Orientation to optimize for EV-A plan in San Francisco Bay area

[araghava]

I don't understand how you will get an orientation of 225/SW if your home is facing west. Is there a roofing surface that faces 225? You're options for a roof mount are essentially limited to the directions in which your roofing surfaces face. If you provide your street address it would probably resolve a lot of confusion. (Then folks can get a look at your roof on google maps.)

Why can't the panels be mounted at an angle. i.e not aligned with the roof.

[araghava]

So did you figure it out? I'm curious to know what you used for input and what you got for results.

I have the raw data but don't know how to sum up the different time blocks. i.e. add up all the blocks for 7am to 2pm, 7pm to 9pm (partial peak) and 2pm to 7pm (peak).
However i can see that production for peak period increases as you orient westward while partial comes down.

[subdriver97]

Why can't the panels be mounted at an angle. i.e not aligned with the roof.

The most common rail systems for roof mounted PV systems align the panels in the same direction of the roof. As far as I know the common rail system allow for some adjustment for tilt, but tilt has a pretty minor affect on power generation.

I suppose it's possible to build a structure to mount panels to any azimuth on a roof, but I'm quite sure the cost for design, construction, and materials far outweighs any additional benefit in power generation. Additionally, it would look pretty ridiculous on the roof.

So assuming you're not going to build a custom structure you'll be limited to the azimuths which your roofing surfaces are perpendicular to. This also greatly simplifies the calculations since you're not limited to just a few azimuths.

[subdriver97]

I have the raw data but don't know how to sum up the different time blocks. i.e. add up all the blocks for 7am to 2pm, 7pm to 9pm (partial peak) and 2pm to 7pm (peak).
However i can see that production for peak period increases as you orient westward while partial comes down.

Just sum up the power generation numbers for each time block and multiple by the associated rate for the time block... then sum those products. Do this for each azimuth and choose the azimuth that is the greatest.

[sensij]

I have the raw data but don't know how to sum up the different time blocks. i.e. add up all the blocks for 7am to 2pm, 7pm to 9pm (partial peak) and 2pm to 7pm (peak).
However i can see that production for peak period increases as you orient westward while partial comes down.

This is an academic exercise more than anything, because I don't really know how you would design your roof mounting to take advantage of the results. I had created a spreadsheet a few weeks ago to evaluate a couple specific orientations on TOU, and modified it to take data from a SAM parametric simulation of tilts and azimuths. Better software could do more, but this is what I could get from excel:

PGE-EVA.PNG

The rows are azimuths, the columns are tilts, and the values in the table represent the annual dollar value of the energy produced by a 3 kW array, using the San Francisco airport TMY3 weather file. The EV-A rate plan used was this one.

Since no particular rate plan is ever guaranteed, I would be cautious about optimizing too tightly on these assumptions. However, as a thought experiment, it is interesting to me, and since this TOU plan has a definition of peak that could be reasonably expected to continue in the future, it has a chance of being useful.

Note that the difference between the absolute worst of the modeled conditions and the absolute best is less than $100 annually per 3 kW of array. If the custom tilt and azimuth mounting is expensive, I think it would be hard to justify.

[cf400]

Hi,

I'm going to have panels installed next week. I have an electric car and am on the EV-A plan. Peak rates are from 2:00 pm to 9:00 pm. Has anyone tried to optimize for this by orientating their panels somewhat west of south. If so could you share your orientation and tilt angles.

Thanks.

Ananth

Charge before 2 or after 9

[russ]

1) Do you have grid tie?

2) East facing would produce slightly more possibly - depending on location and micro climate

[control4userguy]

Charge before 2 or after 9

Read the response he gave me. He is not interested in charging during peak.

[wwu123]

Why can't the panels be mounted at an angle. i.e not aligned with the roof.

It's not just the mounting cost and complexity for additional rail and steel to orient them differently than flat against the roof. Yes, from a geometry standpoint you can put panels on any roof and point them in any direction with enough support. Say if you first laid them all side-by-side against the south roof first as in a typical install, then tilt each one to face southwest, you'd find that during your optimal hours, they would be shadowing each other. Even shadowing a tiny corner of a panel nearly kills all the panel output.

So you'd have to space them farther apart to avoid shadowing each other, esp during your peak production times. And there I think most residential roofs wouldn't have enough area for a decent-sized array with the spacing needed.

[wwu123]

So I think your choices are really only how many panels facing south vs how many facing west. I don't think most folks on this forum live in a region where they can appreciate paying 40 cents a KW, or 4X the price of off-peak power. I think south vs west will make only a minor difference in energy production, but it will make a huge impact in dollar production. Especially with "peak" stretching to 9 pm, if you get home between 6-9 pm from work, offsetting that evening energy use with more solar production between 2 and 6 pm will make a big difference. It doesn't matter if you use more than you're producing, any amount of peak you can offset is huge.

[sensij]

So I think your choices are really only how many panels facing south vs how many facing west. I don't think most folks on this forum live in a region where they can appreciate paying 40 cents a KW, or 4X the price of off-peak power. I think south vs west will make only a minor difference in energy production, but it will make a huge impact in dollar production. Especially with "peak" stretching to 9 pm, if you get home between 6-9 pm from work, offsetting that evening energy use with more solar production between 2 and 6 pm will make a big difference. It doesn't matter if you use more than you're producing, any amount of peak you can offset is huge.

You can see in my post above that if you are comparing due south vs due west for any particular tilt, south wins every time under the terms of the EV-A plan discussed. The improved $ / kWh you get for west is more than offset by the increase in total kWh by facing south.

This will not be true for all installations... local shading or other factors could change the result. However, in general, due south is still better than due west, even for TOU.

[araghava]

You can see in my post above that if you are comparing due south vs due west for any particular tilt, south wins every time under the terms of the EV-A plan discussed. The improved $ / kWh you get for west is more than offset by the increase in total kWh by facing south.

This will not be true for all installations... local shading or other factors could change the result. However, in general, due south is still better than due west, even for TOU.

I started this thread because i read this article.

http://www.nytimes.com/2014/12/02/up...abt=0002&abg=0

[SunEagle]

I started this thread because i read this article.

http://www.nytimes.com/2014/12/02/up...abt=0002&abg=0

If you look deeper into that article you may find that the Electric Utilities may have had some input into the data collected and presented.

First off most POCO's want to make a profit. If they can convince their customers to do something that puts more money into the POCO's pockets they will make it sound like it's the best thing since slice bread.

Look at the data provided by sensij. Even though generating more of your own electricity during the higher rates in the afternoon sounds like a good idea it may not really be. In cases where there is no shading you will generate more power in a 24hour period with the panels facing South then in any other orientation. It is not when you generate, it comes down to how much you can generate and South gets you more than West or even SW.

[prhamilton]

It is not when you generate, it comes down to how much you can generate and South gets you more than West or even SW.

Are you familiar with Time Of Use(TOU) metering? In California it is all about WHEN you generate. Peak prices are 4x higher than off peak, with net metering you are banking $ not kWh. From the spreadsheet looks like 225 is ideal and south vs. west is a wash.

[SunEagle]

Are you familiar with Time Of Use(TOU) metering? In California it is all about WHEN you generate. Peak prices are 4x higher than off peak, with net metering you are banking $ not kWh. From the spreadsheet looks like 225 is ideal and south vs. west is a wash.

I thought that the spreadsheet that sensij showed was based on TOU metering.

He also pointed out that the difference between the best and worst was just $100 per year per 3kw. I don't see that savings as a motivator to add special racking to point the panels more toward 225 then S or W.