Why solar and not other sources?

Good question! The answer may be surprising. In some locations, solar will not be the best, although it will work well in many locations. For example, it probably would not be wise to install solar modules above the arctic circle because, although you would generate energy during the summer, it is very dark during the winter and you wouldn't get much energy. It is important that solar energy be able to compete with other energy sources. Although it often takes some time and money to bring a competing technology to catch up to existing technologies, business dictates that there be some reason for the change. The new technology must be able to stand on its own two feet once subsidies go away. In some places solar energy will be the best option and in other locations it will not. Solar will likely play a significant role in upcoming years in the power grid (in both developed and developing countries), but it will likely not play a role in all places.

In terms of impact, solar energy is capable of making a big difference in the individual lives of people with little access to other energy sources. In addition to contributions to the larger grid used by those who have many resources, these smaller contributions are also valuable. It is important to consider these small-scale but large-impact contributions when going about research. Without light, it is hard for small isolated farmers not connected to the electrical grid to connect with larger communities, learn, read, and thrive. It is much more difficult to sell goods without the internet. Access to the internet, which we often take for granted, broadens horizons.

What are common things solar cells can be found on? Can solar cells charge a reusable battery?

Source: Tower Sign and Signal

Solar cells can and are used to charge reusable batteries. For example, you see this in solar cars. One of the limitations of solar photovoltaics is that they produce energy when the sun is shining and produce none without light. This could be a problem at night if you don't have any other energy sources or ways of storing the energy produced during the day. If we transitioned to mostly solar energy in the larger electric grid, this could be a problem if batteries can't store energy generated during the day for use at night.

Check out this article to find out more about it!

Solar cells are found on many things. You may be most familiar with solar calculators (the calculators that do not run out of batteries--note that, even indoors, they generate electricity since they are still receiving light, albeit not usually as bright as that seen outside). Solar cells are now used to power road signs and some traffic lights. They are also found in garden lights and other outdoor lighting. Emergency phones in remote places often also have solar cells to cut down on the cost of sending electricity to those places. You can use solar cells to charge your electronic devices. People and businesses are now starting to install solar cells on their buildings/houses in order to reduce their energy costs. Satellites also often use solar cells for power. Solar cells are found on an increasingly wide array of things!

Solar battery!

Credit: Yiying Wu, The Ohio State University

The world's first solar battery has been invented! It recharges itself using air and light.

Read more about Ohio State's research here or here!
Their work was recently published in Nature Communications entitled "Integrating a redox-coupled dye-sensitized photo electrode into a lithium-pxygen battery for photoassisted charging", DOI: 10.1038/ncomms6111.