Even for sober science, the word revolutionary gets thrown around far too much. Solar energy gets its share of hyperbole. So the notion that microphotovolatic cells – tiny solar cells about the size of decorative glitter – could revolutionize the solar energy industry might be yet another hyperstretch. Then again, the option to use micro-cells has plenty of advantages. This is what Sandia National Laboratories (New Mexico, USA) is out to demonstrate with its 14-20 micrometer photovoltaic cell.

The Sandia cells are less than a third the thickness of human hair or about 10 times thinner than conventional brick-sized (6-inch-by-6-inch) solar cells. Most of the advantages flow from the shift in scale. For most things solar powered, smaller is better. Here’s a sampling of the advantages for micro-cells:

- More flexible (the small size means the cells are better able to conform to unusual shapes; one day, even clothing)
- Equivalent efficiency (a working micro-cell array is in the same range of efficiency as a traditional cell, 14.7% compared to 13-20%)
- Less costly to manufacture (far less wasteful of materials, especially silicon)
- Use standard tooling procedures (that is, standard for the microelectromagnetic systems (MEMS) industry, not the current solar industry)
- Micro solar concentrators (tiny lenses) can be inexpensively manufactured to increase the efficiency of micro solar-cells
- It’s easier to move small solar arrays to maintain orientation with the sun

The ‘trick’ if there is one to micro-sized photovoltaic cells, is be able to compete with the ‘standard,’ large size cells. They must compete on efficiency, for one thing, but perhaps most importantly they must compete in manufacturing and application. It is here where the small size may have the long term advantage. There are many potential applications, for example flexible substrates (e.g. clothing, curved surfaces) where it’s small cell or nothing.

The solar particles, fabricated of crystalline silicon, hold the potential for a variety of new applications. They are expected eventually to be less expensive and have greater efficiencies than current photovoltaic collectors that are pieced together with 6-inch- square solar wafers.
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Each cell is formed on silicon wafers, etched and then released inexpensively in hexagonal shapes, with electrical contacts prefabricated on each piece, by borrowing techniques from integrated circuits and MEMS.

Said Sandia field engineer Vipin Gupta, “Photovoltaic modules made from these microsized cells for the rooftops of homes and warehouses could have intelligent controls, inverters and even storage built in at the chip level. Such an integrated module could greatly simplify the cumbersome design, bid, permit and grid integration process that our solar technical assistance teams see in the field all the time.”

[Source: Sandia Laboratories]

The public face of Sandia’s new microcell is at the ‘proof of concept’ stage. That’s a long way from showing up at a local builders’ supply store. Many proof-of-concept technologies don’t make it to manufacturing; but this one comes from a large academic, governmental, and commercial consortium. It has the pedigree.