• Energy Research

An analysis of solar water heating systems determines the number of days in each month when solar heated water wholly meets demand above a set temperature. The approach has been used to investigate the potential contribution to water heating loads of solar water heating in two UK locations. Correlations between the approach developed and the use of solar fractions are discussed.

This paper describes variants of using electric power accumulators of various types-lithium-ion and lead-acid storage batteries, flow-through redox storage batteries, and the hydrogen cycle-for the niche of back-up and emergency power supply sources designed for long periods of operation (8–72 h). The schematic diagrams are proposed, and, on the basis of data submitted by equipment manufacturers and designers, the comparative technical and economic analysis of these systems has been performed.

Thin film photovoltaic (PV) technologies were quite popular in 2005-2010 due to relatively low modules costs and low need in silicon or other materials. Amorphous silicon (a-Si) thin films are well known as PV active material with wider light absorption bandgap than for crystalline silicon which allows better module operation in case of diffuse radiation. Low PV energy conversion efficiency (7-11% against 16-19% for crystalline) is a main drawback of such modules. CuInGaSe2 (CIGS) thin films have no such features for absorption bandgap, but have large efficiency (13-14% for PV module and 20,4% for laboratory scale cell). It is also known, that thin film modules have much lower temperature power coefficient, which makes their operation more reliable at hot weather. Nowadays fast progress in crystalline silicon PV technologies led to lower cost for crystalline modules and made thin film technologies less competitive. In Joint Institute for High Temperatures comparative field tests of several thin film and crystalline modules were conducted in 2015-16, using small autonomous power units (PV module, charge controller, small accumulator for charge controller feed and resistive load) as a test bed. Specific energy production for each module throughout different months and the whole test period (10.2015-10.2016) was used as a main criteria for comparison. Economic efficiency (energy production to capital costs ratio for each module type) was also estimated.

Beside continuous implementation of concentrating solar power plants (CSP) in Europe, which stipulate cost reduction by mass production effects, further R&D activities are necessary to achieve the cost competitiveness to fossil power generation. Therefore the cost range of 15–20 cents€/kWh for the currently planned CSP systems in Europe has to be decreased by a factor of 2–4. The European Concentrated Solar Thermal Roadmap (ECOSTAR) study that is conducted by leading CSP research institutes in Europe intends to stipulate the direction for R&D activities in the context of cost reduction. It uses a common methodology approach, based on an annual performance model to identify the most essential technical innovations that will reduce the cost of seven different CSP system concepts, which are currently under promotion world wide. The potential of innovative concepts for solar light weight concentrators, low-cost thermal energy storage concepts, solar receivers/absorbers and power cycles are in the main focus of interest. The results of the study include a description of the value of CSP power, the sensitivity of the electricity cost information, a list of innovations that have been investigated and recommendations for the focus of further R&D work.

The performance of a DHW system fitted with flat-plate and vacuum collectors has been analysed. Simulations were carried out on the basis of equal aperture or gross areas of basis using TMY data for hour-by-hour dynamic simulation generated for 1036 sites located in different regions of the world. The performance indicators of solar fractions and number of days were determined for specific water mean temperatures in the storage tank of 37 °C, 45 °C and 55 °C. It has been shown that vacuum tube collectors provide slightly better DHW performance indicators than typical flat-plate collectors having the same aperture area. However, since the space that needs to be provided and directly or indirectly paid for is what matters to the user of solar heating systems, the analysis was also carried out on equal gross area basis; on this basis, the advantages of using vacuum collectors are not obvious.

This article reviews possible schemes of the power supply of an autonomous reverse osmosis desalination plant that uses a photoelectric converter as primary energy sources. Using the climate data of several regions that have a shortage of fresh water for drinking and technical purposes, a technical and economic evaluation of the use of solar energy for obtaining fresh water in regions with high levels of solar radiation was performed. The prospects of the partial or complete substitution of diesel fuel by energy derived from photoelectric converters in such systems for regions with a high level of insolation and cost of diesel fuel are shown.

The solar energy resources in Central Asia are assessed. Sources of actinometric information—the results of long-term ground-based measurements and mathematical simulation—are analyzed. Actinometric data of the publicly accessible NASA SSE global climate information database for this region is verified and its correspondence to the task was proved. The methods used to assess the gross and technical potential of solar energy are described briefly, and the results of calculations for Uzbekistan and Kyrgyzstan are provided.

A simplified method of calculating the heat flow through a heat exchanger in which one or both heat carrying media are undergoing a phase change is proposed. It is based on enthalpies of the heat carrying media rather than their temperatures. The method enables the determination of the maximum rate of heat flow provided the thermodynamic properties of both heat-carrying media are known. There will be no requirement to separately simulate each part of the system or introduce boundaries within the heat exchanger if one or both heat-carrying media undergo a phase change. The model can be used at the pre-design stage, when the parameters of the heat exchangers may not be known, i.e., to carry out an assessment of a complex energy scheme such as a steam power plant. One such application of this model is in thermal simulation exercises within the TRNSYS modeling environment.

An assessment of the economic expediency of the construction of network photovoltaic stations in some regions of Uzbekistan, Kyrgyzstan, Tajikistan, Turkmenistan, Kazakhstan, and Azerbaijan is presented, with an accounting for climate conditions and the electricity rates that were adopted to encourage the development of renewable power engineering. The analysis covers design variants of 5-MW model solar power plants on photovoltaic modules made according to various technologies with respective modern and advanced cost indicators. The performance indicators of PVPPs with multicrystalline photovoltaic modules and highly efficient HIT technology modules were made by the Hevel company in Russia.