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-The performance of a privately owned photovoltaic (PV) hydrogen production and storage installation in a one-family house at Zollbrück i. E. in Switzerland (altitude 630 m, latitude 46.9°N) has been studied. The manually controled system operates since 1991 and was built by its owner (M. Markus Friedli) mainly from commercial components. It consists of an array of roof mounted PV solar panels (65 m 2 surface, 5 kW p average peak power, 8.4%average efficiency), a DC-DC converter (95% efficiency), an alkaline membrane electrolyzer (5 kW, 62% average electrolyzer efficiency), a hydrogen purification unit, a compressor, and two metal hydride storage tanks, a fixed one (capacity: 15 Nm 3 ) for in-house storage to operate houshold appliances running on hydrogen such as a stove and a laundry machine, and a mobile one (capacity 16 Nm 3 ) for running a hydrogen operated minibus. In-situ measurements during operation on 3 typical summer days and computer modeling based on standard meteorological data suggest a yearly hydrogen production of 1100 Nm 3 (16 Nm 3 /m 2 .year), corresponding to an average efficiency of 3.6% for converting solar energy into hydrogen fuel for seasonal energy storage. †) permanent address :

KeywordsEarth-channel, buried pipe system, sensible and latent heat exchanges, preheating / cooling of air. AbstractOn basis of extensive monitoring and simulation work, we examine the fundamental difference between winter preheating and summer cooling potential of buried pipe systems under Central European climate, as well from an energetic as from an economic point of view. Care is taken to account for exhaustive energy balances, taking into account sensible and latent heat exchanges, as well as diffusion through soil.

Air-soil heat exchangers for heating and cooling of buildings are analyzed under various aspects.Based on the analytically resolved case of a constant airflow subject to sinusoidal temperature input, we start by deriving climate independent design guidelines, for dampening of the daily and/or the yearly temperature oscillation. In a second step, constraints and potential of buried pipe systems are analyzed for the case of a typical Central European climate, for which the constraint between climate and comfort threshold induces a fundamental asymmetry between preheating and cooling potential. Finally, it is shown that the net yield of an air-soil heat exchanger has to take into account more than the mere input-output temperature differential. Keywordsair-soil heat exchanger, earth-air tunnel, buried pipe system, passive cooling and heating.