Scientists at the Massachusetts Institute of Technology (MIT) have come up with a neat way of doubling the performance of photovoltaic cells.
Typically, PV panels are mounted on the roof of a building or attached to the façade. However, researchers have found that by arranging the cells in more complex 3D arrangements (see right) can increase their power output from double to 20 times that of more conventionally mounted panels with the same area.
The MIT team initially used a computer algorithm to explore the vast number of possible configurations, and developed analytic software that can test a given configuration under a whole range of latitudes, seasons and weather. To confirm their model’s predictions they built and tested three different arrangements of solar cells on the roof of an MIT laboratory building for several weeks.
The findings have been published in the journal Energy and Environmental Science, which reveals that the biggest boosts in power occurred in the locations far from the equator, in winter months and on cloudier days.
While the cost of a given amount of energy generated by such 3-D modules exceeds that of ordinary flat panels, the expense is partially balanced by a much higher energy output for a given footprint. Added tio this it offers a much more uniform power output over the course of a day and accross the seasons, as well as when there is blockage from clouds or shadows. These improvements, say the researchers, make power output more predictable and uniform, which could make integration with the power grid easier than with conventional systems.
So why the improvement in power output and uniformity? The reason is the vertical surfaces of the 3D structures can collect much more sunlight during mornings, evenings and winters, when the sun is closer to the horizon, says co-author Marco Bernardi, a graduate student in MIT’s Department of Materials Science and Engineering.
Although computer modeling showed that the biggest advantage would come from complex shapes — such as a cube where each face is dimpled inward — these would be difficult to manufacture, concluded the scientists. However, the algorithms can also be used to optimize and simplify shapes with little loss of energy. It turns out the difference in power output between such optimized shapes and a simpler cube is only 10-15%.
For an accordion-like tower — the tallest structure the team tested — the idea was to simulate a tower that “you could ship flat, and then could unfold at the site”. Such a tower could be installed in a parking lot to provide a charging station for electric vehicles.
So far, the team has modeled individual 3-D modules. The next step is to study a collection of such towers, accounting for the shadows that one tower would cast on others at different times of day. In general, 3-D shapes could have a big advantage in any location where space is limited, such as flat-rooftop installations or in urban environments. Such shapes could also be used in larger-scale applications, such as solar farms, once shading effects between towers are carefully minimized.
Another breakthrough in solar technology has also been made by UK company Naked Energy, which has invented Virtu, a hybrid solar panel that simultaneously heats water and generates electricity.
According to a report in 'The Engineer', the unit integrates electricity-generating photovoltaic cells into a hot-water-generating solar thermal panel. By combining the two technologies it addresses one of the fundamental problems facing photovoltaic cells: when the photovoltaic panels get hot they become less efficient. For every 1ºC rise in temperature above 25°C, the efficiency of a typical photovoltaic panel drops by 0.5%. A very efficient panel has a maximum efficiency of around 18%, but this can be reduced to 4% by the time the panel's surface temperature reaches 65ºC.
With the Virtu unit, heat is transferred away from the photovoltaic cells with a patented thermosyphon technology that harvests the unwanted heat and uses it to heat up water. Trials have shown the arrangement generates over 45% more energy as a result. The unit if currently undergoing further development to make it ready for production.