This article investigates the introduction of hybrid power plants for thermal energy production for the indoor space heating loads coverage. The plant consists of flat plate solar collectors with selective coating, water tanks as thermal energy storage and a biomass heater. A new operation algorithm is applied, maximizing the exploitation of the available thermal energy storage capacity and, eventually, the thermal power production from the solar collectors. An automation system is also designed and proposed for the realization of the newly introduced algorithm. The solar-combi system is computationally simulated, using annual time series of average hourly steps. A dimensioning optimization process is proposed, using as criterion the minimization of the thermal energy production levelized cost. The overall approach is validated on a school building with 1000 m2 of covered area, located in the hinterland of the island of Crete. It is seen that, given the high available solar radiation in the specific area, the proposed solar-combi system can guarantee the 100% annual heating load coverage of the examined building, with an annual contribution from the solar collectors higher than 45%. The annually average thermal power production levelized cost is calculated at 0.15 €/kWhth.

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This article aims to present the results from studies on the energy performance upgrade of buildings and facilities located in Crete, Greece, in a typical Mediterranean climate. In Mediterranean islands, the most buildings remain uninsulated, classified in C or even lower energy performance rank. In this article four reference buildings and one sports facility are investigated: a residential building, a municipality building, a school building, a museum and the Pancretan Stadium. Detailed calculations based on the computational simulation of each examined facility were executed, giving accurate results on the heating and cooling loads, both for the existing conditions and after the integration of the proposed passive measures. Thorough dimensioning and energy calculations have been executed for specific active energy systems too, particularly proposed for each examined case. With this parametric approach, the article indicates the effect and the economic efficiency of the proposed active or passive measures for each examined facility, expressed with specific key performance indicators. The common conclusion for all investigated cases is the huge margin for energy saving, which can reach 65% with regard to the existing annual consumptions. The payback period of the introduced energy upgrade measures can be as low as 15 years.