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Solar Power
Solar power is a proven technology. It gets used by a handful of ardent techies, and die hard off the gridders. However, as of today, the best that can be said for most home solar installation is that it keeps a few lights on in the house. You can, of course buy the expensive an AC 'INVERTER' and run a few motorized appliances, but there it is, the inverters are very expensive and a maintenance issue.

If solar is to ever get into the main stream the appliance engineers must take a lesson from history. That is, When Edison first invented the dynamo it was D.C. (Direct Current). DC is more efficient than AC with less losses. Indeed, the only reason AC is needed is for transmision across long distances. Once you get to the load it is no longer required.

The interesting thing is that there are double wond mortors available today. That is, they can run on AC or DC. Its a matter of a selector switch.

Solar power is a DC source. If you make all the loads DC, then the system becomes much more efficient and less expensive to own and operate.

A simple summary would be, bring AC to the house, convert it to DC, run the whole house instead of just the lights, start getting a real payback. There is more, of course, but the idea is there.

Oma Graves
Posted by ortexgraves.com
6th Nov
+2 Votes
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Yes and No
" DC is more efficient than AC with less losses."

Over long distances, AC is more efficient than DC. The reason for this, as anyone who has studied the physics will tell you is that DC requires the movement of an electron from one end of the wire to the other end of the wire. It's not quite like that. It's more like having a pipe full of marbles. You push one in on one end of the pipe, and one falls out at the other end. The longer the pipe, the harder it is to move them. Edison ran into this problem while trying to deliver DC to the edge of NYC.

With AC however, you are not doing that. You're pulling the first electron out, and then pushing it back in. This sends a wave down the pipe instead. Instead of each electron needing to move forward against the resistance, they just move back and forth without going anywhere. So the energy is being carried by the wave. It's the difference of trying to move 10kg of water from Iceland to NYC and just causing a wave to move the 10kg of water up and down. The latter goes farther easier. Westinghouse had no problem delivering Tesla's AC to the edge of NYC for this reason. And to make it even easier, if the voltage dropped too much over the distance (i.e. the height of the waves got too small), AC could be put through a transformer to fix it while DC could not.

But if one is going short distances, then we run into different issues. When you look at 110VDC and 110VAC and plot them on a graph (or oscilloscope), the area under the (rectified) graph is the energy being transferred. DC has more area and therefore is more efficient but only at these short distances where wire resistance is negligible. (If one looks at 110V RMS, one will see that it peaks at 120V, which it needs to in order to compensate for the fact that it's AC.)
Posted by mheartwood
6th Nov
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It's entirely possible to design applianced to work from AC or DC.
If the motorized appliances use 3-phase brushless motors, running on DC.. The wall plug could be AC or DC. Any appliances not requiring a 'zero crossing detection' for some kind of timing would be OK as long as it had a bridge rectifier up front, and maybe a PFC for a kind of efficiency that benefits the powr utility. Appliances would have a PFC (power factor correction) front end, which is a switching converter that can run on AC or DC. They usually make about 400V. From this, a motor drive can run directly or a step down DC-DC converter can supply the customary voltages. Things with universal motors (motors with burshes) like vacuum cleaners will work on 110-120VDC, some older variable speed electric drills will not, etc etc. Additionally, houses could be wired with two sets of outlets, 120/240VAC as they are today, plus DC of a common voltage like 150-160V, with a physically different socket of course. Many, many line-operated switching power supplies found in today's electronic stuff (which do not have a big iron transformer up front) will run directly from a 150-160V DC source. This is because the first thing that happens inside things like a PC power supply is the 120VAC is rectified, making 140-165VDC, and this is sent to the witching MOSFET.

Houses with dual wiring could later be converted to all-DC or back to all AC if desired. the wiring size and junction boxes could all be the same only the outlets different.

In the past, some (rural) homes had DC power. Those folks had no trouble with vacuum cleaners or any product with a 'universal motor'. They did have to buy radio sets that were designed for 117VAC/DC. This was in the 1930's to 1950's when the gear had vacuum tubes. You can still find old tabletop radios at swap meets that have this rating on the back. "all american 5" was a generic term, as they typically have 5 tubes, made in the USA, and ran on all USA power.

I had a big old VAX 6000 that ran on 3 phase 208V. Inside I found the first suply, the PFC, made 300VDC. After than, there were several power supply boxes that ran off this and made the +/-5V, etc that the comuter used. It was only necesary to suply single phase 120/240V to the thing, and it ran fine. It could have as easily been run on 300VDC. In fact, in the bottom was space for a huge 300V battery. For scale, the machine was the size of a refrigerator and is what would be called a 'minicomputer'. Just to show, DC is totally practical for use in the home.
Posted by opcom
6th Nov
0 Votes
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Some more detail that's hopefully easier to understand
If we're looking at the modern home, everything that doesn't use a motor can easily run on DC, and in the case of home electronics of any kind, internally does. So it makes sense to mass-rectify from the grid and feed our devices from the rectified DC. But to be most efficient, they all need to use the same voltage. As I look through my cordless tools and such, I see 12VDC, 18VDC, 24VDC, and 48VDC. So clearly we have a standards problem here. Too many standards to choose from!

I mentionned the exception being motors. There is no such thing as a truly brushless true-DC motor while there is such a thing as a brushless AC motor. Likewise, you can have a brushless AC generator but not a brushless DC generator. Electricity is created by moving a magnetic field over a wire, or moving a wire through a magnetic field. If you create a coil and place a magnet in it, the magnet rotates thus pushing electrons first with the north pole and then with the south pole. This reversal of magnetic polarity causes a reversal of voltage thus producing AC. A motor is the same contraption but in reverse. To use a DC motor or DC generator, you need brushes and commutators to rectify the AC into DC. A universal motor also uses brushes and commutators, but will run on both AC and DC. New car alternators use the same contraption in reverse to generate electricity, but they require a bit of electricity running through their spinning coil to generate the magnetic field for them to work. But make no mistake, they use brushes to do so. Thus motors and generators are inherently AC devices.

The classic workhorse electric motor is called a "squirrel cage motor". (If you take one apart, you'll see why.) In North America, these run at 60 cycles per second, the same frequency as the AC current. If you want to change the speed, you adjust the frequency. These motors are brushless which makes them ideal for industrial uses because they don't need much maintenance. Many appliances including refrigerators, air conditioners, furnace fans, washing machines, and so forth, use these squirrel cage motors for just this reason.

So if you're running a house on DC, and you have a refrigerator, or a water pump, you classically need to "invert" the DC to AC or you need to replace the brushes and clean the commutators regularly. Modern inverters are quite efficient in doing this, but it's not easy and not perfect. Rectifying DC (through a bridge rectifier with a filtering capacitor and inductor) is much easier and more efficient. Until recently, most home appliances ran on motors. So that's why we have AC in our homes.

Back in high school (some 30 years ago), for a science fair, I built a linear motor. It consisted of a series of electro-magnets all set in a line. You turn them on and off in series to drive a ball bearing down the track. At a local museum, they had much the same thing, but made into an oval. Theirs would move a pure aluminium puck around their oval track. Stretch that oval out into a circle and you have what is called a multi-phase brushless motor. The minimum number of phases for a reliable motor of this type is 3. My brand new off-the-shelf furnace fan uses a 24-phase brushless motor running at 240VDC and my washing machine uses a 15-phase brushless motor running at 120VDC. So the days of the squirrel cage motor are clearly numbered and the ability to make motorized appliances that can and do run on DC are clearly here. And the circuit for these is very cheap and very robust. Mine, made from a 555-timer, TTL D-type flip-flops, and relays still works today [and can still bury a ball-bearing into a piece of pine]. Today, CMOS and power-FETs are the more cost-effective and much more efficient way to go, but the design is the same, and just as cheap, and even more robust.

So the only thing that is holding us back from moving to houses with integral DC wiring and circuitry is the understanding that it is easily feasible, and the will.
Posted by mheartwood
Updated - 6th Nov
+1 Vote
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Follow the Leader
Germany certainly has a lot to admire in their national interest and commitment to sustainable energy. Its time for the US to follow the example of Germany and make a commitment to increase its reliance on energy from renewable resources. Hydro, wind, solar, geo, bio, and other renewable technologies have great advantages to the finite limits of a carbon based energy system. Development of renewables technologies now, is a wise precaution to the future reduction and eventual loss of all the easily obtained carbon sequestered fuels. Congrats Germany for your leadership role.
Posted by dcr100@...
6th Nov
+2 Votes
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And yet, they're expanding their coal-fired capacity.
Clearly, they have a backup plan.
Posted by JohnMcGrew@...
6th Nov
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Posted by wholemkt104
7th Nov
+1 Vote
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It makes my head swim a little hearing you guys talking about how you could make everything run on DC. As a guy who had trouble getting a C in electricity class, I suggest a little simpler and more readily doable interim solution; most houses have the lighting circuits separate from the "wall plug" circuits. Just run all the lights on 12 volt DC. It would be easy and cheap to isolate those circuits to a different breaker panel powered by the sun/wind with battery backup, and all you would have to do is to change out your light bulbs. You can buy 12 volt screw-in bulbs at any RV Store. Also LED 12 volt lights are becoming popular for cars and RV interior lighting. I know this is not a total solution, but all the re-engineering it will take to get all the electric motors in all our appliances to accept DC will take a long time and a lot of money.
Posted by Jeff Cardinal
7th Nov
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