Electric Meter

[Bill Arden]

In their literature, Itron says that "with its low starting watts and low watts lost, the CENTRON meter captures more energy consumption than was measured in the past by electromechanical meters." Neither Itron nor the utility have been able or willing to quantify that.

I've done some tear down analysis of the centron meter. It counts each watt hour, but.... it lacks strong lighting protection. So one really strong zap and it's dead, no display, no readings, nothing.

Then again this is probably better than the old mechanical meters since it is likely to be within 2% until it dies.

[Mikey]

Interesting, in that they're installing them here in the lightning capital of the US. I guess I should just hope it strikes early in the billing cycle . Have you found the smallest load it will accumulate? i.e., if I present a small load for a long time (e.g., .001A @ 120V for 1000 hours) will it do the integration properly? How about .0001A for 10000 hours? etc.

[Master Brian]

The question I have is if they are more accurate, is that a good thing or bad thing for the end consumer?

From what has been posted, it seems obvious that they are better at picking up the small loads from things like cell chargers and TV's that are turned off, but still consuming power, which is bad for the consumer.

So maybe the real question should be, are they more accurate as far as not "over-reading" the bigger loads. I'm not sure how to state this correctly, but it would seem to me if the dial type aren't real accurate on small loads, then they wouldn't be real accurate in measuring load fluctuations. Think of the A/C cycling, if the dial type is slower to react, would it still charge for the higher demand for a few seconds/minutes even after the A/C has been turned off. Does that make sense?

[Mikey]

That would be my guess. The mechanical nature of the device can probably be compared to a flywheel, the end result being a smoothing of the load as seen by the measuring mechanism -- geared dials, usually. The end consumer will win some/lose some, but I have no idea how it would net out. Depending on the sampling interval of the electronic meter, it could be as accurate as desired, which would certainly be fair, but may result in an increase or decrease in charges, based on the nature of the load and the characteristics of the mechanical meter. Judging from Itron's sales pitch, I'd be surprised if it were a decrease.

[Master Brian]

That would be my guess. The mechanical nature of the device can probably be compared to a flywheel, the end result being a smoothing of the load as seen by the measuring mechanism -- geared dials, usually. The end consumer will win some/lose some, but I have no idea how it would net out. Depending on the sampling interval of the electronic meter, it could be as accurate as desired, which would certainly be fair, but may result in an increase or decrease in charges, based on the nature of the load and the characteristics of the mechanical meter. Judging from Itron's sales pitch, I'd be surprised if it were a decrease.

I don't know Itron's sales pitch, but I'd be shocked that the electric company would install a device, which they deemed might possibly end up costing them money through lower meter readings. Of course, I also would be shocked if Itron would use that as any sales pitch, since it isn't the end user that is buying the meter. Of course, if these meters were capable of saving the electric company large amounts of money, they'd replace all of the old ones ASAP.

I do know that the water dept is slowly replacing all of the old water meters in the city. The new ones, don't require the reader to get out of their vehicles to read them or to find out if they've been tampered with. I wonder how long before water, gas and electric meters are controlled from a central station like cable TV is now doing....

[Bill Arden]

The mechanical meters tend to slow down with time and therefore customers tend to see there bills go up after replacement.

I don't see making the meters more accurate as a bad thing since it does not actually increase the price consumers pay. This is because of what's called the "pool". If all the meters were slow it would just cause the price per KWh increase until the difference was made up.

I am guessing that the centron meter can measure loads down to about 1 watt.
200 amps / 16,384(14 bits) = .012 amps
.012 amps * 120V = 1.4 watts

Eventually we will get TOU(Time of use) meters and that will make things both more confusing and also better for renewable energy.

Lets just hope the power company does not take a que from the phone company.
Sarcasm-> "on the x plan you get x price for the first x Kwh's unless it's a night or a weekend...

[Bill Arden]

That would be my guess. The mechanical nature of the device can probably be compared to a flywheel, the end result being a smoothing of the load as seen by the measuring mechanism -- geared dials, usually. The end consumer will win some/lose some, but I have no idea how it would net out. Depending on the sampling interval of the electronic meter, it could be as accurate as desired, which would certainly be fair, but may result in an increase or decrease in charges, based on the nature of the load and the characteristics of the mechanical meter. Judging from Itron's sales pitch, I'd be surprised if it were a decrease.

Actually both average out current variations so they aren't affected much by the current wave shapes.

The mechanical disk averages the impulse energy so that a short high current pulse pushes it just as hard as a long low current pulse.

The electronic unit uses a low pass filter to prevent frequency below the Nyquist frequency. http://en.wikipedia.org/wiki/Nyquist_frequency

[Mikey]

...
Eventually we will get TOU(Time of use) meters and that will make things both more confusing and also better for renewable energy.
...

TECO is touting a new "RSVP" (Residential Service Variable Pricing) plan, which replaces their old time-of-day service plan. It divides the day into 4 pricing periods. P1 thru P3 are defined in a complicated schedule which changes between summer & winter, with rates from $0.03719 to $0.17839 per kWh ("standard" rates are now $0.07331 (up to 1000 kWh) and $0.08331 (over 1000 kWh). P4 is a "critical" period, which they can apparently define on the fly, at $0.65377 per kWh. P4 can only be invoked a maximum of 134 hours per year.

It looks like, with intelligent use of a humongous battery bank, you might be able to move your utility consumption to P1 to charge the batteries, and use battery power during P3 and P4 (if it's ever invoked). If my figures are right, you could save a minimum of $0.03612 per kWh, or about $520/year for 1200 kWh per month. It's probably not enough to pay for the batteries, chargers, switches, and controls over time, but it's fun to think about. You might be able to combine it with a solar array to grab some tax credits. I was told they wouldn't allow that tactic under the old time-of-day plan, but haven't asked about RSVP policy; I doubt it's changed.

[Nate R]

I do know that the water dept is slowly replacing all of the old water meters in the city. The new ones, don't require the reader to get out of their vehicles to read them or to find out if they've been tampered with. I wonder how long before water, gas and electric meters are controlled from a central station like cable TV is now doing....

Our local utilities are working towards that route. At my house, Water, Gas and Electric all are automatically read. I never see a meter reader, and my usage is always actual. I like knowing it's not an estimate.