Shining example

A European-funded project has developed a novel silicon solar panel system that claims to give world-record efficiencies and can be produced much cheaper relative to the power it generates.

The five-and-a-half-year, €28m (£24.5m) CrystalClear project has resulted in solar modules that achieve 16 to 16.4 per cent premium aperture area conversion efficiency, beating Sandia National Laboratory’s record of 15.5 per cent. It also reduced the manufacturing cost of solar modules from more than €2 per Watt-peak (the DC output of a solar module as measured under an industry standardised light test) to €1 per Watt-peak.

CrystalClear brought together 16 partners from across Europe, including nine commercial companies, four research institutes and three universities.

Project leader Prof Wim Sinke said: ‘Wafer-based silicon solar cells represent about 90 per cent. Through CrystalClear we not only redesigned the cells, but also tackled issues over the whole value chain from the starting materials up to the final product — the solar module. As well as increasing the efficiency of solar cells themselves, we also increased the efficiencies of the modules in which they are mounted.’

The conventional cell design used in most modules has a front contact and a rear contact. In each module they are contacted electrically in series by connecting the front of one cell to the rear of a neighbouring cell, making a series with sufficiently high voltage for practical applications.

In CrystalClear’s cell design, both contacts are at the rear so the cell can be connected in series from rear to rear, using a technique similar to surface mounting used in printed circuit boards.

Sinke added: ‘We use a large foil sheet that has conducting paths in a certain pattern designed so that if you mount cells on it, the path on the pattern makes sure that the positive electrode of one cell is connected to the negative electrode of the neighbouring cell. This mounting can be done by a pick-and-place technique in which the solar cells are connected by small dots of conductive adhesive on the foil and the whole module can be made like a sandwich encapsulating the whole package — cells, glass and foils including electrical connections — in one step.’

This technique enables the handling of very thin, fragile solar cells, typically just 120 microns thick, which means much less silicon is used and overall material costs are much lower.

The cost reduction has allowed CrystalClear’s modules to achieve grid parity. This means when the modules are, for instance, used in a roof-mounted solar generator, the typical generation cost is equal to or lower than the retail electricity price for consumers. The ultimate aim in the long term would be to produce a result comparable with wholesale electricity.

The modules have so far been demonstrated on a pilot-line level, and commercial versions could be available in a year or two. Other cell designs produced by CrystalClear have not yet been constructed as they aim at developments beyond the scope of the project. These could form the basis for further research; even lower manufacturing costs or ever higher efficiencies.

‘This approach is one of the first real innovations for crystalline silicon technology that we have seen in decades,’ said Sinke.

Berenice Baker