100% renewable district heating

Experiences of operation

The SUNSTORE 4 components were gradually installed and went into operation in 2012. The data evaluations for the first two years of operation show a good agreement with the design values regarding the yearly heat balance. The solar fraction in 2013 was 34 % and the renewable energy share of the total heat supply was 100 % with a contribution of the bio-oil backup boilers of about 10 %. A comparison of the monitored yearly energy values with the corresponding design values, see Figure 1 and Figure 2, shows a very good agreement. Deviations in the contribution of the oil boilers (3 794 instead of 990 MWh) can be explained by a slightly higher measured total heat load (plus 1 300 MWh) and some operational problems with the biomass boiler in the first months of 2013 that lead to a reduced heat and electricity production of the ORC unit (minus 2 300 MWhth and minus 1 100 MWhel respectively).

Yearly energy flow base on monitoring
Figure 1: Yearly energy flow diagram based on monitoring data from 2013

Yearly energy flow based on design figures
Figure 2: Yearly energy flow diagram based on design figures

The monthly contributions of the main components for the complete period June 2012 until June 2014 can be seen in Figure 3. According to this the summer heat load can be covered completely by the solar system. In spring, autumn and winter the biomass boiler in combination with the ORC unit covers the major part of the heat load assisted by solar heat either delivered directly from the solar collectors or discharged from the seasonal thermal energy storages (STES). The nameable contribution of the bio-oil boilers in the first winter period 2012 – 2013 is mainly induced by problems with the biomass boiler during this period. In the second winter period 2013 – 2014 the contribution of the backup boilers is clearly reduced.

Monthly system heat balance
Figure 3: Monthly system heat balance from June 2012 to June 2014 (no complete data available until February 2013 due to finalisation of component installations and data acquisition system; data gap in April 2014)

Also the component level evaluations show high efficiencies and substantial contributions of the new components added within the SUNSTORE 4 project.

2013 was the first complete year of operation of the rebuilt and extended plant. As there were still some minor operational problems to solve in the beginning of the year even higher contributions of the newly added parts of the system and a reduced input of the backup boilers can be expected in the coming years.

You can see present solar heat production data of the plant following the link below:

Operational data of the plant