MARKETABLE CONSUMER APPLICATIONS

Of all renewable energy sources, solar power is one of the most easily exploitable. The only constraint is its price. Using dye sensitized solar cells, grid parity - the point at which photovoltaic electricity is equal to or cheaper than grid power - is much closer. Compared with silicon based cells the dye-sensitized solar cells are considerably cheaper to manufacture. DSC-technology relies on materials that are readily available in large quantities and relatively non-toxic. For example, titanium dioxide, used instead of expensive high purity silicon as a semiconductor, is a cheap white pigment used in paints.

Cells can also be engineered into flexible sheets. Michael Grätzel displays a fabric-like sheet of flexible DSC-panel. "This panel is cut with scissors from the production line."

The panel is manufactured in a low-cost, roll-to-roll process and the production equipment is similar to manufacturing lines used by the printing, coating and packaging industries.

In 2009 one of the DSC licence holders, G24 Innovations, announced the first ever commercial shipment of DSC photovoltaic modules. The first consumer product, backpacks coated with the cheap and flexible DSC solar cell, for on-the-go recharging of portable gadgets, hit the shelves in January 2010.

The flexibility and low weight of DSC panels are important for powering portable electronics, but the technology also has other virtues. Compared to conventional silicon based photovoltaic technology, DSC can produce electricity in low light conditions and can be directly incorporated into buildings by replacing conventional glass panels rather than taking up roof or extra land area. The panels can also be made transparent. ”Transparent DSC panels that produce electric power for the building could be a very interesting application for glass facades,” Grätzel says.

DSCs are the only solar cells that can be made truly transparent their colour depending on the choice of the sensitizer. By selecting dyes that absorb only in the near IR and UV region it is possible to produce even colourless transparent windows.

Dye-sensitized solar cells reach currently 12 percent efficiency under standard reporting conditions on the laboratory scale while the efficiency of larger modules designed for outdoor conditions is currently about 8–9 %. It is well below the 15% standard for polycrystalline silicon designs. ”But in real working conditions the difference shrinks. This is due to the decrease in performance of silicon cells with increasing angle of light incidence, and temperature as well as cloudy conditions where the DSC has an advantage over silicon,” Grätzel explains.

Silicon cells only allow you to capture power when light is intense. DSC cells capture power in low light or even rainy conditions. That means the cells give a better performance over the whole day, even if they are less efficient under ideal conditions.

Business growing fast

The first commercial DSC applications are already generating power for mobile electronics. The first company to mass-produce flexible dye-sensitized solar cells is shipping its products. The next major step toward inexpensive and large-scale commercialisation of dye-sensitized solar cells might be taken in the building industry. Building-integrated photovoltaics (BIPV) is one of the fastest growing segments of the photovoltaic industry. Photovoltaic materials may be used to replace conventional building materials in parts of the building envelope such as the roof, skylights, or facades.

Glass manufacturer Pilkington North America and DSC material supplier Dyesol recently signed an agreement to form a joint venture to produce electricity generating DSC glass panels for BIPV applications. Dyesol is also developing DSC films integrated onto coil steel for large scale commercial building claddings.

Photovoltaic is the world’s fastest-growing energy technology. Today, solar power accounts for only 0.54% of global energy usage. Of this, the predominant part is solar heat and only 0.04 % solar electricity. The average annual market growth of the photovoltaic industry has been 35–40 % for several years, and, for example, in 2007, grid-connected PV was the fastest growing source of energy with its 83% increase.

In the early 1990s, when Grätzel travelled with his prototype cells, ready to showcase the technology, he already had commercial production in mind. "I was convinced that this finding could be taken to commercial applications. It just took longer than I thought. But that is entirely normal. You have to find the people who believe in your technology, have the money to invest and have the possessions to go over all the hurdles that arise."