Jan 1, 2010

How Solar Cells Produce Power

You probably have a calculator or watch that works without batteries because it’s solar powered. It actually uses photovoltaic cells, which are gadgets that harness light energy from the Sun. These cells directly convert sunlight to electricity, thus producing solar power, one of the many forms of green energy. This article talks about how photovoltaics generate power, how energy produced by them can be stored, and where photovoltaics are used.

How Solar Cells Produce Electricity

Solar cells use light (photons) to generate power (voltage). It naturally follows that this process be called the photovoltaic effect.

When solar radiation is absorbed by solar cells, photons from the sunlight enter the cell and bump into electrons and displace them. At this point, special electrical semi-conductors  within the solar cell capture these electrons and complete a circuit between the top (negative charge) and bottom (positive charge) of the solar cell.

The process may vary slightly depending on the various types of solar cell, but the basics remain the same as shown in the diagram to your right (credit, NASA). The diagram talks about an anti-reflective coating, which is spread over the glass cover of each panel in order to maximize the light absorbed.

The amount of power generated by photovoltaic (PV) solar cells is determined by:
  • the number of PV cells linked to form a solar panel (or photovoltaic module), 
  • the temperature, and
  • the amount of solar radiation present.
So depending on your energy requirement, you’ll either use a single module of 40 photovoltaic cells, which generates around 12 volts (perhaps for a single emergency telephone) or setup an entire array of photovoltaic modules to generate hundreds of volts of electricity (perhaps for your house).

If you want to learn more about the photvoltaic effect, click here and if you’re interested in reading about the advancements in photovoltaic cells, click here.

Storing Solar Power Created Through PV Cells

You may have guessed the output of solar panels could vary considerably. True. But you won’t be left sitting in the dark on cloudy days or at night because you could switch back to normal electricity or take advantage of stored solar power. On particularly sunny days when the energy generated by solar power systems exceeds your requirements, the excess can
  • be used to charge a solar power battery (i.e. stored in a lead-acid battery) and used later, or
  • be sold back to solar PV power companies and bought back later when you face a shortage, or
  • be stored in the form of heat (also referred to as thermal storage).
Uses of Photovoltaic Cells

Photovoltaics were first used to power spaceships in the 1960s but they are pretty common these days thanks to advancements in technology, falling prices and favourable government policies. Some areas that benefit from PV solar systems are:
  • Buildings, both commercial and residential
  • grid-connected power stations
  • hybrid cars/vehicles
  • small gadgets like solar powered calculators and watches
  • water heating systems
  • street lamps
  • and remote roadside telephones, signboards, schools, etc.
Solar panels usually need to be replaced after a decade or two depending on their quality. The output of the PV cells falls over time, but they never stop generating electricity unless they get damaged.

The credit for the photovoltaic effect goes to Albert Einstein who discovered this phenomenon about a hundred years ago. Science has come a long way since then and we now see new inventions every other day. It may be helpful to know there is another type of solar power system, referred to at concentrated solar power (CSP) which is mainly used at solar power plants.

It’s amazing resourceful the Sun is to man; our own private star can singlehandedly fulfill all our energy needs for the future.

Sources: Wikipedia, NASA, NREL, Renewable Energy World, Energy Education (Image A)
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