As the demand for energy grows, our supply of fossil fuel decreases as an alarming rate. This has led to the use of renewable resources such as solar power. Solar power is the conversion of sunlight to electricity. This is done two ways: “directly using photovoltaic energy (PV), or indirectly using concentrated solar power (CSP).” Photovoltaic energy is a method of converting solar radiation into direct current radiation “using semiconductors that exhibit the photovoltaic effect” (Wikipedia). The photovoltaic effect is similar to the photoelectric effect, but use different processes. When any light, including sunlight, shines on a photovoltaic material (monocrystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride, and copper indium gallium selenide/sulfide), the electrons present absorb energy and become excited. This means that the electron began to “jump around” and become free. These excited electrons diffuse and reach a junction where they are accelerated. This generates an electromotive force. (Tritt) This converts light energy into electrical energy. Besides the “direct excitation” of electrons, a photovoltaic effect can also arise from heating caused by absorption of the light. The heating leads to an increase in temperature, which is accompanied by “temperature gradients” (Wikipedia). These temperature gradients may generate a voltage through the Seebeck effect. The Seebeck effect is the conversion of temperature differences into electrical energy. When two different metals are joined in two places with temperature differences, a current loop and magnetic field are created. This means that an electric current is created and is coined thermoelectricity. Whether direct excitation or temperature effects dominate the photovoltaic effect will depend the materials and the environment. The most common way to gather sunlight are photovoltaic cells, or solar cells. Solar cells were first used to power orbiting satellites and spacecraft. There was no way to keep the satellites full of fuel because it was costly to send a spacecraft up to refill it. This meant that another energy source was needed. Solar cells are perfect for powering satellites because they are in direct sunlight most if the time. This means that they can constantly be recharged without requiring the added hassles and expenses. More recently, solar cells have become more popular because of the increase in energy costs and the decrease in fuel availability. More solar cells are being purchased that are connected to the energy grid. Residents in suburban areas are purchasing solar cells and installing them on rooftops. This allows the residents to produce their own electricity while helping supply the rest of the area with electricity. Solar cells are also being built in large areas of land such as farms and in the desert. Another way to harness energy from sunlight is Concentrated Solar Power. In CSP, a system of mirrors and lenses to concentrate a large area of sunlight onto a small area. The concentrated light is then converted into heat