Circuit Laws and Solar Panels

Every square meter of the earth's surface receives about 1,000 W of power while the sun shines.¹² This is an incredible amount of power and energy—as much energy in a single hour, in fact, as all of humanity uses in almost a full year. Harnessing this free and ubiquitous power, however, is a little more tricky.

Solar cells are the byproduct of decades of semiconductor technology advancements. Semiconductors are neither conductors nor insulators, but can switch back and forth when triggered. In a solar cell, sunlight is the trigger, causing the cell to spontaneously generate a current when exposed to light. We can treat solar cells as "current sources" the same way a battery in a circuit is a voltage source: while batteries add a potential V to the circuit, solar cells create a current I. Ohm's Law, of course, still holds, and every solar cell has an operating voltage that appears across it.

But each cell has a very low voltage and doesn't create much current—and so no one cell can power a building or a home. Cells must be connected into solar panels: arrays of cells that build up the total voltage and current to useful levels. The trick is to connect them in such a way as to make both big voltages and big currents.

Kirchhoff's Current Law states that the current around a loop of wire is constant. So connecting solar cells in series, where each cell is in the same loop as all the other cells, can't possibly change the overall current generated. But the voltage drop across each cell adds to the next one, which adds to the next one, which adds to the next one, until a large overall panel voltage has been built up in little cell-sized steps. Each of these strings of high-voltage, low-current cells can then be connected in parallel to increase the overall current of the panel.

And just like that, you've turned your little solar cells into a device that creates high currents at a high voltage. The equation P = IV means you now have power overwhelming—and just imagine the amount of vespene gas emissions you can mitigate with solar panels.