Thanks to a Radio Shack solar project kit I owned in my youth, solar power and LEDs have always held my attention.  Solar accent lights are neat and handy for a number of reasons.  An entire industry of electronics parts exists just for these types of devices, not only simplifying the circuitry, but also lowering the prices to ridiculous levels -- motion-activated solar LED lights can be purchased for under $5!

The yard variety of these lights tend to suffer from a hazing of the resin or other material used over the solar panels, eventually preventing them from getting a good charge off a day's sun.  In the past I tried various regular household cleaners, fungicides, mold and mildew treatments, buffers, and super-fine grit sandpaper to clean them, yet to no avail.  Many of these have wound up discarded because I could not get them restored.

Early this spring I was staring at one and mulling over a number of variables when something clicked.  The bottom line: these look a lot like water spots on black car trim.  I could have tried some CLR or Lime-Away on the lights, but I was concerned these would be too harsh and cause damage.

Thinking back to my car, a nonsense idea occurred to me: Mothers Back to Black.  Recommended to me by my body shop to put the sheen back into the unreasonable amount of black plastic trim on my car, I figured it could not hurt to try.  Such a simple solution, and it works a treat.  Of course, like anything else which gets cleaned or restored, this is not a fix which lasts forever.  I found that I have to re-apply after a month or two, depending upon rain and yard watering.  (Oh, and bird poop.)  I also have added a little bit of a tilt to them to help water run off, though you may be able to tell the coating over the panels in my lights shown are recessed and tend to create a small pool.

Mind you, this does not account for the yellowing of lower-quality resin or plastic covering a solar panel.  That is a whole other problem with which to deal (or just chuck and replace.)  I had about twenty at one time I picked up from Ace Hardware.  The cover on those was domed and helped prevent water build-up, but it also yellowed and darkened to the point of being unable to produce a good charge voltage or current.  The ones I show here are from WalMart and are about seven years-old.

Another tip for longevity is to replace the batteries which come with the lights.  Every one I get has a cheap cell holding about 200mAh to 450mAh, which is not only not enough to keep them lit for long periods of darkness, but also less than what the panels will pump into them in a fairly well-lit yard over the course of a day.  This will result in overcharging the battery, eventually causing battery damage and leakage.

You can pick up larger capacity NiMH cells from the WalMart garden center or many local outlets.  I get the 1500mAh "AA" and they can keep a simple 5252F-based circuit with a color-changing LED running for almost eight hours.  As well, the cells are 1.2V, and the panels shown here output right at 1.2V under moderate to full sunlight.  Many smaller lights have smaller cells: some AAA, but I have picked up a few recently which have 2/3AA and smaller.  Thus, replacing the battery may prove to be more difficult.  I have not tried commercial brand rechargeable batteries like Energizer or Duracell.  While I suspect they will work just as well, these lights get very hot under direct sunlight so that may effect longevity of the battery.  As always, your mileage may vary (YMMV.)