New guy to the forum. Need small off grid system input

MIhunter
MIhunter Registered Users Posts: 1
in Off Grid Solar & Battery Systems #1
My apologies up front as I am sure you guys get tired of seeing the constant "new guy" threads daily. However I am trying to wrap my head around this project of mine and need some insight. Here is my issue.......

I have a family owned hunting cabin in the U.P. of Michigan just off of Lake Superior. It consist of 250 acres with a 1400sqft log cabin about 2 miles off the the lake and power grid. I looked at running power back to the property but they want $60K to do it. Thats not going to happen anytime soon. Currently everything is being run off of a generator that is need to include basic lighting and power tools as need. The place is very quiet and and we love the area. We are also tired of burning though gas and hearing the generator run just for a couple of lights 4-5 hours per night. My goal is to get us off the gas and onto solar just for the basic lighting of the place.

Now, this is only a occasional use property and it may see activity 6 to 8 weeks per year. This is mostly during bear/dear/fishing seasons in the fall/winter when direct sunlight is at it's lowest. Here is what I am looking at as far as a system..

(2) 235 Watt Sharp mono panels (24v)
(4) 6v Batteries wired in series
(1) Sinewave converter (not 100% sure on size yet)
(1) MPPT contoller (Morning Star 45amp

I want to stay at 120 AC so I may be able to charge a laptop or phone along with a couple other occasional use items and ease of use. The current light is 8-- 75watt lights and one exterior 120watt flood. I already have the LED's to swap out so that will lower my consumption. So if I were to run all 8 lights at once (worst case) for 5 hours at night, I am looking at 15watts x 8 lights = 120 watts x 5 hours = 600 watt hours per day. Here are my main questions....

1. Is my system large enough to accomodate my needs even with the winter sun exposure?
2. Because this is occasional use only, do I need to disconnect the batteries ect when I leave?
3. Is this over kill for what I need?

Any info is welcomed.
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: New guy to the forum. Need small off grid system input

    Welcome to the forum.

    Sounds like a nice place to me. :D

    600 Watt hours is fairly small. You will probably find that once you have that, you want more. Be prepared!

    Batteries come in many Amp hour capacities, so saying four 6 Volt batteries doesn't mean much. For that small of a system you could use a 12 Volt system (Morningstar makes a very nice 300 Watt 12 Volt inverter). In that case you are looking at approximately 110 Amp hours @ 12 Volts minimum. This means a set of 'warehouse' golf cart batteries would do nicely: 220 Amp hours @ 6 Volts times two to get 12 Volts. That's up to about 1200 Watt hours, or two days' worth at your estimated needs.

    Now as for recharging them two 235 Watt Sharp panels is more than enough. But they would require the MPPT controller due to the Voltage difference. (In fact since they are 30 Vmp they would need the MPPT controller for a 24 Volt system too.) That would be 470 Watts, enough for up to 300 Amp hours @ 12 Volts on a good day. Not all days are good, though, so having this 'extra' capacity may be quite helpful for those Michigan Winters.

    On a good day that 470 Watts would yield about 977 Watt hours AC. On a bad day? How bad does it get? Really bad.

    But you have a generator! When you're there and need power you can bulk with the generator through a stand-alone battery charger. When you're not there and not using any power the panels will still provide enough to keep ahead of the self-discharge rate; just disconnect all loads and make sure the panels can get whatever sun will be available (tilted to Winter angle or more to keep snow off).

    How are we doing so far?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3
    Re: New guy to the forum. Need small off grid system input
    MIhunter wrote: »
    My apologies up front as I am sure you guys get tired of seeing the constant "new guy" threads daily. However I am trying to wrap my head around this project of mine and need some insight. Here is my issue.......

    Welcome to the forum... We never tell folks (new or old) to go use the search tools to find the "answers". If you knew enough how to find the answers, you probably are 80% to knowing them anyway.

    Many of us here that help to (sometimes correctly) answer questions started in very similar state to you. Been there, done that.
    I have a family owned hunting cabin in the U.P. of Michigan just off of Lake Superior. It consist of 250 acres with a 1400sqft log cabin about 2 miles off the the lake and power grid. I looked at running power back to the property but they want $60K to do it. Thats not going to happen anytime soon. Currently everything is being run off of a generator that is need to include basic lighting and power tools as need. The place is very quiet and and we love the area. We are also tired of burning though gas and hearing the generator run just for a couple of lights 4-5 hours per night. My goal is to get us off the gas and onto solar just for the basic lighting of the place.

    Yea--most any of the solutions are not cheap... Honestly, if you can get away with it a small genset (like a Honda eu2000i), four golf cart batteries, a small TSW 120 VAC Inverter, and a small AC battery charger is probably the place to start--You can add some solar panels to reduce generator run time and keep the batteries charged in the off seasons.
    Now, this is only a occasional use property and it may see activity 6 to 8 weeks per year. This is mostly during bear/dear/fishing seasons in the fall/winter when direct sunlight is at it's lowest. Here is what I am looking at as far as a system..

    If you have clear skies during much of the time--Solar can still work OK... If you have dark winters (overcast)--You really cannot expect much from pure solar.
    (2) 235 Watt Sharp mono panels (24v)
    (4) 6v Batteries wired in series
    (1) Sinewave converter (not 100% sure on size yet)
    (1) MPPT contoller (Morning Star 45amp

    I want to stay at 120 AC so I may be able to charge a laptop or phone along with a couple other occasional use items and ease of use. The current light is 8-- 75watt lights and one exterior 120watt flood. I already have the LED's to swap out so that will lower my consumption. So if I were to run all 8 lights at once (worst case) for 5 hours at night, I am looking at 15watts x 8 lights = 120 watts x 5 hours = 600 watt hours per day. Here are my main questions....

    1. Is my system large enough to accomodate my needs even with the winter sun exposure?
    2. Because this is occasional use only, do I need to disconnect the batteries ect when I leave?
    3. Is this over kill for what I need?

    Using PV Watts for Traverse City Mich--Tilted to ~45 degrees, fixed array: 
    Month    Solar Radiation
(kWh/m 2/day)
1      2.30     
2      3.55     
3      4.98     
4      5.34     
5      5.59     
6      5.70     
7      5.63     
8      5.23     
9      4.55     
10      3.30     
11      2.20     
12      1.68     
Year      4.17

    Lets say bear season is around 2.2 hours of sun per day. The estimated AC power output from your array would be:
    • 470 watts * 0.52 system eff * 2.2 hours winter time sun = 538 Watt*Hours of AC power per day (average)

    So--At least you are close to your requirements.

    Regarding battery bank--1-3 days of no sun and 50% maximum discharge--start with 2 days:
    • 600 WH per day 1/0.85 inverter losses * 1/12 volt battery bank * 2 days no sun * 1/0.52 system eff = 235 AH @ 12 volt battery bank

    So, my suggestion would be for 2x 6 volt @ 220 AH golf cart batteries in series for a 12 volt battery bank. And I would suggest this MorningStar 300 watt TSW 12 VDC inverter (with standby power settings).

    You could go with a larger array and get some more solar power...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #4
    Re: New guy to the forum. Need small off grid system input

    Welcome,

    A couple of thoughts.


    All choices stem from the load calcs, any other way, and you replicate the single most expensive mistake in off grid PV,, that is "ready, aim fire!". That said, the next rule is,, that loads ALWAYS grow with time,, so do your calcs, and then add in a reasonable margin for growth. Next, people almost always over estimate thier solar potential,, so e reasonable in your expectations. Finally there is my simple rule of thumb for of grid folks: Take the name plate rating of the PV, divide it by two to accout for all cumulative system loses, then take that number and multiply it by 4 to account for the hours of good sun you can expect, on average, per day over the course of the year.

    So a 500 watt PV system would look like this,,,500/2=250*4=1000 WH/day. Your estimate of 600 WH/day is pretty low. We do that, but we have a tiny house, and limited needs. I might aim for 1 kwh/day as a place to get. (I would also get rid of the 75 watt incandescent bulbs and live with CFLs or LEDs for that function.

    Remeember, as you calc your loads, you will end up with a radio, perhaps a tv, or sat box, or cell phone charger,,perhaps an ISP system eventually. Pumping water and the fridge are other issues. LP fridges are a pretty good bet for occasional use, but conventional fridges are a better bet as you come closer to full time. Your fall insolation is likely to be a problem, so I would do a good PV watts calc, weighed heavily for the fall.

    Good luc, and keep in touch,

    Tony
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  • CATraveler
    CATraveler Solar Expert Posts: 98 ✭✭✭✭
    #5
    Re: New guy to the forum. Need small off grid system input

    When I last lived in MI it was very overcast for many days and it could get downright cold. If fact we cheered when the sun came out...

    Also being a family cabin what about battery maintenance when it's cold? If someone departs with a light on or batteries not fully charged or just the disconnect on and it snows then the batteries might freeze.

    Something to consider.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #6
    Re: New guy to the forum. Need small off grid system input

    A fully charged FLA battery won't freeze until -40. Use a positive disconnect for the loads when you leave, leaving he charge regimen in place.

    Cold will not hurt batteries but will only decrease capacity while cold. Cold actually adds longevity.


    http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

    http://www.batteryfaq.org/

    Also consider mounting your PV on the wall, on hinges. That way you can properly orient them while you are there, but fold them against the wall so that they won't accumulate snow when you are gone. I have a set of batteries that are on float 11 months a year in a climate equally cold, and they ar12 years old.

    Tony
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