Solar Panels

NixxNixx Registered Users Posts: 1
I need to run a 23'' led tv  which consumes 35 watts and set top box which consumes 10 watts and a ceiling fan which consumes 50 watts. Which solar panels , battery of what ah I need to buy ... Is there anything else I need to buy .... When sun goes I need a back up of 3 hrs .... So do specify the needed things... As I m new to solar .... Any advise will be appreciated..... :)


  • billybob9billybob9 Registered Users Posts: 141 ✭✭
    Are you living in a camper on a Baja beach ? When I was I had three 100 watt panels in parallel a 30 amp controller and Two 12 volt batteries in parallel. You will probably need more to go the 3 hours so just keep adding till there's enough.
  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    Depending on location, I'd agree with @billybob9, 2-3 x 100w panels and 30a charge controller.  I'd use a pair of 6v 225ah golf cart batteries.  You'll also likely need an inverter - this one is nice:

    Cheaper inverters available at hardware stores etc tend to be modified sine (stepped square) wave types, which can make loads like yours run hot or possibly not at all.
    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
  • BB.BB. Super Moderators, Administrators Posts: 32,027 admin
    Assuming you are:
    • Mumbai India
    • 5 hours of TV+Set top box+Fan
    • 2 days of "no sun operation"
    • 50% maximum battery bank discharge (for longer life)
    • Assume flooded cell batteries
    A quick set of calculations would look like:
    • (35 watts TV + 10 Watts set top box + 50 Watt fan) * 5 hours a day (or evening) = 475 Watt hours per day
    • 475 WH per day * 1/0.85 AC inverter eff * 2 days of storage * 1/0.50 max battery discharge * 1/12 volt battery bank = 186 AH @ 12 volt battery bank
    In North America, we would use 2x 6 volt @ ~200 AH batteries (golf cart batteries flooded cell lead acid) for a 12 volt @ 200 AH battery bank.

    For sizing the solar array, we do two calculations. The first based on the size of the battery bank (larger battery bank needs more charging current). The second based on your daily load and hours of sun per day.

    For charging, suggest 5% for emergency/weekend sunny seasonal power, 10%-13%-20% for daily year round loads of charging current. An example of 10% rate of charge:
    • 200 AH * 14.5 volts charging * 1/0.77 solar panel+controller deratings * 0.10 rate of charge = 377 Watt array nominal (10% rate of charge)
    And then there is sizing the array based on your loads and hours of sun per day... Assuming fixed array facing south for Mumbai India:

    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 71° angle from vertical:
    (For best year-round performance)

    Good amounts of sun... The least amount of sun you get is August at 4.85 hours of sun average (long term daily average for August):
    • 475 Watt*Hours per day load * 1/0.52 off grid solar AC system efficiency * 1/4.85 hours of sun per day (Aug) = 188 Watt array minimum
    Normally, you don't plan on using 100% of your predicted harvest... You have to decide on what is a daily "base load" (loads you want to run every day) vs optional loads (washing machine, vacuum cleaner, etc.)... Let's say that you want to run these loads every day (keep kids busy while you work around/at home). I would suggest that you plan on using 50% to 65% of daily harvest:
    • 188 Watt "break even August" array * 1/0.50 base load factor = 376 Watt array suggested for loads and sun
    Which happens to work out to be about 10% rate of charge array at 377 Watt array... So, for a 200 AH @ 12 volt battery bank a 377 Watt array (with a 200-300 Watt AC inverter) and a ~25 amp Solar charge controller would be a nice fit.

    Details matter--The above sizes the battery bank and solar array... You need to decide if the assumptions here are correct for your needs. And then you need to look at hardware. What batteries are actually available (good price/availability), what size solar panels (a single ~377 Watt panel, or 3x 120 Watt panels, etc.) and what solar charge controller type (MPPT or PWM) will work.

    You should do several paper designs and see what combination of panels+charge controllers make sense (377 Watt panel is "cheap" but MPPT controllers are expensive; 3x 120 Watt panels are more expensive, but PWM charge controllers are cheaper).

    Anyway--Just a quick run at the assumptions you need to make and the math to figure out the supporting hardware. The battery bank is the "heart" of your system. And the solar array (plus how you run your loads) can make your battery bank "happy" or "murder it". 

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,658 ✭✭✭✭✭
    edited July 2019 #5
    Nixx said:
    I need to run a 23'' led tv  which consumes 35 watts and set top box which consumes 10 watts and a ceiling fan which consumes 50 watts. Which solar panels , battery of what ah I need to buy ... Is there anything else I need to buy .... When sun goes I need a back up of 3 hrs 
    So you need to be able to run these things 3 hours a day or 3 hours after sunset and longer during the day? Any use during the day may eat into your available energy for charging the batteries.

    As for something else to buy, you will want an inverter to make AC electric to run these items unless they are 12 volt DC?

    Basic math is that each hour the tv consumes 35 watts, the 'top box' consumes 10 watts and the ceiling fan 50 watts. SO 3 x35 = 105 watt hours for the TV, 30 watt hours for the 'Top Box' and 150 watt hours for the  ceiling fan for a total of 285 watt hours, 2 golf cart batteries store about 210 amps at 12 volts,  so 2 store about 2.5 kwhs (2500 watt hours) of which 1.2 is useable though you may  want to save some extra for rainy days and worry about recharging them.

    You would normally want enough solar array to charge the batteries at a 10% rate if you will be using them daily. That would be 21 amps at charging for 12 volts. Roughly 400 watts.

    I had started this, then lost my connection and posted this morning. Since then Bill, who can look into you ISP posted you were from India. You have the advantage of having long days.  You might use slightly less charging  with regular long days.
    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.
  • littleharbor2littleharbor2 Solar Expert Posts: 1,628 ✭✭✭✭
    Keep in mind that things like the Set Top Box and likely the TV will consume power 24/7 if not disconnected from the power source. You can get a power strip and turn off the power when not in use.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 540 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • russelrussel Registered Users Posts: 1

    A ceiling fans + top box + led tv uses about 100 watts. So 10 hours of use = 1 KwH.

    But you'll have the 3h sleep timer on right? 0.5 kwH

    Lets say you want 2 fans, or use it at high speed and want to round up for safety. You need around 2 kwH of storage.

    As for charging, you could buy a 24v solar panel. Hook it up to that 24v inverter you already have. To be safe, you'd need at least 300W of solar panels to recharge the batteries. I thinks Q CELLS DUO 335W is nice, read this.

    Or just go buy power kit, but going the DIY way would knock maybe half off that cost.

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