Rolf Crook

Climate change impacts on future photovoltaic and concentrated solar power energy output

Building large solar power plants requires significant long-term investment so understanding impacts from climate change will aid financial planning, technology selection, and energy output projections. In this article we examine how projected changes in temperature and insolation over the 21st century will affect photovoltaic (PV) and concentrated solar power (CSP) output. Projected climate data was obtained from the coupled ocean-atmosphere climate models HadGEM1 and HadCM3 under the IPCC SRES A1B scenario which describes a future world of rapid economic growth with a balanced use of renewable and fossil fuel power generation. Our calculations indicate that under this scenario PV output from 2010 to 2080 is likely to increase by a few percent in Europe and China, see little change in Algeria and Australia, and decrease by a few percent in western USA and Saudi Arabia. CSP output is likely to increase by more than 10% in Europe, increase by several percent in China and a few percent in Algeria and Australia, and decrease by a few percent in western USA and Saudi Arabia. The results are robust to uncertainty in projected temperature change. A qualitative analysis of uncertainty in projected insolation change suggests strongest confidence in the results for Europe and least confidence in the results for western USA. Changes in PV and CSP output are further studied by calculating fractional contributions from changes in temperature and insolation. For PV there is considerable variation in contribution depending on location. For CSP the contribution from changes in insolation is always dominant.

Measuring the work function of TiO2 nanotubes using illuminated electrostatic force microscopy

The varying nature of TiO2 nanotube work function as a function of illumination wavelength has been determined using illuminated electrostatic force microscopy. The dark work function was found to be 4.902 eV, with the largest change in work function due to illumination being at 300 nm, which was higher than the work function for bulk TiO2 (4.899 eV). The change in work function due to illumination arises from the flattening of the energy bands at the surface due to charge migration.

Impacts of Stratospheric Sulfate Geoengineering on Global Solar Photovoltaic and Concentrating Solar Power Resource

In recent years, the idea of geoengineering, artificially modifying the climate to reduce global temperatures, has received increasing attention due to the lack of progress in reducing global greenhouse gas emissions. Stratospheric sulfate injection (SSI) is a geoengineering method proposed to reduce planetary warming by reflecting a proportion of solar radiation back into space that would otherwise warm the surface and lower atmosphere. We analyze results from the HadGEM2-CCS climate model with stratospheric emissions of 10 Tg yr-1 of SO2, designed to offset global temperature rise by around 1°C. A reduction in concentrating solar power (CSP) output of 5.9% on average over land is shown under SSI compared to a baseline future climate change scenario (RCP4.5) due to a decrease in direct radiation. Solar photovoltaic (PV) energy is generally less affected as it can use diffuse radiation, which increases under SSI, at the expense of direct radiation. Our results from HadGEM2-CCS are compared to the GEOSCCM chemistry-climate model from the Geoengineering Model Intercomparison Project (GeoMIP), with 5 Tg yr-1 emission of SO2. In many regions, the differences predicted in solar energy output between the SSI and RCP4.5 simulations are robust, as the sign of the changes for both the HadGEM2-CCS and GEOSCCM models agree. Furthermore, the sign of the total and direct annual mean radiation changes evaluated by HadGEM2-CCS agree with the sign of the multi-model mean changes of an ensemble of GeoMIP models over the majority of the world.

Methodology to Stochastically Generate Synthetic 1-Minute Irradiance Time-Series Derived from Mean Hourly Weather Observational Data

Well geographically distributed high temporal resolution solar irradiance data is scarce, resulting in many studies using mean hourly irradiance time-series as an input. This research demonstrates that by taking readily available mean hourly meteorological observations of okta, wind speed, cloud height and atmospheric pressure; 1-minute resolution irradiance time-series that vary on a spatial dimension can be produced. The synthetic time-series temporally validates against observed 1-minute UK irradiance data with 99% K-S test confidence levels across 3 metrics of variability indices, ramp-rate occurrences and irradiance frequency. A new methodology is applied to existing research that produces two-dimensional cloud cover using a vector approach to add spatial correlation to irradiance time-series, as well as improvements to the clear-sky index calculations. The methodology is applied to a hypothetical configuration to demonstrate its capabilities.

Changes in Solar PV Output due to Water Vapour Loading in a Future Climate Scenario

Under a future climate, it is shown that the total atmospheric water vapour will increase over present levels. Water vapour has several distinct absorption bands in the visible and near-infrared parts of the spectrum, which is critical for PV conversion. The sensitivity of current world-leading c-Si, thin film and perovskite solar cells to the solar spectrum under different water vapour loadings is investigated. Semiconductors with bandgaps above 1.4 eV are more resilient to increases in atmospheric water vapour due to the avoidance of two large absorption bands in the near-infrared. Global changes in atmospheric water vapour are then taken from the HadGEM2-ES climate model under the RCP8.5 scenario, and used to determine the changes in PV output for clear-sky conditions for crystalline silicon (c-Si) and amorphous silicon (a-Si) solar cells. For some regions of the world, a decrease in power output of up to 3% for clear-sky conditions is seen for the spectral response of the current world-leading c-Si cell due to increasing water vapour, whereas a-Si performs better with a global power output decline of less than 1%.