Newbie Help

careyx1careyx1 Posts: 2Registered Users, Users Awaiting Email Confirmation
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.
Thanks!
- X



Comments

  • EstragonEstragon Posts: 2,955Registered Users ✭✭✭✭✭
    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
    pvwatts.nrel.gov
    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.
    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
  • BB.BB. Posts: 28,083Super Moderators, Administrators 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?).

    https://www.solar-electric.com/kiacpomome.html
    https://www.amazon.cn/dp/B01N1795ZL (example from Amazon.cn)

    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
    3.60
     
    3.22
     
    3.16
     
    3.60
     
    4.04
     
    4.43
     
    Jul Aug Sep Oct Nov Dec
    4.59
     
    4.32
     
    4.37
     
    4.62
     
    4.50
     
    3.66
     
    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.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • careyx1careyx1 Posts: 2Registered Users, Users Awaiting Email Confirmation
    BB. said:
    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?).

    https://www.solar-electric.com/kiacpomome.html
    https://www.amazon.cn/dp/B01N1795ZL (example from Amazon.cn)

    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
    3.60
     
    3.22
     
    3.16
     
    3.60
     
    4.04
     
    4.43
     
    Jul Aug Sep Oct Nov Dec
    4.59
     
    4.32
     
    4.37
     
    4.62
     
    4.50
     
    3.66
     
    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.

    -Bill
    Thanks so much! 
    I'd just like to clarify a few things first,
    We don't plan on using the laptops while connected, only charging them (60w).
    But you had lots of great points, however, I'm still a bit confused on some of them.
    Does this mean we need 962w+ of solar panels? (5 * 200w solar panels?), some detail regarding volts, amps, and watts between the different modules would be greatly appreciated.
    As for the battery, is there a safer, more self-maintained battery? I've read about a few but I still need help understanding them better.
    Could you possibly recommend some parts for us to buy? 
    As you mentioned, we need:
    • 600-800AH @12v Battery Bank (AC/DC outputs and inputs, do they matter?)
    • 750w AC Power Supply
    • Charge Controller
    • Inverter
    Etc. Right?

    Just a little more simplified help would be great, even some recommendations about what we should do pushing forward.
    Thanks again.

  • EstragonEstragon Posts: 2,955Registered Users ✭✭✭✭✭
    Before thinking about parts to buy, we really need to get a better grasp on loads. As Bill suggested, using a kill-a-watt type meter to measure the consumption for a laptop charge cycle would be a good idea.
    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
  • BB.BB. Posts: 28,083Super Moderators, Administrators admin
    Careyx1,

    Can you confirm that, what I guessed, for your loads and location are accurate?

    Is there "seasonal usage" (i.e., solar power systems only work when it is sunny--Many schools let out during the summer--Meaning that you have to generate power from the sun during winter/bad weather/monsoon season (looking at the Hong Kong solar "hours of sun" per day--fair amount of clouds during the year blocking some sun?).

    What do you need to know about Volts, Amps, and Watts? Volts is electrical "pressure". Amps is electron "flow". And Watts is power (Joules per second). And Watt*Hours is the "amount" of energy...

    Watts is like miles per hour, and Watt*Hours is like miles driven.

    If you have done electrical work with vehicles, boats, etc... You may see Amp*Hour used a lot... And it is perfectly OK if you are dealing with "one voltage" (like a 12 volt car power system). However, it is "missing" the voltage component of the energy. For example:
    • 10 amps * 12 volts = 120 Watts
    • 10 amps * 240 volts = 2,400 Watts

    Or, if you have a 10 amp @ 240 volt load, and are drawing power (Watts) from a 12 volt battery bank:

    • 10 amps * 240 volts = 2,400 Watts
    • 2,400 Watts / 12 volts = 100 amps (on your 12 volt battery bus--excluding losses from your DC to AC inverter).

    Suggesting equipment may be a bit frustrating--If you are in Asia, the US standard components may not be cost effective/available for you (or may not meet your electrical code standards).

    If you can, please tell us more about your energy needs (and if you have measured the Watts/Watt*Hours of your loads). A bit about where the system will be installed. Will you have clear access to full sun from 9:00 to 15:00 (at least)? Any shading on your solar array (buildings, vents, overhead wiring, etc.) can cut your solar array output by 1/2 or more. And arrays only output "useful" energy when exposed to full sun.

    Do you have somebody with electrical experience to help you?

    Why are you doing an off grid power system? Is it to save money, be used in remote region (no utility power)? Demonstration of "green energy"? -- Will you have (or need) a backup generator (bad weather, if you run 2x classes per day sometime, etc.)?

    Before you purchase any hardware--Do several paper designs first to see that everything fits together and will meet your cost goals. Solar power is not cheap (typically 5-10x the cost of utility power in a major city).

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SupraLanceSupraLance Posts: 21Registered Users ✭✭
    edited February 28 #7
    First thing I would do is buy 12v car chargers for the macbooks to eliminate the inverter and converter losses.  Those big boxes attached to the AC charger are converting to DC, so it makes no sense to convert your solar to AC and have the chargers convert it back.  Secondly, if your just charging laptops during the day as a project, the system doesn't have to work on cloudy days, and perhaps it can charge only when the sun it out [if you can still use the AC chargers on grid power if a charge is needed overnight or when too cloudy].  This saves you a lot of $, as cloudy/overnight charging is out of your budget.  You still need a battery to keep the system at 12v, but if you don't discharge it very much it will last longer and doesn't need to be as big or costly.  So at this point you need solar panels, a charge controller, a  12v battery, and 10 fused cigarette lighter plugs off the battery.  Now we have something doable in your budget to at least charge the laptops when the sun is shining.   
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