Good thing HN wasn't around durning the development of most of humanity's great inventions. "So your telling me I'm going to have to hold my food over this fire for 15 minutes before I eat it? No thank you, I'd stick with my raw meat."
Definitely more negative comments on HN these days (although it's always been a skeptical audience).
Real problems: Dismissive people who don't/can't/wont listen to good responses. Good founders/ideas but just really bad at communicating. Those are basically the type i and type ii errors of this format.[1]
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[1] A grey area exists in some other areas too (some people just get 'lucky'; others for good reason can't disclose everything the key answers/insights for competitive reasons)
On their webpage they say " The biggest single cost is the hole, but it is expected that firstly this will have a very long life and secondly, as the technology rolls out, the costs of drilling will reduce significantly. So the economics will improve in time."
Drilling will not get cheaper without a serious reform of the law, and that's unlikely to happen. There are two primary kinds of drillers; water and energy. Folks involved in water have VERY protective rules in all states. The reasons are 1. good lobbying and 2. if you screw up you destroy the water supply.
Energy drilling is no cheaper. Drilling rigs are huge machines that aren't moved easily and cost at least $50k a day on land and $500k a day for seagoing. That's before you pay another $20k per day in staff and god knows how much for fuel for everything; a rig will produce at least 5MW of power.
Could they custom build a rig just for drilling for their idea and would that work? Sure. But they'd probably spend several million and then you've got to have it running 24/7 for it to pay off.
The regulatory hurdle is going to be non-trivial as well. They're going to case it which helps. But the casing would probably need to be cemented in place which is a non-trivial cost as well. And convincing lawmakers that this doesn't quack like some other kind of well is going to be no easy feat.
I'm not sure this has much to do at all with water and energy drilling. They're talking about using abandoned mine-shafts. Those are much wider and shallower than the kind of holes used to reach petroleum.
These guys may be on to something. Scaling down seems to me to be the key. Full gridless operation with solar panels (at least in earthquake-free zones).
The problem with going shallower is that the system capacity is directly proportional to depth and weight. Too shallow and you have to have huge weight and that means a large diameter hole and really big cables and such.
But going deeper requires drilling through rock, and aquifers which are located within the rock. That means big regulatory hurdles because nobody wants to poison the aquifer on accident. Plus the large costs of drilling through rock.
I really like the idea from a theoretical standpoint. It's very elegant. But it doesn't seem practical from an economic or regulatory standpoint. If there are places where you can get the diameter and depth for free, it's clearly genius. But I don't think purpose-drilled holes for this will become a thing -- at least barring some kind of immense breakthrough that I can't even imagine.
The potential energy of a mass in joule is simply
m * g * h
So, for example, 100 ton lifted 100 metre gives 98MJ.
That's 1MW for 98 seconds.
To make this very concrete my house uses, in the summer, about 40kW-hr per day for water heating, cooking, and the rather large amount of computer equipment we have.
That is 40000 * 3600 = 144MJ. So assuming that your solar power system can supply that over a 12 hour period we need to store half of it, 72MJ, to keep us going after dark. Your ten metre deep hole would need a 734 ton weight: 735000 kg * 9.8 m/s^2 * 10 m = 72MJ
Either way, I think you'd have to round your estimate to order-of-magnitude anyway, because of the rather big assumption "that your solar power system can supply that over a 12 hour period we need to store half of it, 72MJ, to keep us going after dark", because getting max solar power for half the day and no solar power for the rest is not exactly how it works, nor does one use the same amount of energy during day and night (which is why I can opt in to an energy plan that gives you discount on electricity at night, because there's a surplus then).
Even if we accept your figure the peak daily use is probably at least double your 9kW-hr/day (winter for example) and even if you use less at night you still need probably about 12MJ storage to allow solar to work per household, etc., etc. So, yes, in the Netherlands you need a smaller mass but it is still in the order of 100 ton.
The point of my reply was to show the person I was replying to how easy it is to find out how much mass and height is needed, you just have to plug in your own energy consumption and generation figures.
I'm looking through all the dismissive comments to see if any of them are pinpointing it as a scam - because this is, after all, the kind of idea that is simple enough to captivate laypeople and lift dollars out of their pockets. But judging from this kind of response, it seems like it's also the kind of idea that is simple enough to be dismissed as a "they would have done it already if it worked," rationalized via fuzzy back-of-the-envelope math.
Ultimately, since I have no stake in this one, I'll just wish them luck.