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When considering TOU, it very much does matter when you generate and not just how much you generate. We all know that South facing is ideal to maximize how much you generate. The original question on this thread was "what is the optimal azimuth" when considering TOU. I agree that it doesn't make much sense to build a special rack to face 225. However, a more plausible situation it a home that has roofing surfaces facing in SE and SW directions. In that case it would make more sense to choose SE over SW. In my personal situation my roof faces 125 and 305... so it was an interesting question to consider if 305 might actually be better for a TOU rate plan, turns out it doesn't because too much production is lost going that far away from south.
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IMO, that article is a lot of simplistic B.S., the author needed a story and, knowingly or not, acted as a shill for the CA POCOs.
Some simplistic thoughts:
What follows is mostly for SDG & E cust., but probably applicable to at least some others and perhaps useful as illustrative to other situations.
This is a complicated subject but more manageable to my way of looking at it if taken piece by piece. I try to remember that things are changing fast in CA at least, and the future is never certain anyway, so the best I can likely hope for is to stick a wet finger in the wind and SWAG it. Thus:
One interesting factoid before I go farther, if I read the testimony correctly, an SDG & E employee named Leslie Willoughby, in testimony before the CPUC last Feb., stated that only about 1% (one percent) of SDG & E's residential customers are on T.O.U. and that T.O.U has been around since 1983. I'm checking on that. Seems surprisingly light.
As usual, there are, for starters, at least 2 ways to view things, the POCO's and the customer's.
The POCO's version may go something like this: Among other things, they'd like to get some way to maximize revenue, help balance/meet their peak loads, and as long as they're stuck with net metering, use it to their advantage. Incentivizing shifts in use patterns ( i.e. draconian pricing during peak use times) is one way to do this. Note that concern for the solar customer's generation revenue is probably not part of the thinking, nor should it be in any big way.
I'd assume the T.O.U. customer, solar owner or not, wants to minimize or at least reduce their bill. Note that the profoundly simple and most cost effective way to do this is to use less electricity. After that, the next best way (for the T.O.U. customer) is to avoid using electricity during peak hours, and confine use as much as possible to off peak or super off peak hours. Vampire laundry at 2 A.M. for example ? Maybe so, but in any case the amount of electrical use or use patterns have nothing to do with the capacity of a solar generating system to produce revenue under a T.O.U. tariff (or any other tariff for that matter).
For the T.O.U. customer who also has a solar energy system, one additional and perhaps helpful way to think about this business is to separate solar generation revenue from electricity expense, and think of the solar electric system solely as an income generator. To do this, the system probably can't be sized for more than 100% of the load.
Any properly operating grid tied solar energy system will generate power or not, independent from and irrespective of how much or when the residence is drawing power. Software and spreadsheets are commonly available to estimate the solar system's power output on an hourly basis (or smaller time increments) for periods of one year. Usage is not needed to determine this # (PVWatts with hourly output option seems the easiest, but least accurate, SAM, others). The key to this (and the PITA) is loading 8,760 hourly tariff $$ values for 1 kWh of electricity onto a PVWatts spreadsheet, but not as bad as it sounds - more like loading 168 hourly T.O.U. tariff values (for 7 days) and copying 52 times plus 1 day, then adjusting for holidays, at least as far as SDG & E is concerned.
Then, multiply the hourly system output by the hourly T.O.U. rate, sum 8,760 of those and voila - yearly system revenue - again, provided the estimate of system output is less than 100% of the annual load.
Do that for several or as many array orientations as you please and you'll likely zero in on an optimum (max. annual) revenue. The best system orientation for max. revenue is independent of customer use or use pattern. Provided that the system produces less than 100% of the household use, a system that produces, say 9,500 kWh/yr. in some particular orientation and, because of the T.O.U. tariff in effect produces, say, $2,500 in income, will do so regardless of the household use or time/pattern of that use given TMY or a "Solaranywhere" year data to estimate output.
The annual residual bill is the difference between revenue and expense. At least for SDG & E T.O.U. customers who are not "excess generators". Those folks currently get about $.05/kWh or so for the excess on a yearly basis.
I've done something similar to the above for my system. It's sort of an academic exercise since my and most other systems are fixed. However, it does seem to shoot down the idea that west facing arrays (270 az.) are more cost effective.
In my case, I took a 20 deg. tilt (common) and varied it in 10 deg. az. increments. I used some spreadsheet stuff I did years ago, before SAM, which produces output very similar to SAM's, but easier to work with, and quickly zeroed in on an op. revenue az. for DR-SES tariff ( T.O.U. for users with solar energy systems) of about 205 deg. That seems similar to data Sensij provided in a prior post. I'd not be surprised if 20 to 30 deg. west of south az. at most commonly used tilts produces the most income for the greater part of CA under most T.O.U. schemes. That's most of the reason why I'm of the opinion that the Times article is bogus road apples.
More on my data and revenue as f(az.), and gory details in a later post if anyone is interested. As I wrote, it appears similar to what Sensij found.
For customer electrical use and annual bill - the use is often available in hourly or smaller increments from the POCO - that's one benefit of smart meters. Do the same for electrical cost as done for revenue = hourly use times hourly per kWh cost, sum 8,760 times and you have a yearly bill.
A nice little bennie to all this: To zero out a bill, or to any other amount and/or to optimize system size as you choose, depending on how you do the process economics, the procedure usually becomes the following: setting the tilt and az. to the roof where the system will be located, figuring out how much revenue $$ 1 kW of nameplate capacity will produce as described above, then divide your bill by that 1kW revenue $$ amount. The result will be the required nameplate capacity in kW.
SWAG, Q.E.D.Comment
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