The configuration of a solar combi+ system with seasonal storage (SST) has shown interesting results in terms of solar fraction since it can practically reach 100% of energy demands for domestic hot water, space heating and cooling. As expected, the cost of the HIGH-COMBI system (referred to as system “A”) is substantially higher compared with system “B” (same collectors area but without SST), but comparable with system “C” (a larger collectors’ area combi+ system with similar solar fraction). Consequently, solar systems with relatively small SST could be a valid option for high solar fractions.

In fact the alternative (to the SST) solution with similar solar fraction (solution C) presents various disadvantages; the most important being the increase of the solar collectors area (twice as big compared with “A”) which may exceed the available space (e. g. building’s roof area).

The following aspects have been identified in order to further investigate the concept presented in the current work:

Ground heat exchangers (GHE) around the SST should be simulated in order to identify an optimal combination of SST volume, insulation and GHE length and geometry.

The use of low cost thermal insulation materials (to lower the U-value) should be further analyzed.

The optimization procedure should include more variables such as the type and control for the heating/cooling delivery system, the solar collectors, SST insulation aspects (especially if GHE are implemented) etc.

The use of an adsorption heat pump (HP) as the auxiliary heating and cooling source should be examined as it may allow taking full advantage of the SST (extending its use in summer time). Moreover, this combination may lead to a 100% renewable energy coverage of the heating/cooling

demands with a smaller and cheaper plant. In this case, the solar gains should be enough for driving the HP in summer (keeping the SST at lower temperatures) but when there is not enough solar radiation for heating in winter then the HP could be driven by a biomass boiler or, simply, by a fireplace. In this way the HP will cool the tank and may create even an inverse heat flow from the ground into the tank. The solar collectors’ efficiency will obviously increase substantially.

Finally, it will certainly be interesting to examine similar systems in energy and financial terms in other Mediterranean and/or central European countries

Acknowledgments — The High-Combi project (www. highcombi. eu, 2006-2010) is partly financed by the European Commission (6th Framework Programme, EC DG TREN) and is a collaborative effort of 12 partners from 6 European countries.

Thanks are due to all High-Combi partners and especially to those that have contributed directly or indirectly to this work. Particular thanks to Thomas Schmidt, Tomas Nunez, Jochen Doell and certainly to Thomas Paushinger & Co, as well as to Anastasia Benou for their (not only technical) support. Last but not least, many thanks to professors Petros Ditsas and Stefanos Trahanas for teaching the art to distinguish what is essential and what superficial.

References

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