The selection of the input or the output method depends on the application of the data. Eurostat makes energy balances and therefore the energy input of a conversion process is seen as the energy production. This is in line with the method for e. g. biomass or coal. The output is useful if you want to know the amount of useful heat that is actually used. The final energy as it is used in the renewable energy directive [1] can be input or output. If a solar water heater is placed in a private home the final energy is the energy delivered to the house, which means the energy input to the solar water heater (the input method). If a large solar water heater delivers heat to a network, the final energy is the solar heat delivered to the end-user. In that case the final energy is the output of the solar system (minus distribution losses).

2. Conclusions and outstanding issues

The main conclusions of this paper are:

• Data on the installed collector area is available for most European countries.

• The quality of the statistics on collector area is reasonable, but a the average life-time for solar systems should be included.

• The energy production of the solar systems is still uncertain. The data from Eurostat shows an difference in production per square meter of collector which is not acceptable.

• A large difference is caused by mixing up the input and the output definition.

• To fit in the Eurostat method the input method should be used.

• For the output method the simple formula is an easy way to calculate the average output. The data vary still a lot between countries.

Outstanding issues

• Define the input method. The proposal is 50% of the solar radiation falling on the collector

(which is the insolation at the optimal angle).

• More monitoring data are needed to come to a reliable coefficient for the average output for the

collector. The data is needed for different applications and collector types.

References

[1] European Union, (2008), Proposal for a Directive of the European Parliament and of the Council on the Promotion of the Use of Energy from Renewable Sources, Com(2008) 19, 23-1-2008, Brussels.

[2] Eurostat Energy Yearly Statistic 2006, (2008), Eurstat, Luxembourg, http://ec. europa. eu/eurostat

[3] Solar Thermal vision 2030, (2006), European Solar Thermal Technology Platform (ESTTP), www. esttp. org

[4] Strategic solar thermal research agenda, (2008), to be published see www. esttp. org

[5] The ThERRA project, several reports see www. therra. info , EU-contract: EIE/05/129/SI2.420023

[6] ThERRA, Proposal for the definition and calculation principle for renewable heat, (2007)

[7] L. Bosselaar, The role of solar heating in the European heat demand, (2006), Eurosun 2006.

[8] R. Segers, (2007), based on the Eurostat data, private communication.

[9] W. Weiss, I. Bergmann, G. Faninger, (2008), Solar Heat World Wide, markets and the contribution to the energy supply 2006, www. iea-shc. org

[10] Technical note: Converting solar thermal collector area into installed capacity (m2 to kWth), (2004), IEA Solar Heating and Cooling programme, Estif e. a.

[11] R. Segers, (2008), ThERRA Benchmark: Test of a Method for Calculating Renewable Heat, CBS,

Therra, www. therra. info

[12] H. Tretter, (2008) WP4: monitoring report, www. therra. info