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  • Small off grid solar usb charging station system.

    Hello, tried to make sense of what I need myself, but I cant seem understand how big of a solar panel I need, battery size, or if I can actually use solar for this purpose.

    I want to make an off-grid USB charging station with a solar panel, preferably with one panel, I have 6 devices that have a total battery capacity of 30000 mah (2500 mah to spare), are there charge controllers that have at least 4 USB ports in them? I would assume if I would charge my load from the controller directly, I wouldn't need an inverter? Otherwise the charging station is a 40w load, I would assume it's more the more devices you charge. I have no clue of how long these devices would charge, I know the USB charger is rated at 5v/2.4A

    The purpose of this system would be in a grid-down situation, I wouldn't use this daily, but assuming once the grid is down, I would use the system once every 5th or 6th day, I don't mind keeping the system up, but I'd prefer maintenance-free batteries. I have 4.8 sun hours where I live.

    My question is, what's the most cost-effective way to make this system, does the fact that I would only use the system for USB charging change the battery capacity or panel size? Is solar even a choice if I would use this system weekly, not daily? Note: I am on a tight budget (I'm a student), I would like to spend no more than 250$ for the whole system (except the load).

    Sorry if there's dumb questions, I'm pretty new to solar, and batteries and such.

    I appreciate all answers, and thank you for your time.

  • #2
    You need to come up with a few more numbers. Calculating power requirements in Watt Hours is a more universal way than other convoluted methods.

    30000 mah = 30Ah @ __what voltage 5V, 12V ?___
    30x5 = 150wh
    30x12= 360wh Big difference. Most charge controllers require a 12V battery to power their internals. so that battery has to be accounted for also.

    Doing this under $250 is going to be rough
    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister

    Comment


    • #3
      Originally posted by Mike90250 View Post
      You need to come up with a few more numbers. Calculating power requirements in Watt Hours is a more universal way than other convoluted methods.

      30000 mah = 30Ah @ __what voltage 5V, 12V ?___
      30x5 = 150wh
      30x12= 360wh Big difference. Most charge controllers require a 12V battery to power their internals. so that battery has to be accounted for also.

      Doing this under $250 is going to be rough
      Hi, I assume the charge controller would be 12V, but I would use the power only through the 40w usb charger which changes the voltage to 5V only, I am not sure on how that would change the required system size, that was one of my original questions, we can ignore the budget and just look at the most cost-effective way, I suppose that would be best.

      Comment


      • #4
        What is your load:
        30x5 = 150wh
        or
        30x12= 360wh

        Your 12V battery needs to be 2x the size of your load.

        360Wh @ 12V = 30ah. 60A is a battery found in a small car. A cheap 12V 80ah marine battery is about your only choice, or spend 2x as much for a lawn tractor battery at 60ah, depends what you can get in your area.

        To charge that, you need a 100 - 150V pv panel, with a Voltage Max Power of about 18V Vmp=18V, Voc=21V
        Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
        || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

        solar: http://tinyurl.com/LMR-Solar
        gen: http://tinyurl.com/LMR-Lister

        Comment


        • #5
          Originally posted by Mike90250 View Post
          What is your load:
          30x5 = 150wh
          or
          30x12= 360wh

          Your 12V battery needs to be 2x the size of your load.

          360Wh @ 12V = 30ah. 60A is a battery found in a small car. A cheap 12V 80ah marine battery is about your only choice, or spend 2x as much for a lawn tractor battery at 60ah, depends what you can get in your area.

          To charge that, you need a 100 - 150V pv panel, with a Voltage Max Power of about 18V Vmp=18V, Voc=21V
          My load would be 150wh, then I assume a 32ah would do just fine? I've found a AGM deep cycle solar battery for 100 dollars, The panel necessary would be 100 - 150 watt? Would an inverter be required for the system?

          Comment


          • #6
            An inverter is required, if you have loads that need 120VAC If you can get by with 12V dc loads, or simply only using the USB output of the controller, you don't need an inverter
            Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
            || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
            || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

            solar: http://tinyurl.com/LMR-Solar
            gen: http://tinyurl.com/LMR-Lister

            Comment


            • #7
              Originally posted by Mike90250 View Post
              An inverter is required, if you have loads that need 120VAC If you can get by with 12V dc loads, or simply only using the USB output of the controller, you don't need an inverter
              Would the fact that I'd only use the system weekly, change the solar panel size? Since I don't need it to charge the battery that quickly? What amperage of a charge controller would I need? I've found a 8A charge controller, I would assume it would work for the battery, if the battery is rated at 7.5A max current?
              Last edited by AllOuT; 04-01-2018, 06:13 AM.

              Comment


              • #8
                Why on earth would you use solar for this? You would be throwing away money. Do you like throwing money away?

                You can do what you want easily and the really good thing is it will work better, and you can power a lot more things other than charging cell phones. It is so simple a 10-year old can make it.

                Battery Charger > 12 volt Battery > 12 Volt USB Hub Charger

                The beauty of it is you could oversize and buy say a 15 amp battery charger to charge a 12 volt 150 AH battery. That would be enough to charge. That would be enough to charge roughly 150 cell phones over periods of weeks/months without power. However add an Inverter and you can watch TV and have a few lights. It would cost less than your plan.

                Now if you want to limit it to just cell phones and tablets, all you need is a Wall Wart 2-amp 12 volt charger, a smaller 12 volt 10 to 15 AH battery, and your 12 volt USB Hub Charger. It would still run circles around your idea and cost 1/4 of what you want to do. Enough to charge 10 to 15 cell phones over a period of a few days without power.
                MSEE, PE

                Comment


                • #9
                  Originally posted by AllOuT View Post

                  Would the fact that I'd only use the system weekly, change the solar panel size? Since I don't need it to charge the battery that quickly? What amperage of a charge controller would I need? I've found a 8A charge controller, I would assume it would work for the battery, if the battery is rated at 7.5A max current?
                  Your fact is Tom Foolery. Assuming you had a 100 watt panel, enough to generate 8 amps of charge current would destroy a 7.5 AH battery in a week. You charge batteries at C/10 rate, not 1C. 8 amps into a 7.5 AH battery is greater than 1C charge rate. With 8 amps of charge current requires a 80 AH battery.
                  MSEE, PE

                  Comment


                  • #10
                    Originally posted by Sunking View Post
                    Why on earth would you use solar for this? You would be throwing away money. Do you like throwing money away?

                    You can do what you want easily and the really good thing is it will work better, and you can power a lot more things other than charging cell phones. It is so simple a 10-year old can make it.

                    Battery Charger > 12 volt Battery > 12 Volt USB Hub Charger

                    The beauty of it is you could oversize and buy say a 15 amp battery charger to charge a 12 volt 150 AH battery. That would be enough to charge. That would be enough to charge roughly 150 cell phones over periods of weeks/months without power. However add an Inverter and you can watch TV and have a few lights. It would cost less than your plan.

                    Now if you want to limit it to just cell phones and tablets, all you need is a Wall Wart 2-amp 12 volt charger, a smaller 12 volt 10 to 15 AH battery, and your 12 volt USB Hub Charger. It would still run circles around your idea and cost 1/4 of what you want to do. Enough to charge 10 to 15 cell phones over a period of a few days without power.
                    Okay, cheaper sounds good, but is it renewable without grid power present? What would charge the battery charger so it could charge the system? A 150 ah battery would cost as much as a 100w mono 36v solar panel, 12v 32ah agm battery, 300w inverter, and a charge controller (330 dollars, not including shipping) I don't understand that, but I'm willing to make the system as cheap as possible. I don't understand, using a wall wart? My intention for this system is to be off-grid, reusable weekly, for as long as the battery lives. How would I connect a usb hub directly to a 12 volt battery?
                    Thanks for the input, looking forward to your answer.

                    Comment


                    • #11
                      Originally posted by Sunking View Post

                      Your fact is Tom Foolery. Assuming you had a 100 watt panel, enough to generate 8 amps of charge current would destroy a 7.5 AH battery in a week. You charge batteries at C/10 rate, not 1C. 8 amps into a 7.5 AH battery is greater than 1C charge rate. With 8 amps of charge current requires a 80 AH battery.
                      What I meant was the current, would the battery be compatible with the 12v 8A charge controller 13,9V charging voltage, but the system I'm looking at is a 100 w panel that's rated at 2,81A and the battery is AGM 32ah 12v rated at a max charging current of 7.5A, Capacity at hr10 (c10) 30ah (3.0A, 1.75V). Would that still kill the 32ah battery? Or is this fine?

                      Comment


                      • #12
                        Originally posted by AllOuT View Post
                        Okay, cheaper sounds good, but is it renewable without grid power present?.
                        No it is not renewable energy, that is a myth with a battery system. It makes you an energy hog and a heavy polluter. The amount of energy t takes to make the battery alone has a negative EROI meaning it will never give you more energy in its lifetime than it took to make the battery. Compound that with the huge amount of energy it takes to make the panels, controller, Inverters, chargers etc is a huge waste of resources that could be better utilized. Two things you cannot do with off-grid is save money or earth. At a small scale like you are going after coupled with poor energy utilization of what power can be utilized from such an inefficient system, you will be paying up 10 to 20 times more for power, and knowing that also means you are pumping out around 10 to 20 times more emissions for the same amount of given power from the POCO. It is a huge looser.

                        MSEE, PE

                        Comment


                        • #13
                          Originally posted by AllOuT View Post

                          What I meant was the current, would the battery be compatible with the 12v 8A charge controller 13,9V charging voltage, but the system I'm looking at is a 100 w panel that's rated at 2,81A and the battery is AGM 32ah 12v rated at a max charging current of 7.5A, Capacity at hr10 (c10) 30ah (3.0A, 1.75V). Would that still kill the 32ah battery? Or is this fine?
                          Lets get a couple of facts straight. Just because you have an 8 amp charge controller does not mean you will have 8 amps of charge current. Charge current is determined by the panel wattage, battery voltage, and charger controller type being used of either PWM or MPPT.

                          With PWM Controllers Output Current = Input Current. So if you had a 100 watt battery type panel the max Imp (current @ max power) equal roughly 5.33 amps at high noon, something less at all other times. Some quick mat 5.3 amps x 12 volt battery = 64-ish watts from a 100 watt panel for a few minutes around noon.

                          MPPT Output Current = Panel Wattage / Battery Voltage. So a 100 watts / 12 volts = 8.33 amps. Surprise you actually get close to 100 watts from a 100 watt panel for a few minutes around noon.

                          If you are looking at a 8 amp charge controller, I am certain you are looking at a Chi-Com PWM controller where the box it comes in is worth more than the controller. Ideally with a Pb battery the optimum charge current is C/10. If charge current is 5.3 amps you are looking at a 50 AH battery, you can figure out on your own if the charge current is 8 amps.

                          Now this is where things get really funny, educational, and you will just love. Lets say you charge two cell phones each day. Everyday you completely drain your cell phone battery to 0%. A large cell phone battery is 3.6 volts x 3.5 AH = 12.6 watt hours. So to recharge two cell phones requires 25 watt hours to recharge every fricking day. Let say you use a 12 volt 50 AH battery with a 100 watt panel. Such a system is capable of generating roughly 300 to 400 watt hours per day if you used it. That is called full utilization. Enough to charge 16 to 20 cell phones a day or about 5-cents of electricity. A low end 12 volt 50 AH battery cost roughly $100 and will last 2 years at best. 365 days per year x 2 years = 730 days. If you use 25 watt hours per day for 2 years = 730 days x 25 wh = 18.25 Kwh. That means in just battery cost alone you paid $100 / 18.25 Kwh = $5.47 per Kwh. Depending on where you live in the USA electricity cost 8 to 25 cents per Kwh. That means to go solar you are paying up 22 to 68 times more for electricity just in battery cost alone not counting anything else like panels and controller plus all the gas money you spent getting materials home

                          On the other hand if you could possible utilize every watt hour the panel is capable of generating everyday, impossible to do, would yield 300 wh x 730 days = 219 Kwh. That brings the Kwh cost down to $100 / 219 Kwh = $0.46 per Kwh or 2 to 5 times more than the POCO would charge you. Unfortunately the environment and your children loose because it took 5 times more energy to make the batteries than what you got out of them.

                          Told you it was funny.
                          MSEE, PE

                          Comment


                          • #14
                            Originally posted by Sunking View Post
                            Lets get a couple of facts straight. Just because you have an 8 amp charge controller does not mean you will have 8 amps of charge current. Charge current is determined by the panel wattage, battery voltage, and charger controller type being used of either PWM or MPPT.

                            With PWM Controllers Output Current = Input Current. So if you had a 100 watt battery type panel the max Imp (current @ max power) equal roughly 5.33 amps at high noon, something less at all other times. Some quick mat 5.3 amps x 12 volt battery = 64-ish watts from a 100 watt panel for a few minutes around noon.

                            MPPT Output Current = Panel Wattage / Battery Voltage. So a 100 watts / 12 volts = 8.33 amps. Surprise you actually get close to 100 watts from a 100 watt panel for a few minutes around noon.

                            If you are looking at a 8 amp charge controller, I am certain you are looking at a Chi-Com PWM controller where the box it comes in is worth more than the controller. Ideally with a Pb battery the optimum charge current is C/10. If charge current is 5.3 amps you are looking at a 50 AH battery, you can figure out on your own if the charge current is 8 amps.

                            Now this is where things get really funny, educational, and you will just love. Lets say you charge two cell phones each day. Everyday you completely drain your cell phone battery to 0%. A large cell phone battery is 3.6 volts x 3.5 AH = 12.6 watt hours. So to recharge two cell phones requires 25 watt hours to recharge every fricking day. Let say you use a 12 volt 50 AH battery with a 100 watt panel. Such a system is capable of generating roughly 300 to 400 watt hours per day if you used it. That is called full utilization. Enough to charge 16 to 20 cell phones a day or about 5-cents of electricity. A low end 12 volt 50 AH battery cost roughly $100 and will last 2 years at best. 365 days per year x 2 years = 730 days. If you use 25 watt hours per day for 2 years = 730 days x 25 wh = 18.25 Kwh. That means in just battery cost alone you paid $100 / 18.25 Kwh = $5.47 per Kwh. Depending on where you live in the USA electricity cost 8 to 25 cents per Kwh. That means to go solar you are paying up 22 to 68 times more for electricity just in battery cost alone not counting anything else like panels and controller plus all the gas money you spent getting materials home

                            On the other hand if you could possible utilize every watt hour the panel is capable of generating everyday, impossible to do, would yield 300 wh x 730 days = 219 Kwh. That brings the Kwh cost down to $100 / 219 Kwh = $0.46 per Kwh or 2 to 5 times more than the POCO would charge you. Unfortunately the environment and your children loose because it took 5 times more energy to make the batteries than what you got out of them.

                            Told you it was funny.
                            I see your point, but the point of this system wouldn't be daily use, plus its not for money saving, or environmental reasons, its for self-sustainability, I calculated my watt hours, and it would be around 170wh that I would use weekly, I live in Europe, and the parts would be shipped to me, no clue about the shipping price though. The battery advertised is rated to work 10 years, the controller is called steca solsum 8.8f, it costs 35 bucks so I assume it is PWM. So what your saying is that a 100w panel is overkill? I'd really like to make this work, as I said, it is necessary for it to be off-grid, the load would be 170wh that'd I'd use on a weekly basis.
                            Thanks for your input.

                            Comment


                            • #15
                              Originally posted by AllOuT View Post

                              I see your point, but the point of this system wouldn't be daily use, plus its not for money saving, or environmental reasons, its for self-sustainability, I calculated my watt hours, and it would be around 170wh that I would use weekly, I live in Europe, and the parts would be shipped to me, no clue about the shipping price though. The battery advertised is rated to work 10 years, the controller is called steca solsum 8.8f, it costs 35 bucks so I assume it is PWM. So what your saying is that a 100w panel is overkill? I'd really like to make this work, as I said, it is necessary for it to be off-grid, the load would be 170wh that'd I'd use on a weekly basis.
                              Thanks for your input.
                              OK first understand the battery will not last 10 years.

                              Your main issue is you pulled the trigger to quickly. All parts of the system need to be matched up to work with each other and sized to support the daily power demand. 175 wh weekly is not a design goal. It is daily usage for an off-grid system. But never mind that for now, you lost that opportunity when you bought the first component.

                              So what do you have now? Lets work with that. Example lets say you already have a 100 watt panel and are going to use a PWM controller. That dictates everything down stream. With a PWM controller take a look at your 100 watt panel Imp spec (current at maximum power) it should say something like 5.5 amps. If using a PWM controller a 100 watt panel can support a 12 volt battery size as low as 40 AH up to 60 AH. Anywhere in that range. Battery charge current have minimum and maximum amount of current that must be met called C-Rate. The ideal charge rate is C/10 where C = the battery Amp Hour Capacity and the Integer 10 is Hours aka 10 Hour charge/discharge rate aka C-Rate.

                              Amp Hours = Amps x Hours
                              Hours = Amp Hours / Amp
                              Amp = Amp Hours / Hours

                              So C/10 rate on a 50 AH battery = 50 AH / 10 Hours = 5 Amps. As a general rule of thumb for Pb batteries minimum charge rate is C/12, and max is C/8, and C/10 is ideal. If you were to use a MPPT Controller you would harvest more current. With a 100 watt panel roughly 8 amps which will support a larger battery of 65 to 100 AH with 80 AH being ideal. Understand how I did that?

                              OK being gin the sunshine capital of the world of good ole England, you have very few sun hours to work with. That means you want to use a C/8 charge rate or as fast as you can charge to make up for short sun hours. My bad the Sun is that bright glowing orb in the sky you see once a week. So if your max charge current is 5 amps x 8 hour charge rate = 40 AH battery. Understand?

                              Now what can a 100 watt panel with a 40 AH battery generate each day for you? About 150 to 200 watt hours per day. In a week would be 1000 to 1400 watt hours. Way more than you wanted.

                              But like I said there is no need for solar to do this. It can be done a lot less expensive and works far better by just buying a Battery Charger and Battery. Say a $30 5 amp charger and a $100 12 volt 50 AH battery. You just leave the charge plugged in which keeps the battery charged up. If you loose power, the battery has a capacity of 12 volts x 50 AH = 600 watt hours with 500 watt hours usable. A cell phone stores roughly 10 watt hours. You could charge 50 phones from the battery. Not likely you would have a two month power outage.

                              So you only need roughly 30 to 50 wh per day if even that much. A 20 to 30 watt panel with the smallest PWM controller you can find charging a 12 volt 15 AH battery would have been overkill. With a 100 watt panel forces you to use at least a 40 AH battery and you can charge cell phones for a month without sun or commercial power Understand?
                              Last edited by Sunking; 04-02-2018, 11:32 AM.
                              MSEE, PE

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