Wednesday, June 13, 2018

Supercooling in the Desert: May 22, 2018 a day that will live in infamy !

This is the day I got clobbered by APS (my power company)

Look just before 8PM (20:00); see that bunch of spikes? My peak billing period lasts until 8, and something was sucking power before the period ended ! Let me expand the little piece that shows the problem:

That little period from about 7:24 to 8:00PM was the clothes dryer.

Yes, just a little before the end of my peak period a guest started the dryer to do some clothes. It wasn't their fault, they didn't know that the fascist power company would be watching to see if such a thing happened.

The peaks run as high as 7.4 kW, and it was doing this for a little over a half hour. The APS chart shows it like this:

And it was almost impossible to find. I looked for quite a while before I noticed it. I put the arrow on there to show you the tiny little green area that resulted. It shows up a little better on a single day chart:

That minor little slope up in the green area is where the meter saw the dryer running. It's recorded as "usage 3.18" during the 7-8PM hour. In theory, this should be my high 'demand' number that is calculated into my bill for the month.

I guess I should do a little calculating to see how this works to help me understand and avoid it even more stringently in the future. Let's look at the detail portion of my bill first:

So, the demand number wound up being 3.17 and is used as a multiplier in several items in billing. Here's the rate sheet for the plan I'm on:

So, my 'On-Peak Demand Charge' is 17.438 * 3.17 for $55.28. But, there's nothing on my bill that says that. Guess what? To make it more complicated and harder to understand, they actually split the $17 charge into two components and calculate them separately. From their tarif sheet again:

Notice how the two numbers, $4.000 and $13.438 add up to the $17.438 they call the 'On-Peak Demand Charge'. OK, fine, I have a calculator and can punch in numbers like anyone else. 4.000 * 3.17 = 12.68 and 13.438 * 3.17 = 42.60, and they add up to the 55.28 I got above. So I should see:

Delivery On-Peak Charge 12.68
Generation On-Peak Charge 42.60

Or something similar on the bill, and indeed I do. Sort of:

Demand charge on-peak - delivery $12.40
Demand charge on-peak - generation $41.66

If you look at the bill, you'll see them on there. The sum of the two charges is $54.06 which is darn close to my initial $55.28. The reason for the difference is that APS made a mistake in the original rate change request and has to use the demand number to one significant digit and they can't round, so the actual demand number they get to use in this case is 3.1kW. That's on the bill also, so I don't even have to do the truncation itself:

Your billed on-peak demand in kW 3.1

That's a good thing because rounding would have put me up to 3.2 and would be paying even more.

Now, I got the cost all figured out, the dryer running cost me some amount, but how much extra based on past performance. To get that, I'm going to look at last month to see; taken from last month's bill:

Your billed on-peak demand in kW 1.5
Demand charge on-peak - delivery $6.00
Demand charge on-peak - generation $20.16

That stuff totals up to $26.16, so my dryer cost me $27.90 last month because I didn't keep it under control. It's actually a little bit higher because the rate per kW during peak is higher ($0.08683 vs $0.05230), but that's only 3 cents per kw, and the dryer only uses 7.5 kW at around a 50% duty cycle for 3.75 kW or $0.32 extra. I'm willing to ignore that.

Now is the appropriate time to talk about how APS gets that demand number. As I mentioned in another post, they average each hour and compare it to the maximum hour during the billing cycle. That gives me 5 vulnerable periods each day: 3-4, 4-5, 5-6, 6-7, 7-8. So, the dryer kicked on and sucked power in bursts like all electrical heating appliances and those bursts pulled 7.5 kW for a short period. The bursts were roughly half the time, so it worked out, on average, to the 3.17 kW number that APS measured. It would be too much to read if I did all the calculations, but you see what I mean. That 3.17 was the highest reading so far that month, so it kept it and continued to look for a higher hour; fortunately, it didn't find one, and that's how the month's bill came to be. Next post I'm going into how to read our smart meter so folk can actually see what is coming. Unless one goes to the trouble of doing what I've done, you can't catch it real time and stop it; you can only see the what's already happened.

This is not going to break me, but it does lose me some bragging rights. Because I didn't keep control, I'm out about 28 bucks. Be warned though, if the hot water heater had kicked on, and the stove was running, this would have been a monetary disaster. Thank goodness it was only the clothes dryer and that close to the end of peak !

There you are, an example of how power can get out of control no matter what you do and how much attention you pay to it. Something will slip in and get you from time to time. Overall though, keeping tabs on my power has saved me thousands over the years. This post is also good for folk that don't completely understand how that 'Demand Billing' stuff actually works, and how to tell if you're messing up.

The parts to prevent this from happening to me again are already on order.

Previous post in this series is <link> then next is <nothing yet>


  1. That's criminal! For a small time of use! How did this happen? The commission run by liberals allowed this increase, now that those resigned,left the new members to hold the guilt , election time people have no idea who allowed this. Just vote em out. No, do your research. Vote out the Democrats and those who supports mandatory solar.

    1. It happened because we have the best Corporation Commission that money can buy.

  2. Absolutely incredible!
    I thought my electricity was expensive, especially due to the small number of off peak periods (midnight to 7am weekdays, saturday is a mixture during the day, sunday off peak all the time):
    Per day: 0.3835€
    Peak: 0.2028€ / kwh
    Off peak:0.0969€ / kwh
    There are a few more taxes to be paid... all in it's half taxes half electricity cost.
    But there's no way half an hour at 3,2 kw would be that much!!

    1. That for a 6.9kw contract; the higher the energy allowed, the costly per day it will be

    2. thk, now you see why I posted my bill. There are folk out there that wouldn't believe the things that are happening politically with power. There are others that believe it, but do nothing.

      I like the first type of people better.

  3. Dave...enjoyed browsing your site and reading the comments. I'm not an electrician so, not diving into any of those projects. I too have been dissecting the APS bill and have created a detail billing spreadsheet to analyze plans and usage by day and hour during each billing period. APS shoved me into their Choice plan after being on a grandfathered 9 - 9 plan that worked well for us. After one month, it's clearly the worst plan for a lot!!! The spreadsheet I've created shows the best plan for me depends upon my peak usage during each of the 3 - 8pm periods (Peak Demand) of the billing period. If I can keep below 3 kW in any of the Peak Demand periods, the best plan is Choice Max. If not, the best plan is Choice Plus.

    One observation.....your dryer usage didn't cost you $28.00 with 3.1kW peak during the month. It cost you the difference between the 3.1kW and your next highest peak demand hour during that entire billing period. It is easy to determine when that might have been by downloading the detailed weekly reports on the APS site. It's possible the best plan for you might actually be Choice Plus?

    1. The next highest peak hour was 1.05, and I had a couple of those during the month. Quite often I have a 1.9 show up when there's the perfect storm of appliances going off at the same time, or I'm smoking meat in the electric smoker. That didn't happen in this particular month though.

      So, you're right, it didn't cost me that much, it actually cost me more. I used the number from the previous month because it is easy to find, and in my case pretty consistent over the long term. It's also easy for folk to understand that don't do this stuff every day.

      It's a pain downloading a file for each week. I only do that when I have to. I remember looking at the meter a couple of days before and the demand was .9 and I was ready to celebrate because that's the lowest I've managed to get. Then that stupid dryer got me.

  4. There isn't much we can immediately do as regards the AZCC and APS rate programs offered. We are given the chance to change plans twice a year. Since you're a numbers guy, suggest you create a spreadsheet to show your exact usage by day & hour during each billing period to see which plan would have resulted in the lowest cost. It will also tell you if Super Cooling actually pays off given your home insulation and orientation. As we both agree, the real key is not allowing electrical appliance use during the Peak Demand hours. I've got my A/C set to 85 degrees during the Peak Demand period and this past Thursday, it kicked on. If it's any comfort, my usage for a comparable period to yours was 1382 hours Off Peak and 129 hour On-Peak with a total cost of $222.01. Again, I'm on Choice (thank you to APS) right now but moving to Choice Max next billing cycle.

    1. The problem is thinking we can't do much. No insult intended at all, but I used to think that way and I'd always whine about my bill. If we keep complaining and sending emails (easy), filing with the AZCC in support of the opposition and against APS, eventually the mighty news will pick up on it.

      Now, I used to supercool when the demand period was from noon to seven, but recently, I just haven't had to. My insulation is good enough to keep the temperature rise down to five degrees in all but one room. I may have to in the late summer when the ground has built up heat, but I'll have to see when it happens.

      I'm on savers choice max right now because it has the lowest per kWh charges. That way I can really eat the power up in the off peak periods.

      I am going to set up a spreadsheet, but it's been about 20 years since I scraped a web site to get data. I'm sure I could relearn it, but it would be painful. I just refuse to load each of the files in turn. I could get it all in one file, but that file doesn't separate the peak and off peak numbers, I'd have to do it myself.

      That will probably be a web post at some point.

  5. Our local utility credits us about $.08 when they're charging us $.13 per kwh. It's a scam that they've managed to get by but as more people catch on, it's going to be harder for them to continue. You have to audit these criminals every month. Make sure the numbers match. I've caught them twice now, in 3 months, making mistakes that cost me money. Today I'm going after the toll road authority for the mistakes they're trying to pass off...

    1. That's the way to do it. I check the meter readings constantly, and they seem in line, I have a spreadsheet that does the fees and stuff. I found a couple tiny items, but never anything worth bothering with.

      My big deal is keeping them honest about the peak period. So far, since the smart meter got installed, they've been right on. I look for the clock on the thing to be wrong someday though.