Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!


Forgot your password?

Slashdot videos: Now with more Slashdot!

  • View

  • Discuss

  • Share

We've improved Slashdot's video section; now you can view our video interviews, product close-ups and site visits with all the usual Slashdot options to comment, share, etc. No more walled garden! It's a work in progress -- we hope you'll check it out (Learn more about the recent updates).


Comment: Re:Help me out here a little... (Score 1) 493

by dgatwood (#49517525) Attached to: Utilities Battle Homeowners Over Solar Power

Let's take water as our analogy. Water flows to meet demand in the form of open taps. But very few of those taps are strictly regulating, and the outflow is a function of how far the tap is opened and the pressure in the system. Put more water into the mains and the pressure goes up, therefore more water is delivered at the tap. If your house has pressure regulating valves, you won't see this, but the pressure is then further increased at someone else's house.

That analogy doesn't really work very well, for two reasons:

1. Water pressure is more closely equivalent to voltage, not amperage. Adding more solar panels increases the amperage, not the voltage.

2. Most electrical equipment is strictly regulating (ignoring inrush). Resistive loads consume a consistent amount of current regardless of how much current is available. That's why it doesn't matter whether you power a 12V bulb with eight AA batteries or a 12V car battery. The latter can provide a lot more current, but the bulb still draws just as much current as it needs.

I think a better analogy is to think of the voltage as the height of a water tower, and the amperage as its diameter. If you have a ten-foot-diameter tower that forms a 50-foot column of water, the pressure is proportional to the 50-foot height of the water column. An overheating condition would be equivalent to the pipe breaking because someone is sucking water out of the pipe faster than the pipe can pass it.

If you expand the tower to be thirty feet in diameter, the column is still about 50 feet high, so the pressure is about the same (assuming the sides of the tank are vertical and the bottom is flat). However, doing so allows you to add more pipes and/or larger pipes out the bottom so you can provide water to more houses without drawing down the reservoir too quickly (and thus causing... what, a vacuum in the water tower? This is where the analogy starts to break down unless you're talking about a battery).

Comment: Re:My B.S. Detector is Going Off (Score 1) 68

by Bruce Perens (#49515639) Attached to: Old Marconi Patent Inspires Tiny New Gigahertz Antenna

If the end of the coil that is hanging is grounded (earthed), it becomes an autotransformer. As it's shown, it's a variable inductor and the disconnected end is irrelevant and has no meaningful physical effect at the frequency a spark transmitter could have reached.

This comment seems to get closer to what they actually mean in their scientific paper. But the article about it is garble and the paper might suffer from second-language issues, and a lack of familiarity with the terms used in RF engineering.

Comment: Re:Hmm, I guess I invented this as well... (Score 1) 68

by Bruce Perens (#49513567) Attached to: Old Marconi Patent Inspires Tiny New Gigahertz Antenna

Damn, I wish I would have patented that and all its quantum magic...

I noticed that my vertical transmitting antenna often works better if I connect a horizontal wire about the same length as the antenna to ground at its base! The wire isn't connected to the transmitting side of the circuit at all! And how well it works varies depending on the length! Obviously there is some deus ex machina at work here...

Comment: Re:My B.S. Detector is Going Off (Score 1) 68

by Bruce Perens (#49513517) Attached to: Old Marconi Patent Inspires Tiny New Gigahertz Antenna

Clearly you missed the bit where they invoked quantum mechanics, surely that explains away all the inaccuracies, like the fact you can already buy chip scale dielectric antennas

The thing that I really hate about Innovation Stories is that the reporter invariably doesn't understand what's going on, and invariably is easily convinced that The Obviiously Very Technical People have some very valuable invention.

Comment: Re:Help me out here a little... (Score 1) 493

by dgatwood (#49511979) Attached to: Utilities Battle Homeowners Over Solar Power

Well yes and no. Overcurrent failures are not caused by receiving too much power, but rather by drawing more power than the wiring is capable of handling.

There's always orders of magnitude more power available on the grid than could safely be pulled through your house's wiring. However, your wires don't burn up because the actual current draw through those wires is always much less than they can handle, just like that filament I described, through which the current draw is near zero because the air has very high resistance and thus sinks very little current. Each house has breakers or fuses to ensure that you never draw more than the wires can handle (or at least not for a long enough period of time to damage the wires).

In a similar way, if solar panels on the roof are producing more power on the roof than is needed by all of the consumers, that typically shouldn't be a problem. It only becomes a problem when someone consumes that power through a circuit path that wasn't designed to handle it or when it causes mechanical generators to go berserk in some way.

And power flowing through an insufficient circuit path means that either the solar panels are allowed to produce more current than the house wiring was rated for (which should result in fines for the installer that put in the oversized master breaker without getting the line upgraded) or the feeder line into the neighborhood is actually too small to handle the all of the houses using their maximum current rating at the same time (in which case the system was designed dangerously to begin with, and the power company just got lucky before). Either way, the problem isn't specific to solar power generation being present.

Comment: Re:Help me out here a little... (Score 1) 493

by dgatwood (#49508035) Attached to: Utilities Battle Homeowners Over Solar Power

By aluminum foil, I was thinking about the contents of a fuse—a thin enough and narrow enough strip of foil that it would burn up if a person were getting electrocuted through it.

And the idea was that the foil would be sticking out of one pole of an outlet, which effectively means that no current whatsoever would be flowing through it, because there would be no current sink on the other end of the foil. (Okay, so technically even insulators like air probably sink a little bit of current, but you get my point....)

Comment: Re:Help me out here a little... (Score 3, Interesting) 493

by dgatwood (#49506497) Attached to: Utilities Battle Homeowners Over Solar Power

The extreme case is if everyone is on solar and it's a sunny day. Everyone is trying to dump power into the grid, but there's no where for it to go. That's when you'll start causing overloads.

On those days, everyone will also be trying to run their air conditioning full blast, and although newer homes will be adding power to the grid, it probably won't balance out the extra usage from all the older, less insulated homes and businesses.

Besides, unless I'm misremembering my basic electronics, having extra power available is usually not a problem unless there is someone to consume it (*). I can hook up one side of a 110 volt outlet to a piece of aluminum foil, and until someone is stupid enough to touch it, it won't burn up. Overloads are caused by demand exceeding the available supply as it passes through some resistance (the wiring, for example). If all the houses are producing way more power than they need, that's not a problem, because the current isn't flowing anywhere. It becomes a problem when some business that normally draws power through some massive feeder lines from a cogen plant starts drawing power from all of those houses through wires that weren't designed to allow that much current draw.

Basically, the utility companies are mad because for the most part, they used to be able to ignore residential usage of electricity, because it almost never involved enough power to require precise monitoring. Now that they're suddenly able to produce power that might be consumed elsewhere, the wiring has to actually be big enough to potentially carry all the current that their rooftop systems might produce, and that requires a little bit more safety planning, and in some cases, limiting the number of solar installations and/or increasing the size of wires and transformers.

(*) There is an exception to this rule. When you have mechanical generators, having excess power is bad, because the generators have to run within a certain speed range, both to prevent damage to the generators themselves and to stay in phase. If the draw is too low (or too high) for the amount of mechanical energy going in, you could have a serious problem unless the generators have built-in governors. Of course, this problem can be solved by shutting down generators that aren't needed. More importantly, power companies have to do this anyway in response to varying load throughout the day, so the presence of solar doesn't change things very much except for possibly making the fluctuations more or less frequent and/or more or less severe.

Comment: Re:vs. a Falcon 9 (Score 1) 73

by Bruce Perens (#49501071) Attached to: Rocket Lab Unveils "Electric" Rocket Engine

They can carry about 110kg to LEO, compared to the Falcon 9's 13150kg. That's 0.84% of the payload capacity. A launch is estimated to cost $4 900 000, compared to the Falcon 9's $61 200 000. That's 8.01%. That means cost per mass to orbit is nearly an order of magnitude worse.

Yes, this is a really small rocket. If you are a government or some other entity that needs to put something small in orbit right away, the USD$5 Million price might not deter you, even though you could potentially launch a lot of small satellites on a Falcon 9 for less.

And it's a missile affordable by most small countries, if your payload can handle the re-entry on its own. Uh-oh. :-)

Comment: Re:You Can See (Score 1) 113

Microminiature accelerometers are really cheap and very very light, and you don't have to wait for them to spin up or deal with their mechanical issues. I doubt you will see a gyro used as a sensor any longer.

Similarly, computers make good active stabilization possible and steering your engine to stabilize is a lot lighter than having to add a big rotating mass.

In a consumer society there are inevitably two kinds of slaves: the prisoners of addiction and the prisoners of envy.