• Energy Research

Abstract This study describes the development of manufacturing processes for a mechanically manufactured selective C/Al2O3/Al surface and its basic characterization. The composition and structure of the surfaces were characterized by scanning electron microscopy and electron microprobe analysis. Spectroradiometer and FTIR-spectrometer were used for optical characterization. The manufacturing process has been developed from manual abrasive grinding followed with an acid bath to mechanically operated grinding alone. The surface consists mainly of Al2O3, with some C adsorbed on the surface during the grinding process. The microstructure of the surface consists of small grooves, organized in a heterogeneous two-dimensional matrix. The width of the grooves varies typically between 1 and 2 μm. The absorptance of a surface from the latest stage of development is 0.90 and the emittance 0.25.

Abstract The public support in photovoltaic (PV) technologies and increasing markets have resulted in extensive applications of grid-connected PV, in particular in the consumer side and electricity distribution grid. In this paper, the effects of a high level of grid connected PV in the middle voltage distribution network have been analyzed. The emphasis is put on static phenomena, including voltage drop, network losses and grid benefits. A multi-purpose modeling tool is used for PV analysis in Lisbon and Helsinki climates. All network types studied can handle PV without problems with an amount of PV equaling at least up to the load (1 kWp/household). The comb-type network showed the best performance. The PV is unable to shave the domestic load peak in the early evening hours but through orientating the PV panels both to east and west, the noon peak from PV can be reduced by 30%. PV integration reduces network losses positively up to a 1 kWp/hh (100% of annual domestic load) level. For 2 kWp/hh all but the comb-type networks demonstrate clear over-voltage situations and the annual network losses are much higher than without PV.

Abstract For the new energy technology markets to grow, demand, prices, and business conditions need to be in balance. It is not just declining prices and increasing volumes that are important, but the business in the new energy sector also needs to be healthy, which is not always the case at present. We have analyzed the ability of businesses in the new energy sector to invest in new production capacity, which influences the total volume growth. Using the self-financeable growth rate (SGR) as an indicator, a declining trend was found among PV and wind power manufacturers. The prospects of initiating new investments through returns from operations are poor or negligible at present, which is explained by tougher competition, shrinking public support, and new entrants, among others. Reducing the cost of sales would be the most effective way to improve the growth prospects, though increasing revenues, e.g., through higher product prices, comes close to achieving the same result. Market measures such as consolidation, rationalization, better asset use, improving efficiency, etc. are equally important. The analysis results imply a growth limit of ca. 15–25% per year with present market conditions, which may also be a more permanent level, supported by findings from technology diffusion and growth model studies. The results suggest that it is not self-evident that the new energy technologies will meet the future goals set for these in the climate and energy policy strategies, unless policymakers and decision makers properly address the issue of restoring and securing sound business conditions.

The compound parabolic concentrator (CPC) is a highly interesting solar collector technology for different low-concentration applications due to no tracking requirement. The CPC with a tubular absorber is the most common type of CPC. Here, a comprehensive state-of-the-art review of this CPC type is presented, including design features, structure, applications, etc. Key design guidelines, structural improvements, and recent developments are also presented.

Abstract Degradation mechanisms of unglazed solar absorber surfaces based on aluminium substrate were studied. Rough graphite-aluminium surfaces were total-immersion subjected to aerated and de-aerated simulated neutral and acid rain. Test conditions were based on calculated absorber stagnation temperature and global rain acidity measurements. Changes in optical properties, elemental composition and sample mass were examined by spectrometry, energy dispersive X-ray spectrometry and thermogravimetry, respectively. The absorbers exhibited almost no degradation at pH value of 3.5. At pH 5.5 alumina on the surface hydrated significantly degrading the optical properties of the surfaces severely in most cases. Therefore these absorber surfaces can not be recommended to be used in non-glazed applications if they are exposed to rain with pH exceeding ∼3.5–4.5. The total-immersion test needs to be developed further as the test results exhibited poor temperature and time dependency thus preventing accurate service lifetime estimates. Still, these tests were useful in determining favourable and non-favourable operating conditions for the absorber surfaces based on aluminium substrate.

Abstract In this article, we present an updated potential of distributed photovoltaics in cities in Chile, which is one of the most promising regions for solar energy utilization because of high insolation, high energy costs and rapid urbanization. The study is based on detailed analysis of the spatio-temporal solar potential including load matching in a southern Chilean city, which is then extrapolated to all cities with more than 15,000 inhabitants. In addition, we estimate the cost-effectiveness of such solar city schemes. Our results show that in the city of Concepcion PV could cover up to 90% of the annual electricity demand. On national scale, cities could on average produce 83% of their annual electricity demand, but in the northern part this could exceed even 100%. If scaling the PV yield from distributed PV in cities to whole Chile that would correspond to 22% of country’s electricity demand. The cost (LCOE) of PV in cities seems to be cost-effective against grid electricity, i.e. in the Chilean context PV has already reached grid-parity in cities.

Abstract A straight-through all-glass evacuated tube collector (ETC) made of high-quality borosilicate glass was developed for large-scale low and medium temperature solar hot water systems. It consists of an inner and outer tube without a free end and was shown to be mechanically stable with a thermal expansion coefficient of (3.3 ± 0.1) × 10−6 K−1. Due to turbulent conditions in the straight-through all-glass tube, a higher heat transfer rate could be achieved than in a Dewar-tube ETC, leading to increased heat extraction and decreased heat losses. The photo-thermal efficiency was improved, indicating that a straight-through tube could be more cost-effective. At the same time, active flow in the tube can result in a better water quality as the accumulation time in the tube was short.