The Promise of Thin-film Solar

Enlarge Image Image Gallery Solar panels don’t have to be conspicuous. The panels on this house are energy-efficient and fit neatly into the roof. ROB & LINDA COLLINS

Every hour, the sun beams more energy to the Earth’s surface than the global population uses in a year. Meanwhile, humanity struggles with the effects of pollution, climate change and fossil fuel dependence. Could it be that the solution to these problems is right above us? Modern photovoltaic (PV) technologies take advantage of renewable energy from the sun by converting sunlight into electricity. So why aren’t more of us using this remarkable technology to power our homes? When asked, the reason most people give is the cost of installing a PV system. But new thin-film PV products are getting better and cheaper all the time. This technology could soon change the way we think about electricity and make sunshine our “fuel” of choice.

The Rise of Thin-film Solar

The type of solar-electric module currently dominating the industry is crystalline silicon, which is made by encapsulating wafers of highly refined silicon under rectangular sheets of glass framed with aluminum. These modules have been the primary solar energy technology for more than 50 years. Since the invention of the first modern silicon solar cell in 1954, incremental improvements have resulted in modules capable of converting 12 to 18 percent of solar radiation into electricity.

Crystalline modules still dominate in PV sales, but in the last few years most new development work has focused on thin-film PV technologies. In 2005, more than 95 percent of the PV market was served by crystalline modules. Since then, thin film’s share of the market has risen steadily and is now 25 percent. Hundreds of thin-film companies have entered various stages of product development or production.

Large-area thin-film PV modules and laminates have been commercially available since the ’90s, and the current products have conversion efficiencies of 6 to 11 percent. The higher the efficiency, the less area and support structure required to produce the desired amount of electricity, so it’s worth noting that, overall, thin-film modules still aren’t as efficient per unit area as crystalline silicon modules. However, thin-film PV has other advantages over crystalline silicon. Perhaps most importantly, thin-film solar is much less expensive to produce. Many thin-film panels are produced from amorphous silicon. These solar cells require much less high-grade silicon than it takes to produce crystalline silicon panels. Thin-film solar cells can also be made from other semiconductor materials, including copper indium gallium diselenide (CIGS) and cadmium telluride (see “Four Thin-film Solar Technologies,” below).

Going Solar in a Big Way: Utility-scale Thin-film Projects

A critical question in the field of renewable energy is when utility-scale photovoltaics will reach grid parity — the point at which PV power will be cost competitive with electricity from fossil fuels. In fact, utility-scale PV power is already cost-competitive with nuclear energy, but is not yet as cheap as electricity produced from other sources, such as coal.