re:Efficiency (Score:5, Insightful)

        by fyngyrz ( 762201 ) on Monday March 07, 2016 @11:03AM (#51653105) Homepage Journal

        They can go hand in hand; they don't have to go hand in hand. Generally speaking, efficiency of power conversion is fairly high, 95% isn't all that uncommon for a design that tries hard. Some of the problems are that when you're doing conversion at the KW level, 5% is 50 watts, which tends to be RFI (both direct and indirect) and heat - that's efficient in one sense, and a serious problem in another. Going from 95% to 97.5% cuts that to 25 watts; and that's not space saved once per installation, that's money saved and more energy for other things and less crap in the air every moment the conversion is ongoing.

        In the case of houses and cars, where KW is the order of the day, space is a minor problem; efficiency is the major problem. I'd take a 97.5% efficient box at 10x the volume over at 95% converter any time. But it isn't even 10x the volume, generally speaking.

        That's why the first thing I looked for was competition for conversion efficiency, and why I was a little put off by it not even being there.

        • Re:Efficiency (Score:4, Informative)

          by DeathToBill ( 601486 ) on Monday March 07, 2016 @12:13PM (#51653457) Journal

          According to [1], the winner achieves 95.4% efficiency - not actually that impressive as inverter efficiencies go.

          [1] http://littleboxchallengecetpo... [littleboxc...tpower.com]

          • by arth1 ( 260657 )

            According to [1], the winner achieves 95.4% efficiency - not actually that impressive as inverter efficiencies go.

            So, in the space saved, they can fit a small stirling engine? :)

    • Yeah... from the website [littleboxchallenge.com]:


      An open competition to build a (much) smaller power inverter, with a $1,000,000 prize.

      Design and build a kW-scale inverter with the highest power density (at least 50 Watts per cubic inch).

      Efficiency is not mentioned anywhere. I see somebody arguing that efficient with space is still being efficient. This is true, but is not what is commonly meant when referring to the efficient of an inverter, and misusing the word in this context is confusing.

      • Re:Efficiency (Score:5, Informative)

        by PIBM ( 588930 ) on Monday March 07, 2016 @10:50AM (#51653017) Homepage

        If you had read the challenge when it was proposed (or went to read the rules), the efficiency was required to be > 95%

        . Produce a DCAC conversion efficiency of > 95%

        From https://www.littleboxchallenge... [littleboxchallenge.com]

        • Re:Efficiency (Score:5, Insightful)

          by Stewie241 ( 1035724 ) on Monday March 07, 2016 @10:59AM (#51653079)

          Ah, I didn't look that closely to see that. On the other hand, I still wouldn't consider them 'astoundingly efficient' as the headline claims. This article [electronicdesign.com] discusses a design for a 97.09% efficient inverter. (I admit at this point I'm beginning to be argumentative, but I still think the headline should have been astoundingly dense inverters, though my theory is that slashdot injects in intentional errors to drive comments and traffics from those who like to nitpick submissions).

          • by Anonymous Coward on Monday March 07, 2016 @11:06AM (#51653127)

            There's probably a joke to be made at your expense, here.

          • Re:Efficiency (Score:5, Informative)

            by Ol Olsoc ( 1175323 ) on Monday March 07, 2016 @11:21AM (#51653215)

            Ah, I didn't look that closely to see that. On the other hand, I still wouldn't consider them 'astoundingly efficient' as the headline claims. This article [electronicdesign.com] discusses a design for a 97.09% efficient inverter. (I admit at this point I'm beginning to be argumentative, but I still think the headline should have been astoundingly dense inverters, though my theory is that slashdot injects in intentional errors to drive comments and traffics from those who like to nitpick submissions).

            I disagree that you're being argumentive. While efficiency can mean a lot of things, it's a dead lock given that in a story about electric inverters, that efficiency would mean conversion efficiency.

            Because the "efficiency" they were actually referring to was efficiency in th enature of efficiency apartments.

            I certainly don't want to disparage what they did, because it was very impressive. This was more an issue with the person who wrote the original article.

            • Consider a mobile installation of such an inverter. Electric cars might be far cheaper if AC power to the wheels was used instead of the DC from the battery packs. Higher powered DC brushless motors seem to be very expensive. Higher powered AC motors seem to be much cheaper but I can't comment on what industrial, bulk buying, prices might be. The weight of AC motors seems to be less as well. So being able to carry a tiny DC to AC converter might be far more efficient in an electric car or truck. Appa
      • Re:Efficiency (Score:5, Informative)

        by Anonymous Coward on Monday March 07, 2016 @10:56AM (#51653053)

        From the website https://www.littleboxchallenge.com/:

        In brief, the other specifications are :

        * Must be able to handle up to 2 kVA loads
        * Must achieve a power density of equal to or greater than 50 W/in3
        * Must be able to handle loads with power factors from 0.7–1, leading and lagging in an islanded mode
        * Must be in a rectangular metal enclosure of no more than 40 in3
        * Will be taking in 450 V DC power in series with a 10 O resistor
        * Must output 240 V, 60 Hz AC single phase power
        * Must have a total harmonic distortion + noise on both voltage and current of 5%
        * Must have an input ripple current of 20%
        * Must have an input ripple voltage of 3%
        * Must have a DC-AC efficiency of greater than 95%
        * Must maintain a temperature of no more than 60C during operation everywhere on the outside of the device that can be touched.
        * Must conform to Electromagnetic Compliance standards as set out in FCC Part 15 B
        * Can not use any external source of cooling (e.g. water) other than air
        * Does not require galvanic isolation

        • by ArchieBunker ( 132337 ) on Monday March 07, 2016 @12:31PM (#51653565) Homepage

          Sounds like Google had very specific design requirements and didn't want to spend the money in house doing development. So they dream up a contest and offer a cash prize. Meanwhile Google saves way more than the $1 million they paid out.

          • by asylumx ( 881307 )
            Welcome to the 'gig economy' -- in this gig, many people do the work but only one gets paid!
          • by tsqr ( 808554 )

            Sounds like Google had very specific design requirements and didn't want to spend the money in house doing development. So they dream up a contest and offer a cash prize. Meanwhile Google saves way more than the $1 million they paid out.

            Are you implying that Google somehow assumed ownership of the designs? TFA didn't say that the submitted designs ended up belonging to anyone aside from the submitters; it was, in fact, mute on the subject of ownership. Do you have a source to cite that says Google ended up owning any of the designs?

      • by bytesex ( 112972 ) on Monday March 07, 2016 @11:20AM (#51653213) Homepage

        They want to put it in your mobile phone! Have a solar panel on the one side, your house fuse box on the other, and your phone in the middle! That's why they wanted the highest energy density per volume!

    • Re:Efficiency (Score:5, Informative)

      by slashkitty ( 21637 ) on Monday March 07, 2016 @10:50AM (#51653019) Homepage
      95.4% efficient in the conversion per the Datasheet http://littleboxchallengecetpo... [littleboxc...tpower.com]
    • I don't understand your attempt at pedantry. Density is spacial efficiency. If you make something smaller, you make it more efficient in the dimension of size.

    • Space efficiency is technically a type of efficiency as well as all the other points above. :)

    • Consumption of space is an efficiency in itself. For example, suppose your car engine could be made the size of a pack of cigarettes with the same power output. Even if that small engine was made of pure gold it would have less weight and therefore, your car would use less fuel. You could also reduce the frontal area and wind drag on the vehicle. Bulk almost always means less efficiency.
    • Space efficient :-p

      Also, smaller may additionally imply cheaper, or lighter.

  • by Anonymous Coward on Monday March 07, 2016 @10:51AM (#51653027)

    Are guys fucking serious?!?

    If you really want to use your old units, why not horse power per cubic inch?

  • Does any one know what power density the inverters for HVDC [wikipedia.org] transmission lines achieve? I know that this is not a comparable use case, i'm just interested.
    • The first iteration was around 80% conversion efficiency, but I understand they are in the low 90% range now. The challenge is the IGBTs need to be chained for the voltage, which increases switching losses.

  • by stevel ( 64802 ) * on Monday March 07, 2016 @10:57AM (#51653059) Homepage

    Gallium Nitride transistors have a lot of nice characteristics, but low yields and high costs have slowed their introduction. Two tiny laptop chargers, the FinSix Dart [finsix.com] and Avogy Zolt [avogy.com], were said to use GaN transistors. The Dart still hasn't shipped, a year past its claimed release date. The Zolt has but is apparently using older Silicon Carbide-substrate transistors instead [chipworks.com] (Also see here [pointthepower.com].) (I received my Zolt recently and it is working well.)

    It won't be a surprise to anyone following this technology that it can make inverters more efficient - that's what FinSix and Avogy have been claiming/demonstrating for two years at least.

    • Re: (Score:2, Interesting)

      by Anonymous Coward

      I work in RF, Ku band stuff, we use GaN parts like candy. One day I noticed that these things always come straight from Japan in hand-written and hand-packed little boxes... I asked what the BOM cost was and it was very high!

      These things are so cutting-edge that you can't even google for the part number they ship you; it's not even on the manufacturer's page! You need to ask for the datasheet and often it's just screen printouts from the VNA...

      I've also noticed that they smell different when the top explode

      • GaN isn't cutting edge. It's just super expensive. The only real use for GaN, due to the cost, is in radio transmitters and a few other niches where they need the ability of GaN to run at faster MHZ than silicon can support and can afford to pay the ridiculous process costs. GaN will remain a niche in process tech until they can find a way to make chips cheaper and they've been trying for a very long time. A lot of companies have come and gone trying to improve GaN because of the promise.

        I can remember in t

      • by MattskEE ( 925706 ) on Monday March 07, 2016 @03:34PM (#51654735)

        RF GaN parts are certainly expensive - the GaN is grown on silicon carbide substrates which is incredibly expensive by itself, and high-speed RF stuff has much more demanding fabrication needs like very small T-shaped gates, better contact resistances, and so on.

        GaN for power electronics is much cheaper, grown on 6 inch silicon substrates, and produced in much higher volumes. You can buy GaN parts from EPC on Digikey for a couple of dollars each, the other GaN power device manufacturers aren't selling publicly that I know of (just to partners, or nobody) but the cost per unit is not tremendous - a bit more than the same voltage and current rating silicon device but the GaN part can switch faster.

  • Genuine question. The web site talks about inverters being 1-2 cubic feet in size, and it wants them smaller. I understand that smaller is better. What's the application that requires a 2kW inverter smaller than that?

    • by swb ( 14022 )

      Marine or other mobile applications?

      2-5kw is a sweet spot for these applications. Most marine generators in recreational applications are about 5kw -- and most of that is usually to drive air conditioning or similar high voltage applications.

      2kw or so, though, is pretty decent for off-battery use of lower powered items and might even provide enough power (if you can use all 2k) for a small microwave.

      • by afidel ( 530433 )

        Heck a 10,000 BTU AC unit in a small travel trailer only needs 700W once running so a 2kW setup would net you almost 3:1 runtime:collection (or about 2:1 once all inefficiencies are accounted for). The big problem is that 2kW of panels takes a lot more room than you have on a travel trailer (at least the ones that only need one 10k A/C!)

    • An obvious one for me is for solar cells. As small/flat as possible to minimize the size/mass of an array.

      When I've looked at home arrays, the inverter is a large box that fits off to the side in its own enclosure. I can see that having a small inverter that is part of the array would be an advantage in terms of cost and installation workload.

      • by Kohath ( 38547 )

        Yeah, but solar cells to generate 2 kW are large. The size of the inverter doesn't seem like a limiting factor in that kind of installation.

        • by Tx ( 96709 )

          You don't need to use the solar cells directly, you charge up your batteries from your solar panels, or from cheap off-peak grid power, and you then need an inverter so you can run all your AC appliances from the batteries. The basic Tesla Powerwall model is 3.3kW, so that should give you a pretty strong hint of at least one application.

          • by Kohath ( 38547 )

            That helps. I don't foresee a lot of applications that have room for those batteries but not for the inverter though. I can definitely see the merit of the complaint that the inverter is too large compared to the batteries. I'd still like to know what makes it very important rather than just something that's nice to have. Maybe nice to have is an adequate motivation for Google ...?

    • Matching inverters to an appliance would be my guess.

    • That's the right question. I think you'll eventually reach the inevitable conclusion that we must hack their inverters, with the end result of filling the Google data center with freshly popped popcorn.

  • Trifecta (Score:4, Funny)

    by PopeRatzo ( 965947 ) on Monday March 07, 2016 @11:09AM (#51653151) Journal

    We may have just hit peak Google. Three stories in a row.

    • by houghi ( 78078 )

      As the postings are all about different subjects, it just shows how big Google is.

  • Split phase (Score:5, Interesting)

    by Shawn Willden ( 2914343 ) on Monday March 07, 2016 @11:20AM (#51653207)
    Another nice improvement the winners made above the requirements was that Google asked for 230 or 240 VAC output, but the winning device provides 240 VAC split phase, which means it can also be used to provide two legs of 120 VAC. Not that it's terribly hard to add a 240 VAC -> 120 VAC transformer, but with this design there's no need.
  • Cubic inches? (Score:5, Insightful)

    by HammerToe ( 111872 ) on Monday March 07, 2016 @11:21AM (#51653217) Homepage

    Cubic inches?! So this isn't a project intended to be looking beyond the borders of one country?


    • by fibonacci8 ( 260615 ) on Monday March 07, 2016 @11:30AM (#51653253)
      And in English no less, the third most commonly spoken first language in the world. Could we please get these summaries in Mandarin and Spanish? If we're going to base things in the US on what more people are doing elsewhere, why stop at measurements?
    • First of all, you mean two countries, right?

      Second of all, by "one country" you mean "the most important and powerful country that has ever existed through all of history, including Rome". So, yeah, okay fine, not intended to be looked at beyond that country.

      Also, if we are going to keep pretending that Europe is more than one country, then I insist that Europeans recognize the USA as fifty countries. Then, any time they complain that Americans don't know the King of whichever European theocracy, they can p

    • by rsborg ( 111459 )

      Cubic inches?! So this isn't a project intended to be looking beyond the borders of one country?


      It's a secret ploy to force all those millions of non-imperial-units-aware challengers to use Google:
      https://www.google.com/search?... [google.com]

      Someone call the antitrust department!

  • I'm still puzzled by the economics of these prize driven challenges. Look at the winning design: (pdf) [littleboxchallenge.com]. R&D costs of it (including expertise, etc) well exceed $1mil. And having a lot of teams working on their designs... Assuming that there are at least 3 other good teams means then expected payout is laughable $250k...

    As a professional, I expect to be paid for the work I do for hire. Sure, some things are done for fun, but building entire product is rarely is... Like, look at the open source softw
    • by raymorris ( 2726007 ) on Monday March 07, 2016 @12:07PM (#51653437) Journal

      If you started with nothing and had to buy all of the tooling and equipment, recruit people, etc., I could see this easily costing $1 million, but the winner is an inverter company. They already have all of the tooling, equipment, expertise, etc.

      They "just" needed to optimize one of their existing designs for size. Also, they only needed a working prototype, not a full production model. How do you figure that costs a million dollars?

      • by sshir ( 623215 )
        What you described is essentially a marginal cost of R&D. Which indeed is well below $1mil. But just to put a better contrast on what I've said before: try to go to Intel and ask them to design and produce for you "only a prototype" custom (non fpga) CPU for $1mil., for 10mil... They will laugh you out of the building.
    • Another angle: even if you don't need money, there are plenty of engineers who do - google can afford paying for these things full sticker.

      Google is not avoiding paying one team, but several. Not only are they avoiding dealing with exclusively a firm at random, who, lacking financial competition, is likely to build in a decent profit margin, but they're soliciting from several teams who understand the nature of the competition. Regardless, they're catching a price break. Successful companies often get that

      • by sshir ( 623215 )
        That publicity is great for the people, not for the firm that paid the bills. You can bet your ass that most of folks, whose names were printed, will be gone from CE+T by the end of the year.
    • I suppose the publicity of winning is worth something, though maybe not as much as $1 million.

  • "Google Challenge Results In Astoundingly Efficient Inverters"

    Sooo, what is that number? I can't find it anywhere.

    Commercial PV inverters are about 97% peak, 93% average. Not a lot of room for movement there.

  • Watts per cubic inch (cm or whatever) is just one measure. It's a fine target for aerospace and automotive applications. But it is of secondary importance for fixed installations like solar. Here, the efficiency I'd be interested in is power conversion efficiency. Particularly across a wide range of loads. And I'd like that efficiency to come at a reasonable price as well. Where I can evaluate the dollars spent to save a Watt of inverter loss vs the dollars per Watt that a larger solar panel will cost me.


  • by fahrbot-bot ( 874524 ) on Monday March 07, 2016 @12:53PM (#51653717)

    ... the Mythbusters test it - oh, wait ... damn (sigh).

"If you lived today as if it were your last, you'd buy up a box of rockets and fire them all off, wouldn't you?" -- Garrison Keillor