This paper gives an overview of the application of silicon epitaxy as a doping technology in bulk crystalline silicon solar cells. The large degree of flexibility in designing a doped profile in one process step, and the elegant way of locally creating doped regions, or simply achieving single-side doping by selective epitaxy, are presented. Other advantages – such as the absence of subsequent steps to drive in the doped region, to activate the dopants and to heal any damage or remove glassy layers – position the technology as a strong alternative to classical diffusion. Silicon epitaxy is possible on the flat and textured surfaces of solar material, and is compatible with cleaning sequences suited to industrial implementation. The integration of epitaxial layers in solar cells is capable of providing not only high efficiencies but also simplifications of the cell fabrication process, and, therefore, reductions in the cell cost of ownership (CoO). The proof of concept at the cell level has been demonstrated by the integration of boron-doped epitaxial emitters in n-type IBC and PERT solar cells: 22.8% efficiency for IBC (4cm2) and 21.9% for PERT (238.9cm2) devices have been obtained.
Extended crystal defects, such as grain boundaries and dislocations, have long been considered the main factors limiting the performance of multicrystalline (mc-Si) silicon solar cells. However, because the detrimental effects of these crystal defects are reduced as a result of improvements in the solidification process as well as in the feedstock and crucible quality, the degradation caused by boron–oxygen complexes is expected to be of increasing importance. Light-induced degradation (LID) occurs in both p- and n-type crystalline silicon solar cells that contain both boron and oxygen. Because of the fundamental differences in the solidification processes, mc-Si silicon contains less oxygen than Czochralski silicon; nevertheless, the oxygen content in mc-Si silicon is still sufficient to cause degradation, although to a lesser extent than in the case of Czochralski silicon. Whereas B–O-related degradation of 0.5 to 1% abs. can be found in Czochralski cells, the degradation in conventional mc-Si cells is limited to around 0.1 to 0.2% abs.
In recent weeks the benefits of coupling solar with battery storage technology have gone from being a niche topic to the talk of the chattering classes. Thanks to some slick publicity work from Elon Musk and his PR team, tales of the Silicon Valley stalwart’s first forays into the world of stationary storage have found their way on to newspaper front pages the world over. Hype there was aplenty, and only time will tell if Tesla’s bid to revolutionise the solar-plus- storage offer lives up to it. Yet if nothing else, the company’s high-profile launch has shone a light into one of the less glamorous but fundamentally important corners of the storage debate – namely the business models that will enable the technology to pay its way.
As PV Expo rolls into Tokyo for its eighth outing this month, it coincides with what has been a pivotal time for solar in Japan. Behind the headlines of explosive growth over the past couple of years, some darker currents have been swirling that have threatened if not to bring the wheels off, then certainly to prompt questions over the longevity of Japan’s solar success story.
The market outlook for utility-scale PV installations is very positive. These PV plants have the capability of supporting grid operation, and the ability to do this is being increasingly required in grid codes. Testing the capabilities of very large PV inverters, however, is demanding for laboratories. Gunter Arnold, Diana Craciun, Wolfram Heckmann and Nils Schäfer from Fraunhofer IWES discuss current developments and resulting challenges and address the gaps and diversity in testing guidelines and standardisation.
As early as 2010, Phoenix Solar along with Saudi Aramco installed the first of three PV test facilities in Dhahran, Saudi Arabia, putting four different module technologies (monocrystalline, amorphous-microcrystalline, CdTe and CIS) to the test in extreme climatic conditions. Klaus Friedl of Phoenix Solar LLC shares some hints and lessons learned from the tests.
Maximising production from a PV system is critical, since nearly all of the investment is made prior to system activation. Monitoring of PV systems allows operators to identify any performance or safety problems early so that they can be repaired quickly, thus minimising energy losses. Joshua Stein of Sandia National Laboratories and Mike Green of M.G. Lightning Electrical Engineering discuss some new monitoring strategies that are necessary for expeditiously identifying and locating system faults.
New inverter technologies offer installers the choice of central of distributed systems for PV arrays. Deciding which system is the most optimal to use isn’t always based on the size of a solar system, writes Alvaro Zanon.
A significant part of the risk management process associated with large-scale solar PV installations is ‘technical due diligence’, which seeks to define and minimise all technical risks associated with the project. Fred Martin and Nick Morley of TÜV Rheinland explore due diligence challenges for PV power plants in Japan.
More than ever, the global PV market provides attractive new investment opportunities, but the elements driving such rapid expansion also increase the risk of solar financial assets failing to meet long-term fiscal and performance goals. Boris Farnung, Björn Müller and Klaus Kiefer of Fraunhofer ISE, and Peter Bostock and John Sedgwick of VDE Americas explore major quality-assurance measures and the challenges today for achieving bankability of utility-scale PV plants.
