Solar Setup just for my Tablet

joeysolar
joeysolar Registered Users Posts: 1
Hi All,

I'm new to solar panels (will buy soon) and looking for a good setup that can keep my work tablet (Surface PRO) powered for a few days on one battery bank. I'm thinking of having two battery banks so that the other bank discharges while the other recharges. I don't know if that's a good assumption in having a good solar panel setup.

Anyways, on a regular basis, I work 8-10 hours a day and between that time I charge and discharge my Surface PRO. I start charging the Surface when it hits low at 10% and discharging it when it reached 90%.

Surface PRO requires 44W to run and charges with 12v at 3.6amps. And I don't know what controller and inverter I need. Will a 100w panel (mono) with (2)x100amp deep cycle battery sufficient enough for one battery bank setup or is it too much just to run a tablet? (maybe I'll need to add LED lights, 12v fan in the future...)

By the way, I live near the equator that has around 7-8 hours of sunny time. ;)

I highly recommend your thoughts.

-Joey

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Solar Setup just for my Tablet

    Welcome to the forum Joey!

    First, I would suggest finding a Kill-a-Watt type power meter. Accurately measuring your daily power usage is better than estimating. Also, if you have a network, printer, etc. you need to run, you should check that too. But, using the numbers you have provided, we can start.

    Assuming this is a full off grid system (as opposed to an emergency backup system for unreliable power), a quick set of calculations using nominal rules of thumbs would look like (2 days of no-sun storage and 50% maximum discharge for longer battery life):
    • 44 watts * 10 hours per day * 1/0.85 AC inverter eff * 1/12 volt system * 2 days of backup power * 1/0.50 max discharge = 173 AH @ 12 volt battery bank
    A pair of 6 volt @ 220 AH golf cart batteries would work very nice for this.

    Next, need to size the solar array. We base the calculations on meeting two needs, first how much charging current the battery bank needs and second based on the hours of noon time equivalent sun per day + your loads.

    First, based on size of the battery bank. We recommend 5% to 13% rate of charge. A 5% rate of charge is minimum and good for a emergency backup system/weekend/seasonal use system. For a full time of grid power system, 10% to 13% is recommended:
    • 220 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 207 Watt minimum array
    • 220 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 414 Watt nominal array
    • 220 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 538 Watt "cost effective" maximum array
    Next, based on the amount of sun and energy usage per day. And almost no place gets 7-8 hours of noon-time equivalent sun per day other than, perhaps, an equatorial desert.

    So, guessing you are in Philippians, Manila, using a fixed array and the Solar Electric Handbook, we see:
    [h=3]Manila
    Average Solar Insolation figures[/h] Measured in kWh/m2/day onto a solar panel set at a 75° angle (from vertical):
    (For best year-round performance)

    Jan
    Feb
    Mar
    Apr
    May
    Jun


    4.58

    5.01

    5.41

    5.42

    5.19

    4.72



    Jul
    Aug
    Sep
    Oct
    Nov
    Dec



    4.29


    3.75

    4.14

    4.11

    4.18

    4.05



    Because of weather, haze, etc., we see around 4 to 5.5 hours per day, your system would need:
    • 44 watts * 10 hours per day * 1/0.52 end to end system eff * 1/3.75 hours of sun per day minimum = 226 Watt array minimum
    Your system would need around a minimum of 226 Watt array and you could use 414 Watt array nominal and justify up to ~538 Watts of solar panels.
    These numbers are typically long term average weather conditions (~20 years typically)... So, if you need power during prolong periods of bad weather, you should through a small generator + AC battery charger in there too.

    If you have utility power and the system is just for 2 days of emergency backup, you could start with an AC inverter+Battery Bank+AC battery charger. The above batteries will give you 2 days of emergency backup power. You can add solar panels and a genset later as your savings and needs dictate.

    A nice little 300 Watt True Sine Wave Inverter with remote on/off and "search mode" would be from MorningStar would work well.

    Solar Charge contorllers, there is a wide range available. You need to find the solar panels that you can find locally and are cost effective. You can get "12 volt" panels which are around 17.5 volts Vmp and use a PWM type charge controller (the less expensive type of solar charge controller), but 12 volt panels tend to be more expensive per Watt.

    Or you can get an MPPT type charge controller which is more expensive but can use higher voltage Vmp panels (typically around 30-36 volt Vmp panels) which are less expensive. MPPT charge controllers are also very nice for longer wiring distances from the array to the charge controller/battery bank. You have longer wire runs with smaller diameter copper cable (12 volt panels can require some very heavy copper cables to keep the voltage drop down on longer wire runs).

    For an AC battery charger, you need around a 10% to 20% rate of charge (22 to 44 amp on a 220 AH @ 12 volt battery bank). An Iota type charge controller with an IQ4 charge controller (IQ4 only needed if you have utility power 24x7) would be nice.

    A Honda eu2000i or equivalent Yamaha, etc. would power a 30 amp charger nicely for bad weather/emergency backup power.

    Anyway, a starting point. As you supply more information about your location and needs, we can adjust the numbers and design of the system.

    Questions ?

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