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Abstract: The utilizability or ϕ-curve method is a design method for some types of solar energy systems that use flat-plate solar collectors. It can be a very useful design tool, for the preliminary design or the design of small systems, cases where methods easy to use and apply are required. In this paper, a simple method to calculate monthly average hourly and daily flat plate collector utilizability is presented. It is based on empirical correlation of ϕ with independent variables that separate meteorological and collector parameters, making possible quick evaluations of changes in collector design and collector inlet temperature. In general, the method reduces the calculations required to determine ϕ, and gives good results compared to long-term hourly simulations as well as to existing hourly and daily utilizability calculations methods. [Copyright &y& Elsevier]

A neural network approach is used in the present study for modelling and estimating the energy consumption time series for a residential building in Athens, using as inputs several climatic parameters.The hourly values of the energy consumption, for heating and cooling the building, are estimated for several years using feed forward backpropagation neural networks. Various neural network architectures are designed and trained for the output estimation, which is the building’s energy consumption. The results are tested with extensive sets of non-training measurements and it is found that they correspond well with the actual values.Furthermore, “multi-lag” output predictions of ambient air temperature and total solar radiation are used as inputs to the neural network models for modelling and predicting the future values of energy consumption with sufficient accuracy. [Copyright &y& Elsevier]

Cities face important overheating problems caused by the local and global climate change. Detailed mitigation and adaptation plans and strategies, are designed and applied to counterbalance the impact of the overheating challenges. Albedo management seems to be among the more considered mitigation strategies. A barrier to the wider use of reflecting technologies is the lack of quantitative experimental data and concrete knowledge about their mitigation contribution. Up to now, the performance of the reflective mitigation technologies is assessed based on simulation results considering the initial optical properties of the materials and neglecting ageing and weatherization phenomena. The article present information on the global performance of reflecting mitigation technologies, as measured in a large scale urban mitigation project employing several types of reflecting technologies. It is shown, that because of the weatherization effects, the mitigation potential of the materials is reduced, during the first year after their installation, by at least, 25%. Despite the ageing effects, reflective pavements have found to contribute in reducing the peak summer ambient temperature up to 1,7 K, while their surface temperature was up to 12,3 K lower than that of conventional pavement reducing considerably the sensible heat released to the atmosphere. [ABSTRACT FROM AUTHOR]

The present study describes a neural network approach for modeling and making short-term predictions on the total solar radiation time series. The future hourly values of total solar radiation for several years are predicted, by extracting knowledge from their past values, using feed-forward back-propagation neural networks. The results are tested using various sets of non training measurements, the findings are very encouraging and the model is found able to simulate the future values of total solar radiation time series based on their past values. 'Multi-lag' output predictions are performed using the predictedvalues to the input database in order to model future total solar radiation values with sufficient accuracy. Furthermore, an autoregressive model is developed for analysing and representing the total solar radiation time series. The predicted values of solar radiation are compared with the observed data series and it was found that the neuralnetwork approach leads to better predictions than the AR model. [ABSTRACT FROM AUTHOR]

Ground albedo can influence the estimation of solar radiation incident on tilted surfaces. Depending on the model used to calculate the skv diffuse radiation and the estimated albedo value, it is possible to introduce a significant error in the prediction of global radiationon a tilted surface. In this paper, several methods for calculating ground albedo values used for estimating the global radiation on a tilted surface, are proposed and evaluated. The predicted global solar radiation values are compared with measured data on a south facing vertical surface. from four representative south and north European locations. It appears that there is a significant impact on the accuracyof calculating the global solar radiation incident on a tilted surface using different methods for calculating ground albedo values. [ABSTRACT FROM AUTHOR]

• High temperatures reduce the efficiency of photovoltaic systems (PVs). • Reflecting roofs mitigate temperatures and increase the PV energy production. • In monofacial modules + 0.1 roof albedo translates into + 0.7% energy production. • In bifacial modules + 0.1 roof albedo translates into + 4.5% energy production. • Local conditions and type of installation modulate the extra energy production. Photovoltaics (PVs) provide clean and affordable energy contributing to the decarbonisation of the energy sector. High surface temperature of the PV modules reduces their efficiency and the corresponding energy production and increases the sensible heat released to the atmosphere contributing to urban overheating. For roof mounted PVs, increase of the roof albedo helps to decrease the surrounding ambient temperature, raises the efficiency of the PVs and increases the reflected solar radiation received by the modules. Numerous studies have assessed the impact of increased roof albedo on the energy yield of the monofacial and bifacial PVs for given installation characteristics and specific climatic conditions. There is a serious need to collect, analyse, compare, and parameterize the existing information in order to provide more global and holistic knowledge to the PVs industry. We have analysed 13 and 57 case studies reporting the impact of modified roof albedo on the energy yield of monofacial and bifacial PV modules, respectively. It is concluded that, on average, increasing the roof albedo by 0.1 contributes to enhance the energy production of monofacial and bifacial PV modules by 0.7% and 4.55% respectively while delivering important co-benefits to urban heat mitigation. Parametric relations between the potential increase of the roof albedo and the increase of the annual energy yield are proposed for both monofacial and bifacial PV modules. The impact of the geographic and installation parameters on the energy production of the modules is analysed and discussed. The results of such a study could help to identify the optimal roof albedo for maximizing energy performance and reducing energy costs. [ABSTRACT FROM AUTHOR]

Buildings are responsible for about the 40% of the global annual energy consumption, therefore, innovative strategies for buildings’ energy efficiency are under development. Strategies of re-roofing with “cool” materials have a non-negligible cooling energy saving potential, as they contribute to the reduction of the peak ambient temperatures during summer and, moreover, they contribute to the improvement of the urban microclimate by decreasing the intensity of heat island phenomena. In this paper, the experimental characterization and optimization of a new membrane for buildings’ roof is carried out. To this aim, laboratory measurements were performed to determine its optic-energy properties and, therefore, to optimize its “cool roof” behavior. A full scale field test was also setup in order to measure the global solar radiation reflected by each membrane, before and after optimization, with varying boundary conditions, e.g. time during the day, seasonal period, and weather conditions. The in-field experimental campaign allowed to characterize the optic-energy behavior of the cool membranes in real boundary conditions, showing non-negligible variation of measured solar reflection capability with varying environmental constraints in winter conditions. The research showed interesting results from the in-lab optimization campaign, and non-negligible unreliability due to environmental agents affecting in-field albedo measurement. [ABSTRACT FROM AUTHOR]

Abstract: Commonly used materials in the construction of the building façades located in warm climates, often entrap a great amount of heat from the incoming solar radiation, leading to a respective thermal increase in the interior. The aim of the present study is to examine mineral-based coatings as a passive solar technique that contributes to buildings’ energy efficiency. A series of mineral based samples are developed and tested. Their thermal performance is estimated by infrared thermography and surface temperature measurements. Their optical properties are also measured while the energy efficiency is quantified using simulation techniques. The results revealed that renders based on hydraulic and/or hydrated lime with additions of calcium carbonate powder, as well as mineral paints comprised either of lime wash or silicate minerals can behave as cool coatings and contribute to a significant reduction of the cooling demand in warm climates. [Copyright &y& Elsevier]

The estimation of diffuse irradiance that impinges on a window or photovoltaic panel is of major importance for the determination of their performance. The present paper introduces the concept of angular shading factors (ASF) for the calculation of time-varying diffuse irradiances to be performed without the need to repeat time consuming intereflection calculations at every time step. For the calculation of ASF, a Monte Carlo backward ray tracing technique was used. As a result, geometrically complex scenes consisting of surfaces with diffuse and specular reflectances, while transparent and translucent surfaces can be modeled as well. After that, the calculation of diffuse irradiance can be performed in a dynamic way, by taking into consideration the sky radiance distribution variability. [Copyright &y& Elsevier]