Conference report | In April, the deployment of solar in West Africa came under the spotlight during a two-day event in Accra, Ghana. Reporting on the event, Ben Willis heard huge excitement over
the prospects for solar in the region tempered by the realities of scaling up a new technology in a challenging part of the world.
Emerging markets | Mexico remains a market of undoubted potential, but there’s a growing opinion that it will struggle to live up to its hype amid regulatory uncertainty. Liam Stoker asks if last year’s
sweeping energy reforms will continue to hold the market back, or result in a solar explosion by 2018.
Potential-induced degradation (PID) of the shunting type (PID-s) is one of the most severe forms of PID, which is caused by the negative potential of p-type solar cells with respect to grounded frames/mounting. Although this negative potential can be completely avoided at the system level, that is not the case for a large number of modern PV systems. PV modules that are able to sustain PID-s stress for at least the duration of their service life are therefore essential. To assess whether modules fulfil this requirement, laboratory tests are currently recommended in which the modules are exposed to a certain constant level of PID-s stress for a given amount of time. These types of test with constant stress levels, however, are only feasible in the case of degradation mechanisms that are not reversible in the field, for which non-coherent stress episodes simply sum up to the total stress. Unlike other mechanisms, PID-s is reversible under field conditions; as a consequence, the level of PID-s of a fielded module is the result of an intricate interplay of phases of degradation and regeneration. This behaviour cannot be replicated in a laboratory test using a constant stress level; the currently recommended laboratory tests for PID-s with constant stress levels are therefore not appropriate for assessing the service life duration, and can only be used for differentiating the susceptibility to PID-s stress and for monitoring the stability of production processes. For monitoring the PID-s resistance of its products, Hanwha Q CELLS uses tests for PID-s with constant stress in accordance with the draft for IEC PID test method 62804. This assures that all the products of the Q CELLS brand come with Anti-PID Technology (APT). The expected service life duration with respect to PID-s is assessed by simulating the interplay of degradation and regeneration under non-constant outdoor conditions that are based on meteorological data.
Most development work in the laboratory is dedicated to efficiency enhancements at the cell level; improvements in efficiency can lead to higher cost-competitiveness of PV. However, the cost of panel manufacturing is an important aspect as well. For CIGS panels the deposition of the active layer is an important part of the cost, and decreasing the layer thickness can reduce costs. Moreover, cost of ownership calculations can determine how much benefit can be expected from thinner absorber layers from a cost perspective; clearly, a thinner absorber will result in reduced absorption. To avoid losses, modelling can be used to predict the efficiency and viable light management strategies. Other efficiency-enhancing technology is related to the fact that most thin-film solar panels are monolithically interconnected. The area loss involved in this type of interconnection, and the trade-off between conductivity and transmittance of the front contact, impose limits on the maximum efficiency. The impact of improving both of these aspects is demonstrated in this paper. A viable way to improve the front contact is by supplementing the front contact with a metallic pattern. The benefit and the impact of different configurations and dimensions of the cell and metallic pattern are presented.
Competitive bidding | Now into its fourth round, South Africa’s national renewable energy programme has successfully driven down the price of solar energy. But there are growing concerns that this has been at the expense of fostering a diverse local market, writes Tom Jackson.
Business | A growing number of tier-one PV module manufacturers have been changing business models in recent years from once being dedicated module suppliers to becoming project developers. Mark Osborne analyses the progress made by major PV manufacturers in their downstream ambitions in 2014 and expectations in 2015.
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.
