5 ms·

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

by 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.
  - artificialidiot 12y ago
    That DC might as well be AC since it is not as stable as you'd like. Consider this, you have a DC source 5-15V and want to run a usb gadget from it. You still need a regulator between the wall plug and the device. Why not make it compatible with AC grid so your kitchen appliances don't need their own inverters each?
    - mindslight 12y ago
      It's a lot easier to build a converter that steps down from 15V with a shared ground, than from 170V that requires isolation. Of course, house distribution wouldn't be done with 15V, the lowest it'd probably be is 48V.
- deleted 12y ago
  [deleted]
ebiester 12y ago
And people have talked about that, or just having some sort of dual track with an inverter/UPS for the entire house and some sort of switch between solar and outside electric. One problem is that we would have to create a whole new standard of how to connect DC appliances. Now I know on a smaller RV level that exists but we need something that can take more juice if I remember the conversation correctly.
reportingsjr 12y ago
People often say this without thinking about all of the details here. The largest power loads in your house (and in the world, period) are motors which are normally AC so you may not have as much of a benefit as you think. Also, there are other small details to consider such as the safety of switches and plugs. When you disconnect AC it will arc and then self extinguish when it crosses 0V. DC will keep arcing longer than AC will making it a bit less safe. Just keep a lot of that stuff in mind.
- pp19dd 12y ago
  Big appliances are already big, justifying putting an inverter on them if they can't be converted to DC. An inverter of appropriate size and power, of course, rather than a single mega one. My argument is that this contest is a bandaid on an outdated way of thinking about power. Yes, safety is important. However, in your example we don't have to use physical-contact plugs. There are plenty of devices that can be powered or charged via induction.
- tomsaffell 12y ago
  The motor in my LG washing machine is actually DC [1,2]. Sure, lots of other motors in my house are AC, but perhaps they neednt be? Also, San Francisco has a DC power grid downtown, mainly running large DC motors [3] Brushless DC motors are typically very efficient, and long lasting [4] [1] http://www.youtube.com/watch?v=KsNUyD6Nr5s http://www.youtube.com/watch?v=KsNUyD6Nr5s [2] http://www.google.com/patents/US6396190 http://www.google.com/patents/US6396190 [3] http://spectrum.ieee.org/energy/the-smarter-grid/san-franciscos-secret-dc-grid http://spectrum.ieee.org/energy/the-smarter-grid/san-francis... [4] http://en.wikipedia.org/wiki/Electric_motor#Brushless_DC_motor http://en.wikipedia.org/wiki/Electric_motor#Brushless_DC_mot...
sparkman55 12y ago
Each element on an electric stove is roughly 2 kW. Let's say you have a 4-burner stove, and they're all on. That's 8kW of power. Let's say we run your 'simplified' household at 48V (the highest voltage commonly used in boat/cabin DC systems). To run 8kW on 48V you need 167 Amps. For 167 Amps you need something like 2/0 wire. That's really thick and heavy cabling! Can you imagine replacing all of the wiring in your walls with this stuff? http://i1194.photobucket.com/albums/aa378/chance1525/Mobile%20Uploads/WP_002700_zps0b9bf904.jpg http://i1194.photobucket.com/albums/aa378/chance1525/Mobile%...
- pp19dd 12y ago
  No, I certainly can't imagine doing that. However, a person doesn't typically cook 12 hours a day. Instead, they cook in bursts, so it makes sense to put a bank of batteries in or near the stove (firewalled of course), and trickle-charge them with normal cables.
  - coryrc 12y ago
    No, it doesn't make sense to do that. The nice, efficient system we have is far superior to having everyone invest in expensive, fragile batteries everywhere and never be able to cook more than 30 minutes without recharging for 12 hours.
    - mturmon 12y ago
      Now you've got me dreaming about my battery-powered hair dryer. And my battery-powered electric tea kettle, microwave, and espresso machine. Not to mention the battery-powered table saw and air compressor in my garage.
  - bdamm 12y ago
    The "Battery Bank" appliance, with no user serviceable parts inside, and consuming valuable real estate in my kitchen? I'll pay the extra few bucks per decade to not have that in my kitchen.
- miahi 12y ago
dskhatri 12y ago
You still need DC-DC conversion. High voltage DC transmission is already used in some parts of the world [1] [1] http://en.wikipedia.org/wiki/High-voltage_direct_current http://en.wikipedia.org/wiki/High-voltage_direct_current
PinguTS 12y ago
Solar power is one thing. Electric cars are another thing. Power transmission and the whole grid is based on AC. All device you buy are based on AC. The reason is, transmission of three-phase/AC is much more efficient than DC. DC has also other side effects like they are not potential free (hard to explain for me in English as I am German.) But to make it easy, beside the electrical stuff, the whole world is based on AC. So redesign stuff like TV, dishwasher, computer, … just for the few poeple who run their own system is economically not possible. (The hen and egg problem.) The other thing is, everything that runs with a drive these days, like your electric car with a permanent-synchron drive, needs to convert DC to AC to run the drive. The AC frequency defines how fast the drive runs. So even, if the first thing change, the second (running a electric drive) will not change. Besides from those points, I find this contest interesting. Because, I thing in the industrial world, where I am working in, this kind of problem is addressed every day in electrical engineering. EDIT: for the grid, it is not only solar, also wind energy is important. Wind parks are the next big source of renewable energy, in Germany (of course), but also in Spain, China, and the US. GE Wind Power is very strong in the US, AFAIK. With wind power AC is generated with the frequency depending on the wind. So this AC is converted to DC, which then is converted to AC synchronized to the grid. Actually, the market leader for those inverters is based in Nuremberg, Germany, where I am from. AFAIK, they have more than 60% of the market. Because moving such high power requires 3 or more inverters in parallel. But running such things in parallel is a pain in the ass. Because they have to run with less then 1ms accuracy in parallel. Otherwise the whole system will burn.
- lutorm 12y ago
  I actually thought transmission of DC was more efficient than AC, because you don't have inductive losses (hence HVDC underground cables etc) but that the issue is more the ease of AC transmission, since building transformers is easy but converting from AC to HVDC and back was difficult before the advent of switching converters.
  - bsder 12y ago
    Correct. HVDC is significantly more efficient than AC transmission. The problem before modern power semiconductors was always that converting voltages levels was difficult. The Pacific DC Intertie had to use huge Mercury Vapor Rectifier TUBES. Talking about the Pacific DC Intertie on Wikipedia: https://en.wikipedia.org/wiki/Pacific_DC_Intertie https://en.wikipedia.org/wiki/Pacific_DC_Intertie > Even for a frequency as low as 60 Hz the skin depth is less than the 1.6" radius of the conductor used for the Intertie. Hence the effective resistance is greater with AC than DC, so that more power is lost to heat. A DC line is also ideal for connecting together two AC systems that are not synchronized with each other. Also, cascading blackouts are less likely. Interesting point that this was the longest HVDC transmission in the world until the Three Gorges Dam projects.
dpierce9 12y ago
Most residential solar installations in the US are grid tied, meaning that excess generation heads out onto the grid (this is counted as a credit under net-metering regimes). This explains why AC inversion is required. Since most solar production is midday and most household electricity use is in the morning and evening, this arrangement allows for a net-benefit to the homeowner (and to some extent the utility since daytime electricity is more expensive for market-based customers than nighttime electricity for regulated-rate-payers). Otherwise you have to store the electricity and that is expensive and very inefficient. There are other concerns as well (e.g. no standard DC outlet, most AC appliances with DC motors would have to be modified, there would then be two electrical standards in the house since DC is still not suitable for most transmission or distribution needs, firefighters would need to be retrained, etc).
marincounty 12y ago
We almost went with DC. So, yes DC would have been great, but the politics at the time went with AC. I'm just an Electrician, and the only downside to a DC electrical grid is Voltage Drop. Maybe an Electrical Engineer can chime in?
- mindslight 12y ago
  DC is not synonymous with low voltage - voltage drop is a red herring. Problems with DC that I can think of off the top of my head: - Utility companies need to change out pole pigs for DC-DC converters. - When electrocuted, muscles grab and lock up, rather than a mere painful buzzing. - Lower mechanical switch ratings (no zero crossing for arcs to self-extinguish). Check out the printed DC ratings on a listed switch some time. - Corrosion on exposed conductors due to constant potential difference. - Low level magnetization of things next to power conductors. - General disruption and uncertainty that change brings. I bet you could annotate most clauses in the NEC with the incident that prompted its addition. - Nikola Tesla may wake up and finally use that death ray.

by pp19dd 12y ago

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.
- artificialidiot 12y ago
  That DC might as well be AC since it is not as stable as you'd like. Consider this, you have a DC source 5-15V and want to run a usb gadget from it. You still need a regulator between the wall plug and the device. Why not make it compatible with AC grid so your kitchen appliances don't need their own inverters each?
  - mindslight 12y ago
    It's a lot easier to build a converter that steps down from 15V with a shared ground, than from 170V that requires isolation. Of course, house distribution wouldn't be done with 15V, the lowest it'd probably be is 48V.
deleted 12y ago
[deleted]

ebiester 12y ago

And people have talked about that, or just having some sort of dual track with an inverter/UPS for the entire house and some sort of switch between solar and outside electric. One problem is that we would have to create a whole new standard of how to connect DC appliances. Now I know on a smaller RV level that exists but we need something that can take more juice if I remember the conversation correctly.

reportingsjr 12y ago

People often say this without thinking about all of the details here. The largest power loads in your house (and in the world, period) are motors which are normally AC so you may not have as much of a benefit as you think. Also, there are other small details to consider such as the safety of switches and plugs. When you disconnect AC it will arc and then self extinguish when it crosses 0V. DC will keep arcing longer than AC will making it a bit less safe. Just keep a lot of that stuff in mind.

pp19dd 12y ago
Big appliances are already big, justifying putting an inverter on them if they can't be converted to DC. An inverter of appropriate size and power, of course, rather than a single mega one. My argument is that this contest is a bandaid on an outdated way of thinking about power. Yes, safety is important. However, in your example we don't have to use physical-contact plugs. There are plenty of devices that can be powered or charged via induction.
tomsaffell 12y ago
The motor in my LG washing machine is actually DC [1,2]. Sure, lots of other motors in my house are AC, but perhaps they neednt be? Also, San Francisco has a DC power grid downtown, mainly running large DC motors [3] Brushless DC motors are typically very efficient, and long lasting [4] [1] http://www.youtube.com/watch?v=KsNUyD6Nr5s http://www.youtube.com/watch?v=KsNUyD6Nr5s [2] http://www.google.com/patents/US6396190 http://www.google.com/patents/US6396190 [3] http://spectrum.ieee.org/energy/the-smarter-grid/san-franciscos-secret-dc-grid http://spectrum.ieee.org/energy/the-smarter-grid/san-francis... [4] http://en.wikipedia.org/wiki/Electric_motor#Brushless_DC_motor http://en.wikipedia.org/wiki/Electric_motor#Brushless_DC_mot...

sparkman55 12y ago

Each element on an electric stove is roughly 2 kW. Let's say you have a 4-burner stove, and they're all on. That's 8kW of power. Let's say we run your 'simplified' household at 48V (the highest voltage commonly used in boat/cabin DC systems). To run 8kW on 48V you need 167 Amps. For 167 Amps you need something like 2/0 wire. That's really thick and heavy cabling! Can you imagine replacing all of the wiring in your walls with this stuff? http://i1194.photobucket.com/albums/aa378/chance1525/Mobile%20Uploads/WP_002700_zps0b9bf904.jpg http://i1194.photobucket.com/albums/aa378/chance1525/Mobile%...

pp19dd 12y ago
No, I certainly can't imagine doing that. However, a person doesn't typically cook 12 hours a day. Instead, they cook in bursts, so it makes sense to put a bank of batteries in or near the stove (firewalled of course), and trickle-charge them with normal cables.
- coryrc 12y ago
  No, it doesn't make sense to do that. The nice, efficient system we have is far superior to having everyone invest in expensive, fragile batteries everywhere and never be able to cook more than 30 minutes without recharging for 12 hours.
  - mturmon 12y ago
    Now you've got me dreaming about my battery-powered hair dryer. And my battery-powered electric tea kettle, microwave, and espresso machine. Not to mention the battery-powered table saw and air compressor in my garage.
- bdamm 12y ago
  The "Battery Bank" appliance, with no user serviceable parts inside, and consuming valuable real estate in my kitchen? I'll pay the extra few bucks per decade to not have that in my kitchen.
miahi 12y ago

dskhatri 12y ago

You still need DC-DC conversion. High voltage DC transmission is already used in some parts of the world [1] [1] http://en.wikipedia.org/wiki/High-voltage_direct_current http://en.wikipedia.org/wiki/High-voltage_direct_current

PinguTS 12y ago

Solar power is one thing. Electric cars are another thing. Power transmission and the whole grid is based on AC. All device you buy are based on AC. The reason is, transmission of three-phase/AC is much more efficient than DC. DC has also other side effects like they are not potential free (hard to explain for me in English as I am German.) But to make it easy, beside the electrical stuff, the whole world is based on AC. So redesign stuff like TV, dishwasher, computer, … just for the few poeple who run their own system is economically not possible. (The hen and egg problem.) The other thing is, everything that runs with a drive these days, like your electric car with a permanent-synchron drive, needs to convert DC to AC to run the drive. The AC frequency defines how fast the drive runs. So even, if the first thing change, the second (running a electric drive) will not change. Besides from those points, I find this contest interesting. Because, I thing in the industrial world, where I am working in, this kind of problem is addressed every day in electrical engineering. EDIT: for the grid, it is not only solar, also wind energy is important. Wind parks are the next big source of renewable energy, in Germany (of course), but also in Spain, China, and the US. GE Wind Power is very strong in the US, AFAIK. With wind power AC is generated with the frequency depending on the wind. So this AC is converted to DC, which then is converted to AC synchronized to the grid. Actually, the market leader for those inverters is based in Nuremberg, Germany, where I am from. AFAIK, they have more than 60% of the market. Because moving such high power requires 3 or more inverters in parallel. But running such things in parallel is a pain in the ass. Because they have to run with less then 1ms accuracy in parallel. Otherwise the whole system will burn.

lutorm 12y ago
I actually thought transmission of DC was more efficient than AC, because you don't have inductive losses (hence HVDC underground cables etc) but that the issue is more the ease of AC transmission, since building transformers is easy but converting from AC to HVDC and back was difficult before the advent of switching converters.
- bsder 12y ago
  Correct. HVDC is significantly more efficient than AC transmission. The problem before modern power semiconductors was always that converting voltages levels was difficult. The Pacific DC Intertie had to use huge Mercury Vapor Rectifier TUBES. Talking about the Pacific DC Intertie on Wikipedia: https://en.wikipedia.org/wiki/Pacific_DC_Intertie https://en.wikipedia.org/wiki/Pacific_DC_Intertie > Even for a frequency as low as 60 Hz the skin depth is less than the 1.6" radius of the conductor used for the Intertie. Hence the effective resistance is greater with AC than DC, so that more power is lost to heat. A DC line is also ideal for connecting together two AC systems that are not synchronized with each other. Also, cascading blackouts are less likely. Interesting point that this was the longest HVDC transmission in the world until the Three Gorges Dam projects.

dpierce9 12y ago

Most residential solar installations in the US are grid tied, meaning that excess generation heads out onto the grid (this is counted as a credit under net-metering regimes). This explains why AC inversion is required. Since most solar production is midday and most household electricity use is in the morning and evening, this arrangement allows for a net-benefit to the homeowner (and to some extent the utility since daytime electricity is more expensive for market-based customers than nighttime electricity for regulated-rate-payers). Otherwise you have to store the electricity and that is expensive and very inefficient. There are other concerns as well (e.g. no standard DC outlet, most AC appliances with DC motors would have to be modified, there would then be two electrical standards in the house since DC is still not suitable for most transmission or distribution needs, firefighters would need to be retrained, etc).

marincounty 12y ago

We almost went with DC. So, yes DC would have been great, but the politics at the time went with AC. I'm just an Electrician, and the only downside to a DC electrical grid is Voltage Drop. Maybe an Electrical Engineer can chime in?

mindslight 12y ago
DC is not synonymous with low voltage - voltage drop is a red herring. Problems with DC that I can think of off the top of my head: - Utility companies need to change out pole pigs for DC-DC converters. - When electrocuted, muscles grab and lock up, rather than a mere painful buzzing. - Lower mechanical switch ratings (no zero crossing for arcs to self-extinguish). Check out the printed DC ratings on a listed switch some time. - Corrosion on exposed conductors due to constant potential difference. - Low level magnetization of things next to power conductors. - General disruption and uncertainty that change brings. I bet you could annotate most clauses in the NEC with the incident that prompted its addition. - Nikola Tesla may wake up and finally use that death ray.