Hourly output of West facing (270 azimuth) panels

[HX_Guy]

HX...

1. Are these estimates or your real numbers? When I look at my bill, the taxes and "other fees" that vary with usage only total about 13% of the charge for the actual electricity.
2. Is that 32% increase going to hit the off peak rates on the to-be-phased out ET-2 plan, too? I think it is at $.06118 / kWh now.

Looks like the ET-2 Legacy is going to $0.29201 on-peak summer, $0.23677 on-peak winter and $0.07299 off-peak summer and $0.07296 off-peak winter.

The current ET-2 is $0.24477 on-peak summer, $0.19847 on-peak winter and $0.06118 off-peak summer, $0.06116 off-peak winter.

Looks like about a 19.3% increase.

[cnil1]

On the same subject, keep in mind that APS has proposed to raise their off-peak rates by 32% in next year's rate case. While the strategy to do a "peak shaver" may be good today, in my opinion the best long term solution is still a full offset system...especially if you can get grandfathered into the plans they have today.

And that $0.06 off peak rate is really more like $0.075 when you add the taxes associated with usage...so the new rate would be roughly $0.10.

HX...

1. Are these estimates or your real numbers? When I look at my bill, the taxes and "other fees" that vary with usage only total about 13% of the charge for the actual electricity.
2. Is that 32% increase going to hit the off peak rates on the to-be-phased out ET-2 plan, too? I think it is at $.06118 / kWh now.

[J.P.M.]

Right, I found a chart showing it varying between 11:40:24 and 12:11:05 at this location. Bruce

Understood. Thank you.

[bcroe]

Actually, over the course of a year, the actual time difference from the earliest solar noon to the latest solar noon is about 30 minutes, 43 seconds and wobbles around +/- by some fraction of a second or so per year.

Check a nautical almanac or NREL, or see Duffie & Beckman, 2d ed., eq. 1.5.3a, or any decent solar text (Iqbal is a solid solar reference, but it's out of print) for an estimate of the time offset for solar noon as f(day of the year). For 2016, the day of earliest solar noon will occur on 11/02, with the date of latest solar noon occurring on 02/10. Note they are not 183 days apart. The actual civil (clock) times of local solar noon are f(longitude, time zone, daylight saving time). For my location, those times are 11:31:54 P.S.T. (11/02) and 12:02:37 (02/10) P.S.T. The Nov. time will most likely be under standard time unless 1st Sunday in November happens to be 11/01. In that case, solar noon will be at 12:31:54 P.D.T.

Right, I found a chart showing it varying between 11:40:24 and 12:11:05 at this location. Bruce

[J.P.M.]

17 minutes was the total range over a year. Bruce

Actually, over the course of a year, the actual time difference from the earliest solar noon to the latest solar noon is about 30 minutes, 43 seconds and wobbles around +/- by some fraction of a second or so per year.

Check a nautical almanac or NREL, or see Duffie & Beckman, 2d ed., eq. 1.5.3a, or any decent solar text (Iqbal is a solid solar reference, but it's out of print) for an estimate of the time offset for solar noon as f(day of the year). For 2016, the day of earliest solar noon will occur on 11/02, with the date of latest solar noon occurring on 02/10. Note they are not 183 days apart. The actual civil (clock) times of local solar noon are f(longitude, time zone, daylight saving time). For my location, those times are 11:31:54 P.S.T. (11/02) and 12:02:37 (02/10) P.S.T. The Nov. time will most likely be under standard time unless 1st Sunday in November happens to be 11/01. In that case, solar noon will be at 12:31:54 P.D.T.

[bcroe]

17 minutes was the total range over a year. Bruce

[organic farmer]

On the same subject, keep in mind that APS has proposed to raise their off-peak rates by 32% in next year's rate case. While the strategy to do a "peak shaver" may be good today, in my opinion the best long term solution is still a full offset system...especially if you can get grandfathered into the plans they have today.

That is an awful big rate increase.

How much of the day is 'off-peak'? Does this apply to all electric customers?

Doesn't TOU rates only apply if you have a 'smart meter' ?

[J.P.M.]

On the same subject, keep in mind that APS has proposed to raise their off-peak rates by 32% in next year's rate case. While the strategy to do a "peak shaver" may be good today, in my opinion the best long term solution is still a full offset system...especially if you can get grandfathered into the plans they have today.

And that $0.06 off peak rate is really more like $0.075 when you add the taxes associated with usage...so the new rate would be roughly $0.10.

Which brings up a point in my mind that while it's good to have a working knowledge of what's blowing in the wind for the probability and politics of rates, if for no other reason than to be able to get a better guess at the most cost effective system with a view to the long term, there is a certain logic of simply biting the cost bullet and getting a 100% (or +) system and saying screw it. As you note, one caveat, among many, is to lock in grand parenting if possible. Another might be to be very aware of the costs of any decision in terms of both NPV $$'s as well as lost opportunity costs that come with tying up the extra funds needed for the oversize, and not just knee jerk it.

[HX_Guy]

On the same subject, keep in mind that APS has proposed to raise their off-peak rates by 32% in next year's rate case. While the strategy to do a "peak shaver" may be good today, in my opinion the best long term solution is still a full offset system...especially if you can get grandfathered into the plans they have today.

And that $0.06 off peak rate is really more like $0.075 when you add the taxes associated with usage...so the new rate would be roughly $0.10.

[silversaver]

I think South is better than East or West; but in reality, a little toward West like SW 195 might offer you the max production. I personally prefer SW 220 deg because POCO offering TOU here and that will offer you the max credit on your account.

[J.P.M.]

I also am surprised at finding, solar noon here can vary over a 17 minute range each day, in a year. Bruce Roe

Assuming you're referring to the change over a 24 hr. period when the sun crosses the local meridian, I suspect you mean 17 seconds per day, not 17 minutes. ? The actual max. daily change in the time of solar noon is about 21 sec., around the middle of Sept.

[bcroe]

.

As a matter of some opinion/interpretation, and respectfully, I don't totally agree with the above statement. Speaking only about clear day system output, the peaks of the daylong curves of system output as f(time of day) will be skewed east or west, depending on the degree of off south orientation of the array. So, maybe 10 deg. off south orientation probably looks mostly like a south facing output. At a 90 or 270 azimuth - not so sure they'd look the same as south facing and sure wouldn't look like one another - somewhat symmetric about solar noon maybe, but not the same. The differences will also become more pronounced as the tilt angle increases.

I do agree that, somewhat depending on tilt, the greatest instantaneous power output will probably be for a closely south facing array, +/- a few degrees.

My experiments also show quite a difference in the power shape of E, W, and S daily production curves. All start and stop at the
same time, with "tails" reaching the time of the unfavored direction(s). Here is a recent curve from 3 test panels; ignore the top curve.

Yes the S orientation has the highest peak, and more overall energy. But keep in mind, E and W arrays can be compensated
by use of extra panels, WITHOUT expanding the rest of the system in many cases (not micro inverters).

I also am surprised at finding, solar noon here can vary over a 17 minute range each day, in a year. Bruce Roe

[J.P.M.]

If the total panel system face either East, South or West the shape of the production curve would be pretty much the same. The major difference would be the peak being higher on the South facing array then either the East or West.

.

As a matter of some opinion/interpretation, and respectfully, I don't totally agree with the above statement. Speaking only about clear day system output, the peaks of the daylong curves of system output as f(time of day) will be skewed east or west, depending on the degree of off south orientation of the array. So, maybe 10 deg. off south orientation probably looks mostly like a south facing output. At a 90 or 270 azimuth - not so sure they'd look the same as south facing and sure wouldn't look like one another - somewhat symmetric about solar noon maybe, but not the same. The differences will also become more pronounced as the tilt angle increases.

I do agree that, somewhat depending on tilt, the greatest instantaneous power output will probably be for a closely south facing array, +/- a few degrees.

In all likelihood, the biggest impact an off south orientation will have most of the time is to lower the total system energy output. Different and somewhat separate from that, the biggest impact per installed kW that a PV system will have on lowering an electric bill - that is fewer $$ out the door to the POCO per installed kW - is a function of both how a T.O.U. tariff is constructed and just how a specific array orientation's output as f(time) interacts with that tariff.

[SunEagle]

My photovoltaic array faces due South.

I am located near enough to the Magnetic pole that deviation here is large. I built a large sun-dial before construction of our house, so I could establish True North/South. I wanted our house' Passive Solar gain to be maximized. Later when I was constructing our Solar-Power array I built it to run parallel to our house.

I have read other people who have set a part of their PhotoVoltaic array to face East, to maximize the morning rays. I find that an interesting idea. But I think the total number of sun-light hours a panel can utilize would be fewer hours if it is facing anything other than due South.

I can see the idea behind getting a boost in wattage the morning. But I think the total wattage per day would be reduced.

I agree that:


I am not in a state with T.O.U. tariffing. There is no possible 'revenue' from solar power production in my state either. So I never had any reason to consider those parts of a puzzle, that would only apply in some other state.

Your decision is a wise choice.

If the total panel system face either East, South or West the shape of the production curve would be pretty much the same. The major difference would be the peak being higher on the South facing array then either the East or West.

When you then compare the total kWh production to the cost/kWh that the POCO charges you a Western facing array may be a better direction or a combination of a South and West split system especially if you have a TOU rate structure.

It all comes down to where you live and what your POCO rate structure is. From there you can make a financial decision as to what is a better way to orient your solar array.

[cnil1]

Well. I live in Texas and my west facing panels peak around 2:30. About 1/4 of my panels face west with the rest south. The whole array peaks around 1:45. My west facing panels produce about 6% less than the south facing panels.

Thanks! That's what I needed... a 2:30 peak would be great for me. APS rates are about $0.24 / kWh from 12:00 to 7:00 p.m. and $0.06 outside this range. Therefore, even though a West facing panel would produce, per PVWatts, about 17.5% less annual kWh, because of the later peak, I estimate that 80% of the output would offset $0.24 electricity, rather than 50%, if South facing.