How much solar to install?

Discussion in 'Off Grid Living' started by jcsok, Oct 11, 2019.

  1. jcsok

    jcsok Monkey

    I have a dilemma. How many panels will it take to meet my future need? I have built a small cabin, but I really don't live there, so I can't realistically determine, via a killawatt meter, how much electricity I will use. In all fairness, for a 60 day period this summer, I ran an AC unit 24/7, had a refrigerator plugged in, occasionally visited the site to use the lights, and minor use of a water well. I never stayed more than a couple hours, though, because my time was limited. I did use about 24 KW according to my electric bill.

    I have many new panels, way more than I would need for the cabin, and I intend to install a 48V inverter. Would it be reasonable to install (10) 325 W panels? Just guessing.....
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  2. BTPost

    BTPost Stumpy Old Fart Snow Monkey Moderator

    Did you take into account the losses involved in Battery Charging and conversion from Dc to Ac? These losses add up...
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  3. ghrit

    ghrit Bad company Administrator Founding Member

    There is a lot more to consider. Start with expected insolation (days and hours of sunlight on the panels.) But you are WAY too early for that level of planning. You need a better load estimation averaged over cabin occupied time. You'll need a much better estimate of "future needs."

    I'll throw out a thought here, you may prefer to live with the electric bill than drop a lot of money and time into a part time dwelling. Is it fair to say that the 60 days will be an average year? Will you be able to get to the cabin often enough to do maintenance on the panels and batteries?
  4. techsar

    techsar Monkey+++

    Something also to consider, especially if you aren't going to be around the cabin...who is going to keep the panels from growing legs or becoming targets for plinking?
    Vandalism is a big problem for unattended structures. Your panels are no different.
  5. Altoidfishfins

    Altoidfishfins Monkey+++ Site Supporter+

    Oh that would suck.

    I worry about that at my remote place. Installed a gate a few years ago and began locking it. To get around the gate on foot means trudging through thick chest high scrub oak, low hanging tree branches, shindaggers and cactus. Some has grown there naturally and some sorta kinda found its way there and took root :rolleyes:.

    Never had any issues in the time I've had solar panels up here, since 2006. Other people may not be so lucky.

    I use two solar arrays, one with a battery bank to power a travel trailer, the other without a battery bank which is used only for well water pumping.

    No buildings, solar equipment, or travel trailer is visible from the entrance. Only the trees, brush and a crudely cut rocky drive can be seen so that may have helped.
    Last edited: Oct 11, 2019
  6. duane

    duane Monkey+++

    Yep, not only steal panels, mounting poles, batteries, inverters, everything, dopers all know that it is even better than copper. Pile it next to a buddies house and say you have to move and it is too heavy to take with you and it is on sale for a bargain. If pushed they also use line that it was on the house and bank foreclosed and they don't see why they shouldn't sell it as the bank has ripped them off. Dopers are worse than locusts, steal everything to feed habit and some are not only smart, but don't look like street people. Reached the point that although I live in a rural area, I don't tell people when I am going to be gone for a night, come back and lawn mowers, chain saws, tools, etc, are gone and in many cases already sold. Police really don't care and having a tape doesn't seem to help other than for insurance purposes, then they raise your rates and with the deductibles, it isn't really worth reporting. For many of us, the rule of law is already breaking down and if you do "protect" your property, you may spend more time in jail for criminal threatening and such than they will for burgerly of unoccupied dwelling in the day time and most the time they can bargain it down so it isn't a felony. The war on opioids and its bleeding hearts have made it very difficult to protect your home.
  7. Cruisin Sloth

    Cruisin Sloth Special & Slow

    Please post panel specs , 48Vdc is the way I would go , for a first time , also where are you doing this ? Not address , but area of sun ?
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  8. Altoidfishfins

    Altoidfishfins Monkey+++ Site Supporter+

    Ready for a long - winded discussion?

    158 W Monocrystalline panels X6. Two banks of three connected in series for a N.L. output of around 60 volts. That's fed into an OutBack FM80 (future expansion) MPPT charge controller to charge two battery banks, wired series / parallel for a 24 volt system. Two strings, 4 batteries each string, Trojan CG2 solar SSIG 06 255 supposedly designed specifically for RE applications.

    Since this is not a house, I went with a cheaper inverter / charger and have no complaints. It is an AIMS low frequency inverter charger w/ transfer switch. The inverter is rated 3kw, with a 9 kw surge for 20 seconds. It powers the air conditioner on the travel trailer without so much as a grunt. However, since I presently do not have enough solar to prevent battery discharging while the air conditioner is operating, I can't really run such a heavy load for more than a couple hours. For everything else, no problem.

    I can apply 120 VAC from a generator using a standard 30A RV cord that plugs into a power inlet on the side of the electrical enclosure, and the inverter / charger, once it verifies the input is valid (correct voltage /frequency) will transfer the load from the inverter to the generator while simultaneously charging the batteries. I've tried it on numerous occasions. It works, but not while running the air conditioner. That's OK. Seldom have use for the A/C.

    The well pump is a Grundfos (forget the model) designed for solar pumping with a built in MPPT. However, it will also accept up to 250 VAC. I have 9 Kyocera 51 W panels connected in series (got them as surplus for almost nothing) which under N.L. on a cold day will deliver 180 VDC. This is switched through the use of a high voltage DC solid state relay which is controlled via a dual float arrangement mounted in the water tank. The dual floats provide a hysteresis and control the on / off functions to the solid state relay through an extremely simple SCR circuit that I scrawled on the back of a napkin. The tenth 51 W solar panel charges a 12 volt battery that powers a standard RV pump which pushes water from the storage tank to supply the travel trailer.

    The area is a mountainous section on the eastern edge of the Mohave desert. So there's plenty of sun most of the time.

  9. jcsok

    jcsok Monkey

    As for location, my cabin is on about the 35th parallel, or about the same as Amarillo, Texas, or Oklahoma City. Which means a lot of sun. That's why I ran the A/C for 60 days this summer. Sure was nice to stop in to a building that was 65 degrees from the outside temp of 105. Ahhhhh....... And this was my only way to get some estimate of electricity usage. Although I installed an electric on demand water heater, I didn't turn on the hot water much. I consider hot water a luxury that can be replaced w/o use of electricity in the future.

    Security is always a concern; although I am able to visit the site regularly and easily, I realize that valuables attract legs; I just can't live there at this time. My plan is to build a rack for panels, install underground wiring from the panel rack to a very small building designed solely for controller, batteries, and genny, all of which will not be placed in the building until needed. I intend to build a rack from pipe, said rack will be able to manually pviot along two axis, one to manually change pitch of panels to follow seasons North/South, and the other axis to follow sun E/W on a daily basis. I want to design/build the rack in place now, and not subject my panels to use and vandalism at the present time, If the panels aren't in place, few people could figure out what pipe sticking out of the ground would be used for.

    And for BTPost's enjoyment, I have a handful of green gennys, 4 to 6.5 KW. I haven't accumulated enough to get rid of the green disease.
  10. oil pan 4

    oil pan 4 Monkey+++

    The only question and answer that matters:
    How much money do you have to spend?
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  11. arleigh

    arleigh Goophy monkey

    IMO the battery bank is more significant.
    If the battery is full and to powers still available where does it go?
    no where.
    One of my systems I built a large battery bank 18 all together.
    I go them for free working a boat shop . 12 volt deep cycle boat batteries.
    Some customers wanted a new battery every year. good for them, good for me.
    I got batteries the customers turned in the still had some life.
    As those finally died I turned them in to the shop again.
    I also added a small engine alternator to supplement charging during the winter months which the sun barely shone then.
    The AC generator was not as efficient fuel wise so it was reserved for especially heavy shop tools.
    We used a propane gas fired refrigerator and a wood cookstove.
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  12. TnAndy

    TnAndy Senior Member Founding Member

    Don't bother with moveable racks. For the expense you need to go to make a good one that will withstand wind, you're better off buying a few more panels and fixed mount. Add to that unless you go out there and move them every hour, you won't get enough extra to matter. I put mine on home built trackers, which in 2007 made sense since panels were $4/ under a buck/watt, it no longer makes sense....and the trouble you'll have with the really makes it a pain. I've removed mine from trackers and gone to 100% fixed ground mount.

    8" schedule 40 steel pole in several yards of concrete. Heavy steel tubing, shock absorbers to help dampen movement, and STILL got wind damage:

    Ground mount to the left. 1.5" pipe in sonotube of concrete, 3/16" galvanized angle, panels bolted to damage in 5 years. Being extended in this photo to replace trackers.
    Last edited: Oct 12, 2019
  13. jcsok

    jcsok Monkey

    TnAndy...thanks for the photos and advice. We have quite a bit of wind, and I tend to be redundantly redundant in overbuilding. In thinking of the latitude that you may be at, for example, Nashville is 36 degrees versus my 35, and I note the steep angle that your panels have. Is it worthwhile to manually change the pitch N/S with the seasons from basically flat in the summer to quite a bit of angle to the south? At this point the sun is just slightly south of overhead, but by December its pretty far southerly angle, on the short days. I have plenty of panels o_O but somewhat limited because of shading, and I don't want to install the panels in a more open area because of visibility from a road. I should be able to put up at least (12) 325 W. The distance from panels to the inverter/battery bank will be approx. 50 ft., and 50 ft to my cabin.
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  14. Cruisin Sloth

    Cruisin Sloth Special & Slow

    Panel spec,s please
    I have 325 watt and twelve , so were getting close

    Attached Files:

    Last edited: Oct 12, 2019
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  15. BTPost

    BTPost Stumpy Old Fart Snow Monkey Moderator

    We are at 48 North and in the summer they are flat, and winter the are set at 60 Straight south... this helps shed the snow off the panels... Winter Solstus , the sun is only up about 6 hours.... Also we are under cloud cover 75% of the days, so solar is just keeping the batteries charged, and not powering much...
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  16. TnAndy

    TnAndy Senior Member Founding Member

    I'm at 36.3 latitude, and mounted my panels at 45 degrees to give be more power in winter. I simply don't think it's worth (for me) having to build something that I would have to manually move.....but if the number of panels IS an issue, it might be for you, but don't look for more than 10% gain by doing so, and probably less.
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  17. Ganado

    Ganado Monkey+++

  18. Cruisin Sloth

    Cruisin Sloth Special & Slow

    I picked 3 in series over 2 due to 100 foot run of wire to combiner
    Way less voltage drop
    Real specs would well
    be true numbers , this could run a 22seer 12000BTU mini split very EZ plus good storage cold keep it running all night . Now the rest of your power uses and drain is still up in the air.

    Attached Files:

    Last edited: Oct 14, 2019
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  19. BenP

    BenP Monkey++ Site Supporter+

    Welcome and Yes, install as many as you can and go from there. I wouldn't bother with a movable mount, and if you do make sure it only moves 4 or 5 at a time, they are heavy and it's a pain. I copied some information on our setup from another getting started thread that might be helpful:

    I ran 2 water lines from my wood stove location to my water heater location. We make hot water with the wood stove (Wood Stove Water Heater) in the winter and it saves tons of power. When you do need to make hot water you will want a heat pump water heater. In heat pump mode they only draw 400w vs 4500w for a standard water heater. They also help cool your house in the summer. $1300 at Lowes. Heat Pump Air Conditioner/Water Heater

    Drying clothes is another big power user, I found a heat pump dryer (Heat Pump Dryer) that only uses 400-500w vs. 4500w for a conventional dryer and does not require a vent. We just installed this set a few months ago and they work great.


    This is our solar setup, I just use standard breakers for all my DC current, the square D Q/O series from Lowes are rated for DC current.

    Solar Panels 2600W (bought a pallet on eBay for 50 cents per watt, free shipping.)
    Schneider Electric Conext XW MPPT 60 Amp Charge Controller (x2) ($500)
    Schneider Electric Conext SW 4024 3,400 Watts, 24VDC Inverter 120/240 VAC ($1400)
    Schneider Electric Conext XW+/SW System Control Panel (SCP) ($250)
    LiFePO4 Prismatic Batteries 24V, 300Ah ($4000)

    You can make your panel mounts out of uni strut, they sell it at most big box stores as well as the hardware for it. I also did not mention Air Conditioning but you can buy a mini-split air conditioning system on flee bay pretty cheap ($700-800) that will work if you are building a small house. They also have duct versions of the mini-split that I did not know about until after I bought ours. Here is a thread with some pictures of the uni strut and mini-split system: More Panels & Mini Split A/C
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  20. arleigh

    arleigh Goophy monkey

    I don't get a lot of wind, but I bought a windmill any way and it makes a contribution of a few amps each day and sometimes at night.
    My windmill, solar panels, and battery bank are mounted on/in my shop trailer (fixed position).
    I began my solar 40 years ago using used panels, which some are still putting out 2-3 amps. old ones new ones all make a contribution no matter what size they are.
    IMO the battery bank is more important than solar panels because if the storage is already saturated the panel have no where to put the surplus power being made. IMO
    Gator 45/70 likes this.
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