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An extension of previous studies, which did not treat quantitatively possible effect of diffuse skylight on the enhancement of energy gain of solar thermal collectors when sun-tracking instead of fixed position is used, involved consideration of possible contribution of the former to the overall solar power and energy received on the ground under different conditions (time of a year, degree of overcast). The effect on the efficiency of two types of solar thermal collectors: a standard (fixed) one and one of adjustable orientation, is considered. Also, possible advantage of orienting adjustable-position collectors towards maximum light (light-tracking) instead of the astronomic position of the sun (sun-tracking) was discussed, as to conclude that little is to be gained and even that only at the sky totally covered by clouds. Some experimental proof of the validity of conclusions is presented.

An assessment is made as to whether renewable energy use for electricity generation in the EU was beneficial throughout the cycle of high and low oil prices. Costs and benefits are calculated with the EU statistics for the period of low oil prices 1998–2002 and high oil prices 2003–2009. The share of renewable energy in electricity production was 21% of all energy resources in 2008, growing on average 5% a year during 2003–2008 compared to nil growth of the fossil fuels mix. Correlations show significant impacts of growing renewable energy use on changes in consumers' electricity prices during the high and rapidly increasing fossil fuel prices in the period 2005–2008. The growing use has contributed to price decrease in most countries that use more renewable energy and price increase in many countries that use little renewable energy. Costs and benefits are assessed through comparison between the observed consumers' electricity prices and simulated prices had they followed the costs of fossil fuel mix. A net benefit of 47 billion euro throughout the oil price cycle is attributable to the growing use of renewable energy, which is on average 8 billion euro a year. This net benefit is larger than the total public support for renewable energy. The net benefit would be larger had the EU anticipated high oil prices through more public support during low oil prices, as this would create productive capacity, but countries' interests increasingly differed. An anti-cyclic EU policy is recommended

The exploitation and utilisation of solar energy is challenging because of both diurnal and seasonal variation. Seasonal thermal energy storage is a prominent solution to solve the problem of seasonal variation of solar production. This paper investigates both the optimal design and energy management of a renewable energy plant with seasonal thermal energy storage. As a case study, the thermal, cooling and electrical energy demands of a university campus during one year are considered. Three scenarios, characterized by a different available area (20,555 m2, area covered at present; 50,000 m2, potentially available area by exploiting the entire rooftop and parking area; unlimited area) for solar thermal collectors and photovoltaic panels are investigated. In the first two scenarios, the exploitation of solar energy allows a primary energy saving of 31% and 57%, respectively compared to the use of a conventional plant. The seasonal storage reaches an overall efficiency (thus considering both charging and discharging) up to 84%. Finally, the analysis of the third scenario shows that the feasibility of meeting the energy demands by only exploiting solar energy is technically challenging because a large area equal to about 100,293 m2 is needed for solar thermal collectors and photovoltaic panels.

Abstract The paper describes the design process of a photovoltaic (PV)-wind power system to be installed in the very challenging ambient conditions of the French-Italian Antarctic Base. Concordia Base has been built with the collaboration of Italian consortium PRNA, French Polar Institute IPEV and European Space Agency ESA. It is one of the three bases not located on the coast and is open all the year. The electrical load of the base, presently supplied by three diesel generators, has been previously characterised measuring the relevant quantities during a period of one year. During the same year an experimental campaign has been conducted to collect the necessary solar irradiance and wind data of the site. Models of the PV panels and of the wind turbine, previously set up and validated, have been used to simulate the plant behaviour and to estimate the possible contribution of renewable energies to the Concordia Antarctic Base supply in the different seasons. Finally, some economical aspects are discussed and the payback period is calculated.

Abstract In the present study, the effect of different degumming processes on the phosphorus content of Crambe abyssinica oil and resultant biodiesel was evaluated. The non-edible oil was submitted to water degumming and chemical degumming with different concentrations of phosphoric acid and varying the acid to oil volume percentages. Phosphorus content of the products was measured by UV spectroscopy after sample calcination, according to NP 1994:2000. Biodiesel was produced by transesterification using a 6:1 methanol to oil molar ratio and 1 wt% sodium hydroxide as catalyst at 65 °C, during 1 h. The biodiesel produced directly from the crude oil presented high phosphorus concentration (>20 ppm); consequently, a degumming process was required to fulfil the quality standard (

Abstract The present work compares the environmental impact of three different thermal energy storage (TES) systems for solar power plants. A Life Cycle Assessment (LCA) for these systems is developed: sensible heat storage both in solid (high temperature concrete) and liquid (molten salts) thermal storage media, and latent heat storage which uses phase change material (PCM). The aim of this paper is to analyze if the energy savings related to the stored energy of the different systems are enough to balance the environmental impact produced during the manufacturing and operation phase of each storage system. Some hypothetical scenarios are studied using LCA methodology to point out the differences between each TES system. The system based on solid media, due to his simplicity, shows the lowest environmental impact per kWh stored of all three systems compared. In addition, the liquid media (molten salts) shows the highest impact per kWh stored because it needs more material and complex equipment.

Large-Eddy Simulation is adopted to reproduce the wake of an axial-flow hydrokinetic turbine. The process of momentum recovery is correlated with the destabilization of the wake system, starting wake contraction and radial flows from the free-stream towards the wake core. All terms of the momentum balance equation are analyzed. The radial advection dominates the momentum recovery at the outer radii (in the vicinity of the radial boundary of the wake), just downstream of the instability of the system of tip vortices. Further downstream the reduction of the mean radial gradients makes advection less significant and the radial turbulent transport becomes the main source of momentum replenishment at inner radii, near the wake axis. The details of the process of momentum recovery and its correlation with the instability of the wake system, revealed by the present high-fidelity eddy-resolving computations, provide new insight on the development of the wake of axial-flow hydrokinetic turbines.

In the present study, fresh olive mill waste (OMWF) was processed using an innovative pre-treatment based on the adsorption capacity of two natural matrices. The liquid fraction coming from the pre-treatment is an inexpensive feedstock for hydrogen photo-production by means of purple non-sulphur photosynthetic bacteria (PNSB). The culture broth, which contained OMWF (30%) and distilled water (70%) was tested for hydrogen photo-production using Rhodopseudomonas palustris 42OL. The photo-fermentative process was studied under batch growth conditions, at three different irradiances (18.5, 37 and 74 W/m2). The lowest cumulative amount of hydrogen (439 ml-H2/L-broth) was attained at the irradiance of 18.5 W/m2, while the highest one (1030 ml-H2/L-broth) was obtained at the irradiance of 74 W/m2. The resulting average hydrogen evolution rates (HPRavg), which were based on the culture volume and were attained at the three different irradiances (i.e. 18.5, 37 and 74 W/m2), were 1.40, 3.17 and 5.28 ml-H2/L-broth/h respectively. The culture age at which the hydrogen photo-evolution ceased showed an inverse proportionality as compared to the irradiance: i.e. the higher the irradiance, the lower the culture age. On the contrary, the COD removal efficiency (CODRE) increased depending on the irradiance. The maximal light conversion efficiency (1.07%) was attained at the irradiance of 37 W/m2, and decreased at both lower and higher irradiances. ⺠Two adsorbing vegetable matrices for olive mill waste (OMW) dephenolization. ⺠We used pre-treated OMW as feedstock for hydrogen photo-production. ⺠We set up two photo-fermentative steps to enhance the COD removal efficiency. ⺠Irradiance effects on COD removal and light conversion efficiencies were examined.