Solar cells have ridden to success on the backs of other products for decades. First, NASA used the cells in space. Then oil companies stuck them onto off-shore oil rigs. Later, calculators and other small electronics started to include them to generate tiny amounts of power. Now, Katie Fehrenbacher of GigaOm looks at a natural evolution of this trend that's been very underlooked. What if Apple began to include solar cells in its products to extend their batteries' lifespans?