Photovoltaics - Current Developments

Current Developments

Photovoltaic panels based on crystalline silicon modules are encountering competition in the market by panels that employ thin-film solar cells (CdTe CIGS, amorphous Si, microcrystalline Si), which had been rapidly evolving and are expected to account for 31% of the global installed power by 2013. However, precipitous drops in prices for polysilicon and their panels in late 2011 have caused some thin-film makers to exit the market and others to experience severely squeezed profits. Other developments include casting wafers instead of sawing, concentrator modules, 'Sliver' cells, and continuous printing processes.

The San Jose-based company Sunpower produces cells that have an energy conversion ratio of 19.5%, well above the market average of 12–18%. The most efficient solar cell so far is a multi-junction concentrator solar cell with an efficiency of 43.5% produced by Solar Junction in April 2011. The highest efficiencies achieved without concentration include Sharp Corporation at 35.8% using a proprietary triple-junction manufacturing technology in 2009, and Boeing Spectrolab (40.7% also using a triple-layer design). A March 2010 experimental demonstration of a design by a Caltech group led by Harry Atwater which has an absorption efficiency of 85% in sunlight and 95% at certain wavelengths is claimed to have near perfect quantum efficiency. However, absorption efficiency should not be confused with the sunlight-to-electricity conversion efficiency.

For best performance, terrestrial PV systems aim to maximize the time they face the sun. Solar trackers achieve this by moving PV panels to follow the sun. The increase can be by as much as 20% in winter and by as much as 50% in summer. Static mounted systems can be optimized by analysis of the sun path. Panels are often set to latitude tilt, an angle equal to the latitude, but performance can be improved by adjusting the angle for summer or winter. Generally, as with other semiconductor devices, temperatures above room temperature reduce the performance of photovoltaics.

A number of solar panels may also be mounted vertically above each other in a tower, if the zenith distance of the Sun is greater than zero, and the tower can be turned horizontally as a whole and each panels additionally around a horizontal axis. In such a tower the panels can follow the Sun exactly. Such a device may be described as a ladder mounted on a turnable disk. Each step of that ladder is the middle axis of a rectangular solar panel. In case the zenith distance of the Sun reaches zero, the “ladder” may be rotated to the north or the south to avoid a solar panel producing a shadow on a lower solar panel. Instead of an exactly vertical tower one can choose a tower with an axis directed to the polar star, meaning that it is parallel to the rotation axis of the Earth. In this case the angle between the axis and the Sun is always larger than 66 degrees. During a day it is only necessary to turn the panels around this axis to follow the Sun.

Solar photovoltaics is growing rapidly, albeit from a small base, to a total global capacity of 69,684 megawatts (MW) at the end of 2011. The total power output of the world’s PV capacity run over a calendar year is equal to some 80 billion kWh of electricity. This is sufficient to cover the annual power supply needs of over 20 million households in the world, and represents 0.5% of worldwide electricity demand. More than 100 countries use solar PV. World solar PV capacity (grid-connected) was 7.6 GW in 2007, 16 GW in 2008, 23 GW in 2009, and 40 GW in 2010. Installations may be ground-mounted (and sometimes integrated with farming and grazing) or built into the roof or walls of a building (building-integrated photovoltaics). Photovoltaics is now, after hydro and wind power, the third most important renewable energy source in terms of globally installed capacity.

The 2011 European Photovoltaic Industry Association (EPIA) report predicted that, " Europe once again was the global leader in PV market growth, with 75% of all newly connected capacity and about 75% of global installed capacity. But non-European markets are showing signs that they may soon shift this balance in their favour". 2012 could see the installation of 20–30 GW of PV — about the same as in 2011. The industry's capacity continues to expand, to perhaps as much as 38 GW, furthering the PV systems price decline. With proper policy support, balanced market development, and continued industry innovation, photovoltaic (PV) can continue its remarkable growth rate over the short-, medium- and long-term, and even beyond.

The EPIA/Greenpeace Solar Generation Paradigm Shift Scenario (formerly called Advanced Scenario) from 2010 shows that by the year 2030, 1,845 GW of PV systems could be generating approximately 2,646 TWh/year of electricity around the world. Combined with energy use efficiency improvements, this would represent the electricity needs of more than 9% of the world's population. By 2050, over 20% of all electricity could be provided by photovoltaics.

However, the EPIA prediction may be pessimistic since official agencies keep underestimating the growth rate of renewables. A report based on the 2012 BP Statistical Review shows an exponential growth in global solar generation from 2001 to end 2011, with an approximate doubling of generation every two years. This raises the possibility that solar power could reach 10% of total global power generation by the end of this decade. To accomplish this gain in primary energy share, solar will need to advance from the 55.7 TWh generated in 2011 to approximately 2200 TWh. At current exponential growth rates, those levels could be achieved as early as 2018 rather than around 2030 as suggested by the EPIA. Solar would provide 100 percent of the current world energy needs by 2027 if the biannual doubling of generation continues.