Stardate 20030816.1427

(Captain's log): Thanks, folks, for not sending huge amounts of nitpicking mail about my last posts relating to the power grid. And thanks, most of you, for refraining from sending me loads of letters about fad-power-source-du-jour. It looks like my experiment with "DWL" (Don't Write Letters) tags is a success. I won't abuse them, but I know from grim experience that some kinds of subjects tend to bring out swarms of letters, and I'll probably continue using that DWL tag in hopes of forestalling such things.

Just to review, it looks like this: [DWL!] And if you hover your mouse pointer over it, there's popup text. I'm putting extra comments in there which are defensive in nature, intended to forestall predictable responses, which I don't want to include in the main article.

Not everyone resisted the urge. Several sent me pointers to this article which describes how the USAF is currently building the world's largest battery. What they're basically building is the world's largest UPS.

Sorry, this doesn't help if what you want to do is to add significant storage capacity to the power grid so that you can somewhat decouple generation and consumption. First of all, the energy you get out of a rechargeable battery is only a small fraction of the amount of energy you consume to charge it up. The process is exceedingly inefficient. But that doesn't matter for most uses of rechargeable battery technology; electric energy is extremely cheap and portability is very valuable, and we don't really mind wasting three quarters of the charging energy when we recharge our cell phones. Equally, we don't really mind wasting most of the energy which goes into charging the battery in the Uninterruptible Power Supply that keeps our computer online during a power failure.

On the other hand, if you're actually talking about using something like this as part of the power grid, the efficiency becomes a serious matter. No matter when the energy is generated, it has to be paid for. If that energy is dumped into a big storage battery, and then taken out again later, most of the energy is wasted.

Such batteries also aren't cheap. Per unit energy capacity, batteries are extremely expensive. The USAF doesn't really care too much about the expense; for them, the value of keeping their air base running is worth the expense. But for common use as part of the power grid, something like this isn't feasible.

And even though the battery that the USAF is producing is described in this article as the world's largest, it's not even remotely large enough for serious use on the power grid. It would have to be a thousand times as big.

Moving on, several people wrote to say that in fact TM Lutas's idea of bidirectional power meters actually is in place in some areas, including here in California. The power grid itself isn't really designed to handle huge amounts of power generated this way, but there really hasn't been all that much, because as a practical matter there really aren't any reasonable ways yet for small generators to produce power at a competitive price. Jack wrote:

Fox News had an interview yesterday with someone promoting distributed generation as "the internet of power."

There's also a good argument that distributed power is environmentally less sound than the current system. Small plants are less efficient than large plants and hence consume more fuel to generate the same kwh or generate more waste heat if it's a non-fuel burning system. (I've never seen an analysis that demonstrated solar cells were a net generator when all the energy that went into their construction, refining the silicon, etc. was considered.) If you take it to the extreme, I priced out a 20 kw backup generator for the house today. At 100% output, it consumes 2.3 gal/hr of propane. We are currently paying $1.40/gallon for propane, so that's 16 cents / kwh for fuel alone, compared with the 8 cents/kwh the local co-op charges.

When the first electric power systems were first deployed by Edison in NYC, they used DC, and they were all local. Generating plants were placed in the city and would supply power to an area immediately around them. With DC there isn't any other choice. Most of them worked by burning coal, and vented their smoke into the air over the city, and it didn't take long for them to become unpopular.

The big reason we switched to AC is that it's possible to use transformers. Physically speaking, it's possible to ship the same power on a long distance transmission line either as higher voltage with lower current or as lower voltage with higher current, but the latter will waste a lot more of the power as heat. So with AC you can step the power up to very high voltage using transformers, ship it long distances relatively efficiently, and then step it back down again. That's why George Westinghouse thought that AC was better and started pushing it. (And since Edison never gave up on DC, it's why he didn't do as well.) With AC you could build larger power plants a long way from the city and ship the power in. You could also take advantage of hydro power.

In electrical power generation, there is all kinds of economy of scale which kicks in. There are entire power sou