DR-SES SDGE and Solar Panel Orientation (Time of Use)

[Jskeyes2]

So apparently I was way behind in realizing that I could pick another rate tier based on Time of Use and just signed up for DR-SES for SDGE here in San Diego county. This is the schedule where there is a higher tier between 12pm and 6pm and I get grandfathered in for 5 years before moving to TOU from 4pm to 9pm I believe based on timing of install of panels. Right now I offset about 86% of my use and would apparently save another $500 a year if I pick this method.

My question is does this impact the return on panels for TOU - is it better to have S, West or even SW / N orientation to get bigger bang for summer hours of TOU? I am considering adding more panels, and SW / N is the orientation I have left. I will have my contractor calc the KWh for this orientation vs. another just to know the difference, but did this change the game on which direction you point panels based on TOU vs. maximum exposure? Any thoughts would be appreciated.

[ButchDeal]

So apparently I was way behind in realizing that I could pick another rate tier based on Time of Use and just signed up for DR-SES for SDGE here in San Diego county. This is the schedule where there is a higher tier between 12pm and 6pm and I get grandfathered in for 5 years before moving to TOU from 4pm to 9pm I believe based on timing of install of panels. Right now I offset about 86% of my use and would apparently save another $500 a year if I pick this method.

My question is does this impact the return on panels for TOU - is it better to have S, West or even SW / N orientation to get bigger bang for summer hours of TOU? I am considering adding more panels, and SW / N is the orientation I have left. I will have my contractor calc the KWh for this orientation vs. another just to know the difference, but did this change the game on which direction you point panels based on TOU vs. maximum exposure? Any thoughts would be appreciated.

A south / West mix is going to have a better TOU return than a south / east mix.
A SW / N no. I would assume that if it is SW on one face that the other would be NW though not true north as that would be a house with 135 degree angle difference.

The kWh difference is NOT the difference that matters in TOU.
so in your first example of South / West combination the choice is South / West or South / East. They will produce nearly identical amounts of KWh. In fact you can ignore the south part as it will produce the same in both installs.
The East vs West will produce almost the same but the WEST one will produce during peak time of use. Thus more valuable kWh.

[J.P.M.]

Lots of thoughts. Lots of recent threads on that very subject. Bottom lines:

1.) Cost effectiveness for PV under the new T.O.U. times for DR-SES (after the 5 yr. grandfathering period, or for those who didn't make the cut) will be something more than 20+ % less cost effective because of the time changes involved in the new DR-SES times.

2.)The revenue a system produces under DR-SES to offset an electric bill, because that revenue is not dependent on how much electricity a customer uses, is independent of usage and is, for a given system and orientation, only dependent on system output and the rates DR-SES charges according to that hourly schedule of rates and times. Provided the system offsets ~ < 100 % of usage, under DR-SES, a, say 5 kW system will offset the same $ amount of a 10,000 kWh/yr. usage bill as it will a 12,000 kWh/yr. bill. Under the new DR-SES times, the average price of a kWh as revenue a system produces will drop from ~ $0.30/kWh under the old times to ~ $0.23 under the new times. Those rates are somewhat dependent on system orientation, but weakly so.

3.)To be clear: Those revenue rates are different than what you will pay for electricity you use, which average price/kWh can be somewhat controlled by WHEN you use electricity. Bottom line : Avoid summer peak times as much as possible.

Also to be clear, I'm referring to system revenue to offset an electric bill, NOT system revenue from overgeneration (which overgeneration, BTW, only lowers the average value of a kWh produced by the system in a rather disastrous way).

4.) For most owners of residential PV in/around San Diego, from stuff I and a few others have done, if on DR-SES, it looks like 1 STC kW of PV system facing south at a 20 deg. tilt under the new times for DR-SES will produce ~ $400/yr. in revenue to offset an electric bill. That amount will be reduced by something called NBC (non bypassable charges), but that NBC is separate from how much revenue a system will produce.

5.) A similar 1kW system facing 22.5 deg. west of due south at a 20 deg. tilt will produce ~ $406/yr. of revenue to offset a bill. a 20 deg. tilt, 45 deg. west of south azimuth will produced ~ $404/yr. revenue to offset an electric bill. Bottom line for you, if south orientation is full, use the SW orientation. Forget north facing - that's always a loser.

6.)A 270 deg. azimuth (west facing)1kW array will, under the proposed tariff times for DR-SES, and the same 20 deg. tilt, produce ~ $375/yr. in revenue to offset an electric bill.

Multiply by the STC kW capacity for estimates of total $/yr. over that of a 1 kw system for total annual system revenue. For example, a 5 kW system under DR-SES will produce 5X as much annual revenue as a 1kW system.

Bottom line: For most roofs in/around San Diego (which are fixed and often at ~ 20 deg. tilt), best azimuth - not considering shading - is ~ 200 - 210 deg. or so, noting however, not that much better than south facing within a 1-2% or so in terms of annual revenue increase over straight south. And, a west orientation being about, roughly, 5 - 10% lower in terms of how much revenue that orientation will produce vs. a south facing array orientation. West is not better than south. Southwest is marginally better under DR-SES (BTW that pretty much holds true for the old (grandfathered) DR-SES times as well as the new DR-SES times).

BTW - North orientation is a loser under any reasonable or likely scenario, and an east azimuth, while certainly better than north, will produce less revenue than corresponding off south westerly azimuths.

As for having your contractor run stuff to estimate output - do as you please, but I'd do my own using PVWatts, and remember that T.O.U. rates, while they will tend to shift optimal azimuths based on system revenue (or bill offset), most of the time do not shift the ideal azimuth all the way around to the west - usually shifting the optimum by ~ 200 - 210 deg, or 20 to 30 deg. west of south with most of the increase over south, in spite of what you may think, probably quite small.

Last point: All rates and times are subject to changes - and they will. It's a fact of life. So, in planning orientations of a fixed array based on rates and times currently in effect, and for schedules that can and will change, particularly for rates/schedules like DR-SES where rates and usage quantities are independent of customer usage, it may be wise to keep all the changes that can and probably will impact cost effectiveness down the road.

[Jskeyes2]

Thanks a lot for the info. After I posted this I saw some of the other threads too. I guess I need to do a little more homework on orientation / roof that I have left. My problem is that I have my prime roof filled up with solar hot water for pool - for which I have determined is not worth moving to a less idea roof based on the cost to move.

[J.P.M.]

Thanks a lot for the info. After I posted this I saw some of the other threads too. I guess I need to do a little more homework on orientation / roof that I have left. My problem is that I have my prime roof filled up with solar hot water for pool - for which I have determined is not worth moving to a less idea roof based on the cost to move.

FWIW, solar thermal pool heating is ~ 50 - 70% efficient in solar energy to pool heat energy conversion. PV is ~ 15-17 % solar energy to electrical energy conversion on a day long basis. However, if pool heating is replacing nat. gas pool heating, in term of revenue, it may be more cost effective to replace pool collectors that displace relatively cheap nat. gas with PV panels that replace relatively expensive electricity. Some careful analysis is often called for.

[Jskeyes2]

FWIW, solar thermal pool heating is ~ 50 - 70% efficient in solar energy to pool heat energy conversion. PV is ~ 15-17 % solar energy to electrical energy conversion on a day long basis. However, if pool heating is replacing nat. gas pool heating, in term of revenue, it may be more cost effective to replace pool collectors that displace relatively cheap nat. gas with PV panels that replace relatively expensive electricity. Some careful analysis is often called for.

More of a quality of life thing - I refuse to pay gas to heat the pool - only for hot tub. Makes our pool swimable and extends the swimming season...

[J.P.M.]

More of a quality of life thing - I refuse to pay gas to heat the pool - only for hot tub. Makes our pool swimable and extends the swimming season...

Pay your money, take your choice, just know what you're buying before spending.