Journal of Sustainable Energy

3

Authors: NICUSOR I.A., GROSU F.

Discharging reactive power distribution networks contributes to reducing active energy losses and increasing electricity transit capacity. Inappropriate management of reactive power sources in distribution networks, including those from network users, leads to uncontrolled reactive power circulation with effects on voltage levels and losses. Considering that to date the charging of the electricity distribution service is made through simple (monome) rates expressed in RON / Mwh, without considering billing power absorbed and maximum consumption time, the only element by which the user is warned over network behavior is the reactive energy billing mode. Regulatory changes to reactive energy can also lead to changes in addressing technical aspects of installations at the managed delimitation point. Both the change of retailer's revenue from reactive energy and the penalty mode impacts has an impact on the quality of the distribution service. Switching from full billing to capacitive reactive energy (energy sent to the grid) upon admission of an unanswered reactive injection equivalent to 48.44% of active energy is a technical and financial relaxation for users with consequences for distributors. The lack of analyzes or studies related to regulatory changes allow us to present some considerations regarding reactive energy in distribution networks

6

Authors: OCTAVIAN C., SILVIU D.

The increase in domestic electricity consumption have forced the power industry to examine its health. The context is: The climate change exigencies and his threat to the survival of humanity is real; the fossil resources are mostly, politically controlled; In return, the rise of renewable technologies and its the democratic geographical distribution feature is a huge advantage: sun shines everywhere for everyone! Conclusion: mankind is at the turning point of its energy future. And the future power systems sould be a tissue of intelligent energy cells. In Romania (3GW wind and 1,3GW solar - large plant) it is a fear about more renewables, special wind. One root of this fear could be the gap between Romanian authorities: one authorithy establish rules without considered facts and the other authority must oparate in a hostile „enviromnent”. To get an independently opinion about these facts we’ll look on SEN. More, we had to compare the German toward Romanian legislation in the matter of renewables. Further we compare the actual SEN with a future one that is the actual national energy system with an added 1,7GW photovoltaic. Here, this new added photovoltaic are like the other 1,3GW active now în SEN. Another step further, we will model this hipothetical SEN with new 1,7Gw, but not large but small residential photovoltaic cell with storages. From here two conclusions comes out!

8

Authors: MAHJOUBI A.

In this paper, we have studied the solar radiation data available at two meteorological stations located in the south of Tunisia. Measurements of global solar radiation on horizontal surface are compared to predictions made by different methods. The first method is based on Angström-Prescott formula which correlates relative global solar radiation H/H0 to corresponding relative duration of bright sunshine SS/SS0. The second method, a model due to Mechlouch et al., uses cloud cover N, the hours of the day t and the quantum of the year q. The third method, an empirical relation due to Sivkov, uses the monthly sunshine duration nm and the noon altitude of the sun h. The models are compared and tested on the basis of statistical error tests (MBE, RMSE, MPE and R2 ) and the results are presented.

10

Authors: KLADISIOS P., SAGIA A.

Hydrothermal carbonization (HTC) is characterized by simplicity and relatively low reaction temperature and pressure (subcritical water conditions). It is also capable of processing organic material with high moisture content. The combination of the above justifies the growing interest around this specific pre-treatment method of biomass. However, the properties of hydrochar, the main product of HTC, are significantly affected by the process conditions (temperature, residence time, water-to- biomass ratio, feedstock composition etc.). In addition, the exact reaction mechanism is currently partially understood. That is the reason why only the hydrothermal carbonization of specific types of biomass under distinct conditions has been investigated. The purpose of this paper is to highlight the advantages of hydrothermal carbonization, describe the general reaction mechanism and examine the dependence of the products to the process parameters. Representative cases of reaction kinetics modeling based on experimental data were selected for demonstration. The paper concludes with an overall evaluation along with suggestions to improve the efficiency of the process.