-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.

This article presents the complete analytical solution for the heat diffusion of a cylindrical air/soil heat-exchanger with adiabatic or isothermal boundary condition, submitted to constant airflow with harmonic temperature signal at input. It will be shown that, depending on its thickness, the soil layer will induce either one of two kinds of amplitude-dampening and phase-shifting regimes of the periodic input signal. In particular, for a thin layer submitted to adiabatic boundary condition, it is possible to completely phase-shift the periodic input while barely dampening its amplitude, a phenomenon apparently unexploited up to now, which might give rise to interesting energy handling techniques. Analytical results are validated against a finite-difference numerical simulation model as well as against an experimental setup. Nomenclature Latin symbols a s m 2 /s Thermal diffusivity of soil c a J/K.kg Thermal capacity of air (isobaric) c s J/K.kg Thermal capacity of soil h W/K.m 2 Amplitude-dampening exchange coefficient of air/pipe + soil h a W/K.m 2 Convective exchange coefficient of air/pipe h s W/K.m 2 Amplitude-dampening exchange coefficient of soil h  W/K.m 2 Amplitude-dampening exchange coefficient of soil, thickness , steady-state h  W/K.m 2 Combined amplitude-dampening and phase shifting exchange coef.

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.