A larger number of other European Technology Platforms exists, each with its own vision paper and independent Strategic Research Agenda. One topic is common to most of these papers, that in 50 years renewable energy will be the main source of energy and that the efficient use of energy will become more and more important.

The important role of solar thermal energy is well accepted. New, more complex system approaches have to be developed, which combine solar thermal with storage systems — hot and cold — and which enable the combination of:

• Collector and storage unit

• Collector and heat pump

• Heat and electricity (PVT collector)

• Air collectors for heating and cooling

Figures 4, 5 and 6 show some sketches or cross-sections of such systems. Figure 4 shows 2 schematic diagrams of a collector which is integrated into a wall. On the left is a simple system combined with a storage material (such as a phase change material), where heat is transferred to the inner wall and stored there at a low temperature level for heating the room. On the right, a slightly more complex system is shown with additional integration of a small heat pump using the outside collector as a low — temperature heat source or for cooling. Again the system is combined with heat storage materials.

Figure 5 shows a cross-section through a hybrid solar collector, where the collector is used in combination with a heat pump again. First demonstrations of such systems are now running.

Figure 6 finally shows a cross-section through a PVT collector, which produces both low-temperature heat and electricity. One advantage of such systems is the saving of area on the roof. Ideally the PV efficiency is even improved in summer due to the lower temperature of the solar cells. Low- temperature heat can be generated and used for heating or preheating of water. Again here first demonstration systems are being tested and show interesting results.

■ Concepts

^ Direct

— Large solar collector, preferrably in the facade

— Storage size of some days, preferrably integrated into construction

r Indirect

— Solar collector as low temperature heat source

— High efficient small heat pump (goal: COP up to 10)

— Possibly PV-T

— Possible: summer cooling

Figure 4: Cross-section of two variations of wall-integrated collector-storage systems.

Figure 6: Cross-section of a PVT

collector producing electricity and heat.

Another important topic is the integration of solar buildings into the energy supply grid. In most cases, even a so-called 100% solar house will have a connection with the grid for security reasons. This gives the possibility to optimise and minimise the whole energy demand of a village or even a city.

This topic is well known from electricity grids under the headings of smart metering and smart grids. In future, the heating and cooling demand of buildings as well as the thermal storage capacity of the building can be integrated into the total energy management system. There is a high potential for energy conservation and reduction of peak loads, which are the most expensive energy demands. Figure 7 shows a diagram of a future energy supply system with many distributed energy sources, users and integrated storage systems for electricity, heating and cooling.

10 kV

the operating costs

Figure 7: Energy management in local grids.

6. Summary

The SRA describes the research that is essential to expand the application field of solar thermal technologies, so that 50% of the thermal heat demand in the EU can be met in the long term. To reach this goal, a new generation of solar thermal technology needs to be developed for new application areas. Major new applications are: solar combined systems for domestic hot water and space heating using compact seasonal storage units, higher-temperature collectors for industrial applications, and solar cooling. The main research challenges are to develop compact long-term efficient heat storage systems and to develop cheaper materials for solar systems. In addition, a system approach which combines efficient use of energy with integration of solar thermal and other renewable resources is needed. On the long term. a decentralised approaches with many distributed energy sources connected by a smart grid could be the only solution for a sustainable energy supply of the whole world.

References:

SRA Solar heating and cooling for a sustainable energy future in Europe www. esttp. org

www. ectp. org

www. smartgrids .eu