Agis M. Papadopoulos
Renewable energy systems and heat and power co-generation systems have become quite efficient and also cost-effective over the last decades, with a downscaling of the systems making them suitable even for single family houses. At the same time, micro-grids enable the integration of single residence applications into whole urban energy systems, in a much more flexible and effective way than it was considered possible only a few years ago. Therefore, amongst other, it has become a popular solution in Northern and Central Europe, where the heating period is protracted and the thermal loads for heating and hot water dominate the energy requirements of residential buildings, neighborhoods and whole settlements. Still, it is a different issue when thinking of using this technology in the Mediterranean, where the heating period is rather short and the heating requirements comparatively small. The problem of utilizing the generated heat is quite difficult to solve, unless there is a requirement for process heat or there are buildings cooled by means of absorption chillers. Even in the simplest case, when the unwanted heat is being disposed into the environment, this is costly and may contribute to the urban heat island effect in the urban street canyons. This problem is discussed in this paper, based on the example of residential buildings in Greece. Possible solutions have been considered, to provide not only heat and electricity, but also the cooling for several residences, hence the tri-generation solution is discussed. This has been done on a settlement’s scale for single family houses or -in the case of more densely built environment- in multifamily apartment buildings. A mathematical framework developed to enable optimal solutions has been applied, to evaluate the energy production for the micro-grid system, based on PVs and on a Micro-Combined Heat and Power system (Micro-CHP) alternatively to a conventional combination of gas- or oil-fired boilers for space heating and hot water production and room air-conditioners for cooling. The results yielded have been evaluated comparatively, in order to come up with the most efficient and cost-effective solution. In that way the Life-Cycle-Cost and the Pay-Back Period for a micro-grid co-generation system was elaborated and the results indicated, apart from the feasibility of the solution, the need for policies which will make these systems more appealing.