C I R E D 18 th International Conference on Electricity Distribution Turin, 6-9 June 2005 CIRED2005 Session No 4 TECHNOLOGICAL DEVELOPMENTS IN ELECTRICAL MICRO-GRIDS I. Zamora (1) , J. I. San Martín (2) , A. J. Mazón (1) , J. M. Arrieta (2) , J. J. San Martín (2) , V. Aperribay (2) , S. Díaz (2) 1 E. T. S. I. de Bilbao - 2 E. U. I. T. I. de Eibar Department of Electrical Engineering University of the Basque Country - Spain iepzabei@bi.ehu.es iepsadij@sb.ehu.es SUMMARY Electric market liberalization and environmental conditions configure a future guided to energy diversification, with significant increase in the use of clean energies and energy efficiency. This way, a tendency to the development of flexible and adaptable systems, with enough capacity to satisfy foreseen demand is configured. Thus, microgeneration is based on small power units, which are lower than 100 kW, placed in close locations to the consumption point. These sizes are quite small to be connected to local distribution systems, without requiring the connection to the transmission network. Furthermore, they can be installed in most of the commercial and residential buildings, universities, etc. This paper presents a revision of current developed technologies, which can be used for electrical microgeneration installations. INTRODUCTION Microgeneration is any kind of generating source of electric and thermal energy, being a technology in emergent state. These generators efficiency, usually, oscillates between 18% and 60%. Most of these generators have heat interchangers, that allow to take advantage of residual heat, for hot water, heating or industrial process heat, increasing the total efficiency of the system up to 90%. Generating unit’s residual heat can also be used to operate in refrigeration systems. In order to decrease the emission of pollutants to atmosphere, mainly nitrogen oxides, the “thin flame” devices and catalytic converters, have been adapted, to the stationary uses of electrical generation. Noise, inherent to several technologies, can be cleared soundproofing the equipments placed in residential areas. These previous characteristics, although imply a higher cost, make them competitive in front of traditional stations. The most applied technologies in microgeneration are: microturbines, fuel cells, small power wind turbines and photovoltaic cells (PV). In addition, storage dispersed technologies can help to microgenerators to be connected to the network, allowing that intermittent sources provide electricity in a more regular way, independently of the adverse climatological conditions. Flywheels, batteries and supercapacitors are the devices developed at the moment to storage energy. An option with brilliant future seems to be the hydrogen production with the energy that has been generated by PV. Later, hydrogen can be used in fuel cells to satisfy the demand of electricity and heat when necessary. In this context, microgrids present two options, connected to the network or isolated from the network, operating in an autonomous way. With regard to the first option, it is necessary to highlight that they are relevant when aspects like quality supply, global efficiency, use flexibility and costs reduction are considered. In relation to the second option, it is focused mainly to guarantee the energy supply to remote communities. MICROTURBINES They are turboalternators up to 300 kW, which consist of a centrifugal compressor, a radial turbine and a permanent imam’s high speed generator, coupled directly to the rotor of the turbine. The use of permanent imams avoids a electrical connection to obtain the electromagnetic field, which is an advantage, considering the high rotation speeds. Residual heat recovery to preheat the combustion air allows improving cycle energy efficiency, saving between 30% and 40% of fuel. This configuration is the most usual for gas microturbines, because it allows duplicating the electrical efficiency. In a typical microturbine with an electric power of 105 kW, it is obtained an electrical efficiency of 30%, global efficiency of 80% and thermal power of 167 kW (hot water 50/70ºC). Furthermore, it can use more type of fuels than conventional motors: natural gas, commercial butane and propane, diesel, kerosene, biogas, hydrogen, etc. Gas microturbines usually incorporate sealed lead-acid batteries that can be recharged with commercial chargers or by connection to the electrical network. These batteries are used in outburst without connection to the network “Black Start” and in the management of transient events, such as: power supply during high peaks and energy absorption during power high decreases. They can operate in parallel with the L.V. electric network autosynchronizing with this network or they can operate by themselves supplying adjustable voltage. The step to operate isolated is automatic if a failure in the electrical network appears. Microturbines can be used in cogeneration/trigeneration applications in industrial, commercial and residential areas to produce hot water, low temperature vapour and cold water. In Figure 1, a gas microturbine operating scheme can be seen. This microturbine consists of 2 poles permanent imams microgenerator, one stage centrifugal air compressor and one stage radial turbine. The turbine, the compressor and the