Solar power,along with wind,wave,and geothermal energy sources,is seeing accelerating interest in renewable energy research.Once installed,solar panels produce zero emissions as they convert sunlight directly into energy via the photovoltaic effect,bypassing the turbine system found in every other commercial energy source.
The Photovoltaic Effect
Light is converted into electricity by the photovoltaic effect.When light is incident to the cell,the absorbed energy excites bound electrons.This allows them to jump their atomic bonds and become free.The free electrons travel through the material,and the resulting current is harnessed when conductors are attached to either side of the cell.Because there are no moving parts,including turbines,maintenance fees are lower and there is zero fuel use.
Silicon in Solar Cells
The silicon that you’ll now find in a solar cell is highly processed.The material is sourced in silica mines,which are often found in regions with heavy quartz concentrations.The silica is refined to reach metallurgical grade.This process takes place in an electric arc furnace,where carbon is used to release the oxygen in the silica quartzite,resulting in a more consistent silica makeup.However,metallurgical purity doesn’t cut it for a photovoltaic cell.
High-efficiency rates will boost the amount of energy released by the cell,so the purity of the photovoltaic-capable material is of utmost importance.The metallurgical grade silicon is exposed to hydrochloric acid and copper,which produce trichlorosilane gas.Hydrogen is then used to reduce this gas to silane gas,which is in turn heated to make molten silicon.
Pure silicon is crystalline – a structure necessary for photovoltaic cells.The purity level of silicon at this state is anywhere from 99.99999% to 99.9999999% pure.Silicon can be arranged into either a monocrystalline structure,which boasts the highest efficiency rates as well as the highest cost,or a polycrystalline shell.
While the silicon wafers are complete at this point,they won’t conduct any energy until they go through the doping process. This process involves the ionization of the wafers and the creation of a positive-negative (p-n) junction.The wafers are heated in cylinders at a very high temperature and put into water.Then the top layer of the cylinder is exposed to phosphorus (a negative electrical orientation) while the bottom layer is exposed to boron (a positive electrical orientation).The positive-negative junction of the cell allows it to function properly in the solar panel.
After this step,only a few more things need to happen in order to create a functioning cell.Because silicon naturally reflects sunlight,there is a considerable risk of losing much of the potential energy from the sun that the cells are supposed to absorb.To minimize this reflection,manufacturers coat the cells with antireflective silicon nitride,which gives the cells the final blue color we see in installed panels.
From there,manufacturers implement a system for collecting and distributing the solar energy.This is done through a silk-screen or screen-printing process in which metals are printed on both sides of the cell.These metals make a roadmap for the energy to travel through on its way to the receiver.