Review of modern methods and technologies for using of solar energy in the operation of anaerobic digestion systems

The article presents various methods and technologies for using of solar energy in anaerobic bioconversion systems. Various methods of convertion of solar radiation are consistently considered – from its direct use to photovoltaic, thermal, photovoltaic thermal and concentrating. Schemes for introducing solar energy converters into anaerobic bioconversion systems, as well as various solar radiation converters for heat and electricity supply of anaerobic bioconversion systems, are proposed. As power generating components in the article also discusses photovoltaic modules with an extended rated power period, photovoltaic thermal roofing panels with a two-component polysiloxane compound, thermal and photovoltaic thermal solar roofing panels, air-cooled photovoltaic thermal siding panel and concentrator solar photovoltaic thermal module with high-voltage matrix photovoltaic converters. The proposed schemes of systems and design of solar modules will ensure a reduction in the use of thermal energy from the produced gas for power supply for the own needs of anaerobic bioconversion systems, which will make them cheaper and more efficient in operation.     

A critical review of photovoltaic–thermal solar collectors for air heating

Integrated photovoltaic–thermal solar collectors have become of great interest in the solar thermal and photovoltaic (PV) research communities. Solar thermal systems and solar PV systems have each advanced markedly, and combining the two technologies provides the opportunity for increased efficiency and expanded utilization of solar energy. In this article, the authors critically review photovoltaic–thermal solar collectors for air heating. Included is a review of photovoltaic thermal technology and recent advances, particularly as applied to air heaters. It is determined that the photovoltaic–thermal (PV/T) air heater is or may in the future be practicable for preheating air for many applications, including space heating and drying, and that integrated PV/T collectors deliver more useful energy per unit collector area than separate PV and thermal systems. Although PV/T collectors are promising, it is evident that further research is required to improve efficiency, reduce costs and resolve several technical design issues related to the collectors.     

Analysis of solar photovoltaic and wind power potential in Afghanistan

Afghanistan has a need for increased access to energy to enable development. In this paper we analyze the potential for large-scale grid-connected solar photovoltaic (PV) and wind power plants in two of Afghanistan's most populous provinces (Balkh and Herat) to meet a large fraction of growing electricity demand. The results presented here represent the first quantitative analysis of potential capacity factors and energy yields of power plants in the country using measured wind speed and typical solar radiation data. Variability of resources is also investigated by comparing temporal profiles with those of electricity demand, using residual load duration curves to determine penetration and curtailment levels for various demand scenarios. We show that solar PV and wind power plants in two provinces could achieve penetration levels of 65%–70% without significant curtailment, which in turn would mean less reliance on unpredictable and unstable power purchase agreements with neighboring countries, longer life of limited domestic fossil fuel resources, and lower imports of diesel fuel, thus avoiding rising costs and detrimental environmental impacts. Our results point to an alternative development pathway from that of previous recommendations for conventional thermal power plants, controversial hydroelectric projects, and a significant dependence on imported power.     

Solar thermal aided power generation

Fossil fuel based power generation is and will still be the back bone of our world economy, albeit such form of power generation significantly contributes to global CO₂ emissions. Solar energy is a clean, environmental friendly energy source for power generation, however solar photovoltaic electricity generation is not practical for large commercial scales due to its cost and high-tech nature. Solar thermal is another way to use solar energy to generate power. Many attempts to establish solar (solo) thermal power stations have been practiced all over the world. Although there are some advantages in solo solar thermal power systems, the efficiencies and costs of these systems are not so attractive. Alternately by modifying, if possible, the existing coal-fired power stations to generate green sustainable power, a much more efficient means of power generation can be reached. This paper presents the concept of solar aided power generation in conventional coal-fired power stations, i.e., integrating solar (thermal) energy into conventional fossil fuelled power generation cycles (termed as solar aided thermal power). The solar aided power generation (SAPG) concept has technically been derived to use the strong points of the two technologies (traditional regenerative Rankine cycle with relatively higher efficiency and solar heating at relatively low temperature range). The SAPG does not only contribute to increase the efficiencies of the conventional power station and reduce its emission of the greenhouse gases, but also provides a better way to use solar heat to generate the power. This paper presents the advantages of the SAPG at conceptual level.     

Hydrogen from renewable energy: A pilot plant for thermal production and mobility

In the mainframe of a research contract, a feasibility pre-design study of a hydrogen-fuelled Laboratory-Village has been carried out: the goals are the design and the simulation of a demonstration plant based on hydrogen as primary fuel. The hydrogen is produced by electrolysis, from electric power produced by a mix of hydroelectric and solar photovoltaic plants. The plant will be located in a small remote village in Valle d’Aosta (Italy). This country has large water availability from glaciers and mountains, so electricity production from fluent water hydroelectric plants is abundant and cheap. Therefore, the production of hydrogen during the night (instead of selling the electricity to the grid at very low prices) could become a good economic choice, and hydrogen could be a competitive local fuel in term of costs, if compared to oil or gas. The H₂ will be produced and stored, and used to feed a hydrogen vehicle and for thermal purposes (heating requirement of three buildings), allowing a real field test (Village-Laboratory).     

Solar chimney power plants for high latitudes

A solar chimney system for power production at high latitudes has been designed and its performance has been evaluated. A mathematical model and a code on MATLAB platform have been developed based on monthly average meteorological data and thermodynamic cycle. The thermal performance of a 5 MW nominal power production plant at three locations in Canada, namely Ottawa, Winnipeg and Edmonton, is studied. The sloped collector field is built at suitable mountain hills, which also functions as a chimney. Then a short vertical chimney is added to install the vertical axis air turbine. The results showed that solar chimney power plants at high latitudes may have satisfactory thermal performance and produce as much as 85% of the same plants in southern locations with horizontal collector field. The overall thermal performance of these plants is a little less than 0.5%.     

Electromagnetic transients in the control system of output parameters of a solar power plant in Tajikistan Central Asia region

At present, as the demand for electricity increases in all sectors, there is an urgent need to introduce alternative renewable energy sources into modern energy systems. Renewable energy sources, which consist of solar (photovoltaic, PV), wind and hydro power, are key alternative sources of “green energy’’ energies, but it can also be used to produce “green” hydrogen. Thanks to scientific and technological progress, the cost of photovoltaic solar radiation converters is constantly decreasing at a high rate, which makes it possible to build solar power plants of sufficiently large capacity. In the coming decades, solar energy will become an incentive for the economic development of countries that have the maximum “solar” resource. The Republic of Tajikistan is one of these countries with a high potential for solar energy.The article presents an analysis of the resources and potential of solar energy in the Republic of Tajikistan. The study of electromagnetic transients in networks with photovoltaic solar power plants is performed. The main equations, simulation model and calculations of transients are presented, taking into account changes in voltage on DC buses. An algorithm for controlling the system of automatic control of output parameters is proposed. The analysis of dynamic and static modes in parallel operation of a solar power plant with the grid is carried out. A block diagram and computer model is constructed in the MATLAB package together with Simulink and Power System Blockset.     

Solar electricity generation—A comparative view of technologies, costs and environmental impact

The implementation of solar power plants in regions of high insolation is a promising option for an environmentally compatible electricity supply strategy. Today, approximately 80% of the solar generated electricity is provided by solar thermal power plants, while 20% is supplied by photovoltaic systems. Decision-makers have the choice among the following solar technologies: (1) parabolic trough; (2) central receiver; (3) paraboloidal dish; (4) solar chimney; (5) solar pond; (6) photovoltaic cells. This article compared present solar electricity technologies from the point of view of system analysis, taking into consideration their performance, costs and environmental impact. The study shows that the different approaches cover a wide range from units of a few Watts to utiilty-size plants and from isolated to grid-connected systems. It also shows that there is still a need for intense efforts to integrate those technologies into the existing electricity supply scheme. If a continuous development and market introduction is achieved, solar power plants will contribute substantially to the reduction of global CO₂-emissions. A practical tool for decision-makers is presented that facilitates a first estimate of the performance and costs of such plants under local conditions.     

Simulation of a pilot solar chimney thermal power generating equipment

A pilot experimental solar chimney thermal power generating equipment was set up in China. A simulation study was carried out to investigate the performance of the power generating system based on a developed mathematical model. The simulated power outputs in steady state were obtained for different global solar radiation intensity, collector area and chimney height. By intercomparison, it is found that the simulated power outputs are basically in agreement with the results calculated with the measurements, which validates the mathematical model of the solar chimney thermal power generating system. Furthermore, based on the simulation and the specific construction costs at a specific site, the optimum combination of chimney and collector dimensions can be selected for a required electric power output.     

Prediction of global solar irradiance based on time series analysis: Application to solar thermal power plants energy production planning

Due to strong increase of solar power generation, the predictions of incoming solar energy are acquiring more importance. Photovoltaic and solar thermal are the main sources of electricity generation from solar energy. In the case of solar thermal energy plants with storage energy system, its management and operation need reliable predictions of solar irradiance with the same temporal resolution as the temporal capacity of the back-up system. These plants can work like a conventional power plant and compete in the energy stock market avoiding intermittence in electricity production.This work presents a comparisons of statistical models based on time series applied to predict half daily values of global solar irradiance with a temporal horizon of 3 days. Half daily values consist of accumulated hourly global solar irradiance from solar raise to solar noon and from noon until dawn for each day. The dataset of ground solar radiation used belongs to stations of Spanish National Weather Service (AEMet). The models tested are autoregressive, neural networks and fuzzy logic models. Due to the fact that half daily solar irradiance time series is non-stationary, it has been necessary to transform it to two new stationary variables (clearness index and lost component) which are used as input of the predictive models. Improvement in terms of RMSD of the models essayed is compared against the model based on persistence. The validation process shows that all models essayed improve persistence. The best approach to forecast half daily values of solar irradiance is neural network models with lost component as input, except Lerida station where models based on clearness index have less uncertainty because this magnitude has a linear behaviour and it is easier to simulate by models.     

On-site measurement of the performance of crystalline silicon PV arrays

A procedure for determining the rated power of crystalline silicon photovoltaic arrays from on-site measurements in the field is described. It is the outcome of several years' experience in the testing of European pilot and demonstration plants and has formed the basis of an IEC draft standard on the subject. The procedure differs significantly from that followed when measuring the rated performance of solar cells and modules. The reasons for these differences are explained.     

Comparing solar energy alternatives

This paper outlines a computational procedure for comparing the merits of alternative processes to convert solar radiation to heat, electrical power, or chemical energy. The procedure uses the ratio of equipment investment to useful work as an index. Comparisons with conversion counterparts based on conventional fuels are also facilitated by examining this index. The procedure is illustrated by comparisons of (1) photovoltaic converters of differing efficiencies; (2) photovoltaic converters with and without focusing concentrators; (3) photovoltaic conversion plus electrolysis vs photocatalysis for the production of hydrogen; (4) photovoltaic conversion plus plasma arcs vs photocatalysis for nitrogen fixation. Estimates for conventionally-fuelled processes are included for comparison. The reasons why solar-based concepts fare poorly in such comparisons are traced to the low energy density of solar radiation and its low stream time factor resulting from the limited number of daylight hours available and clouds obscuring the sun.     

A two dimensional thermal network model for a photovoltaic solar wall

A two dimensional thermal network model is proposed to predict the temperature distribution for a section of photovoltaic solar wall installed in an outdoor room laboratory in Concordia University, Montréal, Canada. The photovoltaic solar wall is constructed with a pair of glass coated photovoltaic modules and a polystyrene filled plywood board as back panel. The active solar ventilation through a photovoltaic solar wall is achieved with an exhaust fan fixed in the outdoor room laboratory. The steady state thermal network nodal equations are developed for conjugate heat exchange and heat transport for a section of a photovoltaic solar wall. The matrix solution procedure is adopted for formulation of conductance and heat source matrices for obtaining numerical solution of one dimensional heat conduction and heat transport equations by performing two dimensional thermal network analyses. The temperature distribution is predicted by the model with measurement data obtained from the section of a photovoltaic solar wall. The effect of conduction heat flow and multi-node radiation heat exchange between composite surfaces is useful for predicting a ventilation rate through a solar ventilation system.     

Critical factors affecting the photovoltaic characteristic and comparative study between two maximum power point tracking algorithms

This paper presents the characterization and the modeling of the electric characteristics of currentvoltage and power–voltage of the photovoltaic (PV) panels. The philosophy behind digital simulation of solar energy systems is that experiments which normally should be done on real systems under high assembling costs can be done numerically in a short time on a computer, thus saving time and investments. The electric parameters of PV cells and the optimal electric quantities of PV panels have been analyzed (voltage and power) according to the meteorological variations (Temperature, solar irradiation …). The obtained results show that the diode parameters of the PV cells depend on solar irradiation: the current saturation increases with solar irradiation. This induces a decrease of the optimal voltage with solar irradiation; when the solar irradiation varies from 600 W/m² to 1000 W/m². By taking into consideration all the modeling results, the electric behavior of the cells association in parallels or in series, as well as the aging of a PV panel have been analyzed. Moreover, a comparative study between two types of MPPT techniques that are used in photovoltaic systems to extract the maximum power have been introduced which are Perturb and Observe (P &O) and Incremental Conductance (INC).     

Economic evaluation of solar-only and hybrid power towers using molten-salt technology

Several hybrid and solar-only configurations for molten-salt power towers were evaluated with a simple economic model, appropriate for screening analysis. The solar-specific aspects of these plants were highlighted. In general, hybrid power towers were shown to be economically superior to solar-only plants with the same field size. Furthermore, the power-booster hybrid approach was generally preferred over the fuel-saver hybrid approach. Using today's power tower technology, economic viability for the solar power-boost occurs at fuel costs in the neighborhood of $8.90 to $15/MW h ($2.60 to $4.40/MBtu, low heating value) depending on whether coal-based or gas-turbine-based technology is being offset. These fuel prices exist today in certain areas of the world (e.g. India). The cost of CO₂ avoidance was also calculated for solar cases in which the fossil fuel cost was too low for solar to be economically viable. The avoidance costs are competitive with other proposed methods of removing CO₂ from fossil-fired power plants and appear to be within the range of interest (<$29/mt) to environmental protection organizations such as the Global Environmental Facility.     

Solar gas turbine systems: Design, cost and perspectives

The combination of high solar shares with high conversion efficiencies is one of the major advantages of solar gas turbine systems compared to other solar-fossil hybrid power plants. Pressurized air receivers are used in solar tower plants to heat the compressed air in the gas turbine to temperatures up to 1000 °C. Therefore solar shares in the design case of 40% up to 90% can be realized and annual solar shares up to 30% can be achieved in base load. Using modern gas turbine systems in recuperation or combined cycle mode leads to conversion efficiencies of the solar heat from around 40% up to more than 50%. This is an important step towards cost reduction of solar thermal power. Together with the advantages of hybrid power plants—variable solar share, fully dispatchable power, 24 h operation without storage—solar gas turbine systems are expected to have a high potential for market introduction in the mid term view.In this paper the design and performance assessment of several prototype plants in the power levels of 1 MW, 5 MW and 15 MW are presented. Advanced software tools are used for design optimization and performance prediction of the solar tower gas turbine power plants. Detailed cost assumptions for the solarized gas turbine, the solar tower plant and further equipment as well as for operation and maintenance are presented. Intensive performance and economic analysis of the prototype plants for different locations and capacity factors are shown. The cost reduction potential through automation and remote operation is revealed.     

Renewable energy in the South Pacific—options and constraints

Over the last fifteen years the small island nations in the South Pacific have seen the introduction of various forms of renewable energy technologies. In spite of high expectations from the development of indigenous renewable energy resources using nonconventional approaches (wind power, wave power, ocean thermal energy conversion, biogas digestors, biomass gasifiers), these technologies have largely failed to develop into viable alternatives to conventional approaches (based on imported petroleum, biomass and hydroelectric power). Among the few exceptions are solar photovoltaic power for remote islands, especially when provided through a utility type institution, solar water heaters, and the use of biomass wastes by agroindustries. As a result, all the island countries are still heavily dependent on fossil fuels for their energy requirements. Some of them to such an extent that their petroleum imports are up to 500% of their total exports.As far as acceptance of new renewable energy technologies by the Pacific communities goes hasty decisions and introductions have done more harm than good.     

Perspectives for solar thermal applications in Taiwan

Taiwan has long depended on imported fossil energy. The government is thus actively promoting the use of renewable energy. Since 2000, domestic installations of solar water heaters have increased substantially because of the long-term subsidies provided for such systems. However, data on the annual installation area of solar collectors in recent years indicated that the solar thermal industry in Taiwan has reached a bottleneck. The long-term policy providing subsidies must thus be revised. It is proposed that future thermal applications in Taiwan should focus on building-integrated solar thermal, photovoltaic/thermal, and industrial heating processes. Regarding building-integrated solar thermal systems, the current subsidy model can be continued (according to area of solar collectors); nevertheless, the application of photovoltaic/thermal and industrial heating systems must be determined according to the thermal output of such systems.     

Technical and economic evaluation of the utilization of solar energy at South Africa's SANAE IV base in Antarctica

The technical and economic feasibility of utilizing solar energy at South Africa's SANAE IV station in Antarctica was evaluated in order to estimate potential financial and external savings, and to alleviate the programme's dependence on the special blend of diesel shipped annually from Cape Town. The average global horizontal and tilted insolation rates at the base were studied, energy consumption data of the station was investigated, technical performance characteristics of devices for harnessing solar energy were assessed and an economic analysis was completed. It was shown that at SANAE IV flat-plate solar thermal collectors could potentially be used in conjunction with the snow smelter (a device that meets the station's fresh water demand) and that photovoltaic modules could feasibly be used to reduce the station's electrical demand. Flat-plate solar thermal collectors could collect solar energy at an average of 3.13 R/kWh (viz. 0.49 US$/kWh) from a suggested 143 m² array, while comparatively a 40 kWp photovoltaic system would be less economically sound and only able to pay back costs at the end of the system's expected 25-year lifetime, generating electricity at an estimated 3.20 R/kWh (annual electrical consumption at SANAE IV amounts to more than 1062 MWh). The total diesel savings of the solar thermal and photovoltaic systems were estimated at approximately 12 245 and 9958 l, respectively, which represent savings in externalities of R67 338 and R55 879 each.