We recommend getting the largest solar panel you can get that will fit your system and cost constraints. The answer will depend on a) how much power your project needs and b) your expected solar conditions. Assuming reasonably good conditions (the panel is angled toward the sun, limited shade or clouds), we assume that you can get 60-70% of a panel's rated output into your battery or device as usable power. This means if you are using a 6 Watt solar panel outside for 5 hours, you will generate 18-21 Watt-hours of power. If you're storing power in a battery, getting that power out of that battery requires power so expect to lose 20% of that power. To calculate your Watt hour power consumption, multiply Current Draw * Voltage * Hours or use the battery capacity in your device as a guide.
Power Production into Battery per Day (Assumes 5 hours of good sun a day)
However, consistently perfect conditions are rare in most parts of the world. If you expect to have fewer than five hours of clear sun per day, you need to increase the size of the panel or decrease the power consumption of your device. Also consider moving the panel (we have 1, 4 and 10 foot extension cords) to get the panel into a sunnier spot. If you are expecting lots of overcast days, then you need to combine a panel size increase (more power generation in less time) with a bigger battery buffer to get you through days when not much power is generated.
If your device or project needs to run continuously, battery storage is often needed. Testing is required, but we generally size systems so that the device can run 3-4 days on its own without any solar power. To calculate the daily power consumption in Watt-hours and multiply by 3-4.
All of our battery packs (15, 44, and 88 Watt hours, respectively) charge efficiently from solar and have an" Always On" mode which keeps them on whether or not a device is drawing any power.
If you are using our solar panels to charge our batteries, no. If you are charging a raw Lithium Ion or Lithium Polymer cell, yes. Here are two charge controllers from <a "http://www.adafruit.com/products/390?gclid=CObs16P1lsMCFdQvgQodgY8A3w">Adafruit and Sparkfun.
If you do not use a charge controller, you risk over-charging the battery and causing a fire.
Is there anything special about Voltaic solar panels?
Yes, our panels can go straight from prototype to production. They are designed to live outside 24x7, 365 days a year for up to ten years. Unlike other small panels, our panels are coated in urethane, not epoxy or PET. This means the coating will not yellow, crack or otherwise break-down in the sun.