Pretty close, Andy. But it would be "... /15 hours" not 18. In any case, it's irrelevant, because I totally screwed up on one of my assumptions. When I ran my calculations, I completely forgot that the billing is bi-monthly, not monthly, so John is only using half the amount of electricity I was basing my projections on. Thus he is safely removed from the clutches of the dreaded DAC rate.

In a word, "No". At least, not as of four years ago when I prepared the attached Excel spreadsheet. The up-front costs at that time were prohibitive. To tie into the existing grid, a minimum of six panels is required in order to match the line voltage. In view of my original error (see above paragraph), even though it would reduce John's electric bill to less than seven dollars per month, it would still take more than 25 years to amortize the expense of the initial installation. Even if the cost of the panels has decreased significantly since the last time I checked, it would not be financially optimal.

I did that this morning. The TV set and the associated cable box and the cable company's provided surge protector come to 150 watts. John's total usage is 160 KWh per month, of which (by Andy's/my calculations) means the TV is accounting for about 70 KWh per month, far less than the top-of-my-head estimate of 80% of the total.

As Shonky pointed out, 2% estimate for lighting seems unreasonable. Well, I calculated (rather than guessed) based on the number of lights he has, their wattage, and his usage and the true value would be closer to 4%. Really. He sits in a dark apartment watching television 15 hours a day, he doesn't use much lighting.

That leaves the refrigerator as the only other significant power user. The Kill-A-Watt shows it is running at 125 watts. In order for it to use the remaining 80 KWh of the 160 KWh actually used during the month (after subtracting out the television, the lights, and another 5 KWh for Miscellaneous), that would suggest that the refrigerator is actually running 21 hours per day. I don't think that is the case, but I will plug the Kill-A-Watt back into it and let it run for six hours or so and see how many minutes per hour it actually does run. And, double and triple check that the incandescent light inside the refrigerator actually turns off when the door is closed! (The light itself doesn't use much... but the energy required to remove the heat generated by the light is, I suspect, substantial.)

My house is divided into four apartments, each with its own meter. I am beginning to suspect that the circuit allocations have one or more circuits going to John's meter from other apartments.

In any case, it isn't something to be as concerned about as I was originally. His electricity costs, assuming usage similar to the past two months, still only come to about $18 or $19 USD per month. He can afford that. But nonetheless I am curious about just where all that electricity he is paying for is going.

tanstaafl.

ps: If you are (like me) an Excel nerd, you may find the attached spreadsheet intriguing. A LOT of work went into it, and I received a good bit of help from Paul Grzelak who, while not an Excel expert is a quite competent programmer who could quickly put his finger on the things I did wrong that kept the spreadsheet from working as expected. Try it out, see what happens when you change the variables, and gain an appreciation for just how incredibly complicated the electric company's three-tiered billing structure actually is.

db