Measured and modelled JV characteristics of crystalline silicon cells below one sun intensity have been investigated. First, the JV characteristics were measured between 3 and 1000 W/m 2 at 6 light levels for 41 industrially produced mono-and multi-crystalline cells from 8 manufacturers, and at 29 intensity levels for a single multi-crystalline silicon between 0.01 and 1000 W/m 2. Based on this experimental data, the accuracy of the following four modelling approaches was evaluated: (1) empirical fill factor expressions, (2) a purely empirical function, (3) the one-diode model and (4) the two-diode model. Results show that the fill factor expressions and the empirical function fail at low light intensities, but a new empirical equation that gives accurate fits could be derived. The accuracy of both diode models are very high. However, the accuracy depends considerably on the used diode model parameter sets. While comparing different methods to determine diode model parameter sets, the two-diode model is found to be preferred in principle: particularly its capability in accurately modelling V OC and efficiency with one and the same parameter set makes the two-diode model superior. The simulated energy yields of the 41 commercial cells as a function of irradiance intensity suggest unbiased shunt resistances larger than about 10 kO cm 2 may help to avoid low energy yields of cells used under predominantly low light intensities. Such cells with diode currents not larger than about 10 À9 A/cm 2 are excellent candidates for Product Integrated PV (PIPV) appliances.

h i g h l i g h t s Simulated the 2050 West-European power system with 40%, 60% and 80% RES penetration. Assessed if 5 options can complement intermittent RES and lower total system costs. 3 options lower costs: demand response, gas-fired generators(+CCS) and curtailment. Power storage is too expensive and extra interconnectors are valuable at RES P60%. Virtually all generators encounter a revenue gap in the current energyonly market.

Silicon heterojunction (SHJ) cells offer high efficiencies and several advantages in the production process compared to conventional crystalline silicon solar cells. We performed a life-cycle assessment to identify the greenhouse gas (GHG) footprint, energy payback time (EPBT) and cumulative energy demand of four different SHJ solar cell designs. We analyse these environmental impacts for cell processing and complete systems for both current and prospective designs. On the basis of in-plane irradiation of 1700 kWh/m 2 , results for current designs show that life-cycle GHG emissions could be 32 gCO 2 -eq/kWh for complete SHJ photovoltaic (PV) systems (module efficiencies of 18.4%), compared with 38 gCO 2 -eq/kWh for conventional monocrystalline silicon systems (module efficiency of 16.1%). The EPBT of all SHJ designs was found to be 1.5 years, compared with 1.8 years for the monocrystalline PV system. Cell processing contributes little (Ä 6%) to the overall environmental footprint of SHJ PV systems. Among cell processing steps, vacuum based deposition contributes substantially to the overall results, with 55-80%. Atomic layer deposition of thin films was found to have a significantly lower environmental footprint compared to plasma enhanced chemical vapour deposition and sputtering. Copper-based compared with silver-based metallization was shown to reduce the impact of this processing step by 74-84%. Increases in cell efficiency, use of thin silicon wafers and replacement of silver-based with copper-based metallization could result in life-cycle GHG emissions for systems to be reduced to 20 gCO 2 -eq/kWh for SHJ systems and 25 gCO 2 -eq/kWh for monocrystalline system, while EPBT could drop to 0.9 and 1.2 years, respectively.

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