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  • Hybrid - Solar/Battery/Generator Combo?

    Hi all,

    We are building a new, rather large, house and wanted to find out how practical a solution using solar panels and batteries would be or if we should just get a big generator and call it a day? The house will be about 12,000 sq ft and we have estimated we need a 100 kWh generator to power the home and all appliances in the case of an outage. I believe we'd have enough solar panels to be able to make it work out, but using something like the Tesla Power Wall 2 batteries seem to leave us woefully underpowered for any substantial outage (and only 50 kWh output for 10 of them). The Blue Ion 2.0's can be stacked and each have 16 kWh's so you could theoretically do about 10-12 of those with a 9 kWh output per (max) and be able to get 100+ kWH of throughput. We have 2 Tesla EV's so that is part of why the power output is so high. We estimate using 16,000 kWH per month during peak summer months.

    So basically my question is can something like this be done practically? I'd like to have solar to help offset power costs during regular usage, but also have a backup system to power the entire house for multiple days if necessary (off grid). Would you rig the solar panels to power the batteries and then have a generator with an auto transfer switch to power the batteries? Is that the best practical solution?

    thanks for the insight.

  • #2
    Whoa. 100Kw is power for a small town.

    If you mean 100KWh per day, that's enough for 3 or 4 houses.

    You are likely better off getting Grid power brought in. Building up a 100Kwh -daily off grid system, means you need storage reserves for at least 3 days. Then you start the generator. As you have already noticed, batteries are small & expensive and you will need quite a few of them. And at this scale, you need 3 identical backup generators, if you want reliable power. And a fuel depot.

    Or you could super insulate the house, follow Passive Haus guidelines, and save a lot of energy. Of course you have somewhat higher construction costs with it, but with a 12,000 sf house, that's not looking to be a issue.
    http://www.passiv.de/en/index.html

    You wire up the house for "normal" conditions, and then for the backup - you wire "Critical Circuits" grandma's Iron Lung, beer cooler, mini-split heat pump for the pool house, you know, ONLY the things you need to survive until the main power comes back on.
    Something of this scale, you will need to model it quite well, and then have a solar engineering firm verify - this is too large to throw money at and find out afterwards it's only half the size needed, and grid power Would be better.
    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister

    Comment


    • #3
      100kWh would be the generator size for peak output. It would be about 500kWh per day in consumption total.

      I guess system size aside, what would be the best way to construct a solar panel system with battery backup to power the whole house and having a generator available to recharge the batteries to supplement solar generation? The generator would be a Generac or equivalent running on natural gas that can supplement the batteries since presumably we wouldn't be able to generate enough energy daily from solar alone. So at some point during an extended outage, you would need the generator to supplement the power usage if the house is used "normally" with all circuits on.

      Yes, I will certainly get a solar engineering firm involved, but wanted to see if it was something practical to begin with: a 3 phase system with 1) solar panels 2) battery 3) generator all connected to the grid for solar savings daily + extended backup protection when necessary.

      Comment


      • #4
        Originally posted by aviator1960 View Post
        It would be about 500kWh per day in consumption total.....
        Price out a 100KW PV Array. (That's my rough, first Guess) (Racking, inverters)
        then price how much to have Grid brought in.

        Batteries - I doubt you can afford them. 12K sq ft - OK, you CAN afford them but I suggest they are pointless.

        My really honest suggestion :
        Install Grid power, add 2 backup generators, and Auto Transfer switch. Just like a hospital. They don't have batteries, and live with the
        30 seconds it takes to spin up the diesel backup. They only have one Backup outlet in each room, and don't do much for lighting.
        If you want solar, install Grid Tie (no batteries) and backfeed the grid daytimes, to unwind your meter

        If you go off-grid and batteries, I suggest a couple banks of 24v lead acid forklift battery packs. Use a 48V system You will need 100 - 150Wh of PV +controllers, racks, & inverters
        Build a dedicated Battery house, Electronics house, and Generator house. Keep all 3 in separate buildings - if one burns up, you can limp by with the other 2 for a while.
        Don't use sealed batteries, you can afford someone to water and maintain the system for you - allow 3 hours per week.
        If they are all-in-one, and something bad happens, you are up the creek till you can call a movie rental company and rent a trailer mount generator to run from till you rebuild.

        Last edited by Mike90250; 11-26-2017, 10:17 PM.
        Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
        || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

        solar: http://tinyurl.com/LMR-Solar
        gen: http://tinyurl.com/LMR-Lister

        Comment


        • #5
          Solar is a terrible choice for backup power, for a number of reasons. I got a generator decades
          ago, only used it for real 4 times. Bruce Roe

          Comment

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