The test storage units are being tested on the Plataforma Solar de Almeria (PSA) in Spain, integrated in the parabolic trough test loop (Fig. 3). This test loop comprises 50 m LS-3 and 75 m Eurotrough parabolic troughs with a maximum thermal power of 480 kW using synthetic oil as heat transfer fluid. The storage units have been designed for a power of 350 kW which can be provided by the loop at an average insolation of 800 W/m2, assuming 34 kW of thermal losses of storage units and piping. Within this test loop, either two storage blocks of same material can be operated in series connection, or two blocks of different material can be operated in parallel.

Already before start up of the storage units, the LS-3 collectors have been damaged during maintenance works and had to be taken out of operation completely. Therefore for the whole project the power of the loop was reduced to 300 kW from the Eurotrough collectors. Fig. 4 shows flow rates for charging and discharging as well as the temperature in the core (TC9) of the storage module M1 (ceramic) at four different positions (P1 to P4) of the storage length. Cross section P1 is closest to the oil inlet during charging, so the temperature in cross section P1 is highest and in P4 lowest.

In this test the mass flow rates and oil inlet temperatures during charging and discharging have been kept constant.

An analysis of the power transferred in these cycles on 14.01.04 is shown in Fig. 5. Here the transferred power from the oil has been calculated from the measured mass flow, inlet and outlet temperatures just before and behind the distributors and collectors and specific heat as a function of temperature as given by the manufacturer. The power into and out of the storage module has been calculated from the heat capacities of the materials measured in the lab (see Table 1) and the change of the average storage temperature within a specific time. The average storage temperature is calculated from all thermocouples in all four cross sections P1 to P4.

Integration of these curves results in a total input of energy into the storage from the oil of 391 kWh, and a total output through the oil of 175 kWh during the two discharge phases. So net 216 kWh have been transferred to the storage. During this time the storage has experienced a net temperature raise from 122°C to 169°C, which is a capacity raise of 192 kWh. The difference between the net input from the oil and the capacity raise of the storage, 24 kWh is the net heat loss of the storage. This results in an average heat loss power of 5% of the input power.

Due to the lack of power from the LS-3 collector and unusually bad weather conditions during late summer and autumn of 2003 in the province of Almeria, the full test program could not be finished within the WESPE project. Up to now 325°C storage temperature has been reached. The essential cycle tests in the operating range of 340 — 390°C will be performed as soon as the LS-3 collector has been repaired (probably end of April 2004). Nevertheless test results so far let us expect a high suitability of the realized system for storage use. There was no degradation of heat transfer between heat exchanger and storage material, very high power levels could be realized during cooling already and also high temperature gradients between storage and oil have been handled without problems.