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An open competition to build a smaller power inverter, with a $1M prize

271 points by ismavis 12y ago

iandanforth 12y ago
Anyone know why this is particularly hard?
- bagels 12y ago
  Lots of heat, or, low efficiency.
- deleted 12y ago
  [deleted]
- pmahoney 12y ago
  I actually worked a little on this problem some years ago (as a lab tech; take my knowledge with a gain of salt). One of the largest components in an inverter (such as found in a Toyota Prius) is the capacitor bank. I'll ignore the electrical design and just assert you need X capacitance to get this done. At least in automotive world, polymer film capacitors are used for this purpose. A polymer film capacitor is made from a (very long) sheet of polymer coated on both sides with a thin layer of metal and rolled up into a cylinder. They get quite bulky at capacitances required by these inverters. The other downside is polymer film cannot handle high temperature. I believe the Prius includes an whole extra cooling loop (in addition to the main loop attached to the engine, which runs hotter than the capacitors) to keep the capacitors cool, so that's even more bulk. A multi-layer ceramic capacitor of similar capacitance can be much smaller, and can handle far greater temperatures than any polymer. The reason why polymer film is preferred is that when ceramic capacitors fail, they do so catastrophically in much the same way as a ceramic dinner plate shatters. At sufficient voltage, or at lower voltage with a sufficient defect, the ceramic will breakdown: a conduction path will form between the electrodes through the ceramic, which will heat the surrounding area, causing thermal expansion, shattering, and permanent destruction of the capacitor. The same thing happens in polymer film capacitors, except that because the material is flexible, it does not shatter, and only a small hole around the defect will be ablated away. The remaining capacitor loses some capacitance, but otherwise functions normally. So one way to create a smaller inverter is to use smaller capacitors, but you've got to match capacitance, voltage-handling ability, and fail gracefully.
  - shonn 12y ago
    It seems to me that the solution would be along the lines of a 1 bit DAC. The caps then have less smoothing to do.
    - Florin_Andrei 12y ago
      Increase the frequency, yes. That's what I thought as well. But then you run into other issues. The higher the frequency, the less "neat" are the up/down transitions, so your power elements (MOS-FET or whatever) spend more time in that twilight zone, which is exactly where they dissipate most power. And you want to avoid that. Anyway, it's worth investigating along these lines.
jeremymcanally 12y ago
At first I was like "Why would you do that for only $1m? If you had that big of a breakthrough, you could easily generate that (and then a lot more) by selling it yourself." Then I read that they aren't taking the IP, and are just giving you the cash as a pure incentive. They can publish your high level approach documents, but you still own the invention. I wish more of these contests were run that way. I think they'd yield much high quality and differentiated results with a lot more entrants.
- InclinedPlane 12y ago
  Indeed. It's a much different prospect to have to not only develop some new piece of technology but also build a business around it, figure out how to transition from your day job on the one hand to being handed enough money to make a lot of those risks and problems go away if you're successful on the other hand. It changes the risk/reward equation for someone talented enough to maybe develop this sort of thing in their spare time.
- fryguy 12y ago
  Also, it looks like there are grants available to even get you started with some capital so it doesn't come out of pocket. Even better.
  - vonmoltke 12y ago
    Grants are only for full-time academics.
    - angersock 12y ago
      That's what the academics want you to think. :)
      - _delirium 12y ago
        In general yes, it's a myth that grants are only for full-time academics. However this particular grant is indeed only for full-time academics, according to its terms: http://research.google.com/university/relations/littlebox.html http://research.google.com/university/relations/littlebox.ht... Though the full RfP does also encourage groups of students to recruit a professor and apply as a team. Incidentally, the RfP has a nice summary of what Google thinks the main engineering challenges in winning the award are. The first one on the list is finding a way to deal with 120 Hz ripple in a way other than the current solution of huge capacitors.
ChuckMcM 12y ago
I saw this earlier and briefly considered it. 50W/inch^3 is soldering iron level heat dissipation. And my take on it was that it really isn't possible unless you can cheat and have the "inverter" be the thing on the end of a solid copper bar that is sitting in ice water on the other end :-). So really they are looking for a 10X improvement in efficiency. Which is to say to take something which is 90% efficient and make it 99% efficient. Even looking at the wide bandgap semiconductors they reference on the web site I'm having a hard time getting more than a few percentage points more efficient.
- ISL 12y ago
  I think the power density they quote (50 W/in^3) isn't for dissipation, it's inverted power. I'm not an expert in electrical engineering, but I can't think of a fundamental physics limitation that's a blocker here. If there is one, I'd guess that it'll involve the electromagnetic radiated power of the device. From the specification document [1], they're asking for 95+% efficiency. [1] https://www.littleboxchallenge.com/pdf/LBC-InverterRequirements.pdf https://www.littleboxchallenge.com/pdf/LBC-InverterRequireme... Edit - computed the radiation resistance; not a blocker at 60 Hz. Does anyone know a thermodynamic limit?
  - ChuckMcM 12y ago
    Thanks for the link, you're correct they want to pull 2KVa out of a box no bigger than 40 cubic inches. These guys (http://www.apparent.com/products/ http://www.apparent.com/products/) have what I consider a very workable technology, basically 2W/cubic inch but one inverter per panel. Since you have to have panels anyway, having the panel produce power directly in the form you want eliminates the need for size as the panel is compelled to be a certain size anyway. But instead of changing the question (and age old trick of engineers to arrive at a feasible solution :-) The push here seems to be about efficiency. 95% efficient would be a huge improvement.
    - keenerd 12y ago
      Whatever they go with, the tech is going to make a really killer subwoofer amp. Looking at the requirements (mostly the high DC input) it seems that an IGBT class-D would be the logical starting point, but those are hampered by a 150kHz-ish max switching rate. I think Don Lancaster's Magic Sinewaves (http://www.tinaja.com/magsn01.shtml http://www.tinaja.com/magsn01.shtml) meet the distortion requirements while offering the slowest switching requirements. Would be fun to be on one of the teams for this.
deleted 12y ago
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lutorm 12y ago
Why does inverter size matter? The inverter is already smaller than the battery or PV panel components, so it's not immediately obvious to me what groundbreaking new applications will be possible with an even smaller one.
- tedsanders 12y ago
  Perhaps size is a proxy for cost? I imagine many cost factors scale with size, such as materials cost, shipping cost, installation cost, etc. Or perhaps tiny inverters could be a good example of disruptive innovation, an invention that looks bad along traditional dimensions but opens up nontraditional applications.
- sparkman55 12y ago
  If inverters were smaller and more efficient, they could be placed on a per-panel basis ("string inverters" or "micro inverters") for significantly better performance, particularly when some of the panels are shaded. See this paper: http://tec.appstate.edu/sites/tec.appstate.edu/files/micro%20vs%20central%20inverters%20shaded%20vs%20unshaded%20dave%20lee%20raichle.pdf http://tec.appstate.edu/sites/tec.appstate.edu/files/micro%2... (EDIT: The above point is valid, but I was wrong about cable sizes improving when using micro inverters!)
  - eck 12y ago
    > Panels commonly run at 12V (or some low multiple thereof), That is absolutely not true. Generally speaking nontrivial sized photovoltaic systems are designed with panels in series such that the voltage stays just barely within the 600v rating on the wire. For example, grid tie inverter, MPPT rated 195-550v: http://pdf.wholesalesolar.com/inverter%20pdf%20folder/Schneider-Conext-NA-range.pdf http://pdf.wholesalesolar.com/inverter%20pdf%20folder/Schnei...
    - sparkman55 12y ago
      You're right, panels are generally ganged together in battery to avoid the 'thick copper cable' problem. However, the individual panel assemblies do run at lower voltages (individual cells run at the band gap of the semiconductor, 1 or 2 V). It should be noted that placing the panels in series has a significant effect on panel performance when some of the panels are shaded (The entire string outputs at the rate of the shaded panel), so it would be much better to place panels in parallel when possible.
deleted 12y ago
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elsewhen 12y ago
does anyone know why the list of countries that this contest is blocked from are: "ITALY, BRAZIL, QUEBEC, CUBA, IRAN, SYRIA, NORTH KOREA, AND SUDAN.[1]" aren't the first three places strange to see on that list? [1] https://www.littleboxchallenge.com/pdf/LBC-TermsAndConditions.pdf https://www.littleboxchallenge.com/pdf/LBC-TermsAndCondition...
- kitcar 12y ago
  Quebec has unusual laws with regards to contests (Quebec's legal system is unique in many ways from the rest of Canada's due to its French past) http://business.financialpost.com/2011/09/08/why-many-contests-exclude-quebec-residents/ http://business.financialpost.com/2011/09/08/why-many-contes... "the province’s Lotteries Act ... require you to post security for contests open to Quebec residents where you do not have a place of business in Quebec, the value of any single prize exceeds $5,000 or the total prize value exceeds $20,000."
- pdabbadabba 12y ago
  Not sure, but some Googling reveals that these three are commonly excluded from contests of all sort. They probably either prohibit all forms of contests and sweepstakes, impose taxes, or regulate them so tightly that it's better to just not bother. Also note that it may not just be a function of the law, but also of the benefit gained by offering a contest in a given jurisdiction. I'm seeing some indications, for example, that Japan and Brazil have some similar sweepstakes regulations, but it may be more worth the organizers' time to comply with Japanese law than Brazilian. Just a guess. Some clues: http://www.slideshare.net/Promosfera/sweepstakes-and-contest-in-italy http://www.slideshare.net/Promosfera/sweepstakes-and-contest... (E.g., server receiving registrations must be located in Italy, steep fines for only brief downtime) http://en.wikipedia.org/wiki/Sweepstakes http://en.wikipedia.org/wiki/Sweepstakes ("There are similar laws in Brazil, where sweepstakes must include a "cultural contest", often giveaway questions like 'which brand gives you a house?'") http://www.theglobeandmail.com/report-on-business/small-business/sb-digital/web-strategy/running-an-online-contest-dont-run-afoul-of-the-law/article594793/ http://www.theglobeandmail.com/report-on-business/small-busi... (In Quebec "contest runners have to pay tax on the value of the prize. For another thing, contests with prizes over $2,000 have to register their rules with a government agency, the Régie des alcools des courses et des jeux . . . . To top it off, contests with prizes worth more than $5,000 actually have to deposit an amount as a security with the Régie, as a means of protecting consumers should the contest runner fold or renege.")
pp19dd 12y ago
The simplest solution (just give me the $1mil now) is to cut out the middle man. I mean, there is a needless conversion here from DC to A/C, and then back to DC. Not that many devices need A/C these days - maybe just your alarm clock, if it's cheap enough (since cheap alarm clocks use the alternating current frequency for keeping time, instead of a precise resonating crystal.) Example of what they have now: [solar-dc] -> [inverter] -> [ac/dc transformer] -> [device]. Cut out the inverter, the ac/dc transformer and you have: [solar-dc] -> [device] Required materials: wire cutters, cheap voltage regulator IC, some wire. Done. I'll take a cashier's check please.
- imaginenore 12y ago
  But then you should read on why we use high voltage AC for transmission. Hint: the resistance losses are ~ amperage squared.
  - ebiester 12y ago
    For localized solar, it's not a problem. If your solar is on top of your house, then the transmission losses aren't the problem. Now, I think (as mentioned above) if you have the inverter for the whole house and some sort of UPS at the feed, it becomes an easier problem.
    - obvious_throw 12y ago
      Minor voltage drops can still be a problem for optimal tracking on MPPT charge controllers.
  - pp19dd 12y ago
    No, I get it. Tri-phase is name of the game in the old transmission model. But that model is long overdue for a rebuild. Remember the 2003 blackout? Managing and synchronizing grids is more than a full time job, and this contest seems to promote a bandaid. Anyhow, my point is that in the localized-power game (say solar cells, fuel cells, etc) it's all DC already, and it's all right near where it needs to go. Fuel cells are near cars, and solar panels are right next to what they need to power: TVs, etc. Complications are airconditioners and big appliances, except those things are already massive enough that it makes sense to install an inverter next to each one.
jessaustin 12y ago
Anyone have any ideas why they highlight only "wide bandgap device manufacturers"? I'm hope they'd accept a winning solution with different tech, but surely there are other possibilities they could mention right at the start?
- dskhatri 12y ago
  Some solutions to the problem will utilize a high frequency, high voltage switching inverter. The performance of this type of inverter is limited by the losses generated by the devices making up the inverter. The wide bandgap devices (switches in essence) offer the lowest losses for this type of topology. Furthermore, some novel inverter designs work only if they operate at very high frequencies. Only the wide bandgap devices can switch at these high frequencies.
- sliverstorm 12y ago
  I get the impression the WBG manufacturers are partially sponsoring the prize, in hopes of getting their components adopted in the winning design.
- oofabz 12y ago
  Wide bandgap transistors have two relevant advantages: they work at higher temperatures, so you need less cooling; and they can switch higher voltages, so you don't need a bulky transformer. The only downside is, they are more expensive.
otterley 12y ago
This story was previously discussed on HN: https://news.ycombinator.com/item?id=7730042 https://news.ycombinator.com/item?id=7730042
deleted 12y ago
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phkahler 12y ago
Already done. When I worked in EVs we used a HybridPack2 power module from Infineon. It's about the size of a sandwich but longer, and skinnier. You add a driver board, a logic board, a capacitor, connectors, cold plate. It's about the size of a shoe box and can deliver 100kW continuously. I pushed one under ideal conditions to 200kW. Of course, liquid cooling means a total system that is quite a bit larger than I describe. In order to get rid of liquid cooling at that power level you'd have to get the losses down by a huge margin. We were dissipating 2-3kW at high power, so for air cooling you'd need to get that down by a factor of at least 10. The only way to drive the heat down like that is at the semiconductor device level. This is a challenge that everyone in the field is already aware of and working on, while people outside the field have no ability to do meaningful research. At the small scale, an Arduino with the mega-moto shield can push some hundreds of watts in a few cubic inches. So what exactly is the challenge?
- fryguy 12y ago
  The challenge is getting AC current, not DC as with the mega-moto shield.
  - phkahler 12y ago
    Typically you want AC on the input or output and DC on the other. You can use that shield to produce AC by driving the outputs with PWM (it is intended for that). If there was a 3rd channel on the mega-moto, you could drive a 3-phase AC motor with it. If you put a transformer on it, you can connect it to the line and do DC->AC or AC->DC. Normally we want the DC voltage to be higher than the AC, so it's not the ideal shield for line connection - hence the transformer instead of simple inductors. And yes, the inductors add to the size, but if you are driving an inductive load like a motor, they are normally not needed.
54mf 12y ago
I'm just tickled by how many commenters have a totally obvious solution to this problem. Surely, the hundreds (thousands?) of experts at Google, the IEEE, and the ~8 manufacturers who put this contest together are just fools who couldn't come up with such amazing, brilliant ideas themselves. Congrats in advance, and enjoy your million bucks!
- Dylan16807 12y ago
  I have no idea what you're talking about. I see only two posts suggesting anything close to solutions. One of those posts named an existing product with a probable misunderstanding of the details of the requirements. The other post said that we should avoid AC and not need an inverter. Neither said they had a plan that could win the competition. I don't see a single post that fits your description. Am I looking in the wrong spot? Are you being baselessly condescending?
- CamperBob2 12y ago
  (Shrug) There is no good solution, because it's the wrong problem. We shouldn't be using AC at the home/light-industrial level at all. No matter how efficient the inverter is, it's going to be constrained by the inefficiency of putting switching regulators in everything from wall warts to machine tools. That's the part of the situation that needs to change, but of course it's the chicken-and-egg problem from hell...
  - nsajko 12y ago
    marcosdumay says here AC is better suited for motors: https://news.ycombinator.com/item?id=8071614 https://news.ycombinator.com/item?id=8071614 Would you comment on that?
    - XorNot 12y ago
      AC gives you cheap synchronous magnet motors. These are what you find in most off the shelf power tools. But, they can;t be electrically speed varied, and don't produce max torque from a standstill (treadmills for example use DC motors for this reason). Its not a show stopping constraint anymore - so much so that a ton of electrical appliances can happily run directly off of 200-300V DC because it just bypasses their internal rectifiers.
anigbrowl 12y ago
2. ELIGIBILITY: To be eligible to enter the Contest, you must be: (1) above the age of majority in the country, state, province or jurisdiction of residence (or at least twenty years old in Taiwan) at the time of entry; (2) not a resident of Italy, Brazil, Quebec, Cuba, Iran, Syria, North Korea, or Sudan; (3) not a person or entity under U.S. export controls or sanctions; and (4) have access to the Internet as of July 22, 2014 I wonder why Italy, Brazil, and Quebec are included. The other countries are under special sanctions regimes already but I can't think of a good reason to exclude these three or why the contest would be considered illegal there.
- dustcoin 12y ago
  These jurisdictions likely have special laws regarding contests with prizes. For example: http://business.financialpost.com/2011/09/08/why-many-contests-exclude-quebec-residents/ http://business.financialpost.com/2011/09/08/why-many-contes...
  - marcosdumay 12y ago
    Brazil has some laws quite similar to that. And certainly another entire set of problems our governemnt would put over the winner if he lived here.
  - kabdib 12y ago
    "These handcuffs and regulations are for your protection."
- beejiu 12y ago
  I believe Italy has a 30% tax due from the competition promoter.
- anigbrowl 12y ago
  Thanks for the detailed replies folks.
- stormbrew 12y ago
  Even contests in Canada are either in Quebec or outside it, for the most part. I don't know the specifics, but there is an extra regulatory hurdle of some sort in Quebec that isn't always worth it.
nsxwolf 12y ago
What's the difference between a picnic cooler sized inverter, and the one in my Jeep, which is nowhere near the size of a picnic cooler?
- AlexMuir 12y ago
  The one in your jeep probably puts out 150W, as opposed to the 3kW that's needed to run household appliances.
  - nsxwolf 12y ago
    Makes sense. I've never plugged anything more powerful than a laptop charger into it.
- obvious_throw 12y ago
  Likely peak and typical power output( order of magnitude difference ), as well as waveform( automotive inverters tend to output square-ish waveforms ).
gooseyard 12y ago
Assuming one was starting from scratch and didn't care whether the available appliances of the day required AC or DC power, but all the power coming into the home was solar, what would the motors on the appliances look like? Would it still be desirable to use AC motors, and if not, would it be practical (other than for the obvious reasons) for appliances to use a standard DC voltage? I don't mean to suggest that we abandon ac powered appliances, I'm just curious about what electrical wizards would come up with, if they were doing it all over again.
- marcosdumay 12y ago
  Motors would almost certainly still be AC. They are way more efficient, cheaper to build and require almost no maintaince. DC motors do not have those same characteristics. But they'd probably run on a higter voltage and frequency.
  - mindslight 12y ago
    "Brushless DC" motors seem to be taking over due to switching electronics dropping in price, no? And while those are technically AC motors, it's not the kind of AC that comes right off the line. Motors that run on constant 60Hz seem to be a historical shortcut, whose demand is fading as the control benefits of variable frequency drive are available for less and less. And if HVDC transmission is gaining popularity, then how long are utilities going to keep doing the conversion to AC "for free" ? It seems to me that if we were in a bizarro world where common end-user power had always been DC, every motor would just be paired up with an appropriate driver circuit, even designed around the specific inductance of the motor. With solid state circuitry, all house fans would be infinitely variable, etc. Of course there's a huge installed base of a few types of items that would need 60Hz backwards compatibility. I get a good chuckle from thinking about legacy clocks requiring an inverter that contains a high-accuracy crystal - maybe that inverter could even run ntpd.
    - femto 12y ago
      I looked into this a while ago, when I was replacing the pump on my swimming pool. This is a bit of a special case, as there are gains to be made from using a variable speed drive. Whilst a variable speed drive may increase electrical losses, the slower water flow may reduce losses due to turbulance by a greater amount, leading to a net increase in efficiency for volume of water moved. As far as I can gather, for variable speed motors a brushless permanent magnet DC motor is more efficient for small power applications (< 1-2kW), but as the power goes up, a high efficiency three-phase induction motor with a variable-speed drive become more efficient than the DC motor. A high efficiency induction motor has extra copper in the rotor, to reduce resistive losses. For fixed speed applications, you'd think the above variable speed performance would reflect the performance for a DC supply, as the DC supply requires switching in both cases. For a three-phase AC supply, you'd think the induction motor would win, due to the absence of switching.
swamp40 12y ago
Why is there any need to make it much smaller than the solar panels that will be providing the power? I can see where ultra-thin (and flexible) would be a benefit, but why not allow the electronics to spread out over the entire area of the solar panels? The space is being used up already. That gets rid of the super high power density problem. The sun delivers about 1KW per square meter, so even if the solar panels were 100% efficient, you'd have an entire square meter of room for a 1KW inverter.
- Hytosys 12y ago
  Surely we need to do whatever we viably can to make solar as inexpensive and practical as possible, so I think the hope is that a smaller inverter means higher efficiency and lower production costs. I might be completely wrong. Still, I'm sure we all agree that it's not ever a bad idea to incentivize any sort of energy innovation.
- marincounty 12y ago
  They used solar panels as an example. If anyone succedes in making much smaller inverters the technology will be used everywhere. I applaud Google for doing this! I think Google knows there's a bunch of undisovered Einstein's in the world, and they just using the Internet to find them? I like contests like this. I thought Bill Gates condom contest was a great idea.
- _wmd 12y ago
  Google are the sort of company who would rather have 5,000 crappy, unreliable, but efficient and tiny inverters attached internally to crappy, unreliable commodity servers than spend 5000x on a single, huge, expensive, only slightly more reliable inverter covering all 5,000 servers. It's just another way of pushing unreliability to the network edge where it minimizes systemic effects and can be replicated away cheaply, much like they did with GFS or even their UPS system (at least previous server generations at Google included a large per-server battery).
  - scott_karana 12y ago
    Nothing about your comment is mutual exclusive with the one you're replying to... One inverter per solar panel sounds just like one inverter per server.
dskhatri 12y ago
There are all sorts of specifications/requirements listed (box size, ripple allowed, EMI limits) but the most interesting that is not mentioned is cost. There is no upper limit set on the BOM cost.
- bradfa 12y ago
  The oft repeated engineer's mantra of "quality, price, schedule: Pick 2." The contest has picked quality (the engineering requirements are not easy to hit) and schedule (there's a timeline for demoing). I bet it's expected that the cost, even if it's high right now, will only come down over time. But since there exist 0 inverters which can do this today (presumably), cost isn't a big concern if you can do something new and novel that's never been done before.
mmanfrin 12y ago
Could someone explain, in layman's terms, what the difficulty in building a smaller inverter is? I unfortunately paid less attention in high school Physics than I wish I had.
- dskhatri 12y ago
  The output of a solar array is a DC voltage (constant over time). Our homes are fed by an AC voltage (varying sinusoidally over time at a frequency of 60Hz). A circuit is needed to convert the DC to AC. There is a loss in energy due to the functioning of the circuit. The circuit size and complexity depends on the specifications of the DC to AC inverter including the maximum power capability desired. Traditional converters operate at low frequencies and lose a lot of energy due to the technological limitations of the semiconductors switches used. The switches essentially chop the DC input into a square-wave type output of a frequency in the low kHz range. This square wave output needs to be low pass filtered to allow only the 60Hz to propagate through to the inverter output. For low kHz type square wave, the inductors and capacitors used to make the low pass filter are large. New semiconductor technology has resulted in switches that can operate at MHz frequencies. The inductor and capacitors used to make the low pass filters can be much smaller for MHz frequencies. These switches also have much lower conduction losses than the previous silicon-based switches but they need to be used in more novel topologies in order to minimize what are called switching losses. To see a real-world example of what improvements can be made with the new semiconductor technology, compare the brick power supplies that come with our laptops to the much touted FINsix Dart (http://finsix.com/dart/ http://finsix.com/dart/). The latter uses new GaN switches that operate in the MHz range AND a novel topology that minimizes switching losses.
imranq 12y ago
didn't FINsix solve this problem: http://finsix.com/dart/ http://finsix.com/dart/
- dskhatri 12y ago
  FINsix solved a AC-DC power converter problem. This is a DC to AC inverter problem.
nsajko 12y ago
But a lot of devices convert to DC internally! Would it be hard to dispose of that redundancy? It seems to me there'd be less need for a power inverter that way. EDIT - some semirelevant discussions: https://news.ycombinator.com/item?id=7730205 https://news.ycombinator.com/item?id=7730205 - in the past thread, reasoning about usage of AC vs. DC https://news.ycombinator.com/item?id=8071524 https://news.ycombinator.com/item?id=8071524 https://news.ycombinator.com/item?id=8071670 https://news.ycombinator.com/item?id=8071670 - DC vs. AC
- markokrajnc 12y ago
  Read about Tesla vs Edison war on AC/DC currents at the end of 19th century: http://en.wikipedia.org/wiki/War_of_Currents http://en.wikipedia.org/wiki/War_of_Currents
zw123456 12y ago
Wouldn't it be more efficient to simply drive all our electronics equipment directly off DC? Almost all electronics devices now days run off 5VDC (USB) or 12VDC, Solar panels put out 12VDC, all those conversions seem like a waste of energy. What if you just run our big appliances off 120VAC and run all our small stuff off of Solar directly along with a battery back up. It seems like if a new wiring standard were developed that had both AC and DC distribution it would greatly reduce the cost of installing Solar. In fact, I believe it would be possible to put a DC bias on top of the AC (similar to the way old time phone lines work). Just a thought, rather than shrinking the inverter, think outside the box and get rid of the inverter all together.
- JshWright 12y ago
  Look at the power losses for 12VDC in any wire smaller than your thumb and you'll see why we use AC.
  - pkulak 12y ago
    Because it's 12 volt, not because it's DC. Though, I don't know if stepping DC from 12 to 240 is any easier.
- hrjet 12y ago
  This is something that always caught my imagination: using DC for the last mile. I don't understand electricity well, but it seems that electronic components require regulated DC, and producing that requires an AC somewhere in the transforming circuit. Is that correct?
  - dreamcompiler 12y ago
    In a sense, you're right. Although it's perhaps not the style of AC you were thinking of. Inside every DC-DC conversion circuit there's one or more energy storage elements charging and discharging repeatedly. This internal waveform is AC. It's not sinewave AC, but it's technically alternating current.
  - m4x 12y ago
pkulak 12y ago
Seems like we just need to switch to DC already. 60hz AC is good for resistance heat and... that's about it. We are at a point now where we're creating DC on our roofs, turning it into AC to go through the walls of our house, then turning it right back into DC to charge our cars and power our other electronics. With losses and expensive hardware at each step.
- bradfa 12y ago
  Lower frequency (50/60 Hz) AC is the only really useful choice for transmission on low cost long runs (think 100 km and more). To push high voltage DC on long runs generally means special cables and possibly super conductors. Pushing 60 Hz AC at 230 kV goes over simple cables (granted with fancy insulators for holding it to the towers). Stepping AC up or down in voltage is simple, build a transformer. Stepping DC up or down requires switching electronics, which usually will also have a transformer (if the step is reasonably large). That distribution of power inside houses is AC still is a legacy problem and because half the things in your house still use AC power motors, and generally those things are the big current consumers (air conditioning, fridge, clothes washer, etc). Your PC, phone, etc which run on DC draw tiny amounts of power in the typical house compared to an air conditioning unit, but running an air conditioning unit on DC would likely require an inverter to generate the AC power for the compressors and fans. Motors like AC, it's what makes them spin best. "Brushless DC" motors use an inverter system, usually. Even brushed DC motors effectively generate AC inside themselves with commutation.
  - welterde 12y ago
    > Lower frequency (50/60 Hz) AC is the only really useful choice for transmission on low cost long runs (think 100 km and more). To push high voltage DC on long runs generally means special cables and possibly super conductors. Pushing 60 Hz AC at 230 kV goes over simple cables. I don't think that's true. The point about HVDC is that is is cheaper to do for longer runs than HVAC (that's why they are planning to use HVDC for the new long distance power lines in Germany). Why would you need special cables for HVDC and not for HVAC? DC has less losses than AC for the same current. The only reason AC is used for transmission lines right now is that technology for HVDC wasn't quite ready/cheap enough. It is now.
ackfoo 12y ago
Anyone who has lived off the grid understands that an inverter is the least efficient solution to the problem of running consumer devices from a DC source. We laugh at the newbies running an inverter to supply a laptop PS that takes AC right back to DC. Hopelessly inefficient. DC-DC is the way to go, or else if you need higher voltage, take an auxiliary feed from the charge controller, since most solar puts out 21-25VDC anyway. For more efficient and powerful motors, use series battery banks. Duh. This is just another way of pandering to the people who do not understand efficiency and who are locked into the idea of "house current", in other words, dinosaurs. Our industrialized world is so inefficient that we throw away about 80% of generated power. What a holocaust for the natural environment! When you go off-grid, that just won't fly, because no one wants to upsize their generation capacity five-fold to run some inefficient consumer device, except for the aforementioned newbies who have yet to notice an open artery. Inverters simply extend the inefficiency of the consumer experience to alternative forms of power generation. The smart solution is not to make the inverter smaller but to lose it entirely.
jgmmo 12y ago
Got an email today 'registration declined'. :(
- phaedrus 12y ago
  Any idea why it was declined?
  - jgmmo 12y ago
    They didn't like how I described 'my approach'. Nothing specific. It said I can register again, but something tells me I probably won't be making the cut for this challenge.
markokrajnc 12y ago
Maybe a stupid question: Would that work: create a small electric motor, mount one coil on the rotating wheel and mount another on the stand. Now put DC on fixed coil and AC would be generated on the other side (like in transformer)... Or will this not work? :-) (I am not an electrician.) I know, I know - mechanical parts are not optimal - and also there are losses for electric motor - but the size is in question here...
- kpreid 12y ago
  Rotary motion was used for conversion long before semiconductor devices were invented: https://en.wikipedia.org/wiki/Rotary_converter https://en.wikipedia.org/wiki/Rotary_converter I don't know what the limits on efficiency are, and the Wikipedia article mainly addresses AC-to-DC conversion rather than DC-to-AC, but I assume simply from the fact that they aren't used these days that they aren't an improvement on solid-state inverters.

271 points by ismavis 12y ago

iandanforth 12y ago

Anyone know why this is particularly hard?

bagels 12y ago
Lots of heat, or, low efficiency.
deleted 12y ago
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pmahoney 12y ago
I actually worked a little on this problem some years ago (as a lab tech; take my knowledge with a gain of salt). One of the largest components in an inverter (such as found in a Toyota Prius) is the capacitor bank. I'll ignore the electrical design and just assert you need X capacitance to get this done. At least in automotive world, polymer film capacitors are used for this purpose. A polymer film capacitor is made from a (very long) sheet of polymer coated on both sides with a thin layer of metal and rolled up into a cylinder. They get quite bulky at capacitances required by these inverters. The other downside is polymer film cannot handle high temperature. I believe the Prius includes an whole extra cooling loop (in addition to the main loop attached to the engine, which runs hotter than the capacitors) to keep the capacitors cool, so that's even more bulk. A multi-layer ceramic capacitor of similar capacitance can be much smaller, and can handle far greater temperatures than any polymer. The reason why polymer film is preferred is that when ceramic capacitors fail, they do so catastrophically in much the same way as a ceramic dinner plate shatters. At sufficient voltage, or at lower voltage with a sufficient defect, the ceramic will breakdown: a conduction path will form between the electrodes through the ceramic, which will heat the surrounding area, causing thermal expansion, shattering, and permanent destruction of the capacitor. The same thing happens in polymer film capacitors, except that because the material is flexible, it does not shatter, and only a small hole around the defect will be ablated away. The remaining capacitor loses some capacitance, but otherwise functions normally. So one way to create a smaller inverter is to use smaller capacitors, but you've got to match capacitance, voltage-handling ability, and fail gracefully.
- shonn 12y ago
  It seems to me that the solution would be along the lines of a 1 bit DAC. The caps then have less smoothing to do.
  - Florin_Andrei 12y ago
    Increase the frequency, yes. That's what I thought as well. But then you run into other issues. The higher the frequency, the less "neat" are the up/down transitions, so your power elements (MOS-FET or whatever) spend more time in that twilight zone, which is exactly where they dissipate most power. And you want to avoid that. Anyway, it's worth investigating along these lines.

jeremymcanally 12y ago

At first I was like "Why would you do that for only $1m? If you had that big of a breakthrough, you could easily generate that (and then a lot more) by selling it yourself." Then I read that they aren't taking the IP, and are just giving you the cash as a pure incentive. They can publish your high level approach documents, but you still own the invention. I wish more of these contests were run that way. I think they'd yield much high quality and differentiated results with a lot more entrants.

InclinedPlane 12y ago
Indeed. It's a much different prospect to have to not only develop some new piece of technology but also build a business around it, figure out how to transition from your day job on the one hand to being handed enough money to make a lot of those risks and problems go away if you're successful on the other hand. It changes the risk/reward equation for someone talented enough to maybe develop this sort of thing in their spare time.
fryguy 12y ago
Also, it looks like there are grants available to even get you started with some capital so it doesn't come out of pocket. Even better.
- vonmoltke 12y ago
  Grants are only for full-time academics.
  - angersock 12y ago
    That's what the academics want you to think. :)
    - _delirium 12y ago
      In general yes, it's a myth that grants are only for full-time academics. However this particular grant is indeed only for full-time academics, according to its terms: http://research.google.com/university/relations/littlebox.html http://research.google.com/university/relations/littlebox.ht... Though the full RfP does also encourage groups of students to recruit a professor and apply as a team. Incidentally, the RfP has a nice summary of what Google thinks the main engineering challenges in winning the award are. The first one on the list is finding a way to deal with 120 Hz ripple in a way other than the current solution of huge capacitors.

ChuckMcM 12y ago

I saw this earlier and briefly considered it. 50W/inch^3 is soldering iron level heat dissipation. And my take on it was that it really isn't possible unless you can cheat and have the "inverter" be the thing on the end of a solid copper bar that is sitting in ice water on the other end :-). So really they are looking for a 10X improvement in efficiency. Which is to say to take something which is 90% efficient and make it 99% efficient. Even looking at the wide bandgap semiconductors they reference on the web site I'm having a hard time getting more than a few percentage points more efficient.

ISL 12y ago
I think the power density they quote (50 W/in^3) isn't for dissipation, it's inverted power. I'm not an expert in electrical engineering, but I can't think of a fundamental physics limitation that's a blocker here. If there is one, I'd guess that it'll involve the electromagnetic radiated power of the device. From the specification document [1], they're asking for 95+% efficiency. [1] https://www.littleboxchallenge.com/pdf/LBC-InverterRequirements.pdf https://www.littleboxchallenge.com/pdf/LBC-InverterRequireme... Edit - computed the radiation resistance; not a blocker at 60 Hz. Does anyone know a thermodynamic limit?
- ChuckMcM 12y ago
  Thanks for the link, you're correct they want to pull 2KVa out of a box no bigger than 40 cubic inches. These guys (http://www.apparent.com/products/ http://www.apparent.com/products/) have what I consider a very workable technology, basically 2W/cubic inch but one inverter per panel. Since you have to have panels anyway, having the panel produce power directly in the form you want eliminates the need for size as the panel is compelled to be a certain size anyway. But instead of changing the question (and age old trick of engineers to arrive at a feasible solution :-) The push here seems to be about efficiency. 95% efficient would be a huge improvement.
  - keenerd 12y ago
    Whatever they go with, the tech is going to make a really killer subwoofer amp. Looking at the requirements (mostly the high DC input) it seems that an IGBT class-D would be the logical starting point, but those are hampered by a 150kHz-ish max switching rate. I think Don Lancaster's Magic Sinewaves (http://www.tinaja.com/magsn01.shtml http://www.tinaja.com/magsn01.shtml) meet the distortion requirements while offering the slowest switching requirements. Would be fun to be on one of the teams for this.

deleted 12y ago

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lutorm 12y ago

Why does inverter size matter? The inverter is already smaller than the battery or PV panel components, so it's not immediately obvious to me what groundbreaking new applications will be possible with an even smaller one.

tedsanders 12y ago
Perhaps size is a proxy for cost? I imagine many cost factors scale with size, such as materials cost, shipping cost, installation cost, etc. Or perhaps tiny inverters could be a good example of disruptive innovation, an invention that looks bad along traditional dimensions but opens up nontraditional applications.
sparkman55 12y ago
If inverters were smaller and more efficient, they could be placed on a per-panel basis ("string inverters" or "micro inverters") for significantly better performance, particularly when some of the panels are shaded. See this paper: http://tec.appstate.edu/sites/tec.appstate.edu/files/micro%20vs%20central%20inverters%20shaded%20vs%20unshaded%20dave%20lee%20raichle.pdf http://tec.appstate.edu/sites/tec.appstate.edu/files/micro%2... (EDIT: The above point is valid, but I was wrong about cable sizes improving when using micro inverters!)
- eck 12y ago
  > Panels commonly run at 12V (or some low multiple thereof), That is absolutely not true. Generally speaking nontrivial sized photovoltaic systems are designed with panels in series such that the voltage stays just barely within the 600v rating on the wire. For example, grid tie inverter, MPPT rated 195-550v: http://pdf.wholesalesolar.com/inverter%20pdf%20folder/Schneider-Conext-NA-range.pdf http://pdf.wholesalesolar.com/inverter%20pdf%20folder/Schnei...
  - sparkman55 12y ago
    You're right, panels are generally ganged together in battery to avoid the 'thick copper cable' problem. However, the individual panel assemblies do run at lower voltages (individual cells run at the band gap of the semiconductor, 1 or 2 V). It should be noted that placing the panels in series has a significant effect on panel performance when some of the panels are shaded (The entire string outputs at the rate of the shaded panel), so it would be much better to place panels in parallel when possible.

deleted 12y ago

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elsewhen 12y ago

does anyone know why the list of countries that this contest is blocked from are: "ITALY, BRAZIL, QUEBEC, CUBA, IRAN, SYRIA, NORTH KOREA, AND SUDAN.[1]" aren't the first three places strange to see on that list? [1] https://www.littleboxchallenge.com/pdf/LBC-TermsAndConditions.pdf https://www.littleboxchallenge.com/pdf/LBC-TermsAndCondition...

kitcar 12y ago
Quebec has unusual laws with regards to contests (Quebec's legal system is unique in many ways from the rest of Canada's due to its French past) http://business.financialpost.com/2011/09/08/why-many-contests-exclude-quebec-residents/ http://business.financialpost.com/2011/09/08/why-many-contes... "the province’s Lotteries Act ... require you to post security for contests open to Quebec residents where you do not have a place of business in Quebec, the value of any single prize exceeds $5,000 or the total prize value exceeds $20,000."
pdabbadabba 12y ago
Not sure, but some Googling reveals that these three are commonly excluded from contests of all sort. They probably either prohibit all forms of contests and sweepstakes, impose taxes, or regulate them so tightly that it's better to just not bother. Also note that it may not just be a function of the law, but also of the benefit gained by offering a contest in a given jurisdiction. I'm seeing some indications, for example, that Japan and Brazil have some similar sweepstakes regulations, but it may be more worth the organizers' time to comply with Japanese law than Brazilian. Just a guess. Some clues: http://www.slideshare.net/Promosfera/sweepstakes-and-contest-in-italy http://www.slideshare.net/Promosfera/sweepstakes-and-contest... (E.g., server receiving registrations must be located in Italy, steep fines for only brief downtime) http://en.wikipedia.org/wiki/Sweepstakes http://en.wikipedia.org/wiki/Sweepstakes ("There are similar laws in Brazil, where sweepstakes must include a "cultural contest", often giveaway questions like 'which brand gives you a house?'") http://www.theglobeandmail.com/report-on-business/small-business/sb-digital/web-strategy/running-an-online-contest-dont-run-afoul-of-the-law/article594793/ http://www.theglobeandmail.com/report-on-business/small-busi... (In Quebec "contest runners have to pay tax on the value of the prize. For another thing, contests with prizes over $2,000 have to register their rules with a government agency, the Régie des alcools des courses et des jeux . . . . To top it off, contests with prizes worth more than $5,000 actually have to deposit an amount as a security with the Régie, as a means of protecting consumers should the contest runner fold or renege.")

pp19dd 12y ago

The simplest solution (just give me the $1mil now) is to cut out the middle man. I mean, there is a needless conversion here from DC to A/C, and then back to DC. Not that many devices need A/C these days - maybe just your alarm clock, if it's cheap enough (since cheap alarm clocks use the alternating current frequency for keeping time, instead of a precise resonating crystal.) Example of what they have now: [solar-dc] -> [inverter] -> [ac/dc transformer] -> [device]. Cut out the inverter, the ac/dc transformer and you have: [solar-dc] -> [device] Required materials: wire cutters, cheap voltage regulator IC, some wire. Done. I'll take a cashier's check please.

imaginenore 12y ago
But then you should read on why we use high voltage AC for transmission. Hint: the resistance losses are ~ amperage squared.
- ebiester 12y ago
  For localized solar, it's not a problem. If your solar is on top of your house, then the transmission losses aren't the problem. Now, I think (as mentioned above) if you have the inverter for the whole house and some sort of UPS at the feed, it becomes an easier problem.
  - obvious_throw 12y ago
    Minor voltage drops can still be a problem for optimal tracking on MPPT charge controllers.
- pp19dd 12y ago
  No, I get it. Tri-phase is name of the game in the old transmission model. But that model is long overdue for a rebuild. Remember the 2003 blackout? Managing and synchronizing grids is more than a full time job, and this contest seems to promote a bandaid. Anyhow, my point is that in the localized-power game (say solar cells, fuel cells, etc) it's all DC already, and it's all right near where it needs to go. Fuel cells are near cars, and solar panels are right next to what they need to power: TVs, etc. Complications are airconditioners and big appliances, except those things are already massive enough that it makes sense to install an inverter next to each one.

jessaustin 12y ago

Anyone have any ideas why they highlight only "wide bandgap device manufacturers"? I'm hope they'd accept a winning solution with different tech, but surely there are other possibilities they could mention right at the start?

dskhatri 12y ago
Some solutions to the problem will utilize a high frequency, high voltage switching inverter. The performance of this type of inverter is limited by the losses generated by the devices making up the inverter. The wide bandgap devices (switches in essence) offer the lowest losses for this type of topology. Furthermore, some novel inverter designs work only if they operate at very high frequencies. Only the wide bandgap devices can switch at these high frequencies.
sliverstorm 12y ago
I get the impression the WBG manufacturers are partially sponsoring the prize, in hopes of getting their components adopted in the winning design.
oofabz 12y ago
Wide bandgap transistors have two relevant advantages: they work at higher temperatures, so you need less cooling; and they can switch higher voltages, so you don't need a bulky transformer. The only downside is, they are more expensive.

otterley 12y ago

This story was previously discussed on HN: https://news.ycombinator.com/item?id=7730042 https://news.ycombinator.com/item?id=7730042

deleted 12y ago

[deleted]

phkahler 12y ago

Already done. When I worked in EVs we used a HybridPack2 power module from Infineon. It's about the size of a sandwich but longer, and skinnier. You add a driver board, a logic board, a capacitor, connectors, cold plate. It's about the size of a shoe box and can deliver 100kW continuously. I pushed one under ideal conditions to 200kW. Of course, liquid cooling means a total system that is quite a bit larger than I describe. In order to get rid of liquid cooling at that power level you'd have to get the losses down by a huge margin. We were dissipating 2-3kW at high power, so for air cooling you'd need to get that down by a factor of at least 10. The only way to drive the heat down like that is at the semiconductor device level. This is a challenge that everyone in the field is already aware of and working on, while people outside the field have no ability to do meaningful research. At the small scale, an Arduino with the mega-moto shield can push some hundreds of watts in a few cubic inches. So what exactly is the challenge?

fryguy 12y ago
The challenge is getting AC current, not DC as with the mega-moto shield.
- phkahler 12y ago
  Typically you want AC on the input or output and DC on the other. You can use that shield to produce AC by driving the outputs with PWM (it is intended for that). If there was a 3rd channel on the mega-moto, you could drive a 3-phase AC motor with it. If you put a transformer on it, you can connect it to the line and do DC->AC or AC->DC. Normally we want the DC voltage to be higher than the AC, so it's not the ideal shield for line connection - hence the transformer instead of simple inductors. And yes, the inductors add to the size, but if you are driving an inductive load like a motor, they are normally not needed.

54mf 12y ago

I'm just tickled by how many commenters have a totally obvious solution to this problem. Surely, the hundreds (thousands?) of experts at Google, the IEEE, and the ~8 manufacturers who put this contest together are just fools who couldn't come up with such amazing, brilliant ideas themselves. Congrats in advance, and enjoy your million bucks!

Dylan16807 12y ago
I have no idea what you're talking about. I see only two posts suggesting anything close to solutions. One of those posts named an existing product with a probable misunderstanding of the details of the requirements. The other post said that we should avoid AC and not need an inverter. Neither said they had a plan that could win the competition. I don't see a single post that fits your description. Am I looking in the wrong spot? Are you being baselessly condescending?
CamperBob2 12y ago
(Shrug) There is no good solution, because it's the wrong problem. We shouldn't be using AC at the home/light-industrial level at all. No matter how efficient the inverter is, it's going to be constrained by the inefficiency of putting switching regulators in everything from wall warts to machine tools. That's the part of the situation that needs to change, but of course it's the chicken-and-egg problem from hell...
- nsajko 12y ago
  marcosdumay says here AC is better suited for motors: https://news.ycombinator.com/item?id=8071614 https://news.ycombinator.com/item?id=8071614 Would you comment on that?
  - XorNot 12y ago
    AC gives you cheap synchronous magnet motors. These are what you find in most off the shelf power tools. But, they can;t be electrically speed varied, and don't produce max torque from a standstill (treadmills for example use DC motors for this reason). Its not a show stopping constraint anymore - so much so that a ton of electrical appliances can happily run directly off of 200-300V DC because it just bypasses their internal rectifiers.

anigbrowl 12y ago

2. ELIGIBILITY: To be eligible to enter the Contest, you must be: (1) above the age of majority in the country, state, province or jurisdiction of residence (or at least twenty years old in Taiwan) at the time of entry; (2) not a resident of Italy, Brazil, Quebec, Cuba, Iran, Syria, North Korea, or Sudan; (3) not a person or entity under U.S. export controls or sanctions; and (4) have access to the Internet as of July 22, 2014 I wonder why Italy, Brazil, and Quebec are included. The other countries are under special sanctions regimes already but I can't think of a good reason to exclude these three or why the contest would be considered illegal there.

dustcoin 12y ago
These jurisdictions likely have special laws regarding contests with prizes. For example: http://business.financialpost.com/2011/09/08/why-many-contests-exclude-quebec-residents/ http://business.financialpost.com/2011/09/08/why-many-contes...
- marcosdumay 12y ago
  Brazil has some laws quite similar to that. And certainly another entire set of problems our governemnt would put over the winner if he lived here.
- kabdib 12y ago
  "These handcuffs and regulations are for your protection."
beejiu 12y ago
I believe Italy has a 30% tax due from the competition promoter.
anigbrowl 12y ago
Thanks for the detailed replies folks.
stormbrew 12y ago
Even contests in Canada are either in Quebec or outside it, for the most part. I don't know the specifics, but there is an extra regulatory hurdle of some sort in Quebec that isn't always worth it.

nsxwolf 12y ago

What's the difference between a picnic cooler sized inverter, and the one in my Jeep, which is nowhere near the size of a picnic cooler?

AlexMuir 12y ago
The one in your jeep probably puts out 150W, as opposed to the 3kW that's needed to run household appliances.
- nsxwolf 12y ago
  Makes sense. I've never plugged anything more powerful than a laptop charger into it.
obvious_throw 12y ago
Likely peak and typical power output( order of magnitude difference ), as well as waveform( automotive inverters tend to output square-ish waveforms ).

gooseyard 12y ago

Assuming one was starting from scratch and didn't care whether the available appliances of the day required AC or DC power, but all the power coming into the home was solar, what would the motors on the appliances look like? Would it still be desirable to use AC motors, and if not, would it be practical (other than for the obvious reasons) for appliances to use a standard DC voltage? I don't mean to suggest that we abandon ac powered appliances, I'm just curious about what electrical wizards would come up with, if they were doing it all over again.

marcosdumay 12y ago
Motors would almost certainly still be AC. They are way more efficient, cheaper to build and require almost no maintaince. DC motors do not have those same characteristics. But they'd probably run on a higter voltage and frequency.
- mindslight 12y ago
  "Brushless DC" motors seem to be taking over due to switching electronics dropping in price, no? And while those are technically AC motors, it's not the kind of AC that comes right off the line. Motors that run on constant 60Hz seem to be a historical shortcut, whose demand is fading as the control benefits of variable frequency drive are available for less and less. And if HVDC transmission is gaining popularity, then how long are utilities going to keep doing the conversion to AC "for free" ? It seems to me that if we were in a bizarro world where common end-user power had always been DC, every motor would just be paired up with an appropriate driver circuit, even designed around the specific inductance of the motor. With solid state circuitry, all house fans would be infinitely variable, etc. Of course there's a huge installed base of a few types of items that would need 60Hz backwards compatibility. I get a good chuckle from thinking about legacy clocks requiring an inverter that contains a high-accuracy crystal - maybe that inverter could even run ntpd.
  - femto 12y ago
    I looked into this a while ago, when I was replacing the pump on my swimming pool. This is a bit of a special case, as there are gains to be made from using a variable speed drive. Whilst a variable speed drive may increase electrical losses, the slower water flow may reduce losses due to turbulance by a greater amount, leading to a net increase in efficiency for volume of water moved. As far as I can gather, for variable speed motors a brushless permanent magnet DC motor is more efficient for small power applications (< 1-2kW), but as the power goes up, a high efficiency three-phase induction motor with a variable-speed drive become more efficient than the DC motor. A high efficiency induction motor has extra copper in the rotor, to reduce resistive losses. For fixed speed applications, you'd think the above variable speed performance would reflect the performance for a DC supply, as the DC supply requires switching in both cases. For a three-phase AC supply, you'd think the induction motor would win, due to the absence of switching.

swamp40 12y ago

Why is there any need to make it much smaller than the solar panels that will be providing the power? I can see where ultra-thin (and flexible) would be a benefit, but why not allow the electronics to spread out over the entire area of the solar panels? The space is being used up already. That gets rid of the super high power density problem. The sun delivers about 1KW per square meter, so even if the solar panels were 100% efficient, you'd have an entire square meter of room for a 1KW inverter.

Hytosys 12y ago
Surely we need to do whatever we viably can to make solar as inexpensive and practical as possible, so I think the hope is that a smaller inverter means higher efficiency and lower production costs. I might be completely wrong. Still, I'm sure we all agree that it's not ever a bad idea to incentivize any sort of energy innovation.
marincounty 12y ago
They used solar panels as an example. If anyone succedes in making much smaller inverters the technology will be used everywhere. I applaud Google for doing this! I think Google knows there's a bunch of undisovered Einstein's in the world, and they just using the Internet to find them? I like contests like this. I thought Bill Gates condom contest was a great idea.
_wmd 12y ago
Google are the sort of company who would rather have 5,000 crappy, unreliable, but efficient and tiny inverters attached internally to crappy, unreliable commodity servers than spend 5000x on a single, huge, expensive, only slightly more reliable inverter covering all 5,000 servers. It's just another way of pushing unreliability to the network edge where it minimizes systemic effects and can be replicated away cheaply, much like they did with GFS or even their UPS system (at least previous server generations at Google included a large per-server battery).
- scott_karana 12y ago
  Nothing about your comment is mutual exclusive with the one you're replying to... One inverter per solar panel sounds just like one inverter per server.

dskhatri 12y ago

There are all sorts of specifications/requirements listed (box size, ripple allowed, EMI limits) but the most interesting that is not mentioned is cost. There is no upper limit set on the BOM cost.

bradfa 12y ago
The oft repeated engineer's mantra of "quality, price, schedule: Pick 2." The contest has picked quality (the engineering requirements are not easy to hit) and schedule (there's a timeline for demoing). I bet it's expected that the cost, even if it's high right now, will only come down over time. But since there exist 0 inverters which can do this today (presumably), cost isn't a big concern if you can do something new and novel that's never been done before.

mmanfrin 12y ago

Could someone explain, in layman's terms, what the difficulty in building a smaller inverter is? I unfortunately paid less attention in high school Physics than I wish I had.

dskhatri 12y ago
The output of a solar array is a DC voltage (constant over time). Our homes are fed by an AC voltage (varying sinusoidally over time at a frequency of 60Hz). A circuit is needed to convert the DC to AC. There is a loss in energy due to the functioning of the circuit. The circuit size and complexity depends on the specifications of the DC to AC inverter including the maximum power capability desired. Traditional converters operate at low frequencies and lose a lot of energy due to the technological limitations of the semiconductors switches used. The switches essentially chop the DC input into a square-wave type output of a frequency in the low kHz range. This square wave output needs to be low pass filtered to allow only the 60Hz to propagate through to the inverter output. For low kHz type square wave, the inductors and capacitors used to make the low pass filter are large. New semiconductor technology has resulted in switches that can operate at MHz frequencies. The inductor and capacitors used to make the low pass filters can be much smaller for MHz frequencies. These switches also have much lower conduction losses than the previous silicon-based switches but they need to be used in more novel topologies in order to minimize what are called switching losses. To see a real-world example of what improvements can be made with the new semiconductor technology, compare the brick power supplies that come with our laptops to the much touted FINsix Dart (http://finsix.com/dart/ http://finsix.com/dart/). The latter uses new GaN switches that operate in the MHz range AND a novel topology that minimizes switching losses.

imranq 12y ago

didn't FINsix solve this problem: http://finsix.com/dart/ http://finsix.com/dart/

dskhatri 12y ago
FINsix solved a AC-DC power converter problem. This is a DC to AC inverter problem.

nsajko 12y ago

But a lot of devices convert to DC internally! Would it be hard to dispose of that redundancy? It seems to me there'd be less need for a power inverter that way. EDIT - some semirelevant discussions: https://news.ycombinator.com/item?id=7730205 https://news.ycombinator.com/item?id=7730205 - in the past thread, reasoning about usage of AC vs. DC https://news.ycombinator.com/item?id=8071524 https://news.ycombinator.com/item?id=8071524 https://news.ycombinator.com/item?id=8071670 https://news.ycombinator.com/item?id=8071670 - DC vs. AC

markokrajnc 12y ago
Read about Tesla vs Edison war on AC/DC currents at the end of 19th century: http://en.wikipedia.org/wiki/War_of_Currents http://en.wikipedia.org/wiki/War_of_Currents

zw123456 12y ago

Wouldn't it be more efficient to simply drive all our electronics equipment directly off DC? Almost all electronics devices now days run off 5VDC (USB) or 12VDC, Solar panels put out 12VDC, all those conversions seem like a waste of energy. What if you just run our big appliances off 120VAC and run all our small stuff off of Solar directly along with a battery back up. It seems like if a new wiring standard were developed that had both AC and DC distribution it would greatly reduce the cost of installing Solar. In fact, I believe it would be possible to put a DC bias on top of the AC (similar to the way old time phone lines work). Just a thought, rather than shrinking the inverter, think outside the box and get rid of the inverter all together.

JshWright 12y ago
Look at the power losses for 12VDC in any wire smaller than your thumb and you'll see why we use AC.
- pkulak 12y ago
  Because it's 12 volt, not because it's DC. Though, I don't know if stepping DC from 12 to 240 is any easier.
hrjet 12y ago
This is something that always caught my imagination: using DC for the last mile. I don't understand electricity well, but it seems that electronic components require regulated DC, and producing that requires an AC somewhere in the transforming circuit. Is that correct?
- dreamcompiler 12y ago
  In a sense, you're right. Although it's perhaps not the style of AC you were thinking of. Inside every DC-DC conversion circuit there's one or more energy storage elements charging and discharging repeatedly. This internal waveform is AC. It's not sinewave AC, but it's technically alternating current.
- m4x 12y ago

pkulak 12y ago

Seems like we just need to switch to DC already. 60hz AC is good for resistance heat and... that's about it. We are at a point now where we're creating DC on our roofs, turning it into AC to go through the walls of our house, then turning it right back into DC to charge our cars and power our other electronics. With losses and expensive hardware at each step.

bradfa 12y ago
Lower frequency (50/60 Hz) AC is the only really useful choice for transmission on low cost long runs (think 100 km and more). To push high voltage DC on long runs generally means special cables and possibly super conductors. Pushing 60 Hz AC at 230 kV goes over simple cables (granted with fancy insulators for holding it to the towers). Stepping AC up or down in voltage is simple, build a transformer. Stepping DC up or down requires switching electronics, which usually will also have a transformer (if the step is reasonably large). That distribution of power inside houses is AC still is a legacy problem and because half the things in your house still use AC power motors, and generally those things are the big current consumers (air conditioning, fridge, clothes washer, etc). Your PC, phone, etc which run on DC draw tiny amounts of power in the typical house compared to an air conditioning unit, but running an air conditioning unit on DC would likely require an inverter to generate the AC power for the compressors and fans. Motors like AC, it's what makes them spin best. "Brushless DC" motors use an inverter system, usually. Even brushed DC motors effectively generate AC inside themselves with commutation.
- welterde 12y ago
  > Lower frequency (50/60 Hz) AC is the only really useful choice for transmission on low cost long runs (think 100 km and more). To push high voltage DC on long runs generally means special cables and possibly super conductors. Pushing 60 Hz AC at 230 kV goes over simple cables. I don't think that's true. The point about HVDC is that is is cheaper to do for longer runs than HVAC (that's why they are planning to use HVDC for the new long distance power lines in Germany). Why would you need special cables for HVDC and not for HVAC? DC has less losses than AC for the same current. The only reason AC is used for transmission lines right now is that technology for HVDC wasn't quite ready/cheap enough. It is now.

ackfoo 12y ago

Anyone who has lived off the grid understands that an inverter is the least efficient solution to the problem of running consumer devices from a DC source. We laugh at the newbies running an inverter to supply a laptop PS that takes AC right back to DC. Hopelessly inefficient. DC-DC is the way to go, or else if you need higher voltage, take an auxiliary feed from the charge controller, since most solar puts out 21-25VDC anyway. For more efficient and powerful motors, use series battery banks. Duh. This is just another way of pandering to the people who do not understand efficiency and who are locked into the idea of "house current", in other words, dinosaurs. Our industrialized world is so inefficient that we throw away about 80% of generated power. What a holocaust for the natural environment! When you go off-grid, that just won't fly, because no one wants to upsize their generation capacity five-fold to run some inefficient consumer device, except for the aforementioned newbies who have yet to notice an open artery. Inverters simply extend the inefficiency of the consumer experience to alternative forms of power generation. The smart solution is not to make the inverter smaller but to lose it entirely.

jgmmo 12y ago

Got an email today 'registration declined'. :(

phaedrus 12y ago
Any idea why it was declined?
- jgmmo 12y ago
  They didn't like how I described 'my approach'. Nothing specific. It said I can register again, but something tells me I probably won't be making the cut for this challenge.

markokrajnc 12y ago

Maybe a stupid question: Would that work: create a small electric motor, mount one coil on the rotating wheel and mount another on the stand. Now put DC on fixed coil and AC would be generated on the other side (like in transformer)... Or will this not work? :-) (I am not an electrician.) I know, I know - mechanical parts are not optimal - and also there are losses for electric motor - but the size is in question here...

kpreid 12y ago
Rotary motion was used for conversion long before semiconductor devices were invented: https://en.wikipedia.org/wiki/Rotary_converter https://en.wikipedia.org/wiki/Rotary_converter I don't know what the limits on efficiency are, and the Wikipedia article mainly addresses AC-to-DC conversion rather than DC-to-AC, but I assume simply from the fact that they aren't used these days that they aren't an improvement on solid-state inverters.