The main advantages of PV include: simplicity of the direct photoelectric conversion technology ; ability to generate partial power under cloudy conditions; and the modular and scalable nature of plant design. Another potential benefit of widespread CSP deployment is a much greater GHG emission offset due to the very high albedo of heliostat fields. However, this resulting change in the albedo of the surface as well as the temperature and evapotranspiration of water at a CSP deployment may have implications for local cloud cover. The extent to which such changes would reduce or increase surface warming requires a regional simulation of the cloud properties, cloud fraction, and cloud duration. While both PV and CSP technologies affect the local environment, the extent in which they do so has not been studied in detail. Nemet estimated that the low albedo of PV panels is responsible for lowering the GHG emission offset by 3% when compared with current carbon-intensive energy scenarios. As the penetration of renewable sources increases, that percentage will also increase, and perhaps to a point of being a significant hindrance to continued GHG emission offsets. Even more important, the local thermal balance effects may cause local environmental disruption in desert areas that rely strongly on the very low soil water content. Midday temperature increases of more than 3 K have been observed in desert PV plants. Conversely, heliostat fields in CSP tower plants are characterized by albedos that are 40-50% higher than the original ground albedo, commercial drying racks thus the GHG emission offset for CSP is much higher in comparison to PV technologies. Locally, a temperature reduction of 2 K and reduced rates of evapotranspiration have been observed as a direct result of the increased albedo of heliostat fields.

This Chapter aims at quantifying the albedo replacement effects of large scale solar farms mainly concerns the temperature anomaly calculated from local radiative balance of the PV and CSP surfaces.Large scale solar farms interact with the atmosphere though land surface albedo replacement. Solar PV farms are highly absorbing while CSP farms are highly reflective when compared to the ground. The spectral albedo of regular surfaces, PV panels and CSP heliostats are plotted in Fig. 6.1, where PV panels have spectral albedo smaller than 0.1 while CSP heliostats have albedo greater than 0.9 in infrared and visible bands. Among the six CIRC cases, surfaces of case 1-3, 6 and 7 have nearly the same albedo while the surface of case 4 has much higher albedo in visible and UV bands, indicating the presence of ice or snow. For the analysis of this section, the regular ground is chosen to be the surface of CIRC case 2. PV panels are assumed to be Si pillar solar cells with spectral reflectance data given by Ref.. The reflection of PV panels is assumed to be diffused. CSP heliostats are assumed to be AgGlass 4 mm Flat glass mirrors, with spectral specular reflectance data given by Ref.. All surfaces are assumed to be oriented horizontally facing the open sky. The vertical profiles of temperature, gases, aerosols and optical properties of gases, aerosols, clouds follow the methodologies presented in Ref.. Note that the effects of PV and CSP farms presented in the following sections are the ‘maximum’ effects, because in the one dimensional radiative model, the entire ground is covered by PV or CSP, but in reality, only a portion of the ground is covered.Atmospheric long wave radiation and solar shortwave radiation are essential components of thermal balances in the atmosphere, playing also a substantial role in the design and operation of engineered systems that exposed to open sky, for examples, cooling towers, radiative cooling devices and solar power plants.

To quantify the spectral thermal balances of the atmosphere and engineered systems, especially optically selective devices, comprehensive line-by-line radiative models are developed to simulate atmospheric long wave and solar shortwave radiative transfer in the Earth – atmosphere system, as well as the interactions between engineered systems and the atmosphere. Firstly, simple parametric models are developed to calculate broadband downwelling long wave irradiance at the surface. Under clear skies, fifteen parametric broadband models for calculating long wave irradiance are compared and recalibrated. All models achieve higher accuracy after grid search recalibration, and we show that many of the previously proposed LW models collapse into only a few different families of models. To account for the difference in nighttime and daytime clear-sky emissivities, nighttime and daytime Brunt-type models are proposed. Under all sky conditions, the information of clouds is represented by cloud cover fraction or cloud modification factor . Three parametric models proposed in the literature are compared and calibrated, and a new model is proposed to account for the alternation of vertical atmosphere profile by clouds. The proposed all-sky model has 3.8% ∼ 31.8% lower RMSEs than the other three recalibrated models. If GHI irradiance measurements are available, using CMF as a parameter yields 7.5% lower RMSEs than using CF. For different applications that require LW information during daytime and/or nighttime, coefficients of the proposed models are corrected for diurnal and nocturnal use. Then, an efficient spectrally resolved radiative model is developed to capture spectral characteristics of long wave radiation in the atmosphere, under clear and cloudy skies. For the non-scattering clear atmosphere , the surface DLW agrees within 2.91% with mean values from the InterComparison of Radiation Codes in Climate Models program, with spectral deviations below 0.035 W cm m−2 . For a scattering clear atmosphere with typical aerosol loading, the DLW calculated by the spectral model agrees within 3.08% relative error when compared to measured values at seven climatologically diverse SURFRAD stations.

This relative error is smaller than the aforementioned calibrated parametric model regressed from data for those same seven stations, and within the uncertainty of pyrgeometers commonly used for meteorological and climatological applications. The broadband and spectral forcing of water vapor, carbon dioxide and aerosols are quantified using the model. When aerosol optical depth equals 0.1 are considered, long wave aerosol forcing falls between 1.86 W m−2 to 6.57 W m−2 . The forcing increases with decreasing values of surface water vapor content because the aerosol bands contribute mostly when the water vapor bands are not saturated. When examining the spatial and spectral contributions of water vapor to the surface DLW, we find, as expected, that water vapor in the nearest surface layer contributes the most, especially in the spectral ranges 0 ∼ 400 cm−1 and 580 ∼ 750 cm−1 . Within the atmospheric spectral windows 400 ∼ 580 cm−1 , 750 ∼ 1400 cm−1 and 2400 ∼ 2500 cm−1 , water vapor above 3.46 km has negligible effect on the monochromatic surface DLW. In some spectral regions, there is a decrease in water vapor forcing because water vapor content in the layers below prevents the long wave radiation from reaching the surface. The warming caused by aerosols mostly comes from the layers below 3.46 km. In a narrow spectral band between 1050 to 1150 cm−1 above 3.46 km, there is a decrease in monochromatic surface DLW forcing, since the lower layer aerosols prevent the radiation from reaching the surface by absorption. Spectral and spatial distribution of irradiation is presented for an atmosphere with surface relative humidity of 65% and aerosol optical depth at 479.5 nm equals to 0.1. First order broadband contributions of increased atmospheric CO2 to surface downwelling flux is found to be 0.3 ∼ 1.2 W m−2 per 100 ppm CO2 increment for different water vapor contents. The broadband reduction of TOA upwelling flux is found to be0.5 ∼ 0.7 W m−2 per 100 ppm CO2 increment. Contributions to the irradiation on the top atmosphere layer and outer space layer come from the surface in the atmospheric window bands, cannabis grow systems from the middle of atmosphere in the water vapor absorbing bands and from the top of atmosphere in the CO2 absorbing bands. For broadband flux contributions, the outer space layer dominates the transfer factors to upper layers but the flux contribution is negligible due to low densities and effective temperatures at that level. For the ground layer, 64.4%, 15.3% and 7.5% of its long wave irradiation comes from the nearest atmospheric layer, the 2nd nearest layer and the 3rd nearest layer, respectively. And the contributions mostly from the four absorbing bands. For all layers below the tropopause, the layer itself contributes the most to its irradiation. For layers above the tropopause layer, the largest contributor to its irradiation is the ground layer. Finally, upper layers above the tropopause contribute to less than 4.8% to the irradiance flux to other layers. Then accurate correlations for the effective sky emissivity as functions of the normalized ambient partial pressure of water vapor for both broadband and seven distinct bands of the infrared spectrum are proposed. The band emissivities are correlated by simple expressions to ambient meteorological conditions at the ground level, and allow for the expedient calculation of cooling power efficiencies of optically selective materials designed for passive cooling or heating. Comparisons between band calculations and line-by-line calculations yield errors that are generally within the measurement uncertainty of atmospheric instrumentation , thus validating the combined approach of high fidelity spectral models with ground experiments taken at diverse micro-climates, altitudes and meteorological conditions.

When clouds are added to the spectral model, the representative cloud characteristics are also proposed as empirical functions for different surface meteorological conditions to guide future modeling efforts. These results enable direct calculation of the equilibrium temperature and cooling efficiency of passive cooling devices in terms of meteorological conditions observed at the surface level. The cooling potential of passive cooling materials is found to be as high as 140 W m−2 for dry and hot conditions without the presence of clouds. But the potential diminishes with increased water vapor content and the presence of clouds, because both water vapor and clouds ‘block’ the atmospheric window for cooling. A Monte Carlo line-by-line radiative model is developed for solar shortwave radiative transfer in the atmosphere, with different surfaces . The local thermal effects of albedo replacements of PV and CSP farms are quantified. Under clear skies, the downwelling GHI is being suppressed by the presence of PV farms while being enhanced by the presence of CSP farms , because of the back-scattering of reflected irradiance from heliostats. The TOA upwelling flux enhancement of CSP plant could be as high as 187%, so that CSP fields are able to cool the surface. Under cloudy skies, the GHI enhancement by CSP is amplified by the presence of clouds because multiple reflections occur between highly reflective CSP farms and clouds. By performing a surface thermal balance, the surface temperature of CSP is 3 K lower than the ambient while the surface temperature of PV or regular surface is more than 40 K above the ambient while under direct sunlight. Under cloudy skies, the irradiance and temperature modification of PV and CSP farms are reduced because the effects of clouds, especially optically thick clouds, dominant. The results presented here strongly suggest the possibility of hybrid solar plant designs that employ an outer ring of PV solar field surrounding an inner heliostat field around the central tower. This hybrid design accomplishes two important objectives: minimization of local changes in temperature and humidity by balancing out the heating caused by the PV field with the cooling caused by the CSP heliostats, and the minimization of DNI variability effects on plant operation through the coupling with the less-variable GHI component absorbed by PV panels. In addition, the thermal balance discussed in this work also allows for the consideration of dual land use, especially under the heliostat field. A raised heliostat field with partial shading may be used for agricultural purposes in desert areas where very few plants could survice without partial shade and lower temperatures and higher humidities. Note that PV panels not only increase downwelling infrared radiation to the soil, but also prevent radiative exchange with the desert sky at night, which in many regions is the mechanism that allows for the formation of dew at night. By considering these different heat and mass transfer mechanisms carefully, novel solar power plant designs may reduce their environmental impact on desertic areas.In 2006, Bagged fresh spinach from the central coast region of California contaminated by Shiga toxin-producing Escherichia coli bacteria with the serotype O157:H7 caused 199 illnesses across 26 US states, and at least 3 deaths .