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Planning for Solar Panels and Battery Backup

Michael Rose | Posted in General Questions on

Still in the middle of a renovation. We’re about to remove the mast / overhead power from the house and bury a new line to a panel in the garage.

I have already planned a 220v outlet for an electric car charger, but have recently started looking into battery backups and solar panels.

I believe a service disconnect switch is required for any electrical backup and as far as I know, we currently don’t have one at the meter (or anywhere).

What kind of things should I have the electrician put in now to make adding something like a Tesla Powerwall or solar panels much easier down the road?

Thanks,
Mike

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Replies

  1. Expert Member
    Zephyr7 | | #1

    I recommend you run your underground service inside PVC conduit. Conduit offers a lot of advantages and isn't usually much more cost to install. You may also want to run a few extra conduits for future telecommunications services to avoid the need for additional trenching in the future. I would recommend 1" PVC or HDPE conduit for this purpose. You'll need at least 2" for the power, maybe more -- the service planner at your power co can tell you what their requirements are.

    If you want a generator, you need a transfer switch. I like automatic transfer switches (ATSes) that can run the entire house, but they aren't cheap and they're also long lead time items right now. This may be something you want to consider.

    Power walls and solar panels are typically hardwired, so they need to wire directly into the panel. The best thing to do is don't recess the panel into the wall, so that the knockouts around the perimeter of the tub are accessible. If you want the panel recessed, I would run a conduit (ideally 1.25" EMT) from the panel to a good size (8" square) junction box in the area where you think you might install the future power wall or solar inverter. This junction box will be easier to access than trying to dig into the wall around a functioning electrical panel.

    Note that I also recommend placing the electric panel and ATS indoors, in the house, if at all possible. Panels exposed to the elements don't hold up as well over time, and a garage is much better than outdoors, but will still be exposed to more extreme temperature swings. Putting things in the house helps to avoid the temperature swings and the condensation that often results.

    Make sure you have a single point ground (which is code now, BTW), which basically means you need to bring all of your services (power, telephone, cable TV, anything with a conductive wire) in at the same place on your house so that all their protectors can ground to the same place. This is very important for lightning protection and also for your safety.

    Bill

    1. Michael Rose | | #4

      I believe the panel is already recessed into the wall in the garage. The garage will have a SA WRB (Mavjest 500 SA) and Rockwool in the walls (R15) so it will be somewhat insulated. I'm sure it will still get cold in the winter though. We're in northern Michigan, Traverse City to be specific.

      The walls will be plywood with screws exposed if that helps at all. I think the contractor wanted to glue them though too. Maybe I should avoid that at least in that area so the plywood panels can be easily removed?

      Without an automatic transfer switch... in the event of a power outage, I would have to go manually flip the switch to get it all going, correct?

      What about having a sub-panel of 'critical' circuits, versus keeping it all in one panel and shutting off manually what I don't want to run?

      Thanks!
      Mike

      1. Brad | | #8

        Yes to subpanel for what you want on the backup. If you're not adding a panel or doing a lot of rewiring of the panel it may not save much to do it now vs later tho.

      2. Expert Member
        Zephyr7 | | #10

        Without an ATS, you have to manually start the generator and transfer loads over. You can either use a manual transfer switch (basically a large switch that mounts on the wall), or an interlock kit, which uses a second breaker in the main panel as a "generator INPUT", and the interlock ensures the two sources can't both be on at the same time.

        A subpanel works too, and lets you use an ATS smaller than your main service. This can save some money, but I prefer an ATS that can run the entire house. You can do it either way. I would recommend against the small "generator panels" that have a bunch of seperate switches to manually transfer individual loads. I don't find those to be particularly well made. You'd be better off with a regular subpanel of the same brand as your main service panel and a small ATS if you want to go the subpanel rout. Small 16 to 24 space panels are good for this application, and they can be "main lug" style which is cheaper than the kind that include a main breaker.

        Conduit serves to provide additional protection to the cable, and allows for easier service work if that's required in the future. I try to always run underground cables in conduit for these reasons.

        BTW, another posted recommended "100 amp" cable. You don't want to do that. Run cable good for 200 amp service to ensure you're pretty future proof. 200A service is pretty standard these days, especially if you plan to go with a lot of electric appliances and an EV charger. 200A service is usually run with 4/0 aluminum cable.

        Bill

  2. Expert Member
    DCContrarian | | #2

    In terms of future-proofing, the only thing to run until you know what you're doing is the wire or even just conduit. Plans have a way of changing.

  3. James Howison | | #3

    Not sure if this is in scope, but consider moving plumbing or other penetrations onto North facing roof segments, clearing the area in which you'd like to put panels.

    If you are replacing roof at all, consider using standing seam metal where you will put panels. You can clip directly to the standing seam without penetrations and rails, which is better looking and less expensive (although the combination of metal and clips might be more expensive, but you'll have a metal roof in the meantime).

    e.g., https://www.s-5.com/products/solar-panels-on-metal-roof-pvkit-2-0/

    If you'd like to get deep into what's available in the DIY or small installer market (but all UL listed) check out WIll Prowse's channel:

    https://www.youtube.com/watch?v=2kCIFHHbKwQ

    Also have a think about whether used solar panels make sense for your project. They are already de-rated, but there is a trade off between space (need more for same output), panel cost (much lower), and labor cost (same per panel, so higher overall). e.g., https://store.santansolar.com/product/santan-solar-t-series-250w/

    1. Michael Rose | | #7

      Everything is off the south side except our kitchen vent. I wanted a straight shot on that. However, we just put on a new shingled roof a few weeks ago.

  4. matt151617 | | #5

    Run 100 amp cable, regardless of what your power requirements are now, and make sure it's run in conduit and not direct-buried. Also, as someone else mentioned, have a second run of empty conduit put in for future cables.

    Now is also a great time to think about having gas (heater), water, or sewer put in while the yard is dug up and the trencher is on-site. Personally I would have gas pipe and a water pipe put in now even if I didn't plan on using them right away.

    You can run gas/water in the same trench as electrical but there's minimum spacing requirements, so check your local codes.

    1. Michael Rose | | #6

      What's the benefit of conduit other than the obvious added protection? Ability to re-run the line without digging up the yard again?

  5. Joe Norm | | #9

    It's pretty dependant on your location and what is required by your authorities.

    Get a conduit from the roof to the utility area where the batteries may be and panel is. Depending on what system you go with, that conduit may need to be in EMT. 3/4" will be enough for a pretty large system.

    At the main panel you should create a sub panel with your backed up loads. I like mounting a good sized gutter underneath both panels where the feed runs through. This way, when it comes time to intercept it it's easy to get at. Pipes from the battery and solar can run surface to the gutter. There are a lot of ways to do it and a lot of variables so hard to plan everything without knowing what you want. But that would be a good start.

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