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Powering a laptop is a very useful application of solar for field researchers, technicians, relief workers, SAR, and others. The problem is that, despite what some solar manufacturers seem to say, it is nearly impossible to go directly from the solar panel into your laptop WHILE THE LAPTOP IS RUNNING.
Here's why...
A laptop's power system is designed to maintain a steady level of power to the system. If the grid fails, the laptop will switch over in the blink of an eye to use its internal battery pack. But what happens in the case of having a solar panel attached to the computer? Well, it turns out that unless you have a large panel that is easily capable of producing the 20-30 watts needed for basic computing, reliably, the computer will ignore the panel and use its own battery.
Will the computer still use the power produced by the panel to help slow down the discharge of its own battery?
NO.
Lithium batteries & laptop power supplies are designed to work in an either/or scenario. They will not "pass-through" power to the load and make-up the difference if needed. ie. if the solar panel is producing 10 watts, and the computer needs 30 watts, the lithium battery will not provide the additional 20 watts. Instead, it cuts off the solar panel, and provides the full 30 watts itself.
Turn off the computer, and the panel can provide power to recharge the battery, because there is no longer a load on the battery larger than the solar panel's supply. So, essentially, it is not problem if you only plan to use your laptop at night.
So, all the solar gadgetry out there that promotes itself with phrases like "run your laptop anywhere" are not giving you the whole truth. Yes, you can use their panel to charge your laptop battery, but 'NO', you cannot 'run' your laptop directly from their solar panel.
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Solar powered laptop : system design
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So, if you need to operate your computer during the day for a period of time that exceeds that of your internal laptop battery, the solution is to use an intermediary battery that can act as a float battery. Something that stores the power from the solar panel, and is able to provide all the power the laptop needs. Unfortunately, we have yet to find a lithium battery that will provide pass-through power. ie: act like a float battery. A lithium battery will cut off the solar power and run the load itself if the solar is not at least as much power as the laptop is asking for. So the best solution is still the lowly, tried & tested, SLA (sealed lead acid) battery. These allow pass-through power. A simple stand-by battery will combine with the solar panel to provide the power needed to 'RUN' your laptop & charge its internal battery at the same time.
So, the only thing left to decide, is how much power is needed for the work you need to perform. This requires sizing the solar panel & reserve battery to meet your needs. Check the Modern Outpost website for more information about sizing your solar power system, and contact us if you have questions or would like us to help build your system.
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