3 ms·

Sadly what you say is true. Despite the fact that humanity has been drilling holes into various types of soil for over 8000 years, we don't really have a good w

by waps 12y ago

Sadly what you say is true. Despite the fact that humanity has been drilling holes into various types of soil for over 8000 years, we don't really have a good way to do it. The situation is not quite as bad as you're describing though. It is not $50k per day, more like $5k. That is for machines that can only do soil, not rock, and aren't as much drilling as they're making a hole. But in places where you can do agriculture, you'd have at least 5m of soil above rock, and more usually 50+ meters. I wonder how much power this system would have with a 10 meter deep hole (like is regularly installed for heating water in homes these days). 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).

msandford 12y ago
If you want to go deep enough for the system scale to be reasonable, you have to get a big drilling rig. You'll hit rock within a couple hundred feet or perhaps a thousand, but I'm not sure of anywhere in the world with 5,000-10,000 feet of dirt. 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.
kwhitefoot 12y ago
It is quite easy to calculate how much energy can be stored and how much power can be generated for how long. The potential energy of a mass in joule is simply m * g * h where m is in kilogram, g is 9.8 m/s^2, h is the height in metre. 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
- tripzilch 12y ago
  Average energy use in the Netherlands is 3340 kW-hr per household per year, which amounts to about 9.15kW-hr per day (and seeing that these are averages, I gather that the type of household to pioneer this sort of tech will be sufficiently energy-conscious to use quite a bit less than that). 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).
  - kwhitefoot 12y ago
    3340 kW-hr is a remarkably low figure. Anyway the point was not to be accurate but to show the kind of working that gives the answers. 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.

by waps 12y ago

msandford 12y ago

If you want to go deep enough for the system scale to be reasonable, you have to get a big drilling rig. You'll hit rock within a couple hundred feet or perhaps a thousand, but I'm not sure of anywhere in the world with 5,000-10,000 feet of dirt. 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.

kwhitefoot 12y ago

It is quite easy to calculate how much energy can be stored and how much power can be generated for how long. The potential energy of a mass in joule is simply m * g * h where m is in kilogram, g is 9.8 m/s^2, h is the height in metre. 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

tripzilch 12y ago
Average energy use in the Netherlands is 3340 kW-hr per household per year, which amounts to about 9.15kW-hr per day (and seeing that these are averages, I gather that the type of household to pioneer this sort of tech will be sufficiently energy-conscious to use quite a bit less than that). 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).
- kwhitefoot 12y ago
  3340 kW-hr is a remarkably low figure. Anyway the point was not to be accurate but to show the kind of working that gives the answers. 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.