Solar planning for new construction

[Joe.B]

We are building a new home with ADU - about 4000 sq ft.

Looking to add solar after the final inspection by the city.

If you're building a new home in CA then likely you were supposed to have solar before final, unless your permit is under an earlier code cycle. Even then it should have been at least "solar ready". As others stated, this is not a DIY kind of thing. You should hire a qualified professional, and they should get it permitted.

 

[jaggedben]

If you're building a new home in CA then likely you were supposed to have solar before final, unless your permit is under an earlier code cycle. ...

That's another weird thing that varies by AHJ or even by inspector and seems to be a kind of a Catch-22. Some of them want the solar finaled before the building project is finaled, others do want to let you connect solar to a building that *isn't* finaled. Personally I don't really get the rationale for either.

 

[solarken]

We are building a new home with ADU - about 4000 sq ft.

Looking to add solar after the final inspection by the city. We are thinking of one panel with two meter slots. One for main house and other for ADU.

We are looking to add a battery as a backup from those days when there is no power (1-2 days in a year). Leaning towards 13Kwh battery that can power fridge and some lights for 1-2 days. We do not plan to use heavy appliances or EV charging for those days.

Few questions.

1. What can we do now, to make it solar-ready?
2. How many solar panels should we get? Are 10-12 panels (each generating about 400-450W) good enough to charge the battery?

Any other suggestions that you might have for us?

Thanks,

In addition to the other suggestions in this thread, you should consider:
- Have a rough PV and storage design completed as early in the house design/construction as possible
- Allocate space for the inverter and battery storage into the design plans for the home.
- Think through the interconnection point. Do you want whole house backup? Or only critical circuits. If a transfer switch is needed, allocate space and note conductor paths.
- If ATS or a disconnect will be installed on the outside of the house, install a strong, attractive, weather proofed mounting surface to accomodate the mounting, rather than mounting to siding.
- The amount of PV you need will depend on your usage, and your solar installer should model the output based on the space avaialble and the array orientation, etc, ahead of time. You will need to estimate your usage, but maybe your HVAC contractor can help, or you can estimate based on similar construction home with similar HVAC and appliances. I would think much more than 10-12 400W panels are needed for your 4000 sq ft home, especially with EV charging. Probably more like 10kW.
- Install 1-inch EMT conduit run from the inverter location up through interior walls into attic for the PV output conductors from the array.
- Plan the locations of any roof penetrations needed for the PV circuits from the array on roof into attic. Try and locate them somewhat near the attic access hatch, and install walk boards from the hatch to the penetration locations at/above any blown in insulation level if the attic will be insulated before the penetrations can be completed, so the insulation will not be compressed during the install.
- Install permanent roof ridge anchors under the ridge cap while the roof is shingled, your installer will appreciate and will eliminate a chance for leaks.

 

[jaggedben]

That last post speaks in part to something I see all the time, which is that many GCs and architects still don't understand or appreciate their role in coordinating this stuff to make it come out right. Also the electrical contractors don't want to take responsibility for it, they are the worst among the relevant actors, tbh. I mean some are okay, but as a group they cause me the most headaches. I understand to some extent, because lot of the tactics that ECs use to save time and money don't work with battery backup, or at least need an extra layer of thinking put over them. But also sometimes it's clear they just would rather screw us and move on to the next job. Hopefully this will all change over time, but I see a lot of these folks being really slow to adapt. With the higher end contractors we are starting to see them contract us as subs, which is arguably the best way. But with a lot of projects we still contract with the client separately from the GC, which leaves things open to burden-shifting and finger pointing. It puts the solar/battery contractor and/or the client in the position of being the project manager, which is unfair especially to the client.

Basically GCs need to realize that battery backup requires the same planning and timeline as doing HVAC or any other trade. They need to take responsibility for putting the solar/battery contractor and the EC on the same page (the line diagram page, especially). They need the balls to tell the EC that it needs to be done in a way that works for the client to get what they want and pay for. And they should tell the EC to bid it that way up front, or be willing to to ask the client for a change order if the client brings solar/battery into it late, whatever the situation calls for.

In case it's not clear what I mean, imagine coming into a project as the sheet rock is going up and finding out that all the loads the client wants backed up and doesn't want backed up are all mixed into subpanels in various parts of the house. So now it's impossible to separate them. And also since no one thought ahead about battery location, there isn't enough room to install enough battery to backup all the stuff on those subs, even if the client has the money for it.

 

[Zee]

To be clear, in residential, no setbacks are required on low slope roofs (AKA flat).
Defined as 2:12 (9.5°) or less as per CFC 605.11.1.2.3 & CFC 605.11.1.2.4

I do it all the time. Edge to edge PV.
---------------------------

The greatest difficulty I have with adding battery backup is I cannot back up the main service panel because 99% of service panels ( 'round here) are meter/main combos.
This means there is no place to intercept the service conductors and backup the house.
The solution:
A separate main disconnect and separate service panel.
This would be ideal from the get-go for future battery.
Often this is what we have to have done for about $7k.

 

[Joe.B]

I do it all the time. Edge to edge PV.

What do you do about the plumbing vents?

 

[ggunn]

What do you do about the plumbing vents?

We sometimes used to trim them so that their tops were underneath the modules, but most AHJs around here have stopped allowing that.

For commercial PV systems on new construction, plumbing vents that cannot be racked over can be very problematic because there could be tens of them or more, and they frequently are not shown on roof plans. Surprise!

 

[jaggedben]

Obviously you can't cover the entire roof if there are vents, but I don't think that's what Zee meant. He just meant going right up to the edge in all dimensions that the physical building allows.

 

[Zee]

Exactly. I cannot do anything about plumbing vents - except go around them.
But if planning construction...... it would be nice to group them so they block as little solar as possible.

(Do not chop them shorter, they use the chimney effect to vent and need a certain height)

 

[Zee]

or put vents near a ridge or roof edge where you may leave a setback in any case

 

[Joe.B]

Obviously you can't cover the entire roof if there are vents, but I don't think that's what Zee meant.

Agreed, I didn't think that was the case but I had to check

And I don't know about "obviously" because I've had several installers try to do it because, as @ggunn mentioned, they're usually not shown on the plans. Then I have to dig up a code reference to show them why they can't, which is not as easy as I thought it would be. I took a 2019 Calbo training "Inspection for Solar Photovoltaic and Energy Storage Systems" and the instructor flat out said there was nothing wrong with covering up roof vents. Three or four hands shot up real quick to correct him. The best answer (and the only one I could confirm for myself) was that most panels instructions and listing will explicitly state they can't be installed over plumbing vents because the sewer gasses will shorten their expected life.

 

[Joe.B]

Exactly. I cannot do anything about plumbing vents - except go around them.
But if planning construction...... it would be nice to group them so they block as little solar as possible.

(Do not chop them shorter, they use the chimney effect to vent and need a certain height)

The "chimney effect" was one of the reasons mentioned at that training, but I never found a code to back it up. I think most people just know that it's "wrong" but other than violation the listing I haven't yet found a specific code reference.

 

[Joe.B]

This is the closest I could find in the plumbing code:

310.5 Obstruction of Flow
No fitting, fixture and piping connection, appliance, device, or method of installation that obstructs or retards the flow of water, wastes, sewage, or air in the drainage or venting systems, in an amount exceeding the normal frictional resistance to flow, shall be used unless it is indicated as acceptable in this code or is approved in accordance with Section 301.2 of this code. The enlargement of a 3 inch (80 mm) closet bend or stub to 4 inches (100 mm) shall not be considered an obstruction.

 

[Zee]

frankly that is all i really know: its wrong as of 15 years ago or so

But we used to chop and go over them all the time, but I did a lot of things that, well, anyways.

 

[Zee]

That is why i advise - ideally - putting them on the North Face if that exists and if it is reasonable.

 

[wwhitney]

(Do not chop them shorter, they use the chimney effect to vent and need a certain height)

I don't believe it's correct that they rely on the chimney effect.

I believe the only reason that you can't chop them shorter is that the plumbing code requires a certain height above the roof plane, and it has not been updated for the convenience of the solar installer. Obviously some height above the roof plane is required to avoid leaks and to avoid letting roof surface rainwater into the vent, but less than the plumbing code requires.

If the panels and rails provide enough clearance under them (maybe not too likely in the case of the rails), you could use elbows to turn the plumbing vent to run parallel to the roof surface, out from under the solar panels, and then back to vertical to the required height above the roof. Solar Roof Jack is a product that is made for this purpose. Rerouting in the attic if accessible and unobstructed would obviously be more elegant.

Cheers, Wayne

 

[ggunn]

Exactly. I cannot do anything about plumbing vents - except go around them.
But if planning construction...... it would be nice to group them so they block as little solar as possible.

(Do not chop them shorter, they use the chimney effect to vent and need a certain height)

One of the worst cases I ran into was a commercial roof that had a matrix of 3" roof vents evenly spaced all over the roof. They were only about an inch tall, so we figured it wouldn't hurt anything if they were under dual tilt racked modules, but the spatial frequency of the vents was different from that of the racking, so no matter where we started laying out the array, pretty quickly a ballast pan would land on a vent.

 

[solarken]

Exactly. I cannot do anything about plumbing vents - except go around them.
But if planning construction...... it would be nice to group them so they block as little solar as possible.

(Do not chop them shorter, they use the chimney effect to vent and need a certain height)

It depends on the purpose of the vent. Are you referring to exhaust vents, like from a furnace or hot water tank? Plumbing vents require certain elevations above the trap they are venting, but that has nothing to do with the height of the vent above the roof penetration. In colder climates, it is important to keep the vent clear from snow cover, but cutting a plumbing vent to prevent shading or get it between or beneath a ballasted roof mount is probably not an issue in most cases. I have cut plumbing vents shorter to accomodate solar without any issues.

 

[Zee]

You may be right.
It is a Code violation in these parts though to put PV over a plumbing vent.

 

[Fred B]

We are building a new home with ADU - about 4000 sq ft.

Looking to add solar after the final inspection by the city. We are thinking of one panel with two meter slots. One for main house and other for ADU.

We are looking to add a battery as a backup from those days when there is no power (1-2 days in a year). Leaning towards 13Kwh battery that can power fridge and some lights for 1-2 days. We do not plan to use heavy appliances or EV charging for those days.

Few questions.

1. What can we do now, to make it solar-ready?
2. How many solar panels should we get? Are 10-12 panels (each generating about 400-450W) good enough to charge the battery?

Any other suggestions that you might have for us?

Thanks,

Anyone consider Solar Shingles like shown in this video: Looks like it bypasses several of the issues commented on.