Off Grid Transition System

shastaron
shastaron Registered Users Posts: 24 ✭
in Advanced Solar Electric Technical Forum #1
Well we are ready to make the move to the property after we finish a couple of small projects. We are going to install a off-grid system with diesel generator backup (generator is existing). We will be living in the small 1200 sq. ft. house while we build the main house (4000 sq. ft. probably).

We would like to purchase panels that can be moved and used on the big house system when we get to that point in approximately 2 years.
1) Where is the sweet spot in the market currently on panel size?
2) What panel size would you recommend to be best suited for expansion
in 2 years? (120, 165, 180 etc.)

I am sure I will be back with more questions but thanks for the help.

Ron
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  • System2
    System2 Posts: 6,290 admin
    #2
    Re: Off Grid Transition System

    First questions that will be asked, are what do you plan on running and how much electricity are you expecting to use per day. KWH/day.
    Oh, and roughly where do you live?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3
    Re: Off Grid Transition System

    You should buy panels based on $/watt... Larger panels tend to be easier to install (few of them, fewer things to bolt down, fewer items to wire up). However, if you are on a roof and doing this by yourself--you probably don't want 200+ watt panels.

    Also, as you put panels together, they either need to match Vmp (voltage) if in parallel, or Imp (current) if in series. And, given that panel manufacturers keep making incremental changes to solar panels, it is possible that you will not find exact matches for those you purchase today, for a system upgrade in two years.

    One of the issues is that it is also difficult to add new and old batteries together into one battery bank... Typically, what tends to happen is that say you have your existing two year old battery bank with 8 batteries. And for your new home you want a 16 battery bank. The old and new batteries together will last about as long as the two year old batteries (say 7 year life, the new battery+old battery bank will last only 5 years) because the new batteries will carry more of the load until the "age" down to the capacity of the existing battery bank

    So, your best bet is probably to find a cost effective solar charge controller (like an MX 60 or other equivalent) and, more or less, max out its power with solar panels now (say on a 24 volt battery). When it comes time power the new home, either leave the old system behind for a "guest" home, or move the whole thing to the new home site as is, then add/build the rest of the system (more MX 60 controllers plus battery banks)--but keep the old+new battery banks separate.

    You can add more panel+solar charge controllers (as sets), and add inverters any time... But batteries (old+new) and mixed panels (models, voltage, current) are problematic to mix together.

    Hope the above makes sense...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #4
    Re: Off Grid Transition System

    For an offgrid home, the Sun Branded Evergreen Seconds can't be beat.

    3.34 watt , best tolerances in the industry and a great performing panel. www.sunelec.com

    If you want something with a UL sticker, they have Evergreen Seconds for 3.68 watt
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  • Ralph Day
    Ralph Day Solar Expert Posts: 1,022 ✭✭✭✭
    #5
    Re: Off Grid Transition System

    As everyone here promotes conservation (as well we should) I'll put in my 2 cents worth. 1200 sq feet sounds about right. I've lived in that space for 25 years, raised a family, pets, and can't imagine cleaning/heating/cooling/maintaining anything larger. So here's my question: Why 4000 sq feet? It will cost more to heat/cool/maintain and unless you're running a group home with 8 inmates (oops, clients) then does a primary residence need to be so big, and why?

    Sorry, this is just my pet peeve...large buildings cost more $$ to build/maintain and the resources that go into their construction cost more to the planet. I don't think i'd live in a Yurt, but space is all in the mind.

    Rant over

    Ralph
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #6
    Re: Off Grid Transition System
    Ralph Day wrote: »
    I don't think i'd live in a Yurt, but space is all in the mind.

    Here's a little shoe box for ya...

    If someone is running a home business, and needs 2 offices, a place to entertain clients..... There could be many reasons.
    I've lived in a yurt, but while comfortable by USA standards, in mild weather, in winter they are cold. I didn't have yak hides to wrap it with, but I don't think they get very warm.

    You can build your panels on poles, or other ground mounts, build a battery/generator shed between the 2 buildings, and stub off service to the main house. 120Vac can be run a long way. Consider making a auto-start generator (propane or diesel) part of your system, as a battery bank for even 2 days of cloudy weather, for a monster house, will be prohibitively huge.

    I'd suggest beginning with a 48V system, out of a single string of 6V batteries, and then when you expand to power your monster house, you can continue with the same inverter & charge controllers, and expand inverters & panels as needed. You will learn from your mistakes, and as you upgrade, you won't fry the expensive advanced batteries. And the original string can still power the small house.
    Powerfab top of pole PV mount | 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 ,

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  • shastaron
    shastaron Registered Users Posts: 24 ✭
    #7
    Re: Off Grid Transition System

    Some good information. Please keep the thoughts coming. The diesel generator is a 10K. Wayne I am still doing the energy calc's. I hope to learn a lot from the small house and design the systems to be expandable to meet the needs of the growing family. We are working on conservation and taking advantage of the climate for the houses and agriculture to help sustain.

    In regards to size. It will be a combined two family household with two independent living areas. Grandma and Grandpa will live in one smaller part of the big house. Mom and Dad with 4 kids in the main part of the big house. Two offices for home businesses.

    We have pretty mild climates. We planned well and have good southern exposure at 39 degrees lat. Afternoon up-slope breezes during the hot weather will cool us with lots of shading (not on the panels). We will be using wood and/or pellet for heat. A large propane tank so we can buy in bulk will fuel the stove, dryer and supplement the solar water heater. I also plan to play with some passive hot air panels to warm the detached shop. Our well will be solar to the main storage tanks (large) and then gravity feed to the house and irrigation areas. The well is only 150' so we can pump up to the storage tanks to give us good head pressure.

    Passive design will be a part of the construction.

    Ron
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