Sunday, February 26, 2012

Solar PV lab

Here are students Joshua, Ben, and Adam constructing a solar module of probably about 30 watts capacity, using raw cells.

This is a relative straightforward process, and, unlike many Mythbusters "builds," you can do this at home. It's even technically possible, and in some states legal, to connect the resulting homemade solar module to the grid.

A solar module connects cells in different arrangements of series and parallel connections to make a target output -- the correct voltage and amperage to run an inverter or charge a battery.

Solar designers use an identical process, scaled up from collections of cells to collections of modules. A solar array is a collection of solar modules (AKA solar "panels") connected in different arrangements of series and parallel to make a target output to run an inverter or charge a battery.

The students' work on this particular day was hampered by the lack of sunshine by which they could actually test the cells' output. They had to use a best guess for the voltage output of individual cells and thus for the entire module.

Later this week, when we get a sunny day (if we get a sunny day), their lab instructor will take the module outside and test the output.

Two other student groups worked on the same task using smaller cells. The three groups started, unbidden by me, to compete together to see who could raise the most voltage.

Voltage is of course a useful metric but relatively meaningless in this context. You might have a high voltage module that produced very little electricity. And the lesson of series and parallel is lost when, to get the most voltage, you simply connect the cells together in series.

The proper metric is of course wattage. The proper equation is V = IR, where V is voltage, I is impedance or amperage, and R is resistance. Rearranged, this translates to the more popular watts equals amps times volts.

In this case we need to measure the voltage and amperage output of each homemade module to get at the wattage.

It's possible to make homemade solar modules in this way that are cheaper than the cost of new proprietary modules. Simply buy the raw cells, solder them together to make the proper output, and seal them in a frame with some kind of glazing, and you'll have a working solar module.

It's this straightforward, uncomplicated process that has most recently been effectively outsourced to China with the failure of US module construction plants like Evergreen Solar. The Chinese have lower labor costs for the very simple manual tasks involved.

The US and allies like Germany and Japan have so far managed to hold onto the newer, more interesting and high tech processes like that owned by the Nanosolar corporation, or the dye-sensitive cells made by Sony.

Since it's these other kinds of processes that promise the greatest breakthroughs in prices and capability, I'm not too worried about western dominance in solar PV.

But this is the technology of the future and we'd better start using it in more widespread applications.

For which we'll need trained solar thinkers like these students at all levels of the economy, and in government.

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