Newbie Help

careyx1careyx1 Registered Users, Users Awaiting Email Confirmation Posts: 1
edited February 1 in Solar Beginners Corner #1
Hey everyone!

So I'm extremely new to solar panels, and solar panel systems. But I am planning to construct a charging system at my school.
I have a quite a few questions that I would appreciate your help with. Keep in mind my budget for this is around $500-550USD, my aim is to be able to charge 10ish Mid-2012 Macbook pros, would a 200W (100w x 2) solar panel(s) be enough?

1. What are the components I'll need?
I've read around that I'll need a solar charge inverter, an AGM battery, a charge controller, a combiner box and an AC/DC disconnect. Can someone just confirm/go over this? I'm still puzzled on what they all do and which ones I should be getting. 

2. How do I find out how much power I'll be generating/drawing?
Apparently, If I get a 200w solar panel and have 10 hours of daylight, I'll have 2 kwh of energy... Is this true? and is that a lot/enough? for a charging station. 

3. Building a mounting system...
I figured I could save money by building my own mounting system, could someone recommend a guide to doing so? If it's even possible.

4. Storage and energy...
If I do get 2000w of energy, what sort of inverter and battery and controller and whatnot should I get/need? The internet makes it sound like things could explode (and leak hydrogen!?).

5. Volts, Amps and Watts
What is a 12v vs 6v battery? Does it matter? Same goes for amps and watts. Does this influence the components I'll need?

Anything else that I should know (literally anything, I'm pretty much clueless) is helpful! I really appreciate the it.
- X


  • EstragonEstragon Registered Users Posts: 1,809 ✭✭✭✭
    Welcome to the forum.

    The first step is to better define the loads. If you look at the transformer bricks on the laptop power cords, it should give you input and output volts and amps. Multiplying input volts x amps will give the wattage. Next, estimate the total run time for the laptops per day. Run time times wattage gives you watt-hours. This number will be used to size the battery.

    Next, use a solar calculator such as
    to estimate hours of full sun equivalent for your location at various times of year. You will almost certainly not get 2kw/day from a 200w panel. A 200w panel warmed by the sun might put out ~150w for the best hours (~11am - 1pm) of the day if properly tilted, and diminishing power earlier/later.

    With the above info, we can start looking at equipment needs, options, and trade-offs.
    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 Posts: 27,055 admin
    As Estragon says, you need to measure/better understand your loads. A "Kill-a-Watt" type meter is useful for this (120 VAC power--Notice you may be in Hong Kong--Need 230 VAC 50 Hz power?). (example from

    In some places, you can get Kill-a-Watt type meters from the library (borrow for free for 2 weeks).

    To forewarn you about your project... This will not be a trivial or inexpensive project. If you do not want to purchase 12 VDC Mac adapters (run directly from battery bank), you will need to purchase an AC inverter (takes 12 VDC and converts it to 120 VAC).

    Next, even laptop computers are significant loads... Typically around 60 Watts from computer AC power supply. And average power usage may be ~30 Watts using the computer (60 Watts when recharging computer). (note: these are all guesstimates--Need "real numbers" to plan a real system):
    • 10 Macs * 600 Watts = 600 Watt AC power supply.
    • A little bit of derating 600 Watts * 1.25 NEC derating = 750 Watts minimum suggested power.
    Next, you need to figure out how long the computers are used per day... Say 6 hours at 30 Watts
    • 10 macs * 30 Watts * 6 hours per day = 1,800 WH per day (that is enough energy to run a full size refrigerator freezer)

    Then you need to buy a battery bank. 2 days of storage @ 50% maximum discharge (longer battery life):

    • 1,800 WH * 1/0.85 AC inverter losses * 2 days storage * 1/0.50 max discharge * 12 volts = 705 AH @ 12 volts
    That is roughly 6-8x 6 volt @ 200 AH ~$100 golf cart batteries for a 600-800 AH @ 12 volt battery bank

    To charge the bank, you would need ~10% rate of charge minimum for a full time off grid power system:
    • 800 AH * 14.5 volts charging * 1/0.77panel+charge controller deratings * 0.10 rate of charge = 1,506 Watt array suggested

    There there is sizing your array based on how many hours a day of sun you get. Say a fixed array in Hong Kong:

    Hong Kong
    Average Solar Insolation figure

    Measured in kWh/m2/day onto a solar panel set at a 68° angle from vertical:
    (For best year-round performance)
    Jan Feb Mar Apr May Jun
    Jul Aug Sep Oct Nov Dec
    So based on the amount of sun you get (and angle of array), the minimum is January at 3.60 hours of "noon time equivalent" sun:
    • 1,800 WH per day * 1/0.52 off grid AC system efficiency * 1/3.60 hours of sun "break even January" = 962 Watt array minimum
    So, somewhere a minimum of between a 962 Watt and a 1,506 Watt array would be recommended.

    To be honest--I would be suggesting just building a 1 station solar power system. It would be much less expensive to build and maintain (batteries last 3-5 years for "inexpensive" batteries). Inexpensive inverters may last 2-5 years (could be as long as 10+ years).

    The above is a conservatively designed system that will (probably) meet the needs of the loads you suggested... But it will not save money and if nobody maintains it, can fail in months of usage (+/-). Batteries if maintained, are pretty rugged. Batteries that are not maintained or stressed (over/under charged, over discharged to "dead", water levels not maintained for flooded cell batteries) and they are turned into scrap metal.

    And yes, as you have read, flooded cell lead acid batteries do vent hydrogen (and oxygen) gases while charging (and a little bit of sulfuric acid mist too). They need to be in a vented box away from anything you care about (the electrolyte mist can damage/corrode/rust nearby objects if it collects on stuff).

    Also, a large lead acid battery bank can output 1,000's of Amperes into a short circuit--Fuses/Breakers and properly sized wiring is needed to reduce the chances of fire.

    Solar arrays can attract lightning (need proper grounding if you have lightning in your region). And the framework needs to be strong to withstand high winds.

    Anyway--some basic information on the paper design side of a possible system--It will allow you to lean more about solar and work on a design--Even if you do not ever build a system, you will learn a lot.

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