There you are scrambling over a mountaintop with the sun beating down on you and you are breathing hard and squinting in the hard light and, well, guess what? Your backpack is just getting charged up. What? Yup, as we posted about before, but are posting about again, there are several companies who have developed solar backpacks with embedded with photovoltaic cells that convert the sun’s energy into electricity. The first one is made by Clear Blue Hawaii which offers the Blue Sun Solarpac ($260, battery not included). Another brand is Voltaic Systems which offers the Voltaic Backpack ($229 battery included). Both of these packs operate with an internal lithium battery; the Blue Sun uses a $50 or $150 lithium-ion (the more expensive battery stores more electricity) that put out up to 12 volts, while the Voltaic’s included battery puts out 3.5 to 7.2 volts. A very nice idea. Good to save money on batteries and to do your part not to add to landfills.