Solar on the shady side of the roof

[dreamypenguin]

So, I'm having one of those moments where I don't know what's true between two installers. Maybe wise forumdwellers can help.

Got two sales pitches for Roof + Solar, one from Semper Solaris and one from Simmitri, both reputable companies. My sticking point is one bid had panels on both sides of the roof, one didn't. I use a lot of kWh every month, and here's what they both said:

Simmitri: you can totally put another $10k of panels on the shady side of the roof. They will each produce about 3-4% of your total bill every month, unlike the bright side where they'll produce about 7%.

Semper: it's not worth it to put panels on the shady side of your roof. (doesn't even offer it as an option). Also comments that to put them on the shady side, they would need to install a "tilt kit" and it increases risk of roof leaks, so no bueno.

I have no problem with less-efficient solar panels if they are still significant - e.g. if they pay for themselves in 7 years instead of 4. I can't tell what the subtext is here. Should installers avoid tilt kits because they really do compromise roofs? I was kind of surprised they were concerned about that since I'm buying a brand new roof - seems like they could ensure the whole thing happens properly. Simmitri says they have like a 25 year warranty with no deductible on any repair including leaks.

Is there some risk that because Simmitri hasn't been out to see the house in person (Semper did come out in person) that they might just be wrong and panels on the shady side will be really bad, like 0-1% of my bill instead of 3-4%?

[RichardCullip]

Interesting that the metric is % of a monthly bill. I would rather see the yearly kWh produced for both scenarios. You can run your own solar production estimate using the pvwatts tool found on-line. Just make two runs, one for the sunny side and one for the shady side of your roof. This should give you an unbiased estimate of your solar production which you can compare to your total demand.

[dreamypenguin]

They did tell me the kWh difference in numbers, too. One bid was ~370/month and the other was around 600 (with the both sides of the roof installation).

I tried to go use pvwatts but I am not that technical. It's too complicated for me to use properly, I think?

[J.P.M.]

1.) How may kWh/yr. do you use ?
2.) How many kWh/yr. is each proposal producing ?
3.) How big is each system in STC kW ?
4.) What are your roof orientations, tilt and azimuth ?
5.) What's your zip code ?
6.) Most residential PV systems offset a substantial portion of an annual electric bill, most of the time greater than 2/3 of the usage. Single digit % offsets are unusual. If I'm reading what you have written correctly, if shading is so much it reduces offsets to single digits %ages, PV is probably not going to be cost effective

I'd suggest you need to supply a lot more info before folks here can offer intelligent opinions on what vendors are providing.

[bcroe]

Something to consider. The tilt kit is to allow catching all the sunlight
heading for your roof, with the minimum number of panels. If you just
lay the panels flat, more will be required to catch all the sun, but they
will still get just as much energy. The tilt kit might allow catching some
sun that would have missed the roof entirely, but they have lots of
issues. Under clouds more panels will perform better, the more clouds,
the bigger the advantage. Bruce Roe

[OCJ]

Okay, going to make a couple SWAGS here. Since both of those companies are headquartered in California, you're in California, yes?

California has a thing called Net Metering (NEM) 2. It's about to end and be replaced with NEM 3, or whatever. You have until mid April for what's written below to apply.

I'm guessing since you're talking about tilt kits the "shady" side is the North side?

In Northern California, North facing panels can produce 68% of South facing panels annually. Normally, people in other states might not think that's worth it. Thanks to California IOUs absurdly high electricity rates and the magic of NEM 2, it actually is worth it. PROVIDING you don't pay an absurdly high amount for your panels and/or get absurdly high priced financing, and the shading you're referring to isn't actually trees or buildings.

The reason it still makes sense is in the summer, when the sun is higher in the sky due to the tilt of the Earth and its orbit around the sun, especially in late June, north facing panels will produce 98% of south facing panels, even parallel with your roof. During this time, those north facing panels will generate credits that you can then use later in the year.

That's right, NEM 2 treats production as an annual bucket. Put it in and take it out later. And what you put in goes in at full retail rate as a credit for use later.

Please do provide more information, and provide it quickly as the NEM 2 countdown is in effect. You have a short window of time to lock it in.

[SunEagle]

Okay, going to make a couple SWAGS here. Since both of those companies are headquartered in California, you're in California, yes?

California has a thing called Net Metering (NEM) 2. It's about to end and be replaced with NEM 3, or whatever. You have until mid April for what's written below to apply.

I'm guessing since you're talking about tilt kits the "shady" side is the North side?

In Northern California, North facing panels can produce 68% of South facing panels annually. Normally, people in other states might not think that's worth it. Thanks to California IOUs absurdly high electricity rates and the magic of NEM 2, it actually is worth it. PROVIDING you don't pay an absurdly high amount for your panels and/or get absurdly high priced financing, and the shading you're referring to isn't actually trees or buildings.

The reason it still makes sense is in the summer, when the sun is higher in the sky due to the tilt of the Earth and its orbit around the sun, especially in late June, north facing panels will produce 98% of south facing panels, even parallel with your roof. During this time, those north facing panels will generate credits that you can then use later in the year.

That's right, NEM 2 treats production as an annual bucket. Put it in and take it out later. And what you put in goes in at full retail rate as a credit for use later.

Please do provide more information, and provide it quickly as the NEM 2 countdown is in effect. You have a short window of time to lock it in.

The historical problem is that Northern facing panels in the North hemisphere will rarely produce a lot of power during the Winter months because the sun is too low in the sky.

If you are getting inflated output info then try to remember that if there is a low sun or clouds or smoke then most panels no matter what their tilt will not output anything close to their nameplate wattage let alone 68% and North facing panels fall into the category of low sunlight.

[OCJ]

The historical problem is that Northern facing panels in the North hemisphere will rarely produce a lot of power during the Winter months because the sun is too low in the sky.

If you are getting inflated output info then try to remember that if there is a low sun or clouds or smoke then most panels no matter what their tilt will not output anything close to their nameplate wattage let alone 68% and North facing panels fall into the category of low sunlight.

I have NE and NW panels in SoCal, normally that would be a bad idea and yes winter production sucks, but thanks to SDG&E somehow reaching this far north with their sky high pricing and the magic of NEM 2.0, the summer generation carries the year.

I have Powerwall Dashboard and Home Assistant running in VMs as well as an Emporia Vue Utility Connect, and I've downloaded and summed 4 PVWatts runs (SE, SW, NE, and NW) hourly data into Excel to compare with actuals, as well as Green Button data and CSV import from the Tesla app.

Last June 24th (day after PTO, first day after solstice that wasn't throttled) I was able to record a full day of production. My NE panels produced 2.50 kWh each, NW panels 2.80 kWh each, SE 2.71 kWh each, and SW 2.76 kWh each.

Now fast forward to Winter solstice, NE was 676 Wh each, NW 1.1 kWh each, SE was 1.54 kWh each, and SW was 1.07 kWh each.

Now one thing is my NW and SW panels are paralleled in a string. So while my SW production seems to be "brought down" my NW production seems to be "brought up."

And finally production from June 24th to Dec 24th looked like this: NE 254 kWh each, NW 326 kWh each, SE 350 kWh each, and SW 328 kWh each.

So while not completely North or South, my Northerly production was certainly worth it for me and I would still get those panels if I had to do it again. For my location, PVWatts puts North production at 69.5% of South production, with only azimuth changed. PVWatts has proven fairly accurate for my system so far.

[SunEagle]

I have NE and NW panels in SoCal, normally that would be a bad idea and yes winter production sucks, but thanks to SDG&E somehow reaching this far north with their sky high pricing and the magic of NEM 2.0, the summer generation carries the year.

I have Powerwall Dashboard and Home Assistant running in VMs as well as an Emporia Vue Utility Connect, and I've downloaded and summed 4 PVWatts runs (SE, SW, NE, and NW) hourly data into Excel to compare with actuals, as well as Green Button data and CSV import from the Tesla app.

Last June 24th (day after PTO, first day after solstice that wasn't throttled) I was able to record a full day of production. My NE panels produced 2.50 kWh each, NW panels 2.80 kWh each, SE 2.71 kWh each, and SW 2.76 kWh each.

Now fast forward to Winter solstice, NE was 676 Wh each, NW 1.1 kWh each, SE was 1.54 kWh each, and SW was 1.07 kWh each.

Now one thing is my NW and SW panels are paralleled in a string. So while my SW production seems to be "brought down" my NW production seems to be "brought up."

And finally production from June 24th to Dec 24th looked like this: NE 254 kWh each, NW 326 kWh each, SE 350 kWh each, and SW 328 kWh each.

So while not completely North or South, my Northerly production was certainly worth it for me and I would still get those panels if I had to do it again. For my location, PVWatts puts North production at 69.5% of South production, with only azimuth changed. PVWatts has proven fairly accurate for my system so far.

I am glad those Northern panels are working for you. Most end up spending a lot more then that kind of panel can produce making the payback very long and hard. Hopefully you will reduce your electric bill even with the new NEM rates.

[OCJ]

I am glad those Northern panels are working for you. Most end up spending a lot more then that kind of panel can produce making the payback very long and hard. Hopefully you will reduce your electric bill even with the new NEM rates.

I'm on NEM 2 so I'm good for the next 19 1/2 years or so... unless they manage to push through the fixed charges they are looking at, and the "equity" charges being looked at also. Not the fixed charges for per kW of solar, but income-based fixed charges. If that one ever goes through that is truly a time where I'll get my lazy butt of the couch and mobilize.

[J.P.M.]

I have NE and NW panels in SoCal, normally that would be a bad idea and yes winter production sucks, but thanks to SDG&E somehow reaching this far north with their sky high pricing and the magic of NEM 2.0, the summer generation carries the year.

I have Powerwall Dashboard and Home Assistant running in VMs as well as an Emporia Vue Utility Connect, and I've downloaded and summed 4 PVWatts runs (SE, SW, NE, and NW) hourly data into Excel to compare with actuals, as well as Green Button data and CSV import from the Tesla app.

Last June 24th (day after PTO, first day after solstice that wasn't throttled) I was able to record a full day of production. My NE panels produced 2.50 kWh each, NW panels 2.80 kWh each, SE 2.71 kWh each, and SW 2.76 kWh each.

Now fast forward to Winter solstice, NE was 676 Wh each, NW 1.1 kWh each, SE was 1.54 kWh each, and SW was 1.07 kWh each.

Now one thing is my NW and SW panels are paralleled in a string. So while my SW production seems to be "brought down" my NW production seems to be "brought up."

And finally production from June 24th to Dec 24th looked like this: NE 254 kWh each, NW 326 kWh each, SE 350 kWh each, and SW 328 kWh each.

So while not completely North or South, my Northerly production was certainly worth it for me and I would still get those panels if I had to do it again. For my location, PVWatts puts North production at 69.5% of South production, with only azimuth changed. PVWatts has proven fairly accurate for my system so far.

What's the STC rating of the panels ?

[OCJ]

What's the STC rating of the panels ?

They're 400s. SE is at 147 deg and the other panels offset by 90 deg. $2.50 /watt installed.

The 5 NE panels at 57 deg are set to do at least 2,500 kWh for the year, $5k pre-incentive, $3.5k post, thanks SDG&E for the ridiculous sub 4-year payback on Northerly facing panels. And that was before the January price increase!

[J.P.M.]

They're 400s. SE is at 147 deg and the other panels offset by 90 deg. $2.50 /watt installed.

The 5 NE panels at 57 deg are set to do at least 2,500 kWh for the year, $5k pre-incentive, $3.5k post, thanks SDG&E for the ridiculous sub 4-year payback on Northerly facing panels. And that was before the January price increase!

Forgot to ask: What's the tilt of the panels ?

Thanx,

J.P.M.

[OCJ]

Forgot to ask: What's the tilt of the panels ?

Thanx,

J.P.M.

NW/SE is 12 deg, NE/SW is 20 deg.

[davidcheok]

If I were going to install solar that was only going to knock 7% off my bill, I rather put that money elsewhere.