This Solar Guitar Tuner from ThinkGeek has a solar panel to keep its batteries recharged. The TASCAM TC-15 chromatic tuner has needle, strobe, fine, meter tuning modes, with twelve tone equal temperament tuning and a detection accuracy of within one cent (one hundredth of a semitone). Tune the guitar by plugging it into the Solar Guitar Tuner with the 1/4″ standard mono jack, or use the built-in microphone to “listen” to the guitar. The batteries are also USB rechargeable. The Solar Guitar Tuner is $29.99.