I am looking for ways to reduce my electric bill. But first, a bit of background.

The complexities of my electric company's billing are beyond penetration. Nobody I know understands them fully. In simplified (!) form, if you average <300 KWH/2-month period, you are on the "Basico" rate, which is billed at .71 pesos/KWH. and at that rate you also receive a government subsidy on 50 of the 299 KWHs..

To add another layer of complexity, the billing is bi-monthly (every two months, not twice a month) so that heavy usage one month can negate frugality during the previous or following month.

If you average 300-499 KWH per two-month period, you lose the government subsidy and instead pay a monthly connection fee of something like 73 pesos, and you go on the "Intermedio" rate of 1.414 pesos per KWH, assessed not on the 300-499 KWH portion of the bill, but on the entire 1-499 KWH amount. Someone who averages 299 KWH per two-month period will pay (including tax and connection fee) 414 pesos; someone who averages 300 KWH over two months will pay around 652 pesos. The figures are misleading in that the same fixed costs (tax and connection fee) apply in each case. The cost of the actual electricity doubles. That next kilowatt hour is expensive!

Then, of course, there are the people (like myself) who are on the DAC rate, the "Domestica Alto Consumo" rate that applies to people who average >=500 KWH per two month period. It works like the "Intermedio" rate, except that the rate per KWH jumps to 3.02 pesos/KWH. Someone who averages 499 KWH/2-month will pay 973 pesos. Someone who averages 500 KWH/2-month will pay 1920 pesos. That next KWH costs more than $80 USD!

Note that I never said the word "use" above, but instead said "average". That's because your rate per KWH in any given month is not determined by the number of KWH you consumed in that month, but by the average consumption over the previous 12 months. So even if I dramatically reduce my consumption, it will be at least six months before I see any reduction in my cost per KWH.

The above is a simplified summary of the billing procedure. It does not take into account the 1A, 1B, 1C etc. "tarifas" that vary with location, summer temperature averaged over the previous five years, what is the current season, the 16% sales tax that is only charged for consumption greater than 149 KWH/month, and myriad other things that affect the rates.

My downstairs neighbor and I share the same electric meter. My local bank auto-pays the electric bill, and SWMBO and I figure that we use 3/4 of the power and the neighbor reimburses me 25% of the total bill. She (the neighbor) has a refrigerator, a laptop computer, and maybe half a dozen light bulbs. SWMBO and I have two desktop computers, two scanners, a color laser printer, a cable modem and wireless router that run 24/7, two cordless phone systems (shared with the neighbor, one local, and one OOMA for long distance), a larger-than-the-neighbor's but efficient (top 3% in it's size class) refrigerator, a dishwasher, three ceiling fans, a domestic water supply pump (downstairs neighbor is gravity-fed), close to a dozen wall-warts each taking a watt or two of parasitic power, and maybe a dozen light bulbs.

The most recent electric bill, including 16% tax and monthly connection fee, came to 2445 pesos. At first glance that seems high, but remember it is for two months, shared however asymmetrically among two families. Here is the breakdown for 650 KWH over two months:

Energia..........1963.00 pesos (straight DAC rate at 3.02 peso/KWH)
Cargo Fijo....... 144.76 pesos (connection fee, two months @ 72.38)
IVA @ 16%..... 337.24 pesos (sales tax)
Total:.............2445.20 pesos (about $211 USD)
(Figures are in pesos, about 11.6 pesos per US Dollar)

If you've had the patience to wade through all of the above, you will have seen that the key to electric bill happiness is to get off of the dreaded DAC rate. A quick look shows this to be improbable. My previous 12 month average was 647 KWH/2-month period, my goal is <500 KWH/2-month. That requires more than a 23% reduction in average usage, and I am already being careful, not mlord-fanatical, but paying attention to my usage. [For example, it is 93 degrees (34 degrees C) at my computer right now, and it would be more comfortable if I turned on the ceiling fan (about 75 watts). I'll accept the mild discomfort instead.] So how can I cut 23% off my usage?

The biggest reduction will come from splitting the electrical service between myself and my neighbor. This can be done! I have a worker contracted for 2407 pesos to install a second meter for the downstairs neighbor. This means we will each have 249 KWH to use before the DAC rate kicks in. IF my estimate that she is using 1/4 of the total electricity is valid, then by splitting the service I would just squeak under the DAC rate by about six KWH per month. That is too close a margin, so I am looking for additional reductions.

I am pretty sure my computer is the single biggest electricity user in the house. AMD dual-core 3.2GHz, 256 MB Nvidia video card, 4 GB RAM, 22" LCD monitor, I think there are no less than 7 cooling fans inside the case, four hard drives and a DVD burner. Add some more for the color laser printer... If I had to guess, probably something around 300 watts when running, and that is about 18 hours a day. That's 324 of my 499 KWH all by itself. According to the yellow sticker on my 25 cubic foot refrigerator, it's running 100 KWH per 2-month, so that leaves me 75 KWH left for lights, dishwasher, ceiling fans, etc. every two months. If I left a porch light on for one month it would put me back into DAC.

One thought I had was to install an external power switch to control two of the four hard drives on my computer. There is a 1-TB and a 2-TB drive (E: and F:) that are used only during backups (maybe once a week), but would this save any significant amount? I think those drives are configured to spin down after 30 seconds of non-use. How can I check this?

Probably the most certain thing to do and still remain cost-effective while not drastically changing my life-style is to install solar panels on my roof to carry some of the load. I haven't investigated the costs recently or thoroughly, but I think I can put a kilowatt up there for about 20,000 pesos. That should provide at least 5 KWH per day, and probably more since my house is ideally situated for solar, with 350+ days a year of cloudless sunshine at 5000+ feet elevation and an unobstructed 180 degree view of the sun track. Getting off the DAC rate and having to pay CFE for only 499 KWH/month would reduce my bill (at the current usage level of 650 KWH/2-month) from 1834 pesos for two months (after subtracting out the neighbor's 25%) to 973 pesos for two months, a savings of 430 pesos each month, plus a little bit more than that (optimistically, another 100 pesos is all, call it 500 total reduction) for however many KWHs under 499 I achieve. At that rate it would take 40 months to amortize the cost of the solar panel, more like 45 months if I factor in the earnings I won't receive from the 20,000 pesos. That's a pretty good ROI, I think.

My apologies for dragging this out, I sort of used this as an exercise to get clear in my mind more or less how the CFE ("Comision Federal de Electricidad") billing system works, and perhaps a few of you might find it interesting. I got to write a pretty neat spreadsheet to lay it out as best I could understand it [sample: =IF(A2<50,$B$27,IF(AND(A2>=50,A2<300),A2*$B$24,0)) ] and now I really do have an idea of what my options are.

Thanks for your patience.

tanstaafl.