How it works! Solar Panels

March 3, 2012 by  
Filed under Green Energy News

If you want to go green, switching to solar panels for your electricity is one way to do it.   But how do solar panels harvest light from the sun and convert it into electrical energy?

 Some materials respond to sunlight by throwing off electrons. Solar panels, or photovoltaic cells, take advantage of this tendency. It’s called the photovoltaic effect and it was discovered in 1896 by Edmond Bacquerel, a French physicist.

 The first photovoltaic cells were created in the 1950s, more than a hundred years after the photovoltaic effect was first discovered, but they were expensive and inefficient (they could only convert one to two percent of solar energy into electrical energy).

 In the 1960s, the space industry started to use photovoltaic cells to power satellites and spacecraft. Prices for photovoltaics dropped and their efficiencies rose. When the energy crisis hit in the 1970s, people started eyeing solar energy as an alternative to petroleum.

 The photovoltaic effect is produced in special materials, usually semiconductors. When exposed to sufficient solar energy, the electrons in these materials may be knocked loose from individual atoms and travel freely around the material until they find a new place to rest. This movement creates an electrical current.

 Photovoltaic (or PV) cells are built to maximize that electrical current. Photovoltaic or solar cells can be arranged to make larger solar panels.

 Most photovoltaic cells today are made with silicon, which exists in a crystalline form.  It’s hard to knock electrons off the atoms in a pure silicone crystal, but silicone can be “doped” with other materials that make it easier to create loose electrons.

 Photovoltaic cells made of silicon have two layers.  One is doped with phosphorus, which creates a form of silicon crystal that has extra electrons. This is called the n-type layer. The other is doped with boron, which creates a form of silicon crystal with lots of empty spaces for electrons.

 If an n-type layer is laid over a p-type layer, when light hits the crystal and knocks electrons loose on the n-type layer, they move toward the holes in the p-type layer side, creating an electrical current in the middle zone called the depletion layer. This sandwich of layers is called an n-p junction.

 The electrical current is carried away from the solar cell by a metallic material, usually silver or copper. That energy can be used to charge a battery and stored for use later.

 The main problem with photovoltaic cells made from silicon is that they’re expensive and relatively bulky. Newer photovoltaic technology uses compounds besides silicon, like cadmium telluride or Copper indium gallium selenide, to create thinner solar cells, or “thin film” solar cells.

 Silicon photovoltaic cells are more efficient, converting between 12 to 18 percent of solar energy compared to just 10 percent for the newer thin film cells, but thin film cells are cheaper. That means users can recoup the cost of installation much sooner.

 The new thin films have other advantages. They can be made flexible, unlike the rigid silicon solar cells. Dye-sensitized solar cells use dyes to create the electrical current, and they’re transparent enough to be used for tinted windows.

 The magic combination, though, will be high efficiency and cheap cost. If we can solve that puzzle, it’ll put us much closer to a clean energy future.

 Laney’s own Green Jobs Education Program has a Solar Photovoltaics Design, Sales and Installation track that trains students to design and install solar panel projects, as well as evaluate the costs and savings involved.

 It’s one way Laney students are moving into that sustainable future. Ever wondered how things you use every day work? We’re starting a new feature that explores just that.  Check laneytower.com for more online exclusives and email us at laneytower@peralta.edu to suggest topics for future columns.

Comments are closed.