Uta-Maria Klingenberger, Elmar Bollin, Sascha Himmelsbach Fachhochschule Offenburg, Badstr. 24, 77652 Offenburg, Germany Tel.: +49 781 205122, klingenberger@fh-offenburg. de

The support programme “Solarthermie-2000”, Part Program 2, was developed in 1993 to apply the technology of solar thermal systems for large hot water demands like in hospitals or bigger residential buildings. Large-scale solar thermal system with collector areas greater than 100 m2 should be investigated, demonstrated and standardised. Since 1999 the University of Applied Sciences Offenburg (Fachhochschule Offenburg) is part of this scientific programme. The paper will show the operational experiences, measured results and some reasons for malfunction of the last 5 years.

1. The Research Programme Solarthermie-2000

Since 1993 more than 60 large-scale solar thermal systems for domestic hot water generation were installed as demonstration plants in the frame of the Solarthermie-2000 programme. Financed by the German Ministry of Economics all these systems got subsidies for solar system installation (~50 %) and system monitoring (100 %).

The partial program 2 of the Solarthermie-2000 project, which was focused on domestic hot water heating, aimed:

• to build up to 100 best practice large-scale solar thermal systems all over Germany,

• to build high energy-efficient and cost-efficient plants with specific cost of solar heat below 0,13 €/kWh,

• to transfer know-how concerning solar thermal systems to universities, contractors and solar consultancies,

• to demonstrate solar thermal systems as reliable, sustainable and even cost-effective measure to compete with conventional energy.

At the Fachhochschule Offenburg a group of three scientists is responsible for expertise, planning supervision, data acquisition, monitoring and optimisation of presently six large — scale systems /1/. The scientists supervise the projects in all project phases including conception, planning, call for tenders, set into operation and the detailed long-term monitoring over a two years period of system operation. Meanwhile the detailed monitoring has been finished for five systems (Fig. 1). All plants have met the guaranteed values during the two years of operation within a tolerance of 10 %. One system is still in the monitoring phase: Wellness centre albtherme Waldbronn with a combination of solar potable water heating and pool heating /2/.

Contractors of theses large-scale systems have to guarantee the annual solar yield. This solar yield is part of the call for tenders and is calculated on the base of a dynamic system simulation. If the warranty was not fulfilled, the contractor has to optimise the system.

The economic aspect is an important part of the program. The predicted specific costs have to be below 0,13 €/kWh (based on 20 years lifetime and 6 % interest). So the sizing is based on a small cost minimum which is simulated by a load of 70 litre of domestic hot water at 60 °C per day and m2 collector area.

2. Monitoring

A very complex measurement instrumentation is installed in each plant to evaluate the solar thermal system and the operation. The data flow with the aid of remote monitoring is shown in figure 2.

At each solar thermal system approximately 50 sensors are installed. Measured values are:

• temperature (°C)

• irradiance (W/m2)

• flow rate (m3/h)

• state of the pumps and valves (0 or 1)

• electrical energy consumption (kWh)

The measured values are acquired and stored every 10 seconds. With this data the values like power (kW), energy (kWh), hours of operation and volumes (m3) are calculated. These data are readout every day from the Fachhochschule Offenburg. Additionally there is the possibility to readout the instantaneous values online.

Finally the measured data become characteristic data of the plant like:

• solar yield (energy provided by the solar thermal system to the domestic hot water system),

• system efficiency (how much of the irradiation on the collector area can be used for the hot water),

• Solar fraction (how much is the contribution of the solar thermal system to the domestic hot water consumption),

• hot water consumption

• solar energy costs.

These values enable an evaluation of the solar thermal system operation.

3. Results

Out of five years of monitoring period there are plenty of data. A short overview of the most important and characteristic values will be given below.

3.1 Costs

The specific costs of the six plants (without considering the subsidies and additional costs for measurements) are shown in Figure 3. The biggest contribution to the system costs have the collectors. The kind of substructure has an significant influence on the system costs. For example the solar roof of the hospital in Singen allowed a very cost effective system. Mounting on a flat roof requires an extensive construction for the fixing of the collector, which makes the whole system more expensive like in Freiburg (Fig.3).