PV power plants require proportionally more up-front capital investment to develop and build than their fossil fuel counterparts. Modelling the lifetime performance of a PV power plant is therefore a critical exercise in proving a project’s bankability and securing finance to cover that cost. However, inaccuracies and uncertainties in modelling techniques create risk in the structuring of project finance. Evan Riley of Black & Veatch explores methods for improving the reliability of performance models and how then can be used to demonstrate that a PV facility will meet expectations.
Fixed and tracker solar mounting systems offer various relative cost and performance benefits. But as JA Solar’s Zhang Lan Jun and Gong Tie Yu describe, surprising results from field analysis of different systems used in China hold important lessons for developers wondering which ones to choose.
A next-generation PV plant architecture based on increasing direct current system voltage from 1,000VDC to 1,500VDC holds the promise of a more cost-effective and productive utility-scale plant due to lower installation and maintenance costs. Mahesh Morjaria, Kevin Collins and Michael Stavish of First Solar and Greg Ball of DNV-KEMA Renewables explore some of the challenges associated with the development of the technology and the efforts to address some of those challenges.
Modules based on p-type multi c-Si technologies look set to dominate the PV industry over the next five years, continuing a trend that has developed over the past two years. This paper explores why high-efficiency p-type multi seems destined to remain the workhorse of the global PV industry.
In anticipation of the expected increase in the use of back-contact cells in future PV modules, a number of different concepts have been proposed. This paper focuses on one approach that aims to stay close to conventional solder-based technology (tabbing - stringing) while still allowing the use of back-contact cells (which have more complex back-side metallization schemes). The advantages and disadvantages of such an approach are discussed, and the development of this technology is described in terms of process flow, materials, characterization and reliability.
With lower returns on investment in PV projects, financial institutions have an ever-increasing demand for risk mitigation. Project stakeholders are asked to provide evidence of risk-management actions and have to look for ways to guarantee an adequate level of quality for their systems. Product certification, although necessary to help qualify the design of a product, does not provide a guarantee that mass production will achieve the targeted quality level; it has therefore become necessary to find reliable methods to assess the quality of PV systems on a large scale. Production monitoring, as part of a global quality plan for a PV system, is a cost-effective way to implement real-time checks in the manufacturing facilities, providing reassurance for stakeholders and helping manufacturers to improve their manufacturing processes. This paper details the principles behind production monitoring, the methodology used and how to deploy a production-monitoring project.
With the objectives of reducing cell-to-module losses, improving module efficiency and reducing the price per watt, increasing importance is being placed on the optical properties of backsheets. It is assumed that a higher reflectance backsheet allows a better reuse of incident sunlight. However, this statement is not always true: another factor must be taken in account, namely the angular dependence of the reflected light. In this regard, backsheets with a high specular component deviate from the ideal Lambertian reflectance, resulting in a minor increase in module current. As a result, differences can be found in module power because of the use of backsheets with similar global reflectance but different angular components of reflected light. A total of 33 industrial backsheets with Tedlar, Kynar, EVA and PET layers from different suppliers were analysed. A comparison of backsheets with low and high global reflectances revealed that the power variation in a standard PV module reaches 0.54% abs. In the same vein, and for backsheets with similar global reflectances, it was experimentally found that the angular response of the reflected light was responsible for a power difference of 0.22% abs. in a standard module.
During the past two years remarkable performance improvements have been reported for polycrystalline Cu(In,Ga)Se2 (CIGS), CdTe and perovskite thin-film solar cells. In this paper the key breakthroughs in CIGS thin-film technology are reviewed and the scope for further performance improvements by analysing the stillremaining electrical and optical losses in record-efficiency CIGS solar cells is discussed. On the basis of this analysis it is believed that conversion efficiencies up to 25% are achievable with CIGS solar cells in the mid term. Furthermore, the potential for the concept of polycrystalline multi-junction solar cells to push efficiencies even further, towards 30%, is discussed. Finally, a short review of the CIGS market and an outlook from an industrial perspective are presented.
A recent revitalization of the passivated emitter and rear cell (PERC) concept in the silicon PV industry has resulted in solar energy conversion efficiencies of greater than 20% being achieved on p-type solargrade single-crystalline silicon (mono-Si) wafers during the past two years or so, thanks to technological advance in the use of aluminium oxide for silicon surface passivation. The research efforts carried out at JA Solar in developing an industry version of PERC cells that can be mass produced utilizing the existing conventional back-surface field (BSF) cell manufacturing platform with moderate retrofitting have yielded 20.5% average conversion efficiency, which can be consistently achieved on p-type Si wafers grown by the Czochralski method. Moreover, the experimental results showed that an average conversion efficiency of 20% is achievable when, in combination with JA Solar’s proprietary light-trapping technique, the same technological approach is applied to the cells using high-quality polycrystalline silicon (multi-Si) wafers produced by the seeded directional solidification method.
In this paper large-area (239cm2) n-type passivated emitter, rear totally diffused (n-PERT) solar cells are compared with state-of-the-art p-type passivated emitter and rear cells (p-PERC) to evaluate potential advantages of n-PERT over p-PERC. In particular, an investigation has been carried out of fully screenprinted bifacial n-PERT solar cells, in which the boron-doped emitter is contacted with aluminiumcontaining silver (AgAl) pastes, as well as of n-PERT back-junction (BJ) solar cells, in which the B-doped emitter is locally contacted with screen-printed Al. Using two separate quartz furnace diffusions for the B- and P-doped regions, efficiencies of up to 20.3% on bifacial n-PERT solar cells and of up to 20.5% on n-PERT BJ solar cells were achieved. In comparison, reference p-PERC solar cells that were processed in parallel achieved efficiencies of up to 20.6% before light-induced degradation (LID), but degraded to 20.1% after 48 hours of illumination. In addition, ion implantation and pre-deposition of dopant sources have been evaluated as alternative technologies for forming the full-area doping of the front and rear wafer surfaces, thus reducing the number of processing steps for n-PERT solar cells. Using ion implantation and a co-annealing step, efficiencies of up to 20.6% for bifacial n-PERT solar cells have been achieved, and of up to 20.5% for n-PERT solar cells, in which the P-doped back-surface field is contacted with evaporated Al. By employing a boron silicate glass (BSG) deposited via plasma-enhanced chemical vapour deposition (PECVD) as a dopant source, along with a co-diffusion step, n-PERT BJ solar cells have been fabricated with up to 19.8% energy conversion efficiency.
