Bifacial PV technology raises new challenges for the characterization and modelling of solar cells and modules, as well as for the yield predictions of power plants, as the contribution of the rear side can significantly affect the performance of these types of device.
LONGi, Jolywood and many other large PV manufacturers claim that bifacial mono c-Si technology is the future. Since 2015, bifacial PV installations have been entering multi- MW installation levels, and are expected to enter multi-GW levels in 2018.
To guarantee the long-term competitiveness of the PV industry, the cost of PV power generation ($/kWh) must be continuously reduced. Such reduction can be achieved in two ways: 1) by improving PV module performance (efficiency, annual energy yield, reliability); 2) by reducing manufacturing costs ($/Wp).
Understanding power losses in technical systems is vital to improve products in every industry and photovoltaic modules present no exception. Losses in solar modules are caused by optical and electrical effects or are determined by simple module geometry through inactive areas.
In recent years, potential-induced degradation (PID) has been recognized as a serious reliability issue for large PV systems, potentially causing efficiency losses of more than 90%, and even failures [1–4]. Such large decreases in efficiency may require the modules in the system to be replaced after just a few years’ operation. This has motivated a substantial research effort in the PV community, leading to a better understanding of the phenomenon, as well as to a range of mitigation strategies. A recent publication by Luo et al. gives a comprehensive overview of this research .
Potential induced degradation (PID) of photovoltaic (PV) modules gets a lot of attention since 2010 when Solon published their findings about a degradation mechanism in their PV modules caused by high potential differences. When multiple PV modules are connected in series, a potential difference up to 1000 V or at some places even 1500 V is created between the cell and the grounded frame. This electrical field causes a leakage current and ion diffusion. PID is a multi-level degradation with causes and solutions at cell, module and system level.
A test campaign was conducted within the frame of a feasibility study for pidbull, a curing technology for PID developed by pidbull nv. 80 PV modules were characterized whereof 49 PV modules were stressed and cured for PID. The selected set of PV modules was composed of 49 different module types of 33 brands. The test was done according to the foil-method, as described by the standard in progress IEC 62804. However, to apply higher stressing and curing rates, the modules were tested with an aluminium foil inside a climate chamber for 96 hours. After the stress test, only 22% of the tested modules passed the 5% loss criteria as described by IEC 62804. In other words, 78% out of a set of today's most installed PV modules in Flanders are PID sensitive. Remarkable is that only 16 out of the 49 PV modules have less than 20% PID after the stress test. Additionally, a linear trend for PID reversibility was shown for modules with a stress level of less than 85%. The modules which lost more than 85% due to PID showed a lower recovery rate or in worst case didn’t recover at all.
This paper focuses on the technical progress of high-efficiency crystalline silicon solar cells and modules, specifically with regard to passivated emitter and rear cell (PERC) processes, module description and light induced degradation (LID) data. Through appropriate optimizations of the solar cell and module processes, the cell efficiency achieved in mass production is 21.3%, with module power exceeding 300W. To solve the LID problem, hydrogenation technology developed by UNSW is used, bringing the cell LID rate down to below 1%.
This paper presents a summary of the status of bifacial PV in respect of the technology in mass production, the installed PV systems, and the costs relating both to module production (cost of ownership – COO) and to electricity (levelized cost of energy – LCOE). Since the first bifacial workshop, organized by ISC Konstanz and the University of Konstanz, in 2012, many things have changed. Bifacial cells and modules have become cost effective, with installed systems now adding up to more than 120MWp and the technology becoming bankable. Large electricity providers have recognized the beauty of bifacial installations, as the lowest costs per kWh are attainable with these systems. The authors are sure that by the end of 2017, bifacial PV systems amounting to around 500MWp will have been installed, and that by 2025 this type of system will become the major technology in large ground-mounted installations.
Even though it is now more than five years since potential-induced degradation (PID) began to proliferate, and despite the fact that solutions are under development, it is currently still the most discussed mode of degradation associated with cracking in PV modules.
Conventional ribbons used for interconnecting solar cells in PV modules act like mirrors, causing a large proportion of incident light to be lost. Experimental results indicate that only around 5% of the perpendicular
incident light on the connections can be reused; as a result, this area contributes very little, if at all, to the current generation.
PV Tech can reveal the preliminary top 5 solar module manufacturers in 2016, based as usual on final shipment guidance from third quarter financial results.
PV manufacturing capacity expansions planned this year are expected to push production levels beyond anticipated demand in 2016, creating further cost pressures for suppliers.
The output power of a solar module is the sum of the powers of all the individual cells in the module multiplied by the cell-to-module (CTM) power ratio. The CTM ratio is determined by interacting optical losses and gains as well as by electrical losses. Higher efficiency and output power at the module level can be achieved by using novel ideas in module technology. This paper reviews methods for reducing different optical and electrical loss mechanisms in PV modules and for increasing the optical gains in order to achieve higher CTM ratios. Various solutions for optimizing PV modules by means of simulations and experimental prototypes are recommended. Finally, it is shown that designing PV modules on the basis of standard test conditions (STC) alone is not adequate, and that, to achieve higher CTM ratios by improving the module designs in respect of environmental conditions, an energy yield analysis is essential.
The back-contact (BC) technology currently available on the market is considered to be either highly efficient but extremely expensive (interdigitated back contact – IBC – from SunPower) or, if cost-effective, not very
efficient (metal wrap-through – MWT) compared with what is becoming today’s new standard: passivated emitter and rear contact (PERC) technology. Something in between, such as low-cost, high-efficiency IBC cells
and modules, would therefore be desirable. This paper briefly describes the past, focuses on the present, and forecasts the possible future developments of BC technology in respect of efficiencies, costs and applications.
Potential-induced degradation can cause significant power loss in modules if the appropriate precautions are not taken. In the first part of a new series in PV Tech Power on module failure, Peter Hacke and Steve Johnston assess the current state-of-the-art in detecting, avoiding and mitigating the worst effects of PID.