I recently put in a series of solar powered walkway lights in front of my house. They're equipped with a fairly powerful LED, and correspondingly have a large solar panel (compared to other solar powered walkway lights). I've found that these lights work really well when they are exposed to direct sunlight for a significant portion of the day, but when they are partly or completely shaded, they only charge enough to run for an hour or two after sunset. To fix this problem, I decided to replace the stock solar panel with a larger one. The original solar panel provides 5V to the charger circuit which in turn charges the 3.7V LiFePo4 battery that powers the LED at night. The charger circuit also switches the direction of current flow through the battery; when there is enough sunlight hitting the solar panel that its output voltage is sufficient to charge the battery, the circuit charges the battery. When the solar panel's voltage falls low enough, the charger circuit switches the battery to powering the LED. There is a certain amount of hysteresis built into the system so that the light doesn't flicker on and off when the power level is right around the cutoff/turn on point. Because the circuit requires a solar panel that nominally provides 5V in full sunlight, this is the kind of panel that must be used. I bought my replacement solar panels from a store on eBay that sells them for about $4. This adds about 50% to the total cost of the walkway light, but vastly improves its function. replacing the original solar panel with a larger one enables is to charge in less light, which in turn lets the walkway light fully charge even when placed in a fairly shady location. For the walkway light right in front of my front door, I used a larger 2.5W solar panel to let it charge even though it is completely shaded by a large bush right next to it. This is the walkway light shown below that has a larger solar panel attached to the top.
Step 1: Supplies Required
Solar Panel (any 5V solar panel should work here; the larger the solar panel, the dimmer the light the walkway light will be able to charge in) This is the item I ordered from eBay: http://www.ebay.com/itm/200855961823?var=500129297657&ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
Assorted wire and soldering supplies
Drill and small drill bit
Flat head screw driver
Waterproof glue (I used LocTite FixIt glue, but any strong glue for outdoor use should work)
Clamps to hold down solar panel when gluing it on