Best bang for the buck?

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ricko1966
ricko1966 Registered Users Posts: 3 ✭
in Solar Beginners Corner #1
I have 2 new 250 watt panels and a solar brand wpm charge controller A 1500 watt inverter and. A single group 27 deep cycle battery.And a big woodstove.My only goal is help offset my electric bill this winter.The whole house is electric, grid tie is not an option and I only have about a hundred dollars left to throw at this project.Can I charge a battery to float then dump to an electric heater?Or should I use everything to power one big energy hog?Like water heater,space heater fridge etc. Or should I power the lights tv etc.with the solar?mAm considering adding a water heater timer.Worth it?And going to put a woodstove in the mud room.Any thoughts advice etc.would be appreciated because I know this year I'm not going to be able to afford 400.00 monthly winter electric bills
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #2
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    Off grid electric is MORE expensive than grid electric, almost always. Consider that (not knowing your location) you are likely to have 3-4 hours (max) solar insolation over winter. Solar panels put out about 75-80% of their rated wattage (NOCT value) So max generated with a 500 watt solar array, would be about 400 watts per hour for 4 hours(average) = 1600 wahh hours. If you use the DC energy direct and don't try to store it. It would have the value of 1.6 kWs where ever you are located. likely a max of 20 cents or so in the 48 states. So a value of about 32 cents a day maximum for 30 days, might save you $10 off your bill, if you live in an expensive area for grid electric.

    If you store the energy you lose 15-20% in lead acid batteries, use an inverter to power something lose another 15%...

    I'd concentrate on making sure your home is well sealed and insulated. I'd ask for an energy audit, usually free from the power company, to help figure out where your wasteful energy users are....

    Certain concentrate on adding a woodstove! They are a great source of heat for cheap!
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #3
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    Rick, welcome to the forum.

    Roughly, where are you located, and how many kWatt*Hours per month do you use ($$/kWH, etc. for utility costs).

    More or less--It costs something like 5-10x as much for off grid power vs grid/utility power (I.e., if your utility bill is $0.20 per kWH, in the US, it costs most people something like $1.00 to $2.00+ per kWH, and you pay that much of that bill up front buying parts and installing the system). Batteries are a consumable item, and typically last 3-7 years or so--And it is not uncommon for family to "murder" their first battery bank or two until they get their energy usage and maintenance under control.

    If you have never done any conservation work on your home before... It is not unreasonable to reduce electrical usage by 25 to 50% with conservation (double pane windows, insulated walls, more insulation in ceiling, insulating HVAC ducting, getting more efficient HVAC system, etc.).

    And for HVAC, a heat pump can help... In weather conditions above freezing, an efficient heat pump can use less energy than a resistance (electric heater). Propane (if you do not have natural gas) can also cost less.

    Look at mini-split heat pumps (not just A/C mode) can also be better than central heat/AC... Getting rid of the central heat ductwork cuts heat and air losses.

    It is almost always cheaper to conserve energy than to generate energy. $400 per month is a lot of energy (assuming you do not have $200+ per month connection fees).

    A very efficient off grid home can run on something like 3.30 kWH per day or ~100 kWH per month. A larger off grid system would be around 10 kWH per day (or 300 kWH) per month... Anything larger, is going to cost you lots of money.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #4
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    I'd start by selling the battery and inverter.  The panels could be used to pre-heat something directly (water or air) to the extent they can.

    Like Bill said, your best bang for the buck will be conservation.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • ricko1966
    ricko1966 Registered Users Posts: 3 ✭
    #5
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    Originally was going to go grid tie but the restrictions expenses and hoops I have to jump through make it not practical and with above ground lines I get several power outages a year 2 this month.So since I had all this stuff I was going to make the best use of it that I could.I live in S.E.KS.  Yea the wood stove is happening this weekend.The house is actually sealed up pretty good I've done all I can think of insulation windows etc. But heating a 3000 again ft home with an electric furnace is expensive.I am on 20 acres though and plenty of cull from the last timber harvest. I and have run the house on the inverter run the house on just the inverter and 3 group 27 batteries during the warmer months but was charging the batteries 2 times a day using a gm alternator spun by a honda tiller engine. I actually have three panels and was going to expand later and go with bigger better batteries and more panels just wanted to get started.All this stuff will eventually get moved to an off grid cabin.Thanks for the ideas and input keep it coming.Actually long term I'm hoping to be hybrid I have a complete 5kw onan motor home generator and all the motor home wiring the three panels inverter etc.just getting started.Again thanks.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #6
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    Assuming South East Kansas, pick Wichita, fixed array facing south:

    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Wichita
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 52° angle from vertical:
    (For best year-round performance)

    JanFebMarAprMayJun
    3.82
         		4.13
         		4.88
         		5.32
         		5.40
         		5.58
     
    JulAugSepOctNovDec
    6.02
         		5.65
         		5.33
         		4.87
         		4.01
         		3.56
     

    That is a reasonable amount of sun (anything >=3.0 hours per day is pretty good during winter).

    Let's assume 3.3 kWH (3,300 WH) per day (or 100 WH per month--Look at your bill and see what you currently use for a shock). That is a "near normal" electrical existence for a very conservation minded home. 1x Energy star refrigerator, LED lighting, LED TV, Laptop computer+cell phone, "solar friendly" well pump, clothes washer. This is a "pretty cost effective" off grid solar system.

    Battery design: 2 days of storage (no sun), 50% maximum discharge, 24 volt battery bank, flooded cell lead acid:
    • 3,300 WH per day * 1/0.85 AC inverter eff * 1/24 volt battery bank * 2 days storage * 0.50 max discharge = 647 AH @ 24 volt battery bank
    That is 4x ~220 AH @ 6 volt "golf cart" batteries in series * 3 parallel strings (24 volts @ 660 AH).

    To charge that size battery bank, suggest 5% to 13% (to 20%) for typical solar system. 5% for emergency backup/summer system. 10%+ for daily full time off grid (9+ months a year).
    • 647 AH * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,218 Watt array minimum
    • 647 AH * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 2,437 Watt array nominal
    • 647 AH * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 3,167 Watt array "typical cost effective" maximum
    And there is sizing the solar array based on your daily usage and hours of sun per day... You can pick the worst month, or pick the 4th worse month (February in your case), and make up with a genset in the winter... You do have "lots" of winter sun (relatively speaking), so let's use December:
    • 3,300 WH per day * 1/0.52 off grid AC system eff * 1/3.56 hours of sun (December "break even") = 1,783 Watt array "December Break Even" month (probably have to use genset during spells of bad weather in December and occasionally other winter months).
    So, for a full time off grid home, I would be suggesting 2,437 to 3,167 Watt array...

    Note: this assume you mostly charge during the day and use energy at night... If you have non-standard uses (well pumping, running a business from home during day, want to use less genset), you would probably would want to tweak the above.

    Note--There are base loads that you must use every day (such as refrigerator, well pump for water, LED lighting)--You should plan on using a maximum of around 50-65% of predicted output... Washer, irrigation, etc. would wait for sunny weather and/or possibly genset usage.

    Energy usage is a highly personal set of choices--The system needs to meet your needs--Not my predictions of your needs.

    3.3 kWH per day is not much energy usage... You could probably justify a 3x larger system very easily just based on the size of your home and other energy needs (central heat, kids, etc.). A typical north American home uses around 500 to 1,000 kWH per month (vs the 100 kWH per month for the above system design).

    Before you purchase any equipment... I highly suggest you look at the above math and your current energy usage. A 3.3 kWH system is not cheap (maybe $10,000 to $20,000+ --- Prices are highly fluid and do depend on if DIY or whom you may hire). A 10 kWH per day system, you are looking at 3x (+ or -) system cost.

    Plan on batteries lasting 5-7 years (and lasting under 3 years because of "oops" is not uncommon), and electronics ~10+ years. Panels 20+ years.

    An alternative... A 1 to 3.3 kWH per day system, with or without solar panels (1,000 WH per day will run lighting, laptop, LED TV, cell phone, RV water pump) for "quiet times" (overnight)... And use a genset on propane (or natural gas) during the day/normal larger house loads during power failures. Also, the genset can recharge the battery bank when it is fired up (generally, gensets are most efficient when running 50%+ loads).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • ricko1966
    ricko1966 Registered Users Posts: 3 ✭
    #7
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    Thanks.I cannot spend much of anything on this gotta use what I have to the best of my ability.About 50k upside down in the house we couldn't afford it when we bought it buy couldn't talk the ex out of it with both of us working full time blah blah blah we can afford.So when she bailed and filed for divorce I got stuck with a house I can't sell,I can't afford on one income.I owe 30,000 dollars in back penalties.When I said I ran the house on 3 batteries an inverter and A GM alternator I had too.No electricity for. 7 months because I couldn't afford the. 1800.00 overdue bill.Sorry for going into such detail but it is what it is I have a Menards merchandise credit of about 100.00 bucks,and the stuff I mentioned.Hopin to rent this out eventually and build a little cabin in the north pasture. Thanks again everyone.P.S had the inverter left over from better days taking the kids on trips having to power TV and such, had the GM alternator and the tiller motor thank God or I'd have had no electricity.
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