Solar planning for new construction

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bunty247

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Location
Saratoga, CA
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Engineer
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,
 
One suggestion: consult with an established and reputable solar integration company who can interview you and look at your house plans to come up with some options for the system(s) you want to add to your house. PV systems, especially those which include energy storage systems, are not DIY projects, even for engineers who are not experienced in designing them.
 
keep vents, skylights, chimneys on non-solar (north, shaded etc) roofs as much as possible. You will have a nicer looking solar array and more room to place solar panels.

if roof space is tight, consider a 10 degree pitched roof or less on ADU and/or house: no fire pathways or setbacks needed.... giving you much more room for solar

consider installing a sub panel on main house (near meter) for ADU (useful for EV charger in future, maybe solar for ADU will be placed on house so it ties in here etc)

surface mount electrical panels
 
Separate the loads you want backed up into a different panel adjacent to the main panel, with a chase between them or with the wiring run through the same j-box or gutter.
 
bunty247 said:
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,
Click to expand...

I’d highly advocate against the second meter also. Common practice in the past, not necessary if you get solar. You’ll have to have two solar installs or do a net metering aggregation agreement, which usually comes with a monthly fee that simply isn’t worth it. If you want to meter the ADU, then install a customer aide sub meter. EKM makes a good one.
 
Carultch said:
Where are you getting your information that fire pathways wouldn't be needed on a 10 degree or less sloped roof?
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Pathways are required on all roofs irrespective of pitch, but for roofs of less than 2:12 pitch the rules and pathways are different.
 
ggunn said:
Pathways are required on all roofs irrespective of pitch, but for roofs of less than 2:12 pitch the rules and pathways are different.
Click to expand...
I would expect the pathways on flat roofs would follow the commercial building pathway requirements, which wouldn't help you, since this would mean a 4 ft pathway on all edges.

What pathways are required on residential flat roofs?
 
jaggedben said:
Unfortunately PG&E has been insisting on a separate meter for the ADU in many cases. But your mileage may vary.
Click to expand...

I haven’t had that here. The new business reps can be challenging though.

I just did two main residences and an ADU on a 400a (CL320) service that wanted to do one ground mount for the whole property. Made less sense to do NEMA and pay the monthly fees.
 
Carultch said:
I would expect the pathways on flat roofs would follow the commercial building pathway requirements, which wouldn't help you, since this would mean a 4 ft pathway on all edges.

What pathways are required on residential flat roofs?
Click to expand...
The same as for commercial flat roofs, a four foot clearance from roof edges.
 
Carultch said:
I would expect the pathways on flat roofs would follow the commercial building pathway requirements, which wouldn't help you, since this would mean a 4 ft pathway on all edges.

What pathways are required on residential flat roofs?
Click to expand...
As far as I can see, there are no requirements. Both IRC R324 and IFC 120.5.2.1 (for Group R-3 buildings) have exceptions which say "These requirements shall not apply to roofs with slopes of 2 units vertical in 12 units horizontal (16.7-percent slope) or less."

2021 INTERNATIONAL RESIDENTIAL CODE (IRC) | ICC DIGITAL CODES

ICC Digital Codes is the largest provider of model codes, custom codes and standards used worldwide to construct safe, sustainable, affordable and resilient structures.
codes.iccsafe.org codes.iccsafe.org

2021 INTERNATIONAL FIRE CODE (IFC) | ICC DIGITAL CODES

ICC Digital Codes is the largest provider of model codes, custom codes and standards used worldwide to construct safe, sustainable, affordable and resilient structures.
codes.iccsafe.org codes.iccsafe.org

Cheers, Wayne
 
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BackCountry said:
I haven’t had that here. The new business reps can be challenging though.

I just did two main residences and an ADU on a 400a (CL320) service that wanted to do one ground mount for the whole property. Made less sense to do NEMA and pay the monthly fees.
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If it's all going to be one address and they don't think the ADU will be rented out they'll let you do that. If you apply for a separate address for the ADU then you get stuck with a separate meter. We've seen many of these cases where it turns into a mess because for example the client originally wanted to have a separate address to make it a legal rental and then wants to backtrack to have one solar system.
 
jaggedben said:
If it's all going to be one address and they don't think the ADU will be rented out they'll let you do that. If you apply for a separate address for the ADU then you get stuck with a separate meter. We've seen many of these cases where it turns into a mess because for example the client originally wanted to have a separate address to make it a legal rental and then wants to backtrack to have one solar system.
Click to expand...

That may be AHJ related?

I just built and ADU on my rental house, separate address no separate meter. It was an existing residence though.
 
BackCountry said:
That may be AHJ related?

I just built and ADU on my rental house, separate address no separate meter. It was an existing residence though.
Click to expand...

It comes from PG&E and some of the AHJs help PG&E out with it more than others.

Also it may not get triggered if you didn't upgrade the service and therefore didn't have PG&E involved in approval.
 
jaggedben said:
It comes from PG&E and some of the AHJs help PG&E out with it more than others.

Also it may not get triggered if you didn't upgrade the service and therefore didn't have PG&E involved in approval.
Click to expand...

I did one a few months ago with an ADU, all new construction and separate addresses. Single meter.

Who knows.
 
PG&E Rule 16 and Rule 18 (found at https://www.pge.com/tariffs/index.page under electric rules)

The California Public Utilities Code give these PG&E rules its authority.
“PUC 780.5. The commission shall require every residential unit in an apartment house or similar multiunit residential structure, condominium, and mobilehome park for which a building permit has been obtained on or after July 1, 1982, other than a dormitory or other housing accommodation provided by any postsecondary educational institution for its students or employees and other than farmworker housing, to be individually metered for electrical and gas service, except that separate metering for gas service is not required for residential units which are not equipped with gas appliances requiring venting or are equipped with only vented decorative appliances or which receive the majority of energy used for water or space heating from a solar energy system or through cogeneration technology. (Amended by Stats. 2004, Ch. 694, Sec. 11. Effective January 1, 2005.)”

Same for gas meters...
 
Yeah, just because it's their rule doesn't mean they enforce it. The PUC code surprised me, state code... But codes and laws don't mean much if they're not enforced. Certainly not a building departments job, but once we learned about it we started telling applicants "PG&E may require..."
 
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