help me for how much power do I need

JONESJONES Registered Users Posts: 1
I have a fridge 360ltres and 48"flat Tv and also 3 (60wts lights) so I want to use solar power so how many solar ,batteries ,inverter and regulator =watts,volts and amps do I need to have this is for domestic use


  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    In order to provide information, more information would be required, at very least the product ratings watts or amps, in addition the time of use including if they are to all operate similtaniously. The most accurate means would be to measure the actual consumption with a Kill-a-watt device, once the loads are established, a battery capacity would be possible to select, then the charging equipment to support the batteries needs then finally a PV array to support all the loads, losses etc. geographic location is essential to establish hours of sunlight expected. So it's not as simple as it may appear, on YouTube for example where there are some videos doing disservice to the public in general, want to do it right? You've come to the right place. 
    Welcome aboard 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • PhotowhitPhotowhit Solar Expert Posts: 5,653 ✭✭✭✭✭
    Are you planning on replacing the grid in your current dwelling? If so you could look at your current electric bill for Kwh's used.

    Size, type, age and temperature of the environment around it will effect the electrical usage of the fridge. and your TV.

    I suspect you are referring to LED light or compact florescent that output as much light as a 60 watt incandescent. These are in the 15 - 9 watt range per hour.

    There are meters that you can plug these items into then plug them into your outlet to measure the amount of Kilowatt hours you actually use. Really not enough information yet to get an idea.

    In general, off grid/battery based solar energy is more expensive than electric from the grid. So if you plan is to save money, it's likely not worth the effort. In the states, It's worth looking into if you pay more than @35 cents a Kwh total for your electric and are handy and have a reasonable sunny area. Sometimes cabins in area with high user fees can fall into this range and higher. Some user fees are getting very large.

    Hawaii has some areas where the electric is over 50 cents a Kwh and becoming more expensive since more people there are moving off grid, so the service is more expensive to maintain with fewer customers. How course the costs in off grid are also more expensive since the costs related to equipment is higher...
    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, 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.
  • MichaelKMichaelK Registered Users Posts: 215 ✭✭✭
    Based on your available information, I'd make a few guesses about your daily consumption.  I'll do the math here, so when you come up with more accurate numbers you can replace what I put in with your own real-world values.

    Refrigerator 360 liters, ~12 cubic feet.  This would be a small refrigerator in America, I'd guess consuming around 900 watthours per day. (0.9kwh)

    Big screen TV 250 watts X 3 hours of watching = 750 watthours (0.75kwh)

    60 watt lights X 3 bulbs X 5 hours of light = 900 watthours (0.9 kwh)

    Let's throw in an extra 500 watthours just for miscelaneous things you didn't think about, IE: your computer, stereo, electric can opener.

    So Frig+TV+Lights+Misc= 900+750+900+500= 3050 watthours or ~3kwh.

    For long battery life, you'll want to use no more than 15-20% of your battery bank per day, so 3000/0.15=20,000 watt hours.

    A trojan L16 battery has an 420 amphour capacity.  To get ~ 20,000 watthours of capacity you need 8 of those, wired in series for 48V to get 420amphour X 48VDC= 20,160 watthours.  Note that amps X volts = watts, so 20160 ampvolt hours = 20160 watthours.

    Now, charging a battery that needs 3000watthours per day.
    You don't want to charge the battery at less than 1/12 its capacity, or greater than 1/8 its capacity.
    For a 20160wh battery, that's 20160/12= 1680watts to 20160/8= 2520watts

    Winter gives the fewest sun hours, let's assume it's 3SH?  If you bought 6-300watt panels, you'd produce 1800 watts at noon, or about 1800watts X 3SH = 5400 watthours of power.  That is enough to recharge your batteries completely, assuming you have completely cloud free weather all winter long (how likely is that?)  Suppose there's two days of cloudy weather before there's a sunny day to charge the batteries?  You'd need 3000 watthours X 2 days = 6000 watthours total, plus the electricity you use on day 3, which will total up 9000 watt hours.  You're better off going with 2400-2500 watts of panels to cover the cloudy days you're pretty much guarantied to experience.  Assuming you never get better than 85-90% efficency from your panels, bump the wattage up to 2700.

    Here's what I suggest you buy.
    9 300 watt grid-tie panels (1600-2300$)
    8 Trojan L16 batteries (~3000$)
    60 amp or greater charge controller (I have a midnight 200 classic) (650$)
    >2000 watt sine-wave 48VDC inverter (I'd suggest Schnider's SW4048 (1750$)
    power panel, wiring, breakes, ect 600$

    Total >8000$US
    Is this a digestable number to you?  This is what I'd say is realistic.  Try to cut corners off of these numbers, and you most likely will end up with disappointment and ruined batteries.
    System 1) 15 Renogy 300w + 4 250W Astronergy panels,  Midnight 200 CC, 8 Trojan L16 bat., Schneider XW6848 NA inverter, AC-Delco 6000w gen.
    System 2) 8 YingLi 250W panels, Midnight 200CC, three 8V Rolls batteries, Schneider Conext 4024 inverter (workshop)
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Welcome to the forum Jones,

    Michaelk did a good job of estimating/sizing a system... I will take a stab at it too (see how close our two suggestions compare).

    First, you need to understand your loads. Using LEDs instead of filament bulbs, modern LED TV, high efficiency refrigerator, turning stuff off with a power strip (TV, satellite receiver, DVR, etc.), using a laptop computer vs desktop, etc.

    My suggestion is around 3.3 kWH per day for a "near normal" off grid electric lifestyle (washing machine, well pump, fridge, led lighting, laptop+LED TV). Yours may be a bit more or a bit less (energy usage is a highly personal set of choices--Other than pushing for conservation, we try to address your needs--not what we would do for our lifestyle). Also, solar electric power is expensive... And a huge expense is the battery bank. New batteries are expensive and only last ~5-7 years (typical) in cool climates. And if you have an "oops"--You can kill a bank in days.

    Using a Kill-a-Watt type energy meter on each appliance (run for 24 hour power and see what your WH/kWH per day is). Depending you your local power outlets here is a UK 230 VAC unit:

    The following is using our "rules of thumbs" here to quickly size the system based on "typical" off grid home usage. Your needs may differ.

    Sizing the battery bank, assuming 2 days of backup power and 50% maximum discharge and 24 VDC nominal battery bank (typical for this size system) and 3.3 kWH per day.
    • 3,300 Watt*Hours * 1/0.85 AC inverter eff * 1/24 volt battery bank * 2 days storage * 1/0.50 maximum discharge = 647 AH @ 24 volt flooded cell lead acid battery bank
    Then there is sizing the solar array. There are two calculations. First is based on the size of your battery bank and rate of charge (larger battery banks need more current for proper charging. 5% can work for "weekend"/seasonal cabins. 10%-13% rate of charge (or more) works for full time off grid homes.
    • 647 AH * 29 volts charging * 1/0.77 panel+charge controller deratings * 0.05 rate of charge = 1,218 Watt array minimum
    • 647 AH * 29 volts charging * 1/0.77 panel+charge controller deratings * 0.10 rate of charge = 2,437 Watt array nominal
    • 647 AH * 29 volts charging * 1/0.77 panel+charge controller deratings * 0.13 rate of charge = 3,168 Watt array "typical cost effective" maximum
    And then there is based on where you live--Guessing in the area of Johannesburg, South Africa. Fixed array:

    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 64° angle from vertical:
    (For best year-round performance)
    Jan Feb Mar Apr May Jun
    Jul Aug Sep Oct Nov Dec
    Looks like a very sunny region. To have a "break even" 5.0 hours per day of sun:
    • 3,300 WH per day * 1/0.52 off grid system eff * 1/5.0 hours per day of sun = 1,269 Watt array minimum
    Because you have a lot of sun, you do not need a very large array for 3.3 kWH per day... But flooded cell batteries do better with a 10%+ rate of charge for full time off grid power. Also, if you run loads during the day, this does subtract from battery charging current.


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