A. Louwen

Re-assessment of net energy production and greenhouse gas emissions avoidance after 40 years of photovoltaics development

Since the 1970s, installed solar photovoltaic capacity has grown tremendously to 230 gigawatt worldwide in 2015, with a growth rate between 1975 and 2015 of 45%. This rapid growth has led to concerns regarding the energy consumption and greenhouse gas emissions of photovoltaics production. We present a review of 40 years of photovoltaics development, analysing the development of energy demand and greenhouse gas emissions associated with photovoltaics production. Here we show strong downward trends of environmental impact of photovoltaics production, following the experience curve law. For every doubling of installed photovoltaic capacity, energy use decreases by 13 and 12% and greenhouse gas footprints by 17 and 24%, for poly- and monocrystalline based photovoltaic systems, respectively. As a result, we show a break-even between the cumulative disadvantages and benefits of photovoltaics, for both energy use and greenhouse gas emissions, occurs between 1997 and 2018, depending on photovoltaic performance and model uncertainties.

Evaluation of different indicators for representing solar spectral variation

In studies analyzing the performance of photovoltaic (PV) modules, average photon energy (APE) is often used as an indicator for the effect of solar spectral variation on PV module performance, as it is said to accurately distinguish individual spectra. Especially for a-Si devices, there is a strong correlation between APE and performance. However, there can be significant variation in spectra measured at specific APE values. In this study we analyze the variation of spectra at a range of APE values, and also compare APE as an indicator of spectra to other spectral indicators, namely Blue Fraction (BF), Useful Fraction (UF), Airmass (AM) and Spectral Mismatch Factor (MMF). We compare the indicators by binning spectra at different values of each parameter, and calculating the Root-Mean-Square-Deviation (RMSD) of all spectra in the bin to the mean spectrum in the bin. Subsequently, we compare these calculated results between the different parameters Our results indicate that APE was found the best indicator of spectral variation, with the lowest mean RMSD over the whole range of measured data. However, BF is an almost equally good indicator, and UF and MMF also show a low mean RMSD. Airmass was found to be a quite poor indicator of spectral variation.

PV performance during low irradiance and rainy weather conditions

With data made available by a photovoltaic (PV) test facility located on top of an office building of the Utrecht University the performance of ten PV modules during time periods of low irradiance and precipitation was analysed. Using values for direct irradiance by Bird’s SPCTRAL2 model and measured climatic conditions a weather classification system was designed in order to categorize time periods and make a comparison between rainy and non-rainy time periods possible. Results show that precipitation induces a blue shift in the solar spectrum increasing the short-circuit current (ISC) of the modules (a-Si and CdTe in particular). Furthermore it is shown that precipitation causes module temperature to drop resulting in an increase in open-circuit voltage (VOC) for all modules. In terms of the performance ratio (PR) it is shown that almost all modules perform better under rainy than under non-rainy weather conditions, but it is noted that incorrect measurements of module temperature most likely overestimate the PR for some of the investigated modules.

Cost analysis of two Silicon Heterojunction solar cell designs

Research and Development of Silicon Heterojunction (SHJ) solar cells has seen a marked increase since the recent expiry of core patents describing SHJ technology. This paper investigates the production costs associated with two different SHJ cell designs investigated within the FLASH programme, a Dutch research programme focusing on SHJ solar cells. We performed life cycle costing and common economic analysis to quantify the production costs (€/Wp). One of the aims of the research programme is to decrease production cost by substituting expensive materials and processing steps. We found the analyzed designs to have slightly different production costs: 0.35€/Wp for a “standard” SHJ cell, compared to 0.34€/Wp for a new SHJ cell design in which the indium-tin-oxide TCO is replaced with abundant materials. Sensitivity analysis showed the results to be especially sensitive to changes in wafer (and thus silicon) prices. Further research will be conducted for other SHJ cell designs developed in the FLASH programme.