How to Estimate Solar Charge Time

Unfortunately, solar charge time is not as simple as just dividing your battery capacity (measured in Watt hours) by the power of your solar panel (measured in Watts). Even in perfect conditions, you get loss due to:

  • Voltage drop of solar panel or Maximum Power Point being lower than rated peak panel voltage
  • Energy used by circuit to buck or boost voltage
  • Energy used to convert electrical energy into stored chemical energy – with excess lost as heat

We go through two common battery chemistries and give you some rules of thumb for each.

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Lithium Ion Battery Charge Time from Solar

Voltaic carries a full line of IoT Power Banks and small solar panels. Since the charge cycle slows down considerably after the battery reaches 90% capacity, this calculation assumes full is about 90% of complete capacity.

Battery Capacity (in Watt hours) / Panel Power (in Watts) X 2

We perform better than this on our own panels and battery combinations on clear sky days, but this is a more realistic estimate for less than perfect days.

Example: 6 Watt Solar Panel charging a 4,000mAh, 3.7V Battery – Time = 14.8Wh / 6 Watts X 2 = 4.9 hours

Tip: Get a “USB Multimeter” from Amazon to verify your charge rate.

If you are connecting to an off the shelf battery pack, there are a number of reasons that the charge rate could be worse. We look at those in our post: “Can Your Panel Charge My Battery Pack.” Adafruit and SparkFun both offer Lithium Ion charge controllers that can work well with solar panels.

Lead Acid Battery Charge Time from Solar

The effective capacity of a lead acid battery is about 50% of stated capacity, i.e. you shouldn’t discharge it past 50% full. They also have a lower charge efficiency than lithium ion. For the purpose of this calculation, we’ll assume that the battery capacity is the true capacity.

This is our favorite waterproof charge controller for lead acid batteries.

Battery Capacity (in Watt hours) X 2 / Rated Panel Power (in Watts)

Example: 10 Watt, 18 Volt Solar Panel charging a 12V, 10 Amp hour Lead Acid Battery (120Wh) from 50% full to Full – Time = 60Wh x 2 / 10 Watts = 12 hours

Environmental Factors Will Likely Increase Charge Time

The solar charge times above assume a 25 degree Celsius day with the panel pointed directly at the sun. Some quick rules for estimation:

Heat: Power output of a panel will decrease by about .005% per degree over 25 Celsius.

Angle: As the panel rotates away from the sun, power output drops.

Angle to Sun % Output
90 100%
75 97%
60 88%
45 77%
30 61%
15 32%
0 3%

Clouds: Any haze or clouds will slow down charge time, often significantly. See: Solar Performance in Cloudy Conditions.

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112 Responses

    • Voltaic Systems

      You need to provide the capacity in Ah as well. Lets say it is a 10Ah Battery or 120 Watt hours. You should only be using ~half of that capacity or 60 Watt hours. Charging that 60 Watt hours from a 15 Watt panel will likely take about 6-8 hours in good sun.

      Reply
      • chris rochon

        Hi Im looking for help, I have a 72volt 35ah battery (ebike) i also have a 300 watt solar panel (portable) . how long would it take to charge from empty to full?

      • Voltaic Systems

        It may not work at all. The voltage from the panel typically needs to be higher than the voltage of the battery unless there is some sort of charge circuit that “boosts” the voltage of the panel. You should look at the voltage output of the AC charger that comes with the ebike. You should certainly not connect the panel directly to battery terminals.

        From what you say, it sounds like your bike battery is 2.5KWh (72V x 35Ah). That is a pretty big battery. In good sun, it would likely take about 16 hours. It depends on how the peak charge rate coming out of the panel.

  1. Anthony

    Hello, I was wondering if you could help me with the equation if I have a 6V/1A panel (which appears to be outputting approximately 11V in direct sunlight), charging six 1.2V NiMH batteries connected in series AND powering a wireless video security camera which typically takes four CR123A (3V/1500mAh [4.5Wh]) batteries OR a 6V/1A AC/DC converter. Also, do you think this panel would be sufficient to keep the six batteries charged and power the camera long-term? It is working short-term (a few hours) as I quickly wired this up today. Thank you in advance.

    Reply
  2. Mario

    I have installed a Truck fridge in my Westfalia. It takes on average 2 amp/hour with 12 VDc to keep it cold. What size of solar panel and battery you recommand to keep it running.

    Reply
  3. Lucian

    Nice article.Though I have tried to understand the charging batteries time forumla,I kinda don’t get it..So if I have a total number of panels summing 600W(12v) and I want to charge 6KW summing batteries, in how many hours would those batteries be charged.(90% charging type batteries.) In a sunny day.
    Any help would be much appreciated.Thank you.

    Reply
  4. Vibhor

    Hi,
    Can you explain this calculation please; what is 1.6?
    Also, what is the voltage assumed for the 6W panel?

    Panel Power (in Watts) / Battery Capacity (in Watt hours) X 2
    Example: 6 Watt Solar Panel charging a 4,000mAh, 3.7V Battery – Time = 14.8Wh / 6 Watts X 1.6 = 3.95 hours

    Thanks

    Reply
    • Voltaic Systems

      Vibhor, looks like a typo. We’ve updated the text on the Example. Note that we have gotten faster charge times especially with MPPT in good conditions, but doubling is a useful shorthand.

      Reply
      • Brett

        I’m confused by this equation, as you flip it when you are doing the calculation. You state that it’s Power panel watts / Battery Watt Hours x 2, but then when you show your work you flip that division to Watt Hours / Watts x 2.

  5. PMP

    Hello,

    I’d like to power a modem and cellular device similar to a phone but is meant for ‘country’ internet that will be in a sealed box from the elements. Elements: summer up to +35-40 degrees Celsius. Winters down to -35 degrees celcius. The modem will be connected to a ubiquity dish over PPoE. My home is in a ridge where cellular signal is very weak and this box will sit on top of that ridge and relay internet via dishes to my home. The latency has been taken into account and is minor. Any suggestions to help accomplish this goal would be greatly appreciated. Should more information be needed it can easily be provided. Thank you.

    Reply
    • Voltaic Systems

      To determine how big of a solar system you need, you first need to figure out the average power draw of your device in Watts. You can connect it up to a multimeter or talk to someone from the company (you’re not looking for the rated draw of the charger, but the actual power consumption). Once you know that, then you can properly size the system.

      Reply
  6. Tosin

    Devices and equipment list
    1. 24v 200mh lithium batteries;
    2. 60A MPPT charge controller;
    3. 2.5kva solar inverter;
    4. Average daily sunlight: 9hrs;
    5. Backup time after sun down 9hrs;
    6. Total estimated load: 550watts;
    Please I would like an advice on required panels of 300watts monocrystalline solar panels to charge the batteries and equally engage the inverter

    Reply
  7. Spencer

    How long will it take for 30 x 300w solar panels take to charge a battery bank of 6000ah?

    Reply
  8. Lee

    Hello, I am trying to determine if a 200W (two solar panels approximately 2 x 4 feet in size) will be enough to keep 2 (Everstart 29DC from Walmart) deep cycle batteries charged while I am running an ARB 50 quart refrigerator that takes about 1 amp per hour to operate in hot weather along with led coach lighting at night and a couple of hours of running a small led tv. Is 200W too much or could I get by with less or would I need more? Any additional tips or information would be greatly appreciated. Thank you.

    Reply
  9. Ann

    I want to charge a car battery by solar panel. I use one to charge my motorcycle 10W panel that works as trickle charger when fully charged. Just curious what wattage would be needed as a panel for a car battery.

    Reply
    • Voltaic Systems

      You don’t need a lot of wattage, you need the right voltage, which is somewhere between 14-18 Volts. You can search on Amazon for solar trickle charger and you will see a large range of options. You could certainly use our 9 Watt panel, but you would need to add some extra electrical components (blocking diode or charge controller) to make it work.

      Reply
  10. Future Aztec

    I really appreciate your help. I was on the phone with Rev Power today explaining what my needs were and how my Anker battery was not doing the job. The person on the phone didn’t listen well to what I was say straight off the bat and seemed to be annoyed that I had specific needs I was trying to cover. Then I was put on hold for 15 minutes — I ended up just hanging up.

    I have a couple more questions about your battery banks.

    Would my 28 watt BigBlue solar panel be wasted on the V72 that I see in the kit you linked to. The panel there is only 20 watts. I am sure it is a better panel than the BigBlue, but I think that this 28 watt panel I already have will be fine — at least I hope.

    The other thing I am concerned about is I don’t want my iPad or USB hub to receive a pulse. This causes the charging message to pop up every few seconds and my USB hub to flick on and off. If I were to order the V72 would I get a steady charge from the battery while the battery itself received the usual intermittent charge from the solar panel?

    Finally, to make sure. I want to plug in an iPad and a USB hub at the same time, my setup seemed to work well with 2 usb outs (as I already have the cabling to route this correctly), the V72 only has one USB — will I be able to just plug the iPad into the laptop port and the usb hub into the usb port at the same time?

    I have been trying to get this figured out and drew a picture of my current setup. Here is a link just to try to be more clear on what I am doing. At the moment everything works awesome, until I plug the solar panel into the battery pack.
    https://forum.audiob.us/uploads/editor/fb/bzvckecmber0.png

    Reply
    • Voltaic Systems

      The BigBlue outputs USB, it will not charge our V72 laptop battery which requires ~18 Volts. As long as you don’t need 12V output (it sounds like you don’t), you could get 2 x V44 battery packs and that would give you:
      a) redundancy
      b) more overall output for all your devices – each battery can output 3A

      To split the output from the panel you have into 2 x V44, you would need:
      1 xhttps://www.voltaicsystems.com/3511-musb
      1 x https://www.voltaicsystems.com/f3511-splitter
      2 x https://www.voltaicsystems.com/f3511-5521

      Reply
  11. Future Aztec

    Is it ever possible to use a tablet while hooked up to a battery bank that is hooked up to a solar panel. In principle this is problematic — is there any way around it, or are we still stuck with a 2 step process of charge and use, instead of using the battery while charging a battery from a weak source like the sun (as opposed to a wall outlet).

    Reply
    • Voltaic Systems

      Hi – if your battery has pass through charging (all of Voltaic battery packs have this), then yes, you can use the tablet while hooked up to a solar panel.

      Reply
      • Future Aztec

        Well I have an Anker PowerCore 20100 battery pack and a BigBlue 28w solar panel. The battery pack has two usb outputs, one I have hooked up to a usb hub, the other is poweing my ipad. When I plug the solar panel into the battery pack, both the USB hub and the iPad start to pulse with the incomming power from the solar panel. This surprised me because I thought I could, in a way, slow the draw from the battery pack by feeding it power from the solar panel. I expected that the power from the battery pack would be constant, even though the solar power from the pack is not. In my understanding this is cause by the fact that the solar power to the battery is less than the draw from the battery to the iPad. But I am not certain. It seems like what is happening is that the battery is getting bypassed and the power I am receiving is direct solar — or, at least, it behaves that way.

        I want to make sure it isn’t some error I have made in how I have things hooked up. Or, that there is some kind of module I can implement in my setup to fix this issue.

        I did see a post on a forum thread of a business selling Goal Zero products that, with their equipment, it is possible to have a battery hooked up to a solar panel while using the battery to power a device. I got in contact with Goal Zero and the tech confirmed this.

        Since I had just ordered an Anker battery pack and was not able to figure out how to do this with their product, I contacted Anker to inquire about the issue and see if they had a product that could address it. The tech there told me that it is not common for a battery pack to do what the Goal Zero battery can do.

        So I was surprised to see you write that, “if your battery has pass through charging (all of Voltaic battery packs have this), then yes, you can use the tablet while hooked up to a solar panel.”

        Can you recommend a product that would allow me to charge an iPad Mini 4, while powering a USB hub rated at 5V2A? And if so, my current Anker battery says it will charge an iPad Mini 4: 2.5 times. What sort of comparable volume would a suggested product provide?

      • Voltaic Systems

        Most battery packs don’t charge well from solar and don’t do pass through charging well, see: https://blog.voltaicsystems.com/can-panel-charge-battery-pack/

        A couple of comments:
        – Most companies are extremely optimistic in the number of times they can charge a device – they assume there is zero loss going from one battery to the next, but 2.5X into the Mini from the PowerCore 20100 seems about right
        – The Arc 20W Kit http://www.voltaicsystems.com/arc20w-kit is the closest fit – same battery size, slightly smaller panel

  12. Nicholas

    Can a 5 watt to 10 watt solar panel charge up a 9 volt battrry .. I have a caline echo effects pedal that uses a 9 volt battery to operate . It also has the 9 volt input for an AC power adapter .. I have a USB to 9 volt adapter cable to connect a solar panel to the caline echo pedal .. But I need to know what’s the least amount of watts from the solar panel needed to power up the echo pedal that uses 9 volts .. Thank you

    Reply
    • Voltaic Systems

      What kind of battery? Is it a rechargeable or non-rechargeable. I think you’d have more luck if you used a solar panel to charge a USB battery (like our V44), you can use that USB to 9V adapter to run Caline pedal.

      Reply
    • Voltaic Systems

      Yes. The important things are that it charges safely (no overcharge, no short circuit) and efficiently (doesn’t waste too much power). We use 6V open circuit panels to charge 3.7V LiIon / LiPo cells in a lot of our products.

      Reply
  13. Hozefa

    Hii I want to charge one laptop and 3 smart phones i want to charge with solar panel so how much watt panel i should buy and what voltage output battery i use???

    Reply
  14. Chelsea Inglis

    Hey there, I have been using the 20 watt solar panel with the v72 battery just testing it out. When the battery first arrived fully charged it charged all of my devices with juice to spare. I tentatively have been putting the panel out my window behind a screen and charging it that way. The battery now lights up as fully charged but lasts maybe 10 minutes. Why is it lighting up as fully charged if it isn’t? Thank you!

    Reply
    • Voltaic Systems

      Hi Chelsea, the V72 won’t charge well from behind a window. Make sure you put the solar panel outside and without any shade. It should take about 5-6 hours in full sun with the panel pointing at the sun. What may have happened in this instance is that the V72 gave a false positive of being fully charged. We are working on making the charge indicator more accurate.

      Reply
  15. Erik

    I’m building a remote APRS weather station. I draw about .5amps per hour to run the system. What size battery and what size solar panel do I need if I want it to be able to run year round. The charts for my area show 5 hours of sun per day average. (Eastern washington).

    Reply
    • Voltaic Systems

      Hi Erik – 0.5A at what voltage? If at 5 Volts, that is 2.5 Watts (0.5 * 5V) and 60 Watt hours per day. We tend to assume that you are going to get a batch of bad weather vs. 5 hours of sunlight a day. To plan for that period, we tend to recommend scaling the system so that it can run on 2 hours of sun a day and run for 5 days without any sun. For important systems, be even more pessimistic. I would suggest using something around a 60 Watt panel and a 200 – 300 Watt hour system. You can of course experiment with something smaller or tolerate times when the system goes down during periods of bad weather.

      Reply
  16. Travis

    Hello,
    I Currently have a 12v 12 AH battery that runs a 12v 4 amp water pump. Normally I have to plug the battery in to charge it but was hoping a solar panel could eliminate this. Assuming this pump runs for no more than 2 hours total a day, what size solar panel would I need to purchase? I know their are outside factors so I would rather be safe than sorry. Any help is appreciated!
    Thanks

    Reply
    • Voltaic Systems

      Hi Travis – assuming that the pump uses the full 4A (you’d have to measure to be sure), your pump draws 48 Watts. If you run it for two hours, the pump consumes 96 Watt hours a day. Not every day is sunny so I would tend to overdo it with a 50-100 Watt panel from your local big box hardware store. They are not that expensive, but that will charge the battery in 1.5 – 3 hours of good sun a day.

      Reply
  17. Luke Davis

    Hi,
    I have the array 10 volt back pack.
    It works great in full sunlight, it charged my phone from 45 % to 90 % in 2 hours.
    I charge through window panes, but a lot slower than when in full sunlight.
    However I still havent figured out how to store power. As soon as i take the kit away from the sunlight, the phone stops charging. How do I store power from the sun
    Am i doing something wrong ?

    Reply
    • Voltaic Systems

      It most likely won’t work. You can get a regulator to drop the 12V down to 5V, but the 2W panel is so small that your device will ignore it and won’t charge.

      Reply
  18. Andrea

    Hi Jeff,
    Following your example it means a 4,5V solar panel could charge a 3,7V 2500mah lipo battery? And in how much time if the panel has 3,2W and about 20% of efficency

    Reply
    • Voltaic Systems

      Without some sort of boost circuit, we believe 4.5V is too low of a peak voltage to charge a 3.7V battery. It will charge reasonably well when the battery is flat (3.7V), but as it starts to charge, its voltage will increase and the charge rate will slow down and may not charge it completely full. Over the complete charge cycle, 5-6V (we use 6V) will charge the battery faster.

      The efficiency of the cells in the panel doesn’t matter in this case. What matters is the total power produced by the panel as well as the voltage.

      In your case (and assuming you use a 6 Volt panel) your 3.7V 2500mAh battery is 9.25 Watt hours. Approximate time to charge would be 9.25 Watt hours / 3.2 Watts * 2 = 5.8 hours. This will vary based on cloud conditions, shading, angle to the sun and temperature.

      Reply
      • Andrea

        Thank you very much Jeff, adding a mppt controller is usually make any difference in term of faster charging? Or it is better to have just a simple controller to reset panel when weaked sun or cloudy?

      • Voltaic Systems

        Hi Andrea, MPPT chips can improve performance, but may simply add cost without significant gain. Where we see them most effective is in either very large systems or when space is highly constrained and the circuit needs to get every available bit of power. We’ve seen lots of these circuits under-perform so it is really only worthwhile for expert engineers or someone who is going to put in a lot of time testing output under a range of solar and environmental conditions.

    • Voltaic Systems

      It won’t work. The panel produces so little current that your laptop will not recognize it. In addition, charging laptops directly from a panel is challenging as they expect a very steady flow of current which solar does not provide.

      You could connect your panel to our V72 battery (https:/www.voltaicsystems.com/v72) and use that to charge your laptop. 7 Watts is well below our smallest system for charging laptops which is a bit over 10 Watts so you should be prepared to be patient or get a larger solar panel (in Watts).

      Reply
  19. Idris

    How may watt solar panel that will charge 400Ah battery with 5kva inverter 75% load during sunning time and for how many hours

    Reply
  20. RockAndHardPlace

    I know someone living in their vehicle and they need a cpap machine while they sleep. They have an inverter, and it runs their machine 6-7 hours from the car battery before shutting off. When it shuts off, there is still enough of a charge on the battery to start the vehicle. I think the inverter won’t allow them to run it dead, but it let’s it go until that’s all that’s left. He is about to buy a solar setup from a private party that has a total of 32 watts in two solar panels, and has a charge controller with it. Where we live, it is always completely overcast or raining. Would the panels still charge the battery to full in the 8 hours or so that we have daylight?

    Reply
    • Voltaic Systems

      There are a lot of unknown variables. a) the size of the battery inside the CPAP machine and b) whether the battery inside the CPAP will charge effectively. However, it seems like you could be short on power given the conditions.

      Solar won’t work as well When it is raining, the power output of the panels will likely be about 5% of its rated output or 1.5W. However, the CPAP may not accept this low amount of power so it could be zero. The easiest way to figure it out would be to test on a fully drained CPAP machine.

      Reply
  21. DEEPANKAR

    how can we charge a small solar panel fast. can we use other things to charge without a Sun?

    Reply
    • Tony Kauffmann

      All of our voltaic universal batteries can also be charged from a wall power outlet, either through a USB port or through the included 18V AC charger for the V72. So you don’t need to sun to charge these batteries.

      Reply
  22. raja

    i had 12v 10w panel and 12v 40w panel how much capacity battery and Amps charge controller are require please help me
    I planning for an led garden light

    Reply
    • Tony Kauffmann

      How much capacity of the battery you need depends on the power consumption of your light and how long you want the light to run.

      Reply
  23. Gurpreet

    I want to purchase a 13000 mah 5 V power bank but company donot mention how long it will take to charge power bank fully in a good sunny day…any idea ahow approx it will take to charge it fully?

    Reply
    • Voltaic Systems

      It depends on how efficient the battery charges from solar power and the size of the solar panel. If we assume that the battery charges efficiently from solar, a reasonable estimate is (Battery Capacity in Watt hours) / (Power of Solar Panel) * 2. You need to take the size of the solar panel, divide by 48 Watt hours (the voltage of the internal battery is actually 3.7) and multiply by 2.

      Reply
  24. M faisal khan

    I have 150 Watt soler panel and 105 amp battery. What time is required to charge my 12 volt battry.

    Reply
  25. Selina Zhou

    How long would it take to recharge a IPhone 6s, fully, using a 100 watts solar panel?

    Reply
    • Voltaic Systems

      Same time as from the Apple wall charger, assuming you have a regulated USB output of 5V, 2A. The iPhone has a maximum charge rate so you won’t be able to charge faster than from a wall.

      Reply
  26. olayinka

    I have a need to set up a 30 phone capacity charging station. What kit do I need to have i.e panel, battery, inverter, charge controller

    Reply
    • Voltaic Systems

      It is certainly possible to do without an inverter / charge controller, but you could also do it that way as well. Using our equipment, you could get 7-8 x 9 Watt kits which have a 9 Watt panel and V44 battery. From each V44 you could run a USB hub so that you could charge 4 phones from each V44 battery. In this way, you skip going from DC to AC and back to DC. Or you could get a large panel, say 100 Watts and connect it to a battery over 200 Watt hours with a built in inverter and run lots of USB chargers out of that. Have a look at earthtech products for a range of products in this category.

      Reply
  27. mathsongroup

    Thank You for the instruction. Pls how many female usb regulators or phones can be connected to the output of the 9w panel?

    Reply
  28. mathsongroup

    Pls, i want set up a solar pv phone charging centre in my house (village) to charge about 6 phones (3.7v and 2.5w each) at a time. do i need inverter and controller? pls let someone help me for the calculation of the components; panel, inverter and controller.

    Reply
    • Voltaic Systems

      You don’t need an inverter. Everything can stay in DC. For this sort of application, you could use the 9 Watt Kit which includes a 9 Watt solar panel and the V44, 12,000mAh battery and 2 USB ports. If you really wanted to reduce costs, you could just get the 9 Watt panel and the USB regulator. This would work to charge phones on sunny days, but you wouldn’t have any power storage if you skip the battery.

      See:
      https://www.voltaicsystems.com/9-watt-panel
      https://www.voltaicsystems.com/9-watt-kit

      Reply
  29. Catherine

    Hello
    I am a novice here. What is the least watt/volt solar cell that is needed to charge an iPhone, etc.?
    How does the size of the solar cell fit in to the equation?

    Reply
    • Voltaic Systems

      We typically recommend 3.5 as the smallest panel for charging an iPhone. Smaller than that and you will typically be frustrated with charge times.

      Reply
  30. Robin

    I have a small 4amp fan i wanted to run 2-3hrs a day. I have a 2.2 amp trickle charger..Can I put the trickle charger on the car battery while running my fan to maintain the car battery? Any info would be helpful.

    Reply
  31. Frank

    I have a 6V 4.5 battery and a solar panel 6V and a trail Camera 1000-2000ma how long will it take to charge the battery or can I put a 12V solar panel on a 6V Battery and the camera will it blow it up or not the 12V solar panel vpm-17.3 VDC VOC-21.3 VDC IMP-0.3 Amps ISC.0.33 Amps the camera 1000-2000 MA converter on it

    Reply
  32. Brent

    I just bought a Coleman 6W solar battery charger. I am looking to use a 12V battery during the night to run 2 lights, a small fan, and some small speakers. My plan is to use a 400W inverter attached to the battery at night, then use the solar panel to trickle charge the battery at night. Most likely a car battery, possibly a marine gel battery. Does anyone know if my plan will work? Trying for 4 days/4 nights. Im guessing the solar panel will have a good 12+ hrs in sunlight to charge each day

    Reply
  33. Mark

    Hi, I am going to install a 50 watt solar panel, control charger, 2000 watt continuous/4000 watt peak power inverter, and a group 29 deep cycle flooded battery, what will I be able to run with this set up? I would like to run a 15 amp chest freezer and a 22 inch tv, and one house fan will this be enough and if so how long will I be able to run this before battery runs out?

    Reply
  34. siva

    how many hours are taken to charge 12v battery useing
    10w,12v solar panel

    Reply
    • Kumar

      What is the Amp hour (Ah) for battery. if you have battery Ah then apply below formula

      12V x Battery Ah
      ==============
      Solar panel W (10)

      Reply
      • John

        OK, I have a 109 ah deep cycle battery. When I divide that by 100 watts, I acquire a figure of 1.09. So do I need to move the decimal to the right one spot to reflect it will require 10.9 hours to recharge the battery?
        Thanks-John

      • Voltaic Systems

        The 109Ah battery is 1308 Watt hours. It will likely take 20 to 26 hours to charge.

  35. Eddie

    I have the 13 watt battery charger from harbor freight charges at 12 and 24 volts. I got a 40 amp charge controler and a 1.2 amp inverter that plugs into a cigaret lighter socket, the panel kit came with a cigaret lighter socket that I can this plug into. The question is ….will this supply suffecent power for a power tool charger to and charge an 18 volt battery? Specs of the charger:120 VAC, 60 watt. Or… Can I connect the 18 volt battery direct to the battery charge port on the charge .

    And… What is the average amps hours on 12 volt battery?

    Thanks for your kind response.

    Reply
  36. Andre M

    I am looking to mount one or two solar panels on my cargo bike (long john) for bicycle touring. As such I wonder if I can charge my Thinkpad (it has a 20V input, but the battery itself is a mere 10.8V, 7.8Ah) with one or two of your panels and how I would go about setting it up.

    I doubt it could take 36V input if I took two of your 16.8 and wired them in series, and I wonder how it would do with two of your 16.8 panels wired in parallel?

    I will probably buy the V60 battery, but in order to save losses I would prefer to be able to charge the laptop directly.

    Reply
    • admin

      Hi Andre,

      It might work directly from the panels if wired in parallel, it is hard to tell without testing. In general laptops/tablets have fairly sophisticated charge circuits and are looking for something pretty close to spec. It will definitely work from the battery.

      Reply
      • Andre M

        Thank you, that was quick. I might just give it a go and see what happens. Now, to find the money 😀

  37. webby

    I had a 50 watts solar panel and 12 volts battery 28 amp. how many hrs will take the battery to get fullcharge?

    Reply
    • admin

      It depends on a lot of factors, but in reasonably good sunlight with the panels pointed towards the sun, we would expect about 17 hours. Nothing replaces field testing though! The math is: 12*28/50 * 2.5 = 16.8

      Reply
      • Robert Banda

        I’m following questions and answers well, but please help me understand where 2.5 is coming from. Thank you.

  38. Tim

    I want to charge a laptop battery (about 11V, 4400 mAH) and a 9V, 2100mAH battery for a smaller device. Do I need to get two kits, one 18V and one 12V? Or can one kit charge both? I’m thinking a 12V charger will probably be okay with a 9V battery, but I don’t know about an 18V charger. Thank you.

    Reply
    • admin

      Hi Tim,

      In general, we recommend using the panels to charge our V60 battery and then set the output on the battery to charge your devices. The laptop would most likely charge from the 16V setting on the V60 and the 9V battery from the 12V source.

      In some cases, it will be possible to charge the devices directly from the panels. Its hard to know without knowing the specs of the devices, but you would want to put 12V into the 9V battery and 18V into the 11V battery as you suggest. The key here is to make sure there is some protection to make sure you are charging safely: no over charge, no short circuit, etc.

      Reply
  39. ajmal

    i want to use an ac fan for 6 hours daily by a car battry and i want to charge this battry by a 40w panal. what will be the time required to charge it by this panal? plz help mn

    Reply
    • admin

      It depends on the Voltage of your panel, the size of the car battery, your charge controller that you’re using and the weather conditions. You should be able to do it in about a day of full sun though. Please consider using a deep-cycle rather than a standard car battery, it will work better.

      Reply
  40. Charles Cook

    Could the 16.8 Watt Panel be used to charge a 12 Volt vehicle battery?

    My primary use will be a laptop, cell phone, and a 12 volt battery for my hand held Ham Radio.

    Will one panel be enough?

    Reply
      • Jeremy

        what kind of charge controller was used on that second link – the images and link appear to be mostly broken inside that post. I see that an MPPT Sunsaver was used in the first post , but was hoping the second post yielded a more cost affective solution as the MPPT controllers are a little pricey

      • Tom

        I have converted a mini van a Dodge Ram pro master city into a mini camper inside I built a small snack bar a installed a porta potty and a twin 24 inch wide single bed with TV for intertainment I plan to travel from California to visit friends and family in Virginia I do plan to stay at hotels at times but if I find them to costly I ‘ll stay in mini van to camp in or rest at rest stops I chose the mine van for it’s 4 celinder eng and it’s fuel efficiency the question I have is I purchased five jumper battery to use to operate a DC TV, laptop , charge a cell phone as well I want to install ring DC operated security camera to view from my cell phone if ‘someone messes around with the vans insides while I’m in a hotel room and would like to attach a solar panel to the roof rack to keep the jumper battery’s charged by the use of a cigertte DC connection plug as I driving instead of taking them out to the room for AC to DC charging but I’m not sure of what wattage solar panels to use and would I need a regulate or power controller while changing two at a time I believe I need some where in the area of a DC voltage charging range of 12 to 14 dc charging volts but I’m not sure if anyone knows the answer I’m at Ter5@aol.com I would be very great full thanks

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