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I've thought for a long time that a neighborhood 48V DC exchange might be viable. You'll have to pull thick copper of course, but $1/foot for wires is pretty c

I've thought for a long time that a neighborhood 48V DC exchange might be viable. You'll have to pull thick copper of course, but $1/foot for wires is pretty cheap compared to battery prices. Here in the US the NEC says that anything under 50V isn't really regulated because they don't want to get involved in people's path lighting, phone, ethernet, doorbells, thermostats, garage door opener signaling, etc. The other thing that will help enable going completely off grid are things like inverter AC units (which draw a continuously small amount of power instead of 5 minutes at 3kw and 10-30 minutes at 0kw) and ice "batteries" to store power instead of lead acid or lithium. Ice batteries never really go bad either, at least not the way chemical batteries do.

jacquesm 11y ago
You'll want to think long and hard about how you're going to deal with fuses. For the kind of currents that batteries can put out it can be quite expensive to properly fuse things. 50V was a fairly arbitrary voltage deemed to be 'safe', however there are cases known of people dying from 50V and even lower (in particular, one very nasty accident involving a Swiss ham in pre-internet times). A bus made of thick copper wire would be stolen here pretty much on the day that you installed it (copper theft is on the order of the day). I'm not convinced of the need to have any of this though, I got my power usage down to the point where a fair sized house ran year round from 16 solar panels and a small windmill. The year that we only had the solar panels we still needed the genset with some regularity but the year the windmill went up we used it only twice (when I was running a 12KW plasma cutter from the battery pack they tended to deplete a bit too quickly...).
- thescriptkiddie 11y ago
  You seem to be doubting the feasibility of micro grids, but people are already doing this with 240 V. Granted, it's harder to steal copper wire that is at 240 V.
  - jacquesm 11y ago
    > You seem to be doubting the feasibility of micro grids, but people are already doing this with 240 V. Not doubting them at all. It's just that I have some experience with burying high current / high voltage cabling and keeping such installations safe. > Granted, it's harder to steal copper wire that is at 240 V. Just use VMVK, armored version if you can get it. I got a whole pile of it that was left over after a large construction job on a dam in Canada. Paid pennies on the dollar, basically I just paid the copper market price.
- throwaway1037 11y ago
  You probably wouldn't want to use copper anyway. Power lines in the US tend to be aluminum. It's cheaper and lighter, even though it requires a larger gauge.
  - jacquesm 11y ago
    The problem with aluminum for conduction is that (1) it does not like to be clamped down (it tends to back away from the screw terminals so you will have to re-tighten them or use a different clamping mechanism) and (2) it tends to oxidize so even a slight loss of contact will turn into a much higher resistance on the joint. Copper doesn't have these draw-backs which is why it is used a lot more on the 'low power' side of things. But for the transmission lines the reduced weight more than offsets all the other issues, those are very well taken care of connections with resistances in the milli-Ohms, an expensive connector is not an issue when it comes to power infrastructure.
- msandford 11y ago
  Well, so the other thing I'd say is that you're probably not looking to move hundreds of amps. If I could "borrow" 50 amps from one neighbor on each side of my house at 48V that's nearly 5kW but 2x 50 amp fuses are very, very doable and fairly cheap. I'm not saying this is a panacea BTW, just that it might be easier and cheaper for a few neighbors to band together in this kind of a way than for everyone to overbuild their battery banks. If you can go from needing to have 10kW peak of batteries and can instead get down to 5kW peak since you can borrow peak capacity that means your bank can be half as large.
deleted 11y ago
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jacquesm 11y ago

You'll want to think long and hard about how you're going to deal with fuses. For the kind of currents that batteries can put out it can be quite expensive to properly fuse things. 50V was a fairly arbitrary voltage deemed to be 'safe', however there are cases known of people dying from 50V and even lower (in particular, one very nasty accident involving a Swiss ham in pre-internet times). A bus made of thick copper wire would be stolen here pretty much on the day that you installed it (copper theft is on the order of the day). I'm not convinced of the need to have any of this though, I got my power usage down to the point where a fair sized house ran year round from 16 solar panels and a small windmill. The year that we only had the solar panels we still needed the genset with some regularity but the year the windmill went up we used it only twice (when I was running a 12KW plasma cutter from the battery pack they tended to deplete a bit too quickly...).

thescriptkiddie 11y ago
You seem to be doubting the feasibility of micro grids, but people are already doing this with 240 V. Granted, it's harder to steal copper wire that is at 240 V.
- jacquesm 11y ago
  > You seem to be doubting the feasibility of micro grids, but people are already doing this with 240 V. Not doubting them at all. It's just that I have some experience with burying high current / high voltage cabling and keeping such installations safe. > Granted, it's harder to steal copper wire that is at 240 V. Just use VMVK, armored version if you can get it. I got a whole pile of it that was left over after a large construction job on a dam in Canada. Paid pennies on the dollar, basically I just paid the copper market price.
throwaway1037 11y ago
You probably wouldn't want to use copper anyway. Power lines in the US tend to be aluminum. It's cheaper and lighter, even though it requires a larger gauge.
- jacquesm 11y ago
  The problem with aluminum for conduction is that (1) it does not like to be clamped down (it tends to back away from the screw terminals so you will have to re-tighten them or use a different clamping mechanism) and (2) it tends to oxidize so even a slight loss of contact will turn into a much higher resistance on the joint. Copper doesn't have these draw-backs which is why it is used a lot more on the 'low power' side of things. But for the transmission lines the reduced weight more than offsets all the other issues, those are very well taken care of connections with resistances in the milli-Ohms, an expensive connector is not an issue when it comes to power infrastructure.
msandford 11y ago
Well, so the other thing I'd say is that you're probably not looking to move hundreds of amps. If I could "borrow" 50 amps from one neighbor on each side of my house at 48V that's nearly 5kW but 2x 50 amp fuses are very, very doable and fairly cheap. I'm not saying this is a panacea BTW, just that it might be easier and cheaper for a few neighbors to band together in this kind of a way than for everyone to overbuild their battery banks. If you can go from needing to have 10kW peak of batteries and can instead get down to 5kW peak since you can borrow peak capacity that means your bank can be half as large.

deleted 11y ago

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