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Cake day: June 14th, 2023

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  • Regular trains don’t run underground. Lots of opencast mines exist .

    Basically all mines have an above ground terminal where whatever you mined is unloaded from your underground trains, lifts, haul trucks or whatever else onto storage piles, then loaded onto the actual long distance trains.

    If the mine entry is up a mountain, then the trip down from that point will be a net energy producer regardless of anything else.






  • Any hard drive can fail at any time with or without warning. Worrying too much about individual drive families’ reliability isn’t worth it if you’re dealing with few drives. Worry instead about backups and recovery plans in case it does happen.

    Bigger drives have significantly lower power usage per TB, and cost per TB is lowest around 12-16TB. Bigger drives also lets you fit more storage in a given box. Drives 12TB and up are all currently helium filled which run significantly cooler.

    Two preferred options in the data hoarder communities are shucking (external drives are cheaper than internal, so remove the case) and buying refurb or grey market drives from vendors like Server Supply or Water Panther. In both cases, the savings are usually big enough that you can simply buy an extra drive to make up for any loss of warranty.

    Under US$15/TB is typically a ‘good’ price.

    For media serving and deep storage, HDDs are still fine and cheap. For general file storage, consider SSDs to improve IOPS.





  • I’m not sure there are any power grids past the tens-of-megawatt range that aren’t just a 2/3/4 terminal HVDC link.

    Railway DC supplies usually just have fat rectifiers and transformers from the AC mains to supply fault current/clearing and stability.

    Ships are where I would expect to start seeing them arrive, or aircraft.

    Almost all land-based standalone DC networks (again, not few-terminal HVDC links) are heavily battery backed and run at battery voltage - that’s not practical once you leave one property.

    I’m sure there are some pretty detailed reports and simulations, though. A reduction in cost of multi-kV converters and DC circuit breakers is essential.




  • PV inverters often have around 1-2% losses. This is not very significant. You also need to convert the voltage anyway because PV output voltage varies with light level.

    Buck/boost converters work by converting the DC current to (messy) AC, then back to DC. If you want an isolating converter (necessary for most applications for safety reasons) that converter needs to handle the full power. If it’s non isolating, then it’s proportional to the voltage step.

    Frequency provides a somewhat convenient method for all parties to know whether the grid is over- or under- supplied on a sub-second basis. Operating solely on voltage is more prone to oscillation and requires compensation for voltage drop, plus the information is typically lost at buck/boost sites. A DC grid would likely require much more robust and faster real-time comms.

    The AC grid relies on significant (>10x overcurrent) short-term (<5s) overload capability. Inrush and motor starting requires small/short overloads (though still significant). Faults are detected and cleared primarily through the excess current drawn. Fuses/breakers in series will all see the same current from the same fault, but we want only the device closest to the fault to operate to minimise disruption. That’s achieved (called discrimination, coordination, or selectivity) by having each device take progressively more time to trip on a fault of a given size, and progressively higher fault current so that the devices upstream still rapidly detect a fault.

    RCDs/GFCIs don’t coordinate well because there isn’t enough room between the smallest fault required to be detected and the maximum disconnection time to fit increasingly less sensitive devices.

    Generators are perfectly able to provide this extra fault current through short term temperature rise and inertia. Inverters cannot provide 5-fold overcurrent without being significantly oversized. We even install synchronous condensers (a generator without any actual energy source) in areas far from actual generators to provide local inertia.

    AC arcs inherently self-extinguish in most cases. DC arcs do not.

    This means that breakers and expulsion type fuses have to be significantly, significantly larger and more expensive. It also means more protection is needed against arcs caused by poor connection, cable clashes, and insulation damage.

    Solid state breakers alleviate this somewhat, but it’s going to take 20+ years to improve cost, size, and power loss to acceptable levels.

    I expect that any ‘next generation’ system is likely to demand a step increase in safety, not merely matching the existing performance. I suspect that’s going to require a 100% coverage fibre comms network parallel to the power conductors, and in accessible areas possibly fully screened cable and isolated supply.

    EVs and PV arrays get away with DC networks because they’re willing to shut down the whole system in the event of a fault. You don’t want a whole neighborhood to go dark because your neighbour’s cat gnawed on a laptop charger.





  • Indeed, the US has a major lack of fixed-line competition and lack of regulation. Starlink doesn’t really help with that, at least in urban areas.

    I’m not familiar with the wireless situation. You’re saying that there are significant coverage discrepancies to the point where many if not most consumers are choosing a carrier based on coverage, not pricing/plans? There’s always areas with unequal coverage but I didn’t think they were that common.

    Here in NZ, the state funding for very rural 4G broadband (Rural Broadband Initiative 2 / RBI-2) went to the Rural Connectivity Group, setting up sites used and owned equally by all three providers, to reduce costs where capacity isn’t the constraint.


  • Starlink plugs the rural coverage gaps, but in urban areas it’s still more expensive than either conventional fixed-line connections or wireless (4G/5G) broadband. Even in rural areas, while it’s the best option, it’s rarely the cheapest, at least in the NZ market I’m familiar with.

    It also doesn’t have the bandwidth per square kilometre/mile to serve urban areas well, and it’s probably never going to work in apartment buildings.

    This is a funding/subsidisation issue, not so much a technical one. I imagine Starlink connections are eligible for the current subsidy, but in most cases it’s probably going to conventional DSL/cable/fibre/4G connections.



  • Aggregate bandwidth now rivals or slightly exceeds gigabit wired connections.

    Where that aggregate bandwidth is shared amongst large numbers of users, bandwidth per user can suffer dramatically.

    Low density areas may be fine, but cube farms are an issue especially when staff are doing data intensive or latency sensitive tasks.

    If you’re giving employees docking stations for their laptops, running ethernet to those docking stations is a no-brainer.

    Moving most of the traffic to wired connections frees up spectrum/bandwidth for situations that do need to be wireless.