Mobile Solar Power
Nowadays there are many Mobile Solar Power sources. These can be ideal to carry around when you are going to locations without a decent electricity power supply and you can use them to power your small handheld devices such as iPods, iPads and cell phones. Unfortunately at the moment mobile solar power technology is not efficient enough to power anything much bigger than an iPad.
Mobile Power Source Technologies
There are two types of mobile sources currently on the market – the Photo Voltaic Cell & The Stirling Engine, both of these can be use to charge your portable devices, although the stirling engine is slightly more efficient (and a lot cooler 
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The Photo Voltaic Cell
Photo Voltaic Cells or Solar Cells have come a long way in recent years, they have increased n efficiency from ~ 30% efficient to almost 50% efficient. They are also likely to keep increasing as there are some silicone based cells coming along very soon, their inventors are promising great things from this new technology. You can find some photovoltaic cells here – Iphone Mobile Solar Power
The Stirling Engine
While currently more efficient at converting solar power into usable energy/electricity, the stirling engine and solar cell are likely to have a long drawn out battle n the coming years in attempts at ever increasing efficiency. Although the original stirling engine is almost 200 years old, modern designs are super efficient – 50 % +. The only drawback of the Stirling Engine is that it needs to be a large engine to reduce decent amounts of usable energy. You can see solar powered stirling engine charging systems here – Thames & Kosmos Charging Station