Just starting out

An old girl
An old girl Registered Users Posts: 9 ✭
in Solar Beginners Corner #1
This is going to be the first of many posts as I grow into my understanding and application. The setting: old girl working towards retirement - 2 years to go! Cabin in the mountains - no hydro. My goal is to build an efficient solar system to take care of my needs at the cabin AND THEN to expand this to my retirement home (1000+sq ft plus full basement approx 25X30 ft).

To begin with I have a compostable pottie that requires a fan to run 24/7 (winter, summer, rain, snow, shine). I have no idea of the wattage of the fan, but running it off a fully charged 12V 3.6AH battery gives me approx 13 hours. I only have a 1Watt solar panel at present - so recharging the battery fully takes a while and it is not powerful enough to actually run the fan during the day (duh!). I had read that 30 Watt panels with a 12V 100AH battery would be what I require. I checked out the prices and thought this might be overkill for my application.

So I need your help!

Thank you
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
    Re: Just starting out

    now i'm not a toilet expert and maybe the guys will have better suggestions for handling the subject, but if you must run this or anything else electrical that you must know the power consumption and how long it is consumed to know how much pv to replace it with. in general you will find solar to be a bit of an expense so doing things more efficiently is a must unless one has a large wallet. also you will need a clear view of the sky at the proper angles during daylight hours which means you don't want to find that your pvs are being shaded by trees, especially in the winter when the sun is low in the sky.
    simply put, your loads must equal or be less than the power source minus all losses.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #3
    Re: Just starting out

    Here's a older thread, with LOTS of good compost toilet info.
    http://forum.solar-electric.com/showthread.php?t=5999
    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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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #4
    Re: Just starting out

    Go with a different toilet system if you can!
    I'm traveling and will writer more later, but composting toilets, especially in cooler climes are a tough thing to make work well.

    Tony

    Should be home in a couple of days.
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  • An old girl
    An old girl Registered Users Posts: 9 ✭
    #5
    Re: Just starting out

    Thank you for all your advice. Here is a bit more info: this type of composting toilet does work well in a northern climate. The trick is seperating liquid from solid (which is what Sepparet is about) and 24/7 ventilation. I have been composting, spring, summer, fall and winter for years and no problem even here up north: it does take a routine! In terms of the wattage needs the manufacturer specs says 2.5w in one spot and 25w in another. Since math is not my forte, I thought that running it with the 12V 3.6AH battery would give me an idea! So I think that since it took 12-13 hours to deplete the battery that it must be 2.5w. What do you think? So if it is 2.5w, what kind of system should I put in place to ensure it works 24/7, including possible days where the snow accumulates on the solar panel (the solar panel(s) will be in full sun, open area, facing south, ideally mounted on the ground)ie factor in reserve power in the battery (ies). I know this will be probably overkill for a toilet, but as I said, it is a beginning on which I will add to power the cabin (one room - a few lights, LCD monitor, DVD player, small pump, radio that I currently power through transportable batteries that I recharge at home), so I am not too concerned about the cost as long as I feel that I am not overdoing the system in line with the application. Do I really need a 12V 100AH battery with a 30 watt panel just for the toilet fan? Thanks again!
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    #6
    Re: Just starting out

    OK, for the fan, roughly:
    • 12 volt * 3.6 AH / 12 hours = 3.6 watts estimated load
    So, ~2.5 watts seems like a real number (a 2.5 watt DC fan is a small computer fan--A 25 watt fan is a pretty large computer fan).

    So, lets guess you are near/have weather like Montreal Canada. Using PV watts website, assuming 0.52 derating (efficiency) and fixed mounted solar panel, and 1,000 watts / 1 kW of solar panels for nice round number:
    "Station Identification"
    "City:","Montreal"
    "State:","QU"
    "Lat (deg N):", 45.47
    "Long (deg W):", 73.75
    "Elev (m): ", 31
    "Weather Data:","CWEC"

    "PV System Specifications"
    "DC Rating:"," 1.0 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 0.5 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 45.5"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 0.1 Can$/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value (Can$)"
    1, 3.24, 55, 0.05
    2, 4.02, 62, 0.05
    3, 4.40, 72, 0.06
    4, 4.61, 67, 0.06
    5, 4.77, 69, 0.06
    6, 5.12, 70, 0.06
    7, 5.62, 78, 0.07
    8, 4.76, 66, 0.06
    9, 4.92, 69, 0.06
    10, 3.66, 55, 0.05
    11, 2.01, 29, 0.02
    12, 2.10, 34, 0.03
    "Year", 4.10, 726, 0.63

    So, if you want "year round" power for your fan, December looks like the worst month:
    • 34 kWH per month per 1,000 watts of solar panel
    • 34,000 WH / 30 days = 1,100 WH per 1,000 watts of panels per day
    • 2.5 watts * 24 hours per day / 1,100 watts per 1,000 watts of panels = 54.5 watts of solar panels
    Battery size, we normally recommend 3 days of no sun and 50% maximum discharge. For a 12 volt battery bank:
    • 2.5 watts * 24 hours * 1/12 volt bank * 3 days * 1/0.50 max discharge = 30 Amp*Hour @ 12 volt battery bank
    Note: I have been a bit conservative using 0.52 for a derating factor (usually we use that for an AC inverter with 85% efficiency).

    Also, you have weather issues--if there is a week or so of heavy clouds, then you will need either a LVD (low voltage disconnect) to turn off the fan or a backup genset to recharge the battery bank during inclement weather.

    The main thing you want to watch out for is 1. Running your battery dead, or 2. Running your battery at less than ~75% state of charge (75% full) for days/weeks/months at a time. Either of these conditions will kill a Lead Acid Battery Bank in months--instead of getting 3-6+ years of life from your bank.

    If you are present during bad weather--you can always start up the genset. If you are gone--Then you can probably turn off the fan (button-up for unoccupied seasons) to save the battery bank. And/or, just use a small 5-10 watt solar panel (mounted on a vertical wall protected by an overhang, possibly even a "high" vertical mount will shed snow) directly connected to the fan so you at least get some venting during the winter (you don't want the fumes to accumulate in the cabin/home if in the occupied building).

    If you build the system with larger solar array and battery bank (to support your other A/C loads)--Then you will probably have enough solar panel + battery bank for those times when the cabin is unoccupied to run your small vent fan.

    I would suggest you get a DMM (digital multi-meter) so you can measure the fan current/load accurately anyway... You want to design your system to your real loads--not a guesstimate.

    You can use a Kill-a-Watt meter (a K-a-W meter is highly recommended for measuring your home loads too for conservation) for your A/C loads and a DC Amp*Hour / Watt*Hour meter to measure your DC loads (if you have a lot of DC loads).

    Eventually, if you build a "full sized" off-grid solar power system, you may want to look at a Battery Monitor. They can help you understand your loads/charging with respect to your battery bank (sort of like a car's fuel gauge).

    Batteries are the only part of your off-grid solar system which can be killed with improper maintenance/usage:

    Deep Cycle Battery FAQ
    www.batteryfaq.org

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • An old girl
    An old girl Registered Users Posts: 9 ✭
    #7
    Re: Just starting out

    Thank you very much, Bill, for the insights. I am located 3 hours NE of Montreal.

    Since I am still all tangled up with understanding the calculations, should the calculation not have been done on November at 29KWh and 2.01 KWh/m^2/day? If so then I would need 60 watts of solar panels. Wow! and I thought the 30 watt solar panel was expensive!

    Looking at the table, if I am reading it correctly, is it indicating that the cost of electricity is 0.1 CAD$/KWh whereas solar energy costs 0.63 CAD$/KWh, six times more?

    I guess I could disconnect the fan in the winter months, since I only go up to the cabin for snowshoeing, but I certainly do not go as often as during the other 3 seasons. I like the idea of a direct connect vertically mounted small solar panel since the "outhouse's" back side faces South :roll:

    I guess that when I would disconnect the fan from the 12 Volt 30AH battery, I would keep it charged up with the solar panels (with a controller to prevent overcharging?).

    However, if I would have a 12 Volt 100AH battery, would that be sufficient, combined with a 60 watt panel to 1) keep the fan going 24/7 (365)? and 2) ensure the battery does not get discharged more than 25% at a time (unless I use it for other purposes of course)?

    That is sure a great start for me. Thanks again....Marie
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    #8
    Re: Just starting out
    An old girl wrote: »
    Since I am still all tangled up with understanding the calculations, should the calculation not have been done on November at 29KWh and 2.01 KWh/m^2/day? If so then I would need 60 watts of solar panels. Wow! and I thought the 30 watt solar panel was expensive!
    Oops--Yes, I missed that November was slightly less production. :blush:
    Looking at the table, if I am reading it correctly, is it indicating that the cost of electricity is 0.1 CAD$/KWh whereas solar energy costs 0.63 CAD$/KWh, six times more?
    No--That last number says that your off grid system (1,000 watts of solar panels charging a battery bank and running AC loads, or your fan) will generate about $0.63 Canadian worth of useful electricity per year...

    However, looking at the data--It looks like the PV Watts program has an error in it... It is basing the price of power closer to $0.0001 per kWH.

    1,000 watt of solar array would generate around 726 kWH per year. Or, at $0.10 per kWHr would be worth $72.60 per year vs Grid Power.

    Boy--you are just finding a ton of mistakes today--I could have used you during Code/Hardware reviews. ;)
    I guess I could disconnect the fan in the winter months, since I only go up to the cabin for snowshoeing, but I certainly do not go as often as during the other 3 seasons. I like the idea of a direct connect vertically mounted small solar panel since the "outhouse's" back side faces South :roll:
    You could put a switch that switches to Battery Power when you are there, or to a small XX watt panel for during the winter/when you are not there.

    The big thing is you don't want the fan to discharge your battery bank during the winter/when you are not there if there is a stretch of bad weather. That will kill a lead acid battery (storage below ~75% capacity--which quickly "ages" or sulfates a battery bank; or taking the battery below ~11.5 volts (less than 20% state of charge which will kill cells).
    I guess that when I would disconnect the fan from the 12 Volt 30AH battery, I would keep it charged up with the solar panels (with a controller to prevent overcharging?).

    Yep, you got it...
    However, if I would have a 12 Volt 100AH battery, would that be sufficient, combined with a 60 watt panel to 1) keep the fan going 24/7 (365)? and 2) ensure the battery does not get discharged more than 25% at a time (unless I use it for other purposes of course)?

    You don't want a "huge battery" and a small solar panel--they don't do a very good job of properly recharging the battery bank and self discharge from larger panels will need more solar power to keep the battery charged... Our recommended minimum solar panel (5% to 13% rule of thumb battery charging rate) to battery ratio for a 60 watt panel is:
    • 60 watts * 0.77 derating * 1/14.4 volts = 3.2 amps
    • 3.2 amps / 0.05 minimum charging rate = 64 Amp*hour for 12 volt battery bank
    It is not that I am saying that a 100 AH battery bank will not work, but it may not have the performance/lifetime that you may get with a smaller battery bank--It is just that a larger battery would do very nicely with a larger solar array.
    • 100 AH * 14.4 volts charging * 0.13 max charge rate * 1/0.77 derating = 243 watts of solar panel
    • 100 AH * 14.4 volts charging * 0.05 min charge rate * 1/0.77 derating =94 watts of solar panel
    So, for a 100 AH 12 volt battery bank, the "optimum" range of solar panels would be around 94 to 243 watts.

    Again, the above are just very rough numbers---You can certainly go above or below these numbers--just the farther away the more one thing or another goes out of kilter (too little charging current, electrolyte does not stir correctly, takes a long time to recharge the battery bank; Too much current, waste of money on solar panels and could, in some cases, overheat the battery bank)...

    But, sometimes it is OK to go outside those numbers too... For winter storage--you can get away with smaller panels. For AGM batteries, you could use smaller panels as well too. Or, if you have a lot of power to use during the day (water pumping, work shop, etc.)--then an extra large array can be used to power those loads while the sun is shining.

    In the end, you have other loads to power--So, if you end up powering those with solar (or solar+backup genset and battery charger)--the small fan becomes less of a factor in the overall design as it is swamped by the games/dvd/computers/etc.

    Hope that helps.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • An old girl
    An old girl Registered Users Posts: 9 ✭
    #9
    Re: Just starting out

    Certainly is extremely useful information, Bill.

    Based on everything you are telling me, I think it probably makes more sense to total up my overall power needs now and go from there instead of just focusing on one 2.5watt fan!

    At the end of the day, I will most likely look at loads when I go there more often and stay longer, compared to when I go there less and stay less time(ie winter) and come back to post my proposed design.

    In for a penny, in for a pound, as they say in England!

    Thank you again for all the time you are spending helping me :D

    --Marie
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    #10
    Re: Just starting out

    You are very welcome Marie.

    By the way, look at Tony/Icarus' setup (a few posts back up the thread)... He lives in Western Canada (if I remember correctly--probably not--yea, I was wrong, more in south central Canada: Quetico, Ontario) and he has around 400 watts of solar panels. Lives very comfortably up there in the mountains.

    He uses lots of alternative fuels (propane stove, propane fridge, old gas engine powered washer, etc.)... But he has enough electricity for lights, fan, a few electronics, computer and (satellite?) modem). Plus he uses a little Honda eu1000i for backup/bad weather battery charging.

    I am on-grid in a major city--So talking more with Tony will probably give you some better ideas of what you could aim at.

    Some of the electrical stuff is a matter of choice--For example, a propane fridge makes sense when the cabin is only occupied on weekends. However, if you are there 9+ months of the year, an energy star refrigerator or converted chest freezer may be worth the money for PV power and batteries--to save on hauling propane.

    Chest freezer as a chest refrigerator

    No right or wrong answer--just what you think will work best for you.

    -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 ✭✭✭✭
    #11
    Re: Just starting out

    Northern Ontario, not really mountains, lots of bush, lots of lakes.

    We are not geographically that far north, but socially, climatically, and functionally we are indeed far north. We are 1000 miles north of Toronto, but, there is still ~2000 miles between us and the arctic ocean,, Hudson Bay on the other other hand is only ~ 200 miles away. But enough about me.

    As away,

    Tony
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  • An old girl
    An old girl Registered Users Posts: 9 ✭
    #12
    Re: Just starting out

    Thank you Bill and Tony. I will post as soon as I determine what I need and go shopping! I guess that my market will be very similar to yours, Tony: eastern canadian complete with lots of taxes!8)

    --Marie
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #13
    Re: Just starting out
    An old girl wrote: »
    Thank you Bill and Tony. I will post as soon as I determine what I need and go shopping! I guess that my market will be very similar to yours, Tony: eastern canadian complete with lots of taxes!8)

    --Marie
    Make sure that you determine WHAT you need before you shopping!

    Shout if you have questions,

    T
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  • An old girl
    An old girl Registered Users Posts: 9 ✭
    #14
    Re: Just starting out

    Thanks Tony, I will make sure to take full advantage of all the knowledge available through this awesome site!!

    --Marie:D
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  • peakbagger
    peakbagger Solar Expert Posts: 341 ✭✭✭
    #15
    Re: Just starting out

    Here is a link to a solar powered outhouse in Northern NH at 4000 feet elevation

    Bascially it freezes solid in the winter and thaws out in the spring, for your usage at your cabin you may consider the same idea.

    http://www.uvm.edu/~rlachape/man-rmc.htm
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  • An old girl
    An old girl Registered Users Posts: 9 ✭
    #16
    Re: Just starting out

    Thank you peakbagger.

    Before I look for solar panels per se, I noted that Sunforce has quite a selection of kits but mixed reviews. I also noted reasonably priced kits from Tektrum. Any comments or suggestions (or horror stories)?

    Thanks,

    --Marie :confused:
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    #17
    Re: Just starting out

    I don't know anything about Tektrum---The couple panel systems I saw simply used a blocking diode instead of a charge controller.

    I would suggest going back to deciding how much power you will need, and then cost out several systems (and their features) and decide which works best for you.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • An old girl
    An old girl Registered Users Posts: 9 ✭
    #18
    Re: Just starting out

    BB, does that mean that a blocking diode does the same thing as a charge controller? Is one better than the other?

    Thanks,
    Marie:D
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #19
    Re: Just starting out
    An old girl wrote: »
    BB, does that mean that a blocking diode does the same thing as a charge controller? Is one better than the other?

    Thanks,
    Marie:D

    No. It just keeps the batteries from discharging through the panels at night.
    Go with the charge controller! :D
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    #20
    Re: Just starting out

    As Marc said...

    The "blocking diode" is intended for smaller systems that don't use much power... The panels just "trickle charge" the battery bank. And a charge controller is not really needed. Very common back in the olden days where a company wanted to install a telecom amplifier, radio repeater, flashing lights at the side of the road with solar panels designed to for Vmp of around 15 volts.

    However, for most people here, they want quite a bit of power and long battery life. Both require more wattage of solar panels (with Vmp~17.5 volts or higher) and a true charge controller.

    A diode may cost a few bucks whereas a simple charge controller is ~$30 (or less):

    wind-sun_2119_37537748SunGuard 4.5 amp solar charge controller
    Price: $29.58

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • An old girl
    An old girl Registered Users Posts: 9 ✭
    #21
    Re: Just starting out

    Many thanks BB and Cariboocoot!!:-)
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #22
    Re: Just starting out

    Marie,

    Why the Honda Eu 3000? Sounds like a lot of generator for a small house. Are you running a pump or washing machine off it? You might consider downsizing to a 2000 or even a pair of 1000's, as your fuel efficiency curve will be better if you run them close to capacity rather than closer to no load.

    T.

    PS Don't buy any Charge controller until you have done a really good load calculation and designed a system. It seems that beginners often go cheap on the controller and soon out grow it. I my self am on my 4th! (One went up in smoke due to lightning however!)
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    #23
    Re: Just starting out

    Regarding Tony's suggestions about the Genset... Get the Kill-a-Watt meter and measure your loads... If you can keep them below 1,800 or 900 watts (and no big surges)--The smaller genset can really reduce fuel usage (the eu2000i runs a bit more than 9 hours on 1 gallon of fuel with a 400 watt load.

    If you have a mix of large and small loads--Two gensets may not be a bad idea... Small one for small loads, larger for the occasional big loads.

    If you need electric start of the eu3000i--I am not sure you will find many smaller / fuel efficient gensets.

    In any case, if you use the genset to recharge your batteries (when needed)--Plan on doing the charging in the morning (get batteries to 80-90% state of charge) and let the solar system finish it off in the afternoon.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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