نشریه انرژی ایران
سال هشتم شماره 2 (پیاپی 30، اردیبهشت 1382)

In this paper, a new control method for grid connection of PhotoVoltaic(PV) systems is proposed. The objective of this paper is to show that, with an adequate control strategy, the PV system can transfer the DC link energy into grid, improve the power factor of the electrical system and compensate harmonic currents of the utility. If the PV power generation is not enough to supply demanded power of the load, the utility feeds the active power demand of the load directly and the PV system supplies a reactive and harmonic compensating component of the load current. With the utility fail, the power is transferred from the PV system to the load. Finally, in order to validate the accuracy of the proposed control method, grid-connected PV system is simulated.

In this paper, theoretical performance of an indirect evaporative cooler investigated based on – NTU analysis. Then, the entropy generation of this plate cooler heat exchanger during the process was calculated. As result of this analysis, optimum values of design such as energy efficiency ratio (EER), evaporation efficiency, cooling capacity in terms of design parameters are determined. Results show that using indirect evaporative coolers due to reduction in water moisture in primary air is convenient for Iran climate, probably saving energy consumption.

A long term energy plan that optimize the investment and operation cost of whole energy system in an integrated approach, would have an important effect on economy of the country and can improve Iran’s role in world energy markets. The history of long term energy planning in Iran, has been restricted to some programs provided by local and foreign advisors; however because of not conformity to socio - economic transformations, most of these programs were not so useful. Iran with 8.6% of total discovered oil reserves of the world, has a good potential for oil refining and exportation of products. Regretfully since the last years, even by using 9 petroleum refineries with the capacity of about 1.5 million barrel per day, not only there was not a suitable amount of export, but also there was a considerable amount of import for oil products, especially gasoline. Using refineries with more efficient refining pattern would help to overcome this deficiency and better utilizing the potential of country. In this thesis, petroleum refineries are disaggregated to their internal refining processes and simulated in the national energy network. The aim is determination of optimum petroleum refining pattern during years 2004 to 2029 from the macro viewpoint. Considering the existing potentials and capacities, the results of most scenarios show that future programs in petroleum refining industry must be constructed on basis such as expansion of capacities, tendency to products exportation, especially light products, and expansion of catalytic converter units.

Heat pipes are high capacity heat transfer devices. Therefore, many studies have been carried out on their theory and application in Liquid-Gas heat exchangers and radiators. In the present study, a heat exchanger composed of 18 thermosyphones (heat pipes without wicks) arranged in two rows with staggered configuration was constructed. Heat was absorbed by lower part of the tube from hot water and removed from upper part of the tube by air stream. Analysis showed that the boiling limit is the lowest limit. Since the capacity of each thermosyphone is lower than this limit, it is assured that the designed thermosyphones operate securely at the design condition. Calculations showed that they are capable of transferring 1908 Watts heat from a hot water with 80 degree centigrade temperature and 6 liters per minute flow. Experimental results approved a capacity of 1730 watts. Comparison of the two mentioned values indicates the satisfactory design and construction. Theoretical and experimental values of heat transfer coefficient of inside and outside of the condensing part of the tube are in good agreement. The inside heat transfer coefficient of the used heat pipes was 7900 w/m2.K while this value is 230 for a similar metallic tube.

The reform of the Electricity Supply Industry (ESI) in Australia is an integral element of the wider economic reform agenda of the Australian governments. Such reform, it is claimed, by its supporters, will improve the productive efficiency of the electricity industry, result in lower prices for electricity, and contribute to accelerate the overall growth of the economy. This contention is based on the results of a set of empirical studies, conducted by different research groups over the past decade, focusing on assessing potential gains from ESI reform. The main methodological framework for these studies essentially follows a two-stage approach. The first stage measures reform-induced gains in the productive efficiency of the ESI, typically employing advanced analytical techniques such as the Index Analysis (IA), Data Envelope Analysis (DEA), and Stochastic Frontier Approach (SFA). These productivity gains are then - in the second stage - used to assess macroeconomic impacts, generally in a Computable General Equilibrium (CGE) framework. This paper provides an overview of these studies and argues that this framework is inadequate for developing a realistic appreciation for the wider impacts of ESI reform