since I will be required to use TOU, shouldn’t I look at both $ and kWh? Since the utility wants to generate solar during off peak and charge peak during the evening when there’s no solar
Dear tfan,
Unless you know your daily power cycle very well, it's impossible to pin that down much. As ohmman pointed out, the TOU's are going to be regularly adjusted to minimize the demand curves on the utilities. You can certainly take measures to minimize your electric bill but in terms of optimizing your solar installation, it's hopeless.
A good general guideline for your economic sweet spot is that your system should handle about 80% of your annual needs. Unfortunately, you don't know what your annual needs are! You're going to have to wing it. But unless you're obsessed with trying to go totally off grid or want to be super-green about it, don't install based on your maximum usage.
Don't worry about all this talk about NEM changes. They're going to happen. Over the life of your system, they will continue to happen. The current rate structure is biased heavily to encourage solar installation (yay for us!). It's not economically sustainable, so over time you can expect to see more of the costs shifted onto us. But even if the utilities got everything they wanted in NEM3 (they're only going to get a fraction of that), your system would still pay for itself. It'd just take 12-15 years instead of 8-10.
Here in Daly City the schedule I am currently on has off-peak rates from midnight until 3 PM of about $0.17 per kilowatt hour. Between 3 PM and midnight, the electricity costs 2 to 3 times as much, depending on the exact time of day and year. Obviously I don't want to be charging the car at maximum peak rates — that's as expensive (or more) than gasoline!
I'm self-employed, so this works out just fine for me. Over the 15 months that I've had my Model X, my average daily driving has been about 25 miles. Most days not driving and then the periodic long drives. I take advantage of the free Supercharging when I'm doing a long drive (and I have the spare time) — why not! — but I don't rely on it heavily. I've read that supercharging degrades the battery faster. I don't know if that is still true with the latest version of the software and battery preconditioning and not taking it above 90% except when starting out on long drives. I may be excessively and unnecessarily cautious. Someone may want to correct me on this.
At home, I don't even have a 220 line installed in the garage yet. I've been trickle-charging off of the 110. Adds about 1% of capacity per hour of connect time, 15% total per day over off-peak hours. That, combined with the occasional supercharging, has been sufficient. I'm going to get a 220 V line installed in the next month for the convenience when I need to fully charge in a handful of hours. But I don't know how much I'll use it! Because...
The game I'm currently playing with myself is seeing how cheap I make it. I plug in the car in the morning when I get up and unplug it at 3 PM (or later now, as my panels are still generating net power). I put on 6% charge a day (15-20 miles) using electricity that is only costing me five cents per kilowatt hour (what PG&E/San Mateo Clean would be paying me for that excess generation).
I figure altogether I'm spending about 1-1.5 cents per mile on juice. It's a silly game, but it amuses me.
- pax \ Ctein
[ Please excuse any word-salad. Dragon Dictate in training! ]