Electrical Setup

Electrical wires

The 264 solar panels are wired up in series, 22 panels per row, the top of one cell to the bottom of the next, so that their 16 volt potential is additive in each of these twelve current “strings”. The total voltage and current induced by the solar radiation can produce enough power during a bright day to run five family homes.

The photo-voltaic panels on the solar array are wired in current strings, each one made up of 22 panels connected in series. This means that there are three strings (or sets of panels) on each floor of Goodwin Hall for a total of 12 strings, each at around 350 volts. Each string is then wired in parallel to an inverter, which converts the output to a stable 208 volt 3 phase power for use on the electrical grid.

Because of this arrangement, the voltage on the array is constant at around 350 volts, while the current in each string is proportional to solar radiation falling on the panels. There are three strings on each floor of Goodwin Hall. Each string generates about 4 amps of current in full sunlight (given a maximum of 1366 watts per square meter of sun - the solar constant measured by satellite - falling on twenty-two 75 watt panels, at 350 volts).

The details

Step One

Solar Cell electrical diagram: A solar cell.Solar Cell electrical diagram: A solar cell.

Two layers of silicon are produced using a process called doping, meaning impurities are introduced into the silicon such that one layer has too few electrons (called the p-type layer, which has a positive charge) and the other layer has too many electrons (called the n-type layer, which has a negative charge). When these layers are sandwiched together, the difference in charge between them is an electrical potential of about 0.4 volts.

Step Two

Electrons in the electron-rich layer are attracted to the potential. Some of them even have enough energy to break free of their silicon atoms to move into the electron-poor layer of silicon, to restore the balance in potential. This movement immediately creates a layer of neutral potential in the gap between the two silicon layers.

Step Three

The neutral gap is an area of electrical equilibrium, where the attraction pulling electrons from one sheet of silicon to another is exactly balanced by the force keeping the electrons with their own atoms. This balance is easily disrupted by an externally-added source of energy; when the sun rises, photons in sunlight hit the electrons in the n-type layer, giving them the extra energy they need to break free of the silicon. The potential between the layers then pulls the electrons across the neutral gap. As they move, the gap begins to thin, to such an extent that more and more electrons can move easily across it as they are hit and freed by photons. This creates an electric current when the cells are attached together and the circuit is completed.

Step Four

The panels are receiving photons of different wavelengths. While some sunlight is at the right wavelength affect the silicon's electrons, longer wavelengths pass right through the cells and shorter wavelengths are converted into heat. This is why solar panels are only 10 to 13 percent efficient, and why the area immediately above the panels heats up so quickly during the day.

Step Five

Finally, to close the circuit and start generating current, the panels are connected to an inverter which takes the direct current from the cells and changes it into alternating current at 60 hertz that can be fed into the electrical grid. Disconnect switches are provided on both sides of the inverter, so that no energy will be inadvertently dumped into the grid while maintenance crews are working on the wires.

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