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New solar install planned during renovation. What do I need to know?

Discussion in 'Tesla Energy' started by democappy, Jun 7, 2018.

  1. democappy

    democappy Member

    Joined:
    Jul 13, 2016
    Messages:
    189
    Location:
    Charlotte, NC
    I am pretty new to thinking about getting solar, but I am in the very early stages of renovating a house which includes lot of additions, new roofing, and new electrical. The house also has a back roof facing south. Seemed like the perfect time to add in solar during that construction process. However, I don't really know what I need/want yet because there doesn't seem to be a ton of info online that doesn't just say to call an installer. My goal is simply to offset as much of my electrical use with solar as I can. I would also like to have a battery back-up, but it doesn't need to last a super long time off grid. Located in Charlotte, NC with my power through Duke Energy. Our energy costs are also fairly low here if that impacts your answers.

    Here are my questions:
    1. It seems like just straight forward buying of a powerwall 2 is something you can't do. If battery storage is a secondary concern, does it make sense to set the whole system up to 100% utilize net metering and just leave space for the batteries to be added later? Do you think it is worth waiting for powerwalls to become available versus just using a different companies whose batteries I can get now? The powerwalls seem like a best deal out there assuming you can buy them in the next year or so. Batteries in general seem like a waste of money here (no peak pricing), so I would be doing it entirely because I want to and like the idea of having the back-up.
    2. If you were building a new house and planning to add solar, would you make everything you could electric? For example, should I make sure to use electric home heating, electric tankless water heater (would do this anyway), and an electric pool heater? The stove top, fireplace, and grill are the only things I can think that I would probably have to keep as natural gas. Any disadvantages to doing this?
    3. How much should I worry about roof pitch? I am still in the architectural design stage and I could try to force the issue. However, I really like the interior design so far and I don't want to mess it up by making roof pitch requests if it doesn't even matter that much.
    4. Should I try to limit my array to <10kW? Duke Energy seems to have rule changes on net metering and rebates at the <10kW and <20kW tiers. Would you just go for as much solar as I can fit or would it make sense to limit it?
    Any other things that you think I should be thinking about as I talk with my architect and builder about my plans to add solar?

    I appreciate the help.
     
  2. thx1139

    thx1139 Member

    Joined:
    Aug 1, 2014
    Messages:
    421
    Location:
    Lemont, IL
    1. We live in Illinois and since we have Net Metering we did not add batteries. Just seemed an unnecessary expense. Only reason would be for back up, but in our area power outages are rare. Maybe if we had something that would get badly damaged if power was out we would add.
    2. I think it depends on just how much power your array would generate.
    3. Cant answer the pitch question. Our new home was semi-custom and we couldnt change. One thing I have noticed is that summer sun hasnt caused our peak days to be much larger then winter. Overall during the month we produce much more, but our best day was in early April. This is because the sun is higher in the sky so the pitch if our pitch was flatter we would be generating more in summer. Maybe less in winter. I dont know.
    4. I think an installer would be able to answer this.

    Get multiple bids.
     
    • Informative x 1
  3. Rockster

    Rockster Active Member

    Joined:
    Oct 22, 2013
    Messages:
    1,774
    Location:
    McKinney, TX
    #3 Rockster, Jun 7, 2018
    Last edited: Jun 7, 2018
    I started with my usage. By looking at my usage over the past few years I could gauge how much of that usage I could offset with my available roof area. In my case, my roof is the limiting factor: I can only offset about 2/3 of my energy usage with solar. Other than adding a ground array (which was vetoed by my wife) a 10k system was pretty much all I could do.

    In your case, though, you have two variables: how much do you want to increase your electricity usage and how much solar might you want (not to mention the question of battery usage). In your case, I would probably first answer the question "What is my maximum production capability?" If it's less than your current usage then there's not really any point to swap out gas appliances for electric ones. Similarly, if you're using more electricity than you could ever produce that probably reduces the usefulness of a battery. (It's still a cool backup tool, but storing reserve solar for use at night isn't likely if you can't even offset usage.)

    Your electric company's policy on cogeneration is a factor, too. If producing more than 10k becomes a hassle, that's a barrier for you, too.

    In summary, I would:
    1. Calculate the theoretical maximum that a system on your house could produce. There are sites out there that will scan the google earth image of your home and predict this.
    2. Determine how much of your usage would be offset by this theoretical max.
    3. Go from there.
    And there's nothing wrong with calling a professional. They're used to working with people in this initial decision and planning stage. I met with five companies during a one year period to plan this and finally implemented a 10k system.
     
    • Informative x 1
  4. democappy

    democappy Member

    Joined:
    Jul 13, 2016
    Messages:
    189
    Location:
    Charlotte, NC
    Thanks for the responses so far. One thing that I will address is my energy usage and possible energy generation. I have no idea what it will be. The house is going to be changed by a lot. This renovation will more than doubling the sq footage of the house, adding a pool with heater, changing the roof, removing trees, etc. So I feel like I am going in a little blind.

    The batteries being a waste of money is about what I expected to hear, but good to get the confirmation. My wife really wants them, but power outages are very rare by us.

    Sounds like most of my questions may need an installer to look at my specific situation as there are so many different factors.

    Please continue letting me know what the correct questions to ask should be and what I need to be considering in my decision making process.
     
  5. SoundDaTrumpet

    Joined:
    Jun 22, 2017
    Messages:
    171
    Location:
    Bay Area, California
    1. I have modeled 80% net metered solar + PW and 100% solar. 100% solar is most cost effective. Storage is very expensive. Storage is okay to pay for if you want backup. Tesla's battery system is the lowest cost per kWh. Traditional lead acid is cheaper, and I perceive not as compact. If the purpose is backup, you could size up to 300% and still benefit prolonged winter outage, which marches closer to being off-grid.
    2. All electric home? Factor in speed. Electric dryer takes 2X to dry than gas cousin. Only heat pump storage water heaters can compete with gas, but heats water up slow. Stove can be electric --- see the new fashion of induction stove which can heat the pan faster than gas. I did think about changing my half-busted outdoor stove to induction, but outdoor units don't exist. At least in a power outage most appliances work. A gas stove works with a lighter. Some other gas appliances still need electricity. New entrant into this space include energy star gas water storage (need electricity to operate a damper). During a power outage I will still have the outdoor stove & grill to cook/attempt to bake.
    2a. After PW install, I will have excess credits. and opportunity to reduce gas bill and eat up electricity credits. I am planning switch to easier to clean/faster to boil water induction stove after PW install (I am on an Electric Vehicle rate plan which charges ~$0.50/kWh during dinner).
    3. Roof pitch: I expect the trend is to pitch the roof towards the west now to catch the sunset. It depends if you are after maximizing solar credits or solar energy. If on a flat rate plan, you favor total output at noon. If on a time-of-use, you aim for the sun during dinner. NREL's PVWatts calculator is excellent.
    4. Recommendation: Put in an unfilled 3/4" conduit from near the electric meter to the attic. This will hide the conduit. Please avoid running conduit on your roof. The in-the-wall conduit will have it so the solar contractor doesn't need to open a huge opening to route conduit to break into the eave. My guys brought in stucco experts to patch up afterwards. In my install, the conduit runs vertical from inverter to the eave, punches thru, sharp hard turn into the attic. Also, a separate conduit for inverter data (NEC prohibits mixing power and data in the same conduit / wall cavity).
     

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